52 CoverageCapacity Optimization 44521 Offset of the primary CPICH transmission power and DL transmission power
of reference call 45
522 Target for received power46523 Target for transmitted power49524 Coverage Optimization 50
53 Call setup success rate and call drop rate Optimization51531 Call Set Up Success Rate51
6 Test cases5561 Cell Selection 5562 Paging5663 RRC connection establishment 5664 LocationRouting Area update5865 Mobile Terminated Call Mobile Originated Call61
AbbreviationsAC Admission ControlBLER Block Error RateBTS Base Station
BSS Base Station SubsystemCDMA Code Division Multiple AccessCN Core NetworkCPICH Common Pilot ChannelCRC Cyclic Redundancy CheckCS Circuit SwitchDCN Data Communications NetworkDL DownLinkFMT Field Measurement ToolGUI Graphical User InterfaceIF InterFaceLA Location Area
LC Load ControlLPA Linear Power AmplifierKPI Key Performance IndicatorMHA Master Head AmplifierMOC Mobile Originated CallMSC Mobile Switching CenterMT Mobile TerminalMTC Mobile Terminated CallNEMU Network Element Management UnitNetAct Nokia Network Action SystemNRT Non Real TimeOCNS Orthogonal Channel Noise Simulator
OampM Operations and MaintenancePampO Planning amp OptimizationPC Power ControlPI Performance IndicatorPS Packet Scheduler or Packet SwitchQoS Quality of ServiceRA Routing AreaRAN Radio Access NetworkRM Resource ManagerRNC Radio Network ControllerRRM Radio Resource ManagerRSCP Received Signal Code PowerRT Real TimeSCH Synchronization channelSGSN Serving GPRS Support NodeSHO Soft HandOverSRNC Serving RNCTS Time SlotUE User EquipmentUL UpLinkUMTS Universal Mobile Telephone SystemURA Utran Registration AreaWCDMA Wideband CDMA
This document describes the strategy and required tools as well as main features innetwork elements for WCDMA radio network optimization The goal for optimizationis to provide the network performance to meet the targets set by the operator withcost effective means Network performance means here capacity and coverageprovision in addition to the quality experienced by the end user
Optimization can be defined as that activity which is performed to configure theexisting radio network to deliver optimum performance In a wider sense optimizationalso includes planning aspects and network development related issues like addingequipment or sites to fill in capacitycoverage holes The network elements resourceusage should be monitored as too heavily usage may cause blocking in this case itshould be added some extra equipment while too low usage may indicate that toomuch money has been invested maybe some equipment could be moved to someother cell (eg one LPA)
Optimization actions are usually triggered in case monitored key performanceindicators are out of their predefined range As there are no WCDMA networksavailable yet all the procedures explained in this document have only been testedwith simulations Therefore in this document more focus should be put on the trendof network behavior than on absolute figures
This document will be updated as soon as the measurements and the results of theoptimization process on the test network will be available
This chapter describes the workflow and the different phases present in theoptimization
In Figure 1 is described the process for the optimization of a network
Figure 1 Optimization process
Figure 1 can be divided in three different areas called respectively PreparationsMeasurements and Optimization [5] Those three areas will be analyzed and theinput and output of each of them will be highlighted in the next sub-chapter It shouldbe noted that during the optimization only one parameter per time should bechanged in this way it is possible to see the influence of that particular parameter onthe network Another important issue is to keep track of all the changesimplemented in order to restore the network to the previous configuration if thechanges implemented had some undesired side effects With this process of storingchanges and the network behavior after the changes it is possible to create aresolution database
Previous results of the analysis and verification of the performance of thenetwork
Action plan from the previous optimization cycle
212 Outputs
Qos Criterias short-term and long-term
Measurement Plans for NetAct and Drive Test Measurements
Tool Guidelines
Templates for project reports
213 Descriptions
The starting point for the preparation is agreeing about the Master plan meaningwhat should be done in the network for shortlong terms plan involving theintroductions of New Services New Features Capacity and Service Areasexpansions
The output of the Master Plan are affecting the Preparations phase since it will clarifywhich targets to set for the network as well as gives input for future actions on theshort and long term plan (HW and SW)
Setting the targets for the network performance in terms of capacity coverage andquality will get inputs from the short and long term planning as specified in themaster plan Depending on the life stage and needs of the network and dependingon which target will be selected the Quality of Service Criteria can be set in the formof specific network quality performance indicators Both Customer (Operator) andNW manager should take part in finding the most suitable QoS criteria for thenetwork
If thinking on high level the most common indicators would be Call Drop Rate andCall Setup Success Rate The Nokia approved KPIs can be found in [1]
The selected targets will provide inputs for planning the measurements to be run inorder to make sure that the targets are met
When KPI to be followed (targets) in the network are defined the next step is toprepare a measurement plan and tool guidelines In optimization two major types ofmeasurements can be identified field test measurements and NMS measurementsEach of them has got prorsquos and conrsquos but both should be considered as valuable for
a good assessment of the performance of the network
bull For Field measurement the plan should include the following information
minus Tools used for drive tests
minus Resources and availability
minus Measurement mode Trace Call Generator Receiver (CPICH code power)
minus Service to be measured CS PS 384 Kbs voice hellip
minus Measurement area
minus Routes definition
minus Prepared maps
minus Number of callsdata transfers for each session
minus
Starting and ending time for each sessionminus Measurement parameters for tools
minus Collecting the data in files with proper names and store them
minus Post-process the data in order to have them in easy to analyze format
Radio Network Planner engineers agree on the field measurement mode scheduleroutes and also nominate a sub-group of people to perform the measurementsUsually field measurement teams operate during daytime The drive testmeasurements are focusing on coverage and call related parameters
The measurement route can be divided into sub-routes The length of a sub-route
should not be too long ndash the measurement time (driving time) of a sub-route shouldnot exceed 1-2 hours This arrangement reduces the size of measurement data filesand makes the analyzing work easier
The following road and area types should be included in measurement routes
bull Streets (city urban)
bull Highways (suburban rural)
bull Major roads (urban suburban rural)
bull Minor roads (urban suburban)
bull Special areas (eg airport area shopping centers)
The main focus should be on area types with the tightest requirements for networkperformance in terms of quality capacity and coverage These areas are typicallyfound in the urban regions or in traffic hot spots with densest penetration of mobilesubscribers
One survey consists of several test calls in the cell cluster area along the specifiedroutes The test call length is 2 minutes The measurements are to be done during acontinuous time period of 3-5 working days and the timing should be planned tocover at least network busy hours
bull For NMS measurements the plan should include the following information
minus The measurement schedules start and stop datetime
minus RNC measurements definitions (basic ones and supplementary ones)
minus Measurements period for collecting the data from RNC
minus Selecting at which network level the data are required (Cell BTS RNC arealevel)
minus The averaging period (1 day 1 week or peak hours info)
minus Collecting the results in proper directory
minus Reporting
The needed measurements as traffic resource availability resource accesshandover power control quality etc should be activated on RNC level in order to getthe raw counters needed to build up (K)PI on NMS level By means of scripts in
NetAct Reporter it is possible to get performance indicator on different networkelement level in order to analyze the performance and trouble-shoot the network
It should be noted that at the early stage of the networkrsquos life the NMS statistics arenot reliable due to the small number of subscribers Typically there should be atleast 50 calls during busy hour per cell
The planning of measurements leads to the definition of which tools to be used aswell as guidelines on how to conduct the measurements and what type ofmeasurements are the most suitable for the specific target at hand
If tools are suggested for both the drive test measurements and the network
performance measurements attending a training course should be considered incase it is not possible the user manual should be made available to use the tool inthe appropriate way
At the same time itrsquos important at this stage to define practical issue about how topresent reports the format of those as well as the template to be used The reportscan be in Excel format as well as charted in order to have the results at glanceDepending on the tools used in analyzing the reports can have specific formats
22 Measurements
221 Inputs
Tool Guidelines
Sufficient data storage space allocated for NetAct measurements and also for DriveTest measurements
bull NMS measurements
minus The given list of measurements to activate in the RNC
minus The measurement schedules with start and stop date
bull Drive Test measurements
minus Planned measurement areas
minus The measurement schedules with starting and stopping times
minus The raw data captured on the database system
minus Text files with separators
minus Performance reports
bull Drive test results
minus Reception levels and quality with respect to positioning
223 Descriptions
bull Drive test measurements
minus Driving according to the predefined routes
minus Storing the results onto properly named files
bull NMS measurements
minus The real measurements are run on RNC level according to the predefined listof measurements
minus On NetAct database the raw counters can be grouped on each networkelement level in order to build up formulas to describe the network in terms of(K)PI Itrsquos possible to predefine those KPIs or to tailor them according to the
needsminus The NetAct will be used for the measurements of quality For the recording of
the measurements help of the NMS expert should be taken and it should beclearly specified to himher what alarms should be recorded and for how long
minus When the required tests and measurements are agreed upon the actual datacollection is started Here are a few examples of possible measurementstests and tools
minus Traffic measurements Set up using NetAct or MML for every switch
minus Traffica measurements Centralized real time measurements from the wholenetwork
minus Protocol analyzer Nethawk or similar tool for detailed signalingtroubleshooting
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
52 CoverageCapacity Optimization 44521 Offset of the primary CPICH transmission power and DL transmission power
of reference call 45
522 Target for received power46523 Target for transmitted power49524 Coverage Optimization 50
53 Call setup success rate and call drop rate Optimization51531 Call Set Up Success Rate51
6 Test cases5561 Cell Selection 5562 Paging5663 RRC connection establishment 5664 LocationRouting Area update5865 Mobile Terminated Call Mobile Originated Call61
AbbreviationsAC Admission ControlBLER Block Error RateBTS Base Station
BSS Base Station SubsystemCDMA Code Division Multiple AccessCN Core NetworkCPICH Common Pilot ChannelCRC Cyclic Redundancy CheckCS Circuit SwitchDCN Data Communications NetworkDL DownLinkFMT Field Measurement ToolGUI Graphical User InterfaceIF InterFaceLA Location Area
LC Load ControlLPA Linear Power AmplifierKPI Key Performance IndicatorMHA Master Head AmplifierMOC Mobile Originated CallMSC Mobile Switching CenterMT Mobile TerminalMTC Mobile Terminated CallNEMU Network Element Management UnitNetAct Nokia Network Action SystemNRT Non Real TimeOCNS Orthogonal Channel Noise Simulator
OampM Operations and MaintenancePampO Planning amp OptimizationPC Power ControlPI Performance IndicatorPS Packet Scheduler or Packet SwitchQoS Quality of ServiceRA Routing AreaRAN Radio Access NetworkRM Resource ManagerRNC Radio Network ControllerRRM Radio Resource ManagerRSCP Received Signal Code PowerRT Real TimeSCH Synchronization channelSGSN Serving GPRS Support NodeSHO Soft HandOverSRNC Serving RNCTS Time SlotUE User EquipmentUL UpLinkUMTS Universal Mobile Telephone SystemURA Utran Registration AreaWCDMA Wideband CDMA
This document describes the strategy and required tools as well as main features innetwork elements for WCDMA radio network optimization The goal for optimizationis to provide the network performance to meet the targets set by the operator withcost effective means Network performance means here capacity and coverageprovision in addition to the quality experienced by the end user
Optimization can be defined as that activity which is performed to configure theexisting radio network to deliver optimum performance In a wider sense optimizationalso includes planning aspects and network development related issues like addingequipment or sites to fill in capacitycoverage holes The network elements resourceusage should be monitored as too heavily usage may cause blocking in this case itshould be added some extra equipment while too low usage may indicate that toomuch money has been invested maybe some equipment could be moved to someother cell (eg one LPA)
Optimization actions are usually triggered in case monitored key performanceindicators are out of their predefined range As there are no WCDMA networksavailable yet all the procedures explained in this document have only been testedwith simulations Therefore in this document more focus should be put on the trendof network behavior than on absolute figures
This document will be updated as soon as the measurements and the results of theoptimization process on the test network will be available
This chapter describes the workflow and the different phases present in theoptimization
In Figure 1 is described the process for the optimization of a network
Figure 1 Optimization process
Figure 1 can be divided in three different areas called respectively PreparationsMeasurements and Optimization [5] Those three areas will be analyzed and theinput and output of each of them will be highlighted in the next sub-chapter It shouldbe noted that during the optimization only one parameter per time should bechanged in this way it is possible to see the influence of that particular parameter onthe network Another important issue is to keep track of all the changesimplemented in order to restore the network to the previous configuration if thechanges implemented had some undesired side effects With this process of storingchanges and the network behavior after the changes it is possible to create aresolution database
Previous results of the analysis and verification of the performance of thenetwork
Action plan from the previous optimization cycle
212 Outputs
Qos Criterias short-term and long-term
Measurement Plans for NetAct and Drive Test Measurements
Tool Guidelines
Templates for project reports
213 Descriptions
The starting point for the preparation is agreeing about the Master plan meaningwhat should be done in the network for shortlong terms plan involving theintroductions of New Services New Features Capacity and Service Areasexpansions
The output of the Master Plan are affecting the Preparations phase since it will clarifywhich targets to set for the network as well as gives input for future actions on theshort and long term plan (HW and SW)
Setting the targets for the network performance in terms of capacity coverage andquality will get inputs from the short and long term planning as specified in themaster plan Depending on the life stage and needs of the network and dependingon which target will be selected the Quality of Service Criteria can be set in the formof specific network quality performance indicators Both Customer (Operator) andNW manager should take part in finding the most suitable QoS criteria for thenetwork
If thinking on high level the most common indicators would be Call Drop Rate andCall Setup Success Rate The Nokia approved KPIs can be found in [1]
The selected targets will provide inputs for planning the measurements to be run inorder to make sure that the targets are met
When KPI to be followed (targets) in the network are defined the next step is toprepare a measurement plan and tool guidelines In optimization two major types ofmeasurements can be identified field test measurements and NMS measurementsEach of them has got prorsquos and conrsquos but both should be considered as valuable for
a good assessment of the performance of the network
bull For Field measurement the plan should include the following information
minus Tools used for drive tests
minus Resources and availability
minus Measurement mode Trace Call Generator Receiver (CPICH code power)
minus Service to be measured CS PS 384 Kbs voice hellip
minus Measurement area
minus Routes definition
minus Prepared maps
minus Number of callsdata transfers for each session
minus
Starting and ending time for each sessionminus Measurement parameters for tools
minus Collecting the data in files with proper names and store them
minus Post-process the data in order to have them in easy to analyze format
Radio Network Planner engineers agree on the field measurement mode scheduleroutes and also nominate a sub-group of people to perform the measurementsUsually field measurement teams operate during daytime The drive testmeasurements are focusing on coverage and call related parameters
The measurement route can be divided into sub-routes The length of a sub-route
should not be too long ndash the measurement time (driving time) of a sub-route shouldnot exceed 1-2 hours This arrangement reduces the size of measurement data filesand makes the analyzing work easier
The following road and area types should be included in measurement routes
bull Streets (city urban)
bull Highways (suburban rural)
bull Major roads (urban suburban rural)
bull Minor roads (urban suburban)
bull Special areas (eg airport area shopping centers)
The main focus should be on area types with the tightest requirements for networkperformance in terms of quality capacity and coverage These areas are typicallyfound in the urban regions or in traffic hot spots with densest penetration of mobilesubscribers
One survey consists of several test calls in the cell cluster area along the specifiedroutes The test call length is 2 minutes The measurements are to be done during acontinuous time period of 3-5 working days and the timing should be planned tocover at least network busy hours
bull For NMS measurements the plan should include the following information
minus The measurement schedules start and stop datetime
minus RNC measurements definitions (basic ones and supplementary ones)
minus Measurements period for collecting the data from RNC
minus Selecting at which network level the data are required (Cell BTS RNC arealevel)
minus The averaging period (1 day 1 week or peak hours info)
minus Collecting the results in proper directory
minus Reporting
The needed measurements as traffic resource availability resource accesshandover power control quality etc should be activated on RNC level in order to getthe raw counters needed to build up (K)PI on NMS level By means of scripts in
NetAct Reporter it is possible to get performance indicator on different networkelement level in order to analyze the performance and trouble-shoot the network
It should be noted that at the early stage of the networkrsquos life the NMS statistics arenot reliable due to the small number of subscribers Typically there should be atleast 50 calls during busy hour per cell
The planning of measurements leads to the definition of which tools to be used aswell as guidelines on how to conduct the measurements and what type ofmeasurements are the most suitable for the specific target at hand
If tools are suggested for both the drive test measurements and the network
performance measurements attending a training course should be considered incase it is not possible the user manual should be made available to use the tool inthe appropriate way
At the same time itrsquos important at this stage to define practical issue about how topresent reports the format of those as well as the template to be used The reportscan be in Excel format as well as charted in order to have the results at glanceDepending on the tools used in analyzing the reports can have specific formats
22 Measurements
221 Inputs
Tool Guidelines
Sufficient data storage space allocated for NetAct measurements and also for DriveTest measurements
bull NMS measurements
minus The given list of measurements to activate in the RNC
minus The measurement schedules with start and stop date
bull Drive Test measurements
minus Planned measurement areas
minus The measurement schedules with starting and stopping times
minus The raw data captured on the database system
minus Text files with separators
minus Performance reports
bull Drive test results
minus Reception levels and quality with respect to positioning
223 Descriptions
bull Drive test measurements
minus Driving according to the predefined routes
minus Storing the results onto properly named files
bull NMS measurements
minus The real measurements are run on RNC level according to the predefined listof measurements
minus On NetAct database the raw counters can be grouped on each networkelement level in order to build up formulas to describe the network in terms of(K)PI Itrsquos possible to predefine those KPIs or to tailor them according to the
needsminus The NetAct will be used for the measurements of quality For the recording of
the measurements help of the NMS expert should be taken and it should beclearly specified to himher what alarms should be recorded and for how long
minus When the required tests and measurements are agreed upon the actual datacollection is started Here are a few examples of possible measurementstests and tools
minus Traffic measurements Set up using NetAct or MML for every switch
minus Traffica measurements Centralized real time measurements from the wholenetwork
minus Protocol analyzer Nethawk or similar tool for detailed signalingtroubleshooting
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
AbbreviationsAC Admission ControlBLER Block Error RateBTS Base Station
BSS Base Station SubsystemCDMA Code Division Multiple AccessCN Core NetworkCPICH Common Pilot ChannelCRC Cyclic Redundancy CheckCS Circuit SwitchDCN Data Communications NetworkDL DownLinkFMT Field Measurement ToolGUI Graphical User InterfaceIF InterFaceLA Location Area
LC Load ControlLPA Linear Power AmplifierKPI Key Performance IndicatorMHA Master Head AmplifierMOC Mobile Originated CallMSC Mobile Switching CenterMT Mobile TerminalMTC Mobile Terminated CallNEMU Network Element Management UnitNetAct Nokia Network Action SystemNRT Non Real TimeOCNS Orthogonal Channel Noise Simulator
OampM Operations and MaintenancePampO Planning amp OptimizationPC Power ControlPI Performance IndicatorPS Packet Scheduler or Packet SwitchQoS Quality of ServiceRA Routing AreaRAN Radio Access NetworkRM Resource ManagerRNC Radio Network ControllerRRM Radio Resource ManagerRSCP Received Signal Code PowerRT Real TimeSCH Synchronization channelSGSN Serving GPRS Support NodeSHO Soft HandOverSRNC Serving RNCTS Time SlotUE User EquipmentUL UpLinkUMTS Universal Mobile Telephone SystemURA Utran Registration AreaWCDMA Wideband CDMA
This document describes the strategy and required tools as well as main features innetwork elements for WCDMA radio network optimization The goal for optimizationis to provide the network performance to meet the targets set by the operator withcost effective means Network performance means here capacity and coverageprovision in addition to the quality experienced by the end user
Optimization can be defined as that activity which is performed to configure theexisting radio network to deliver optimum performance In a wider sense optimizationalso includes planning aspects and network development related issues like addingequipment or sites to fill in capacitycoverage holes The network elements resourceusage should be monitored as too heavily usage may cause blocking in this case itshould be added some extra equipment while too low usage may indicate that toomuch money has been invested maybe some equipment could be moved to someother cell (eg one LPA)
Optimization actions are usually triggered in case monitored key performanceindicators are out of their predefined range As there are no WCDMA networksavailable yet all the procedures explained in this document have only been testedwith simulations Therefore in this document more focus should be put on the trendof network behavior than on absolute figures
This document will be updated as soon as the measurements and the results of theoptimization process on the test network will be available
This chapter describes the workflow and the different phases present in theoptimization
In Figure 1 is described the process for the optimization of a network
Figure 1 Optimization process
Figure 1 can be divided in three different areas called respectively PreparationsMeasurements and Optimization [5] Those three areas will be analyzed and theinput and output of each of them will be highlighted in the next sub-chapter It shouldbe noted that during the optimization only one parameter per time should bechanged in this way it is possible to see the influence of that particular parameter onthe network Another important issue is to keep track of all the changesimplemented in order to restore the network to the previous configuration if thechanges implemented had some undesired side effects With this process of storingchanges and the network behavior after the changes it is possible to create aresolution database
Previous results of the analysis and verification of the performance of thenetwork
Action plan from the previous optimization cycle
212 Outputs
Qos Criterias short-term and long-term
Measurement Plans for NetAct and Drive Test Measurements
Tool Guidelines
Templates for project reports
213 Descriptions
The starting point for the preparation is agreeing about the Master plan meaningwhat should be done in the network for shortlong terms plan involving theintroductions of New Services New Features Capacity and Service Areasexpansions
The output of the Master Plan are affecting the Preparations phase since it will clarifywhich targets to set for the network as well as gives input for future actions on theshort and long term plan (HW and SW)
Setting the targets for the network performance in terms of capacity coverage andquality will get inputs from the short and long term planning as specified in themaster plan Depending on the life stage and needs of the network and dependingon which target will be selected the Quality of Service Criteria can be set in the formof specific network quality performance indicators Both Customer (Operator) andNW manager should take part in finding the most suitable QoS criteria for thenetwork
If thinking on high level the most common indicators would be Call Drop Rate andCall Setup Success Rate The Nokia approved KPIs can be found in [1]
The selected targets will provide inputs for planning the measurements to be run inorder to make sure that the targets are met
When KPI to be followed (targets) in the network are defined the next step is toprepare a measurement plan and tool guidelines In optimization two major types ofmeasurements can be identified field test measurements and NMS measurementsEach of them has got prorsquos and conrsquos but both should be considered as valuable for
a good assessment of the performance of the network
bull For Field measurement the plan should include the following information
minus Tools used for drive tests
minus Resources and availability
minus Measurement mode Trace Call Generator Receiver (CPICH code power)
minus Service to be measured CS PS 384 Kbs voice hellip
minus Measurement area
minus Routes definition
minus Prepared maps
minus Number of callsdata transfers for each session
minus
Starting and ending time for each sessionminus Measurement parameters for tools
minus Collecting the data in files with proper names and store them
minus Post-process the data in order to have them in easy to analyze format
Radio Network Planner engineers agree on the field measurement mode scheduleroutes and also nominate a sub-group of people to perform the measurementsUsually field measurement teams operate during daytime The drive testmeasurements are focusing on coverage and call related parameters
The measurement route can be divided into sub-routes The length of a sub-route
should not be too long ndash the measurement time (driving time) of a sub-route shouldnot exceed 1-2 hours This arrangement reduces the size of measurement data filesand makes the analyzing work easier
The following road and area types should be included in measurement routes
bull Streets (city urban)
bull Highways (suburban rural)
bull Major roads (urban suburban rural)
bull Minor roads (urban suburban)
bull Special areas (eg airport area shopping centers)
The main focus should be on area types with the tightest requirements for networkperformance in terms of quality capacity and coverage These areas are typicallyfound in the urban regions or in traffic hot spots with densest penetration of mobilesubscribers
One survey consists of several test calls in the cell cluster area along the specifiedroutes The test call length is 2 minutes The measurements are to be done during acontinuous time period of 3-5 working days and the timing should be planned tocover at least network busy hours
bull For NMS measurements the plan should include the following information
minus The measurement schedules start and stop datetime
minus RNC measurements definitions (basic ones and supplementary ones)
minus Measurements period for collecting the data from RNC
minus Selecting at which network level the data are required (Cell BTS RNC arealevel)
minus The averaging period (1 day 1 week or peak hours info)
minus Collecting the results in proper directory
minus Reporting
The needed measurements as traffic resource availability resource accesshandover power control quality etc should be activated on RNC level in order to getthe raw counters needed to build up (K)PI on NMS level By means of scripts in
NetAct Reporter it is possible to get performance indicator on different networkelement level in order to analyze the performance and trouble-shoot the network
It should be noted that at the early stage of the networkrsquos life the NMS statistics arenot reliable due to the small number of subscribers Typically there should be atleast 50 calls during busy hour per cell
The planning of measurements leads to the definition of which tools to be used aswell as guidelines on how to conduct the measurements and what type ofmeasurements are the most suitable for the specific target at hand
If tools are suggested for both the drive test measurements and the network
performance measurements attending a training course should be considered incase it is not possible the user manual should be made available to use the tool inthe appropriate way
At the same time itrsquos important at this stage to define practical issue about how topresent reports the format of those as well as the template to be used The reportscan be in Excel format as well as charted in order to have the results at glanceDepending on the tools used in analyzing the reports can have specific formats
22 Measurements
221 Inputs
Tool Guidelines
Sufficient data storage space allocated for NetAct measurements and also for DriveTest measurements
bull NMS measurements
minus The given list of measurements to activate in the RNC
minus The measurement schedules with start and stop date
bull Drive Test measurements
minus Planned measurement areas
minus The measurement schedules with starting and stopping times
minus The raw data captured on the database system
minus Text files with separators
minus Performance reports
bull Drive test results
minus Reception levels and quality with respect to positioning
223 Descriptions
bull Drive test measurements
minus Driving according to the predefined routes
minus Storing the results onto properly named files
bull NMS measurements
minus The real measurements are run on RNC level according to the predefined listof measurements
minus On NetAct database the raw counters can be grouped on each networkelement level in order to build up formulas to describe the network in terms of(K)PI Itrsquos possible to predefine those KPIs or to tailor them according to the
needsminus The NetAct will be used for the measurements of quality For the recording of
the measurements help of the NMS expert should be taken and it should beclearly specified to himher what alarms should be recorded and for how long
minus When the required tests and measurements are agreed upon the actual datacollection is started Here are a few examples of possible measurementstests and tools
minus Traffic measurements Set up using NetAct or MML for every switch
minus Traffica measurements Centralized real time measurements from the wholenetwork
minus Protocol analyzer Nethawk or similar tool for detailed signalingtroubleshooting
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
This document describes the strategy and required tools as well as main features innetwork elements for WCDMA radio network optimization The goal for optimizationis to provide the network performance to meet the targets set by the operator withcost effective means Network performance means here capacity and coverageprovision in addition to the quality experienced by the end user
Optimization can be defined as that activity which is performed to configure theexisting radio network to deliver optimum performance In a wider sense optimizationalso includes planning aspects and network development related issues like addingequipment or sites to fill in capacitycoverage holes The network elements resourceusage should be monitored as too heavily usage may cause blocking in this case itshould be added some extra equipment while too low usage may indicate that toomuch money has been invested maybe some equipment could be moved to someother cell (eg one LPA)
Optimization actions are usually triggered in case monitored key performanceindicators are out of their predefined range As there are no WCDMA networksavailable yet all the procedures explained in this document have only been testedwith simulations Therefore in this document more focus should be put on the trendof network behavior than on absolute figures
This document will be updated as soon as the measurements and the results of theoptimization process on the test network will be available
This chapter describes the workflow and the different phases present in theoptimization
In Figure 1 is described the process for the optimization of a network
Figure 1 Optimization process
Figure 1 can be divided in three different areas called respectively PreparationsMeasurements and Optimization [5] Those three areas will be analyzed and theinput and output of each of them will be highlighted in the next sub-chapter It shouldbe noted that during the optimization only one parameter per time should bechanged in this way it is possible to see the influence of that particular parameter onthe network Another important issue is to keep track of all the changesimplemented in order to restore the network to the previous configuration if thechanges implemented had some undesired side effects With this process of storingchanges and the network behavior after the changes it is possible to create aresolution database
Previous results of the analysis and verification of the performance of thenetwork
Action plan from the previous optimization cycle
212 Outputs
Qos Criterias short-term and long-term
Measurement Plans for NetAct and Drive Test Measurements
Tool Guidelines
Templates for project reports
213 Descriptions
The starting point for the preparation is agreeing about the Master plan meaningwhat should be done in the network for shortlong terms plan involving theintroductions of New Services New Features Capacity and Service Areasexpansions
The output of the Master Plan are affecting the Preparations phase since it will clarifywhich targets to set for the network as well as gives input for future actions on theshort and long term plan (HW and SW)
Setting the targets for the network performance in terms of capacity coverage andquality will get inputs from the short and long term planning as specified in themaster plan Depending on the life stage and needs of the network and dependingon which target will be selected the Quality of Service Criteria can be set in the formof specific network quality performance indicators Both Customer (Operator) andNW manager should take part in finding the most suitable QoS criteria for thenetwork
If thinking on high level the most common indicators would be Call Drop Rate andCall Setup Success Rate The Nokia approved KPIs can be found in [1]
The selected targets will provide inputs for planning the measurements to be run inorder to make sure that the targets are met
When KPI to be followed (targets) in the network are defined the next step is toprepare a measurement plan and tool guidelines In optimization two major types ofmeasurements can be identified field test measurements and NMS measurementsEach of them has got prorsquos and conrsquos but both should be considered as valuable for
a good assessment of the performance of the network
bull For Field measurement the plan should include the following information
minus Tools used for drive tests
minus Resources and availability
minus Measurement mode Trace Call Generator Receiver (CPICH code power)
minus Service to be measured CS PS 384 Kbs voice hellip
minus Measurement area
minus Routes definition
minus Prepared maps
minus Number of callsdata transfers for each session
minus
Starting and ending time for each sessionminus Measurement parameters for tools
minus Collecting the data in files with proper names and store them
minus Post-process the data in order to have them in easy to analyze format
Radio Network Planner engineers agree on the field measurement mode scheduleroutes and also nominate a sub-group of people to perform the measurementsUsually field measurement teams operate during daytime The drive testmeasurements are focusing on coverage and call related parameters
The measurement route can be divided into sub-routes The length of a sub-route
should not be too long ndash the measurement time (driving time) of a sub-route shouldnot exceed 1-2 hours This arrangement reduces the size of measurement data filesand makes the analyzing work easier
The following road and area types should be included in measurement routes
bull Streets (city urban)
bull Highways (suburban rural)
bull Major roads (urban suburban rural)
bull Minor roads (urban suburban)
bull Special areas (eg airport area shopping centers)
The main focus should be on area types with the tightest requirements for networkperformance in terms of quality capacity and coverage These areas are typicallyfound in the urban regions or in traffic hot spots with densest penetration of mobilesubscribers
One survey consists of several test calls in the cell cluster area along the specifiedroutes The test call length is 2 minutes The measurements are to be done during acontinuous time period of 3-5 working days and the timing should be planned tocover at least network busy hours
bull For NMS measurements the plan should include the following information
minus The measurement schedules start and stop datetime
minus RNC measurements definitions (basic ones and supplementary ones)
minus Measurements period for collecting the data from RNC
minus Selecting at which network level the data are required (Cell BTS RNC arealevel)
minus The averaging period (1 day 1 week or peak hours info)
minus Collecting the results in proper directory
minus Reporting
The needed measurements as traffic resource availability resource accesshandover power control quality etc should be activated on RNC level in order to getthe raw counters needed to build up (K)PI on NMS level By means of scripts in
NetAct Reporter it is possible to get performance indicator on different networkelement level in order to analyze the performance and trouble-shoot the network
It should be noted that at the early stage of the networkrsquos life the NMS statistics arenot reliable due to the small number of subscribers Typically there should be atleast 50 calls during busy hour per cell
The planning of measurements leads to the definition of which tools to be used aswell as guidelines on how to conduct the measurements and what type ofmeasurements are the most suitable for the specific target at hand
If tools are suggested for both the drive test measurements and the network
performance measurements attending a training course should be considered incase it is not possible the user manual should be made available to use the tool inthe appropriate way
At the same time itrsquos important at this stage to define practical issue about how topresent reports the format of those as well as the template to be used The reportscan be in Excel format as well as charted in order to have the results at glanceDepending on the tools used in analyzing the reports can have specific formats
22 Measurements
221 Inputs
Tool Guidelines
Sufficient data storage space allocated for NetAct measurements and also for DriveTest measurements
bull NMS measurements
minus The given list of measurements to activate in the RNC
minus The measurement schedules with start and stop date
bull Drive Test measurements
minus Planned measurement areas
minus The measurement schedules with starting and stopping times
minus The raw data captured on the database system
minus Text files with separators
minus Performance reports
bull Drive test results
minus Reception levels and quality with respect to positioning
223 Descriptions
bull Drive test measurements
minus Driving according to the predefined routes
minus Storing the results onto properly named files
bull NMS measurements
minus The real measurements are run on RNC level according to the predefined listof measurements
minus On NetAct database the raw counters can be grouped on each networkelement level in order to build up formulas to describe the network in terms of(K)PI Itrsquos possible to predefine those KPIs or to tailor them according to the
needsminus The NetAct will be used for the measurements of quality For the recording of
the measurements help of the NMS expert should be taken and it should beclearly specified to himher what alarms should be recorded and for how long
minus When the required tests and measurements are agreed upon the actual datacollection is started Here are a few examples of possible measurementstests and tools
minus Traffic measurements Set up using NetAct or MML for every switch
minus Traffica measurements Centralized real time measurements from the wholenetwork
minus Protocol analyzer Nethawk or similar tool for detailed signalingtroubleshooting
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
This chapter describes the workflow and the different phases present in theoptimization
In Figure 1 is described the process for the optimization of a network
Figure 1 Optimization process
Figure 1 can be divided in three different areas called respectively PreparationsMeasurements and Optimization [5] Those three areas will be analyzed and theinput and output of each of them will be highlighted in the next sub-chapter It shouldbe noted that during the optimization only one parameter per time should bechanged in this way it is possible to see the influence of that particular parameter onthe network Another important issue is to keep track of all the changesimplemented in order to restore the network to the previous configuration if thechanges implemented had some undesired side effects With this process of storingchanges and the network behavior after the changes it is possible to create aresolution database
Previous results of the analysis and verification of the performance of thenetwork
Action plan from the previous optimization cycle
212 Outputs
Qos Criterias short-term and long-term
Measurement Plans for NetAct and Drive Test Measurements
Tool Guidelines
Templates for project reports
213 Descriptions
The starting point for the preparation is agreeing about the Master plan meaningwhat should be done in the network for shortlong terms plan involving theintroductions of New Services New Features Capacity and Service Areasexpansions
The output of the Master Plan are affecting the Preparations phase since it will clarifywhich targets to set for the network as well as gives input for future actions on theshort and long term plan (HW and SW)
Setting the targets for the network performance in terms of capacity coverage andquality will get inputs from the short and long term planning as specified in themaster plan Depending on the life stage and needs of the network and dependingon which target will be selected the Quality of Service Criteria can be set in the formof specific network quality performance indicators Both Customer (Operator) andNW manager should take part in finding the most suitable QoS criteria for thenetwork
If thinking on high level the most common indicators would be Call Drop Rate andCall Setup Success Rate The Nokia approved KPIs can be found in [1]
The selected targets will provide inputs for planning the measurements to be run inorder to make sure that the targets are met
When KPI to be followed (targets) in the network are defined the next step is toprepare a measurement plan and tool guidelines In optimization two major types ofmeasurements can be identified field test measurements and NMS measurementsEach of them has got prorsquos and conrsquos but both should be considered as valuable for
a good assessment of the performance of the network
bull For Field measurement the plan should include the following information
minus Tools used for drive tests
minus Resources and availability
minus Measurement mode Trace Call Generator Receiver (CPICH code power)
minus Service to be measured CS PS 384 Kbs voice hellip
minus Measurement area
minus Routes definition
minus Prepared maps
minus Number of callsdata transfers for each session
minus
Starting and ending time for each sessionminus Measurement parameters for tools
minus Collecting the data in files with proper names and store them
minus Post-process the data in order to have them in easy to analyze format
Radio Network Planner engineers agree on the field measurement mode scheduleroutes and also nominate a sub-group of people to perform the measurementsUsually field measurement teams operate during daytime The drive testmeasurements are focusing on coverage and call related parameters
The measurement route can be divided into sub-routes The length of a sub-route
should not be too long ndash the measurement time (driving time) of a sub-route shouldnot exceed 1-2 hours This arrangement reduces the size of measurement data filesand makes the analyzing work easier
The following road and area types should be included in measurement routes
bull Streets (city urban)
bull Highways (suburban rural)
bull Major roads (urban suburban rural)
bull Minor roads (urban suburban)
bull Special areas (eg airport area shopping centers)
The main focus should be on area types with the tightest requirements for networkperformance in terms of quality capacity and coverage These areas are typicallyfound in the urban regions or in traffic hot spots with densest penetration of mobilesubscribers
One survey consists of several test calls in the cell cluster area along the specifiedroutes The test call length is 2 minutes The measurements are to be done during acontinuous time period of 3-5 working days and the timing should be planned tocover at least network busy hours
bull For NMS measurements the plan should include the following information
minus The measurement schedules start and stop datetime
minus RNC measurements definitions (basic ones and supplementary ones)
minus Measurements period for collecting the data from RNC
minus Selecting at which network level the data are required (Cell BTS RNC arealevel)
minus The averaging period (1 day 1 week or peak hours info)
minus Collecting the results in proper directory
minus Reporting
The needed measurements as traffic resource availability resource accesshandover power control quality etc should be activated on RNC level in order to getthe raw counters needed to build up (K)PI on NMS level By means of scripts in
NetAct Reporter it is possible to get performance indicator on different networkelement level in order to analyze the performance and trouble-shoot the network
It should be noted that at the early stage of the networkrsquos life the NMS statistics arenot reliable due to the small number of subscribers Typically there should be atleast 50 calls during busy hour per cell
The planning of measurements leads to the definition of which tools to be used aswell as guidelines on how to conduct the measurements and what type ofmeasurements are the most suitable for the specific target at hand
If tools are suggested for both the drive test measurements and the network
performance measurements attending a training course should be considered incase it is not possible the user manual should be made available to use the tool inthe appropriate way
At the same time itrsquos important at this stage to define practical issue about how topresent reports the format of those as well as the template to be used The reportscan be in Excel format as well as charted in order to have the results at glanceDepending on the tools used in analyzing the reports can have specific formats
22 Measurements
221 Inputs
Tool Guidelines
Sufficient data storage space allocated for NetAct measurements and also for DriveTest measurements
bull NMS measurements
minus The given list of measurements to activate in the RNC
minus The measurement schedules with start and stop date
bull Drive Test measurements
minus Planned measurement areas
minus The measurement schedules with starting and stopping times
minus The raw data captured on the database system
minus Text files with separators
minus Performance reports
bull Drive test results
minus Reception levels and quality with respect to positioning
223 Descriptions
bull Drive test measurements
minus Driving according to the predefined routes
minus Storing the results onto properly named files
bull NMS measurements
minus The real measurements are run on RNC level according to the predefined listof measurements
minus On NetAct database the raw counters can be grouped on each networkelement level in order to build up formulas to describe the network in terms of(K)PI Itrsquos possible to predefine those KPIs or to tailor them according to the
needsminus The NetAct will be used for the measurements of quality For the recording of
the measurements help of the NMS expert should be taken and it should beclearly specified to himher what alarms should be recorded and for how long
minus When the required tests and measurements are agreed upon the actual datacollection is started Here are a few examples of possible measurementstests and tools
minus Traffic measurements Set up using NetAct or MML for every switch
minus Traffica measurements Centralized real time measurements from the wholenetwork
minus Protocol analyzer Nethawk or similar tool for detailed signalingtroubleshooting
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Previous results of the analysis and verification of the performance of thenetwork
Action plan from the previous optimization cycle
212 Outputs
Qos Criterias short-term and long-term
Measurement Plans for NetAct and Drive Test Measurements
Tool Guidelines
Templates for project reports
213 Descriptions
The starting point for the preparation is agreeing about the Master plan meaningwhat should be done in the network for shortlong terms plan involving theintroductions of New Services New Features Capacity and Service Areasexpansions
The output of the Master Plan are affecting the Preparations phase since it will clarifywhich targets to set for the network as well as gives input for future actions on theshort and long term plan (HW and SW)
Setting the targets for the network performance in terms of capacity coverage andquality will get inputs from the short and long term planning as specified in themaster plan Depending on the life stage and needs of the network and dependingon which target will be selected the Quality of Service Criteria can be set in the formof specific network quality performance indicators Both Customer (Operator) andNW manager should take part in finding the most suitable QoS criteria for thenetwork
If thinking on high level the most common indicators would be Call Drop Rate andCall Setup Success Rate The Nokia approved KPIs can be found in [1]
The selected targets will provide inputs for planning the measurements to be run inorder to make sure that the targets are met
When KPI to be followed (targets) in the network are defined the next step is toprepare a measurement plan and tool guidelines In optimization two major types ofmeasurements can be identified field test measurements and NMS measurementsEach of them has got prorsquos and conrsquos but both should be considered as valuable for
a good assessment of the performance of the network
bull For Field measurement the plan should include the following information
minus Tools used for drive tests
minus Resources and availability
minus Measurement mode Trace Call Generator Receiver (CPICH code power)
minus Service to be measured CS PS 384 Kbs voice hellip
minus Measurement area
minus Routes definition
minus Prepared maps
minus Number of callsdata transfers for each session
minus
Starting and ending time for each sessionminus Measurement parameters for tools
minus Collecting the data in files with proper names and store them
minus Post-process the data in order to have them in easy to analyze format
Radio Network Planner engineers agree on the field measurement mode scheduleroutes and also nominate a sub-group of people to perform the measurementsUsually field measurement teams operate during daytime The drive testmeasurements are focusing on coverage and call related parameters
The measurement route can be divided into sub-routes The length of a sub-route
should not be too long ndash the measurement time (driving time) of a sub-route shouldnot exceed 1-2 hours This arrangement reduces the size of measurement data filesand makes the analyzing work easier
The following road and area types should be included in measurement routes
bull Streets (city urban)
bull Highways (suburban rural)
bull Major roads (urban suburban rural)
bull Minor roads (urban suburban)
bull Special areas (eg airport area shopping centers)
The main focus should be on area types with the tightest requirements for networkperformance in terms of quality capacity and coverage These areas are typicallyfound in the urban regions or in traffic hot spots with densest penetration of mobilesubscribers
One survey consists of several test calls in the cell cluster area along the specifiedroutes The test call length is 2 minutes The measurements are to be done during acontinuous time period of 3-5 working days and the timing should be planned tocover at least network busy hours
bull For NMS measurements the plan should include the following information
minus The measurement schedules start and stop datetime
minus RNC measurements definitions (basic ones and supplementary ones)
minus Measurements period for collecting the data from RNC
minus Selecting at which network level the data are required (Cell BTS RNC arealevel)
minus The averaging period (1 day 1 week or peak hours info)
minus Collecting the results in proper directory
minus Reporting
The needed measurements as traffic resource availability resource accesshandover power control quality etc should be activated on RNC level in order to getthe raw counters needed to build up (K)PI on NMS level By means of scripts in
NetAct Reporter it is possible to get performance indicator on different networkelement level in order to analyze the performance and trouble-shoot the network
It should be noted that at the early stage of the networkrsquos life the NMS statistics arenot reliable due to the small number of subscribers Typically there should be atleast 50 calls during busy hour per cell
The planning of measurements leads to the definition of which tools to be used aswell as guidelines on how to conduct the measurements and what type ofmeasurements are the most suitable for the specific target at hand
If tools are suggested for both the drive test measurements and the network
performance measurements attending a training course should be considered incase it is not possible the user manual should be made available to use the tool inthe appropriate way
At the same time itrsquos important at this stage to define practical issue about how topresent reports the format of those as well as the template to be used The reportscan be in Excel format as well as charted in order to have the results at glanceDepending on the tools used in analyzing the reports can have specific formats
22 Measurements
221 Inputs
Tool Guidelines
Sufficient data storage space allocated for NetAct measurements and also for DriveTest measurements
bull NMS measurements
minus The given list of measurements to activate in the RNC
minus The measurement schedules with start and stop date
bull Drive Test measurements
minus Planned measurement areas
minus The measurement schedules with starting and stopping times
minus The raw data captured on the database system
minus Text files with separators
minus Performance reports
bull Drive test results
minus Reception levels and quality with respect to positioning
223 Descriptions
bull Drive test measurements
minus Driving according to the predefined routes
minus Storing the results onto properly named files
bull NMS measurements
minus The real measurements are run on RNC level according to the predefined listof measurements
minus On NetAct database the raw counters can be grouped on each networkelement level in order to build up formulas to describe the network in terms of(K)PI Itrsquos possible to predefine those KPIs or to tailor them according to the
needsminus The NetAct will be used for the measurements of quality For the recording of
the measurements help of the NMS expert should be taken and it should beclearly specified to himher what alarms should be recorded and for how long
minus When the required tests and measurements are agreed upon the actual datacollection is started Here are a few examples of possible measurementstests and tools
minus Traffic measurements Set up using NetAct or MML for every switch
minus Traffica measurements Centralized real time measurements from the wholenetwork
minus Protocol analyzer Nethawk or similar tool for detailed signalingtroubleshooting
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
bull For Field measurement the plan should include the following information
minus Tools used for drive tests
minus Resources and availability
minus Measurement mode Trace Call Generator Receiver (CPICH code power)
minus Service to be measured CS PS 384 Kbs voice hellip
minus Measurement area
minus Routes definition
minus Prepared maps
minus Number of callsdata transfers for each session
minus
Starting and ending time for each sessionminus Measurement parameters for tools
minus Collecting the data in files with proper names and store them
minus Post-process the data in order to have them in easy to analyze format
Radio Network Planner engineers agree on the field measurement mode scheduleroutes and also nominate a sub-group of people to perform the measurementsUsually field measurement teams operate during daytime The drive testmeasurements are focusing on coverage and call related parameters
The measurement route can be divided into sub-routes The length of a sub-route
should not be too long ndash the measurement time (driving time) of a sub-route shouldnot exceed 1-2 hours This arrangement reduces the size of measurement data filesand makes the analyzing work easier
The following road and area types should be included in measurement routes
bull Streets (city urban)
bull Highways (suburban rural)
bull Major roads (urban suburban rural)
bull Minor roads (urban suburban)
bull Special areas (eg airport area shopping centers)
The main focus should be on area types with the tightest requirements for networkperformance in terms of quality capacity and coverage These areas are typicallyfound in the urban regions or in traffic hot spots with densest penetration of mobilesubscribers
One survey consists of several test calls in the cell cluster area along the specifiedroutes The test call length is 2 minutes The measurements are to be done during acontinuous time period of 3-5 working days and the timing should be planned tocover at least network busy hours
bull For NMS measurements the plan should include the following information
minus The measurement schedules start and stop datetime
minus RNC measurements definitions (basic ones and supplementary ones)
minus Measurements period for collecting the data from RNC
minus Selecting at which network level the data are required (Cell BTS RNC arealevel)
minus The averaging period (1 day 1 week or peak hours info)
minus Collecting the results in proper directory
minus Reporting
The needed measurements as traffic resource availability resource accesshandover power control quality etc should be activated on RNC level in order to getthe raw counters needed to build up (K)PI on NMS level By means of scripts in
NetAct Reporter it is possible to get performance indicator on different networkelement level in order to analyze the performance and trouble-shoot the network
It should be noted that at the early stage of the networkrsquos life the NMS statistics arenot reliable due to the small number of subscribers Typically there should be atleast 50 calls during busy hour per cell
The planning of measurements leads to the definition of which tools to be used aswell as guidelines on how to conduct the measurements and what type ofmeasurements are the most suitable for the specific target at hand
If tools are suggested for both the drive test measurements and the network
performance measurements attending a training course should be considered incase it is not possible the user manual should be made available to use the tool inthe appropriate way
At the same time itrsquos important at this stage to define practical issue about how topresent reports the format of those as well as the template to be used The reportscan be in Excel format as well as charted in order to have the results at glanceDepending on the tools used in analyzing the reports can have specific formats
22 Measurements
221 Inputs
Tool Guidelines
Sufficient data storage space allocated for NetAct measurements and also for DriveTest measurements
bull NMS measurements
minus The given list of measurements to activate in the RNC
minus The measurement schedules with start and stop date
bull Drive Test measurements
minus Planned measurement areas
minus The measurement schedules with starting and stopping times
minus The raw data captured on the database system
minus Text files with separators
minus Performance reports
bull Drive test results
minus Reception levels and quality with respect to positioning
223 Descriptions
bull Drive test measurements
minus Driving according to the predefined routes
minus Storing the results onto properly named files
bull NMS measurements
minus The real measurements are run on RNC level according to the predefined listof measurements
minus On NetAct database the raw counters can be grouped on each networkelement level in order to build up formulas to describe the network in terms of(K)PI Itrsquos possible to predefine those KPIs or to tailor them according to the
needsminus The NetAct will be used for the measurements of quality For the recording of
the measurements help of the NMS expert should be taken and it should beclearly specified to himher what alarms should be recorded and for how long
minus When the required tests and measurements are agreed upon the actual datacollection is started Here are a few examples of possible measurementstests and tools
minus Traffic measurements Set up using NetAct or MML for every switch
minus Traffica measurements Centralized real time measurements from the wholenetwork
minus Protocol analyzer Nethawk or similar tool for detailed signalingtroubleshooting
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
minus The measurement schedules start and stop datetime
minus RNC measurements definitions (basic ones and supplementary ones)
minus Measurements period for collecting the data from RNC
minus Selecting at which network level the data are required (Cell BTS RNC arealevel)
minus The averaging period (1 day 1 week or peak hours info)
minus Collecting the results in proper directory
minus Reporting
The needed measurements as traffic resource availability resource accesshandover power control quality etc should be activated on RNC level in order to getthe raw counters needed to build up (K)PI on NMS level By means of scripts in
NetAct Reporter it is possible to get performance indicator on different networkelement level in order to analyze the performance and trouble-shoot the network
It should be noted that at the early stage of the networkrsquos life the NMS statistics arenot reliable due to the small number of subscribers Typically there should be atleast 50 calls during busy hour per cell
The planning of measurements leads to the definition of which tools to be used aswell as guidelines on how to conduct the measurements and what type ofmeasurements are the most suitable for the specific target at hand
If tools are suggested for both the drive test measurements and the network
performance measurements attending a training course should be considered incase it is not possible the user manual should be made available to use the tool inthe appropriate way
At the same time itrsquos important at this stage to define practical issue about how topresent reports the format of those as well as the template to be used The reportscan be in Excel format as well as charted in order to have the results at glanceDepending on the tools used in analyzing the reports can have specific formats
22 Measurements
221 Inputs
Tool Guidelines
Sufficient data storage space allocated for NetAct measurements and also for DriveTest measurements
bull NMS measurements
minus The given list of measurements to activate in the RNC
minus The measurement schedules with start and stop date
bull Drive Test measurements
minus Planned measurement areas
minus The measurement schedules with starting and stopping times
minus The raw data captured on the database system
minus Text files with separators
minus Performance reports
bull Drive test results
minus Reception levels and quality with respect to positioning
223 Descriptions
bull Drive test measurements
minus Driving according to the predefined routes
minus Storing the results onto properly named files
bull NMS measurements
minus The real measurements are run on RNC level according to the predefined listof measurements
minus On NetAct database the raw counters can be grouped on each networkelement level in order to build up formulas to describe the network in terms of(K)PI Itrsquos possible to predefine those KPIs or to tailor them according to the
needsminus The NetAct will be used for the measurements of quality For the recording of
the measurements help of the NMS expert should be taken and it should beclearly specified to himher what alarms should be recorded and for how long
minus When the required tests and measurements are agreed upon the actual datacollection is started Here are a few examples of possible measurementstests and tools
minus Traffic measurements Set up using NetAct or MML for every switch
minus Traffica measurements Centralized real time measurements from the wholenetwork
minus Protocol analyzer Nethawk or similar tool for detailed signalingtroubleshooting
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
minus The raw data captured on the database system
minus Text files with separators
minus Performance reports
bull Drive test results
minus Reception levels and quality with respect to positioning
223 Descriptions
bull Drive test measurements
minus Driving according to the predefined routes
minus Storing the results onto properly named files
bull NMS measurements
minus The real measurements are run on RNC level according to the predefined listof measurements
minus On NetAct database the raw counters can be grouped on each networkelement level in order to build up formulas to describe the network in terms of(K)PI Itrsquos possible to predefine those KPIs or to tailor them according to the
needsminus The NetAct will be used for the measurements of quality For the recording of
the measurements help of the NMS expert should be taken and it should beclearly specified to himher what alarms should be recorded and for how long
minus When the required tests and measurements are agreed upon the actual datacollection is started Here are a few examples of possible measurementstests and tools
minus Traffic measurements Set up using NetAct or MML for every switch
minus Traffica measurements Centralized real time measurements from the wholenetwork
minus Protocol analyzer Nethawk or similar tool for detailed signalingtroubleshooting
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Long Term Planning Activities New services new features expansion etc
Measurements data from field measurement tools NetAct and NMS
232 Outputs
Long Term Optimization Activities
Short Term Optimization Activities
Initial values of KPIs
Network Performance Report
Analysis and Verification Reports
233 Descriptions
At this stage the measurements collected and stored are analyzed and processed
The RNP engineers are responsible for analyzing the field measurement results andfinding and solving the potential problem The optimization engineers also take careof the network performance by analyzing NetAct measurements
The alarm history and the Customer complaints help the optimization engineers tofind and solve the problems Also they need to know the configuration of the networkat the moment of the optimization this information can be obtained from NetAct It ishighly recommended that during the period of optimization the network configurationis not changed In this way the effect of the optimization actions can be verifiedbetter If changes are not avoidable they have to be taken into account whenverifying the effect of the optimization actions
In order to analyze the network performance post-processing tools are used Post-processing tools provide a visualization of the measurements and produce differentkind of measurement reports
The availability of a resolution database providing a pool of already experiencedproblems will provide an invaluable help for optimization The optimization actionsand results are filed into the database for future reference
Once the problem is identified it may take time to find the solution There is twodifferent kind of solutions the soft solution and the hard solution there are noprioritization among those two meaning that it is not straightforward to know whichone to apply first but rather it is on a case by case basis With hard solution is meantan hardware change like antenna type direction downtilt fill in site etchellip while withsoft solution is meant parameter optimization Inside the soft solution there is aprioritization first the parameters are tuned but if the problem is still not solved it maybe possible to solve it by making an algorithm optimization eg AC and LCalgorithms
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
A great help for the optimization engineer will be the introduction of the NetActoptimizer This tool will support the Auto optimization feature which will be describedin chapter 3134
Before executing an action plan a request for changes will be forwarded to the rightpersonnel it could be a request for parameter changes antenna relatedmodifications more measurements The request needs approval and execution
A procedure to track changes should be suggested The output of the action plan willbe an action plan request form and the output for tracking changes will be historyfiles The request is followed by the implementation of the changes as well as by arecord of them Such a record will be filed into the change history and it will serve thepurpose to track the changes in the network History files (eg Site Folder) for eachBTS or RNC level should be available for future trouble-shooting
Whatever changes is done in the network should be tracked down (by means forexample of a trouble shooting database) with information on when why and bywhom the changes was performed This will make easier future trouble-shootingactions
The performance will be verified again against the changes onto the network
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
In this section the tools introduced in the previous chapter are described in furtherdetail Please note that at the moment it is not possible to go deeper in details on anyof the presented tools For the FMT it is too early to give any manufacturer name andany feature descriptionlist as they are still under development for updatedinformation please refer to [6]
Particular attention should be paid to the compliance of the test mobile with the3GPP standards During the writing of this document no test mobile available in themarket is in compliance to 3GPP standard Being not compliant with 3GPPstandards will make those tools less useful for the optimization purposes eg if theradio sensitivity of the test tool is much lower then the one specified by 3GPP thenthe measurements done can not be used for optimizing the network
311 Field Measurement Tool
This section describes the basic concepts of Field Measurements FieldMeasurements are used during the roll-out phase and optimization phase of thenetwork Traditionally Field Measurements are performed using a measurementphone connected to a portable computer
Cellular subscribers view the performance of the network on the basis of thecoverage and the call quality The Field Measurements tools are used to verify thisldquosubscribers viewrdquo of the network For example if a subscriberrsquos call is dropped whileoperating in a moving vehicle in a particular location the measurements should beable to duplicate this problem Other examples of subscriber complaints includeblocked calls (access failures) poor voice quality and lack of significant coverageThe field measurement tool makes these measurements stores the data andstamps the data as a function of time and location Block error rate (BLER) is aphone measurement that provides an indication of link quality
The advantage of the Field Measurements Tool compared to a NMS tool is thepossibility of running measurements even if in the network there are not many userswhile with a NMS tool there must be a reasonable number of calls per hour in orderto obtain reliable statistics
There are a number of causes for blocked calls (failed origination) dropped callsand poor BLER These causes can include the following poor RF coverage pilotpollution missing neighbors etc Lack of RF coverage is often the cause of droppedcalls and blocked calls This may occur due to a localized coverage hole (such as alow spot in the road) or it could be due to poor coverage at the extreme edge of thecoverage area
Another possible reason for the blockeddropped call is the pilot pollution which isthe presence of too many WCDMA pilot signals relative to the number of fingers inthe UE The additional pilots act like interference to the subscriberrsquos call
The missing neighbor condition occurs when the phone receives a high-level pilotsignal and it does not appear in the phonersquos neighbor list Again it acts as aninterfering signal and can cause dropped calls and high BLER
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Field measurement tool exploit the fact that the pilot channel transmits continuouslyand provides a means of identifying each base station Scanning the pilots allowsengineers to quickly examine the RF coverage in the wireless network Figure 2 is adisplay of the levels of the strongest pilots measured by a network-independent
digital receiver ie it scans all the pilot channel and not only the one in the neighborlist Note the numbers shown at the top of the bars represent the EcIo of each pilotsignal
Figure 2 Receiver-based field measurement display of the three highest levelpilots
Note also that it is not always the closest base station that produces the highestreceived pilot signal strength Different propagation conditions often exist that allowdistant signals to be received at higher levels presenting difficult-to-solve problemsDepending on whether a phone or a receiver is used to perform pilot scanning thepilot displays are usually measured in units of Ec Io or EcIo Ec is the signalstrength measurement of the pilot expressed in dBm units For example the pilotsignal may have an Ec value of -50 dBm -80 dBm or -100 dBm depending on thedistance of the field measurement tool to the base station transmitting that pilotsignal and also depending on the propagation environmental Io is a measure of thetotal power (dBm) within the 5 MHz bandwidth channel Practically speaking EcIo is
the power in an individual base station pilot divided by the total power in the 5 MHzchannel expressed in dB It provides a useful ratio to compare the power levels ofthe base stations with respect to one another (The more technical definition of EcIois the ratio of energy per chip to the interference power spectral density)
Pilot signals can be displayed by field measurement tool in several ways dependingon whether a network-independent receiver or a test mobile phone performs themeasurements The pilot display shown in Figure 2 is originated from a receiver
The receiver measures all the pilots completely independent of any networkinstructions In contrast a phone-based field measurement tool display will looksomewhat different only the pilots in the neighbor list are showed With a network-
independent tool is possible to spot missing neighbor but on the other hand is not
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
possible to reproduce a real behavior of a UE as it can not be used in connectedmode
Having both a phone and a receiver integrated into the same system assures thehighest level of network optimization The phone can tell what the symptom of theproblem is and the receiver can tell why the problem occurred For example thephone-based software can measure the drop call or BLER percentage High BLERcan cause sub-scribers to experience dropped calls or poor voice quality but thephone does not reveal why this condition is happening The phone can measure theactive and neighbor pilots as shown here but this is not sufficient to locate thesource of the problem On the other hand the receiver can measure all the pilotsand indicates that there is a pilot which is not in the phonersquos neighbor list Thereforethis missing neighbor can cause excessive interference to the phone with high droprates and high BLER If the missing neighbor is the dominant pilot then the problemis even worse
Using a field measurement tool that includes an integrated receiver and phone canhelp engineers to significantly reduce the time and resources spent resolvingwireless network problems Finally post-processing the collected drive-test dataallows the engineer to quickly spot the problems as a function of the userrsquos locationon street-level maps
In the 3GPP standard it is specified which measurements the UE should support Forthe FDD mode the measurements are
bull CPICH RSCP ndash The Received Signal Code Power This is the received power ofthe CPICH channel as measured by UE It can be used mainly to estimate thepath loss as the transmission power of CPICH is either known or can be read
from the system informationbull UTRA carrier RSSI ndash The Received Signal Strength Indicator the wide-band
received power on the channel bandwidth in downlink
bull CPICH EcNo ndash The received energy per chip divided by the power density in theband This is the most important UE measurement in WCDMA for networkplanning purposes as it is a coverage indicator Theoretically it is identical toCPICH RSCPRSSI
bull Transport channel BLER ndash The estimate for the block error rate It is based onthe CRC evaluation on each transport block after radio link combination
bull UE transmitted power
Those are the measurements that any UE has to perform most probably the fieldmeasurement tool will be able to display many more measurements All the othersmeasurements are manufacturer dependent
312 Nemu
Network Element Management Unit (NEMU) is a new computer unit in DX 200 andIPA2800 network elements based on Windows NT software platform and industrialserver technology [11] [12]
The main functions of NEMU are to provide
bull A platform for different network management applications and tools
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
bull Redundant expandable hard disk capacity for storing measurement andconfiguration data database backups etc
bull Scalable hardware to support new applications
bull Easy-to-use graphical user interface (supporting local and remote operation)bull A mediation functionality between DXIPA2800 network element and NetAct that
can be used ie to filter and buffer collected data and
bull Common network element management tools and interfaces for 2G and 3Gnetwork elements
The NEMU Performance Management (PM) service block is used for networkperformance measurements and post processing of measurement data it providesthe following user interfaces
bull The Measurement Handling GUI manages measurements that are running in theRNC
bull The Measurement Presentation GUI creates graphical and textual presentationfrom periodic measurements
bull The Measurement Data Explorer (part of PMViewer application) allows the userto browse the content of the measurement database
bull The Online Monitoring amp Presentation GUIs show the online monitoring data inreal time in either textual or graphical form
The prerequisite for NEMU PM is RNC must implement a PM functionality
NEMU PM transfers measurement data from DX and stores it to NEMU SQL
database It is able to send measurement report file notification events to NMS andsend notifications about the changes of measurement states to NMS (iemeasurement has been stopped and due to that a report is stopped) Onlinemonitoring data is not transferred to NMS
Later release of NEMU PM may include KPI equation evaluationcalculation inmeasurement data presentation NMS sends a KPI formula plan to NEMU whichdefines a group of logical counters that contains the formula for calculating a keyperformance indicator from raw counter data NMS can after that request logicalcounters in measurement reports in addition to raw counters
Another possible feature to be included in the future release is observation An
observation is a NE object level measurement Observations are presenting moreprecise information than the normal periodic measurements therefore they are usedmainly for troubleshooting purposes At the moment there are no commitment for anyobservation support
313 NetAct
NetAct System provides access to creating analyzing assigning monitoringmodifying clearing and closing action requests at all stages of the workflow All thefeatures described in this chapter are related to the OSS 3 version which will bereleased during years 2001-2002
Nokia NetAct common functionality contains the following
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
In Figure 3 it is illustrated the different area that the NetAct family will cover
Figure 3 NetAct
3131 System platform
Alarms and performance data (Alarm Data Collection and Measurement DataCollection) are collected from the network elements through the mediation andadaptation layer and stored centrally in Nokia NetAct Adaptation to elements orelement managers makes it possible to handle alarms and performance indicators inthe same way regardless of technology or origin The network monitoring and
reporting functionality is generic across all network technologies
The network statistics and measurements are collected and stored temporarily in thenetwork elements or element management systems Specified raw counters areprocessed into performance (PI) and key performance indicators (KPI) andtransferred to the Nokia NetAct
Alarm and measurement data are collected and stored in regional or global NokiaNetAct databases for monitoring and reporting purposes according to operatorrsquosneeds Alarm Data Storing enables to receive alarm data in order to reflect the truealarm situation and to store the data to the alarm database of Nokia NetActMeasurement Data Storing includes the data storage for insertion and retrieval of
measurement data When counters are fetched from the database the computationfunctionality gets the counters and performs calculations according to given
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
parameters Generic database schema makes the adaptation to different networktechnologies easy
3132 NetAct Monitor
Monitor provides a set of tools for pre-processing storing and displaying real-timealarms from the network This enables efficient fault detection and analysisimproving the network quality and customer satisfaction
Tools for daily network monitoring tasks offer means for planning effectivemonitoring strategies and optimizing the alarm flow analyzing network datarectifying problems and escalating problem handling within the operator organization
1 Real-time network monitoring
Hierarchical and scalable views over the operatorrsquos entire managed network arevisualized on the Top-level User Interface The views can include a geographical
map that is placed underneath the logical device symbols representing the networkelements and logical components Graphical views are easily adjustable to thedifferent monitoring needs from network monitoring to element level and technologyspecific expert monitoring In upper level views users can quickly see the generalalarm situation of the managed network The sub-level views show the alarms Top-level User Interface is also a starting point to activate other Nokia NetAct applicationsand the embedded online documentation
2 Troubleshooting the network
Monitor tools provide access to a range of effective tools for locating and isolatingfaults in the entire managed network Alarm History Handling is intended for
troubleshooting network problems by making database queries Remote AlarmBrowser speeds up the process of fault location giving the field personnel easyaccess to all fault history data via a remote connection (Intranet LANWAN PSTN orGSM) Both online monitoring mode and history handling mode are available
3 Traffica
Traffica is used for real-time monitoring and troubleshooting in the mobility corenetwork With Traffica it is possible to complete the troubleshooting process bymonitoring every single call attempt in the network
Traffica is a source for real-time information since it shows the operator the service
performance from the end userrsquos point of view Operator is able to monitor both thequality of service (congestion dropped calls etc) and the quality of network Trafficais of valuable help in optimizing the network since the effect of changes made innetwork configuration can be easily verified with Traffica
Traffica extracts information from switches and visualizes the traffic in bothpredefined and user definable format The data is stored in a database for furtheruse
With Traffica operators can export the most essential data fields to another forexample 3rd party system This data includes clear codes MSISDN IMSI and IMEIfor A and B subscriber location of A and B subscriber information about call start
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
With NetAct Reporter operators can view and analyze the network performance faultand configuration data coming from multiple sources Raw data becomes meaningfulinformation that is visualized in graphical and textual reports The same tools for thecreation of ad-hoc and on-demand reports can be flexibly used both at regional andglobal level
Key Performance Indicators are the most important indicators of networkperformance By producing KPI reports regularly or on demand it is possible todetect the first signs of performance degradation and prevent the development ofcritical network problems KPIs on network level can be used for analyzingperformance trends on RNC level for locating problems and on BTS level fortroubleshooting specific BTSs Reporter provides a comprehensive set of predefinedreports based on KPIs The predefined KPIs can also be used in creating customizedreports with Reporter tools
With Thresholds for Measurement Data the operator can analyze the incomingmeasurement data both directly and automatically for example to monitor the QoS inthe network An alarm is generated when abnormal measurement values arereceived The tool automatically verifies the new performance measurement valuescollected from the network against the pre-defined threshold rules It is easy toschedule the activation of thresholds with different thresholding rules for day andnight
Report Builder includes a set of predefined report definitions as well as the possibilityto specify the operatorrsquos own reports ad-hoc Report Builder is designed for locatingproblem areas in the network With Report Builder objects can be selected and
sorted according to user-specific criteria Also predefined static reports for recurringreporting needs are easy to generate with Report Builder Different object levels anddifferent vendorsrsquo network elements can be freely combined to the same report Thefollowing functionality is supported
bull Pre-defined reports
bull Wizard-based report creation
bull Support for object grouping using working sets or Maintenance Regions
bull Report access based on user groups
bull Creating KPIs from raw counters or other KPIs
On-demand Report Toolkit allows developing tailored web user interfaces andreports for filtering highlighting and visualizing performance data Users can defineinteractive reports with a consistent look and feel On-demand reports are executedat the time the user requests them thus always presenting the latest informationfrom the data source On-demand Report Toolkit offers functionality for the followingreporting use cases
bull Combining different objects in one report
bull Combining KPIs with conflicting SQL delimiters
bull Predefined or static reports for recurring reporting
bull Task-oriented interactive data filtering and visualization
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
NetAct Optimizer will offer means for automating parts of the optimization processOptimizer will be part of Nokia NetAct release 40 scheduled to be out in the end of2002
31341 Background for automated optimization process
The control for the radio access part can be divided into three layers The first layeris the pre-operational and statistical mode Meaning the actions performed with anoff-line planning tool or simulator Optimization and radio network performancetuning at this level is based on long term statistical data and is usually combined withnetwork enhancement process The next layer is the statistical feedback loop in the
Operations Support System The third layer consists of the real-time feedback loopsin base station Radio Network Controller Base Station Controller or Common RadioResource Manager
The statistical feedback loop in OSS is based on collection of measurements fromthe network Measurements are combined with a cost function to find minimum andmaximum performance levels The output of this operation is further optimized bytuning the configuration parameter settings Optimization can be targeted to improvethe radio resource utilization by changing the operating point on the capacity-coverage-cost trade-off curve Optimization is involved also when the network isenhanced in terms of new sites or services or changes are made for example in theservice-provisioning
At this level it is possible to enhance the optimization of single KPIs and single cellsto the optimization of the capacity-coverage-cost trade-off between different servicesand cell clusters
31342 Optimization process with Optimizer
Figure 3 presents how Optimizer integrates with the NetAct family
First of all the quality definition is needed The overall end-to-end quality and basedon that the quality criteria for each service type has to be defined by the OperatorThe thresholds for KPIs are then set based on this information NetworkPerformance Data (Measuring and Monitoring) can be gathered from NetworkManagement System tools field drive tests protocol analyzers andor customercomplaints Network Reporting tools provide statistical and pre-analyzed informationabout the performance Based on the network configuration performance isanalyzed in detail and corrections are done interactively in the loop by solving theindividual parameters affecting the reported performance Tuning of the individualparameters can happen in an iterative loop until the performance criteria are met Fornetwork wide performance improvement operations a solution such as that providedby Optimizer is needed to optimize groups of KPIs and cells together After thecorrections have been implemented to the network the quality cycle starts from thebeginning
Optimization process is started when the monitored performance drops below the settargets when a periodical tuning task is to be started or when there is need tooptimize the behavior of new network elements in the network
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Performance data is collected from selected measurements for a predefined periodof time using Nokia NetAct Reporter (or similar tool providing Optimizer compatibleoutput) Collected data is analyzed for causes of lowered network quality Additionaldata and analysis may be needed for pinpointing the problem
Objects from the target area actual parameters and measurements are available inOptimizer via interfaces to configuration management and reporting tools Furtheranalysis and different solution alternatives can be done in Optimizer
Once the problem is solved either manually or by using Optimizer algorithms theeffect of proposed changes is verified in Optimizer Before plan implementation theconfiguration changes are validated and the new parameters are provisioned in thenetwork with the functionality of Radio Access Configurator (or preferredconfiguration management tool) The changes in the network are followed bymonitoring the achieved performance
This optimization process will be described in more detail in a procedure calledOptimizing network using NetAct Optimizer which will be part of Optimizer userdocumentation and NetAct document library
31343 Optimizer functionality
NetAct Optimizer includes the following functionality
bull General functionality
bull GIS Based Visualization Network elements their characteristics andperformance are visualized on geographic display for efficient analysis of networkbehavior It is possible to visualize several type of data in the geographic display
view like terrain type and profile population density traffic distribution and otherperformance indicators When all these are combined with the elementconfiguration data radio signal propagation information and the measuredperformance figures the result is an informative view of the situation
bull Graphical Object and Parameter Management Optimizer presents the networkelements and all necessary parameters in easy and effective way in graphicaluser interface where data searching sorting and mass editing is supported Highusability solutions are provided for processes where large amount of data ishandled
bull Data Interfaces Optimizer is primarily planned to complete the optimizationprocess in Nokia NetAct Framework However Optimizer provides open
interfaces PM data transfer between any preferred reporting tool which is able toadopt the provided data format In addition NetAct has among others open CMdata interfaces for configuration data management
bull Optimization functionality
bull Adjacency Management Optimizer includes functionality to optimize GSMadjacencies create and tune WCDMA adjacencies and create and tune inter-system adjacencies between GSM and WCDMA The tuning is based on mobilemeasurement reports collected by BSCsRNCs Separate measurements arerequired for GSM WCDMA and GSMWCDMA adjacency tuning
bull Mobile Measurement Based Frequency Planning Up-to-date mobile
measurements from the network are used for producing an interference matrixwhich thus will be more accurate than any prediction based information The
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
contents of the matrix can be controlled and even manually managed at all timesif needed Frequency planning algorithm creates a new frequency plan based onthe interference information The resulting frequency plan can be visualized and ifacceptable the retuned frequency plan can be implemented in network or
scheduled for implementation The interference matrix can also be exported to beused with a preferred external AFP tool
bull Automated DL Scrambling Code Allocation Optimizer provides an automatedsolution for primary scrambling code allocation for WCDMA cells based on celladjacency information
bull Co-siting When building WCDMA network on the same area as existing GSMnetwork the same sites are usually preferred The measured GSM service andtraffic information can be analyzed to find out the optimal WCDMA BTS co-sitelocations
bull Traffic and Capacity Optimization Optimizer provides means to balance trafficload in GSM (including dualband) and WCDMA networks by tuning essentialparameters with reported measurement results
For all these optimization functionality it is included a tool for result verification andmanual modification
For more information on Optimizer functionality refer to [20]
314 Load Generator
It is known that in UMTS networks coverage quality and capacity are closely linked
Coverage shrinks with load quality degrades with load EbNo required to achieve agiven quality degrades with load (more interference variations) Due to this reasonssome operators require the acceptance test under loaded conditions
There are three different ways to simulate the load in the network
bull many mobiles in the field
bull noise generator and attenuators
bull OCNS
The first solution requires a big amount of mobiles to create a real load in thenetwork This solution is not feasible at the moment as there are no UErsquos on themarket
The second solution is with noise generator and attenuators The noise generator isput close to the BTS antenna and it is used for simulating the DL load This solutionhas some drawback it requires more then one noise generator in case of a clusteracceptance in load condition basically one noise generator per neighbor cell isrequired The noise generated is white gaussian noise not synchronized with the DLtransmission of the BTS The attenuators are used to simulate the UL load as theload effect on the uplink is the decreasing of the BTS sensitivity which can be seenas an increase in the received power eg 3 dB for 50 load Those attenuators
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
The third solution is through the OCNS (Orthogonal Channel Noise Simulator) whichis a load generator implemented in the BTS It is widely used in the IS95 BTSbecause it is cheap and easy to set It is still not known when this feature will beavailable (RAN 15RAN 2) The OCNS reserves some spreading codes in the BTS
in order to simulate DCHrsquos and they are transmitted on air In this way it is possible togenerate synchronized DL noise It should be possible to define the number ofdummy codes and relative power from the RNC For the UL the idea is to route theDL signal back to UL with adjustable attenuator in order to calibrate the UL load
32 Measurements
In the following sub-chapter it is presented the measurements done with the NokiaWCDMA experimental system for more information please refer to [18] Thisnetwork was according to the ARIB standard which has some small differencescompared to the 3GPP regarding the layer 1 properties The measurements doneregarding the UE Tx power are valid if they are considered as a trend of the network
rather then absolute values please note that the maximum output power of the UEwas 5 W It can be easily seen that the required UE Tx power depends on the speedof the UE and on the configuration of the BTS (diversity)
321 Mobile transmission powers in the laboratory
The measured mobile transmission powers during the laboratory measurements areshown in Figure 4 to Figure 6 These results show the behavior of the WCDMA fastpower control with different mobile speeds and with different degree of diversity Themeasured results look very similar to those obtained in the simulations
0 200 400 600 800 1000 1200 1400 1600-1 0
-5
0
5
10
15
20
25
d B m
Slots (10 second total )
ITU Pedest r ian A 3kmh
No an tenna divers i tyW ith antenna divers i ty
Figure 4 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 3kmh
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Figure 5 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 20kmh
0 200 400 600 800 1000 1200 1400 1600
-10
-5
0
5
10
15
20
25
Slots (10 second total)
d B m
ITU Pedestrian A 120kmh
No antenna diversityW ith antenna diversity
Figure 6 Example effect of antenna diversity in the mobile transmissionpowers in the measurements ITU Pedestrian A 120kmh
322 Mobile transmission powers in a real network
These measurements have been carried out in the Nokia experimental system in thefollowing route Figure 7 According to laboratory measurements (see above) andcorresponding simulations with three speeds (3 kmh 20 kmh and 120 kmh) the20 kmh is the speed that is most vulnerable to power control functionality At this
speed fast power control is no longer able to compensate effectively for fast fadingand the 10 ms interleaving is not yet effective any providing time diversity The
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
behavior of uplink power control at different speeds as a function of measurementdistance (for a 2 meter sample) is demonstrated in Figure 8 (vertically polarized Rxand diversity Rx branches Transmission is vertically polarized) and Figure 9(vertically polarized Rx branch with no Rx diversity Transmission is vertically
polarized) Those figures clearly show how the power control works better at a lowspeed 3 kmh this because of a better fast fading compensation ability At 20 Kmhthe power control can not follow the fast fading anymore thus degrading theperformance of the network higher average transmitted power At high speed 120Kmh the power control still do not work perfectly but the interleaving starts to givesome gain thus decreasing the average transmitting power It must be noted that the2 meter samples shown for the three speeds in Figure 8 and Figure 9 are not exactlyfrom the same spot due to a locationing margin and therefore the individual peakscannot be directly compared
Longitude in KKJ (meters)
L a
t i t u d e
i n K K J ( m e
t e r s
)
3378 3379 338 3381 3382 3383 3384
x 106
6678
66785
6679
66795
668
66805
6681
66815
6682x 106
Figure 7 Selected part of a route drives shown on a map of the greaterLeppaumlvaara region The red crosshairs show the selected routealong the blue line indicating the total length of the road
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Figure 8 MS Tx power (dBm) with the Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
Figure 9 MS Tx power (dBm) without Rx diversity scenario for a shortdistance of 2 meters There are three different speeds (drive 1 = 3kmh drive 2 = 20 kmh and drive 3 = 50 kmh)
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
This chapter describes the main parameters that are supposed to be tuned in thefirst optimization of the network
It should be noted that in an optimization procedure the configuration of the networkis the most important parameter If the location of the site andor the antennadirection are wrong then it is impossible to optimize the network by just tuning someRRM parameters from NetAct
In this document we assume that the implementation is properly done eg noswapped cables
Before starting any of the following Optimization processes the radio planner shouldcheck that each cell has a well-defined dominance area Dominance area is the mostimportant issue in WCDMA planning if the dominance areas are not well-define thenthe interference created will degrade the overall capacity of the network Thedominance area can be controlled in different way ie selecting the right antennalocation on the rooftop defining the correct antenna direction and downtilt
41 Dominance issue
With the 3rd generation system planning is more interference and capacity analysisthan only coverage area estimation During the course of the radio network planningthe base station configurations need to be optimized the antenna selectionsantenna directions and even the site locations need to be tuned as much as possiblein order to meet the QoS and the capacity and service requirements The resultspresented in this chapter are coming from a study made by Jaana Laiho-SteffensAchim Wacker and Pauli Aikio [2] and it shows how radio network planning can beused to meet those requirements and to improve the network performance
The simulations used for this purpose were using a ITU vehicular A channel profileIn the test scenario the Shinjuku area in Tokyo has been used assuming all users tobe indoors The 135 km2 area was covered with 10 sites The selected antennainstallation height was 50 meters the propagation loss was calculated with theOkumura-Hata model with average correction factor of ndash41 dB In the simulationsomni- three- four- and six-sector configurations have been used the site locationswere kept fixed Also 5 different antennas were used with 3 dB beam widths of 120ordm90ordm 65ordm 33ordm and additionally an omni antenna The gains of all antennas was set to15 dBi and for the SHO addition window a value of ndash4 dB was used
In the antenna tilting study the electrical tilting was applied and with the help of theresults it can be seen that an optimum tilt angle can be found the capacity and thecoverage probability both have to be considered The results of this study arecollected in Table 1
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
UL coverageprobability(outdoor toindoor) for864144kbits
OMNI CASE0deg 079 239 28 70 32 40
Three sectored case 65deg antenna
0deg 088 575 40 86 59 62
4deg 075 624 39 91 71 72
7deg 059 697 36 92 76 76
10deg 037 856 30 90 75 74
14deg 038 787 32 81 62 61
Four sectored case 65deg antenna
0deg 109 604 41 92 70 71
4deg 094 707 30 95 81 81
7deg 072 833 26 96 84 83
10deg 047 959 21 94 82 81
14deg 050 886 26 86 69 68
six sectored case 33deg antenna0deg 115 880 48 93 76 76
4deg 103 946 49 96 83 83
7deg 088 1037 45 96 85 84
10deg 073 1054 41 95 83 82
14deg 058 930 33 86 70 69
Table 1 Impact of the antenna tilt on the network capacity
In these simulations the optimum tilting angle is from 7deg to 10deg The relative highoptimum tilt angle can be explained by the big antenna installation height (50m)From the Table 1 it can be seen the trend that by down tilting the antennas the otherto own cell interference ratio i is going down as the tilting is increased This isbecause the antenna main beam is not delivering so much power towards the otherbase stations and therefore most of the radiated power is going to the area that isintended to be served by this particular base station eg good dominance A greathelp to the Optimization is the possibility to change the downtilt of the antennaremotely from the NMS either manually or with an autotuning algorithm This featurewill be available in the future and it is just one of the different autotuning algorithmthat will be available for the optimization another one is the pilot power optimization
In this analysis it is illustrated the capacity improvement as a function of thesectorisation each base station has been simulated as omni-site and as a site withthree four or six sectors Furthermore by simulating the scenarios with antennashaving different beam widths the importance of correct antenna selection for a
sectored configuration is emphasized with help of some examples For all scenariosthe MHA was in use the maximum MS transmit power was 24 dBm and antennaswere not tilted The results related to the sectorisation study are in Table 2
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
UL coverageprobability(outdoor toindoor) for864144 kbits
OMNI CASE
omni 079 240 28 70 32 40THREE SECTOR CASE
120deg 133 441 39 85 50 59
90deg 119 461 35 87 55 62
65deg 088 575 34 86 59 62
FOUR SECTOR CASE
120deg 172 489 54 90 62 68
90deg 149 510 51 92 67 72
65deg 109 604 41 92 70 71
33deg 092 691 40 88 65 64
SIX SECTOR CASE
120deg 218 593 64 95 75 79
90deg 197 627 59 96 80 82
65deg 143 758 55 96 80 81
33deg 115 880 48 93 76 76
Table 2 Impact of the antenna selection
With the results in Table 1 and in Table 2 it can be concluded that with rather simpleradio network planning means (antenna tilting and correct antenna selection for eachscenario) the interference can be controlled and the capacity of the network can beimproved without changing any parameters In the simulations presented in the studyeach of the base stations was optimized in a similar manner In reality the basestations antennas are not installed at equal height and thus the optimization of thebase stations should be performed site by site
42 Key parameters
During the first half of 2001 one of the main activity of the 3G FMF [10] was tofinalize the Telecom and RRM parameters Those parameters are stored in theparameter dictionary The default values are coming from simulations andexperience At present time there is no test network to validate those values so beaware that they may change in the near future The latest approved parametersvalue can be found in [7]
From those hundreds of parameters some has been selected as the most importantparameters for the optimization [13] Those 68 parameters should be considered asthe first one to be tuned during the optimization of the network they can be found inTable 3 They are divided according to the area of influence
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Further more different sets of default values for different environments (urban suburban rural) and for different cell layers (macro micro pico) are collected and
explained in [17]
A smaller set of parameters are illustrated in Table 4 they can be divided into threedifferent categories Handover Control Admission Control and Power Control Withthe help of simulations and experience the influence of those parameters on thePIKPI is explained in [8]
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
The parameters marked with rsquorsquo are belonging to a set One set is a collection of allthe parameters relative to the handover There can be up to 100 different sets storedin the RNC and the radio planner has to associate for each cell one set for the RTconnection and one for the NRT connection Those sets influences the handoverperformances of the network like Soft HO overhead or the Total Net Erlang eg Ifthe MaxActiveSetSize is too big then DL Total Net Erlang goes down as there aretoo many cells in soft handover leading to a waste in resources On the other hand ifthat parameter is set too low we have an increase in the Call Drop Rate as the UEsees a strong pilot but it can not add it to the active set this will increase theinterference therefore the Call Drop Rate The same effect can be seen with theparameter Replacement Window if it is set too high the new cell will be a strong
interferer before been admitted in the active set
The parameters CPICHToRefRabOffset PrxTarget PtxTarget are related toAdmission control Their main influence is on the Call Setup Success Rate Indownlink the AC will use CPICHToRefRabOffset to estimate the interference that thenew RAB will introduce and if this calculated interference plus the actual totaltransmitted power is higher than PtxTarget then the new RAB will not be admitted Inuplink the bitrate and EbNo of the new RAB is used for received power increaseestimation and if the estimated total received power is higher than PrxTarget then thenew RAB will not be admitted Those three parameters plus PrxOffset and PtxOffsetalso have a strong impact on the Call Drop Rate as if the interference will be higherthen the Target plus the Offset AC will enter in the overload condition and will start
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Particular attention should be paid in defining the CPICHToRefRabOffset as if it isset too low there will be a higher estimation of DL power increase due to a newbearer This can cause frequent downlink call rejections leading to deteriorated CallSet-up Success Rate and less DL throughput If it set too high DL power increase
due to a new bearer will be estimated too low and undesirable call admission mayhappen so the system will operate in overloaded condition resulting in poor FERpossibly increased Call Drop Rate and Call Set-up Success Rate Notice thatCPICHToRefRabOffset has also a direct effect to DL coverage since it specifies themaximum transmission power of the reference service which is calculated (in dBm)by subtracting the value of the parameter from the transmission power of the primaryCPICH Maximum power for other services are scaled by bitrate and EbNo Sowhen setting that value it should be paid attention to not set it too high otherwisethere will not be enough power for the Radio link at the cell border
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
This chapter describes the optimization procedures on parameter level It is assumedthat the hardware level optimization has been completed For example cleardominance areas exists
The following results are from research performed by Nokia Korea [14] [15] [16]
The following studies are based on dynamic simulations not on the real networkmeasurements it is important to interpret the data (graphs and tables) in the senseof trends not absolute numbers The reason is that the tool is not calibrated egfor example the call drop rate is depending on the dropping criteria It is just a modelof a network not real one with layered protocol etc
51 Handover performance
This chapter reports and analyzes a simulation campaign intended for the validation
of a Soft Handover Overhead (SHOO) optimization procedure and Soft HandoverGain From that simulation the handover parameters which have a significantinfluence on SHOO have been found to be AdditionWindow DropWindow and MaxActive Set Size (Assize)
This simulation is designed to decrease SHOO by varying handover parameterswhile monitoring the whole network performance or general optimality
511 Target values
The target for the metric is found from Table 5 This target is a value for a maturenetwork usually at the beginning of the networkrsquos life this value is higher The
complete list of KPIs and their target values is displayed in the document 3G RANKey Performance Indicators [1]
Metric RT + NRT
SHOOverhead
lt 50
Table 5 Target value
This target value is mainly based on the hardware requirements for example toprevent running out of codes When the upper limit of Soft Handover Overhead hasbeen reached the optimization of Soft Handover Gain can start See the SHO Gain
procedure
A high Overhead is generally not a problem for the uplink In the UL the power fromthe mobile is on air anyway but the overhead is increasing processing load at theBTS For the downlink however there exist an optimum value At this optimum thehandover gain is maximal This means that all BTSrsquos in the active set contributepositively to the received signal in the UE By following the Call Drop Rate CallSuccess Rate and BTSTxPower it is possible to get an indication of the gains Thiscan be clearly seen in the simulation results presented in chapter 514
512 Parameters
This chapter discusses the input parameters that are present in Nokia RAN 10 [7]and are directly related to Soft Handover Overhead The parameters of interest arebased on the document from the SKT-Nokia RampD Collaboration ndash project [8]
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
minus Description Addition Window determines the relative threshold (A_Win) which isused by the UE to calculate the reporting range of event 1A The threshold iseither relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of a monitored cell (M_new) enters thereporting range the UE shall transmit a Measurement Report to the RNC in orderto add the monitored cell into the active set
minus M_new gt= W M_sum + ( 1 - W ) M_best - A_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 4 dB
The bigger the Addition Window the wider the Soft HO area and Soft HO OverheadIf it is set too high unnecessary soft HO branches will be added and DL Throughputwill decrease
If it is set too low Soft HO Overhead is too small decreasing the UL macro-diversitygain UL Throughput will get down Frequent HOrsquos due to Ping-Pong effect are alsoexpected when both Addition Window and Drop Window are smaller than requiredhysterisis margin Accordingly signaling overhead increases and the slight radiocapacity reduction is expected See Figure 10
Note that this is mainly for city environment Coverage is not taken into accounthere
AdditionWindow
Too wide soft HOarea
Too small soft HOarea
+ Soft HOOverhead
UL macrodiversitygain decrease
- UL Troughput
too high
too low
unnecessary softHO branch
addition- DL Troughput
frequent HOs+ signallingoverhead
Figure 10 The impact of AdditionWindow
5122 Drop Window
minus Abbreviated name DropWindow
minus Parameter group HCConfiguration
minus Description Drop Window determines the relative threshold (D_Win) which isused by the UE to calculate the reporting range of event 1B The threshold is
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
either relative to the CPICH EcNo measurement result of the best active set cell(M_best) or to the sum of active set measurement results (M_sum) dependingon the value of the parameter Active Set Weighting Coefficient (W) When theCPICH EcNo measurement result of an active set cell (M_old) leaves the
reporting range the UE shall transmit a Measurement Report to the RNC in orderto remove the cell from the active set
minus M_old lt= W M_sum + ( 1 - W ) M_best - D_Win
minus Range and step 0 145 dB step 05 dB
minus Default value 6 dB
If it is set too high unnecessary Soft HO branches will remain undropped Thisincreases Soft HO Overhead expands Soft HO area and accordingly decreases DLThroughputIf it is set too low eg the same value as AdditionWindow branch deletion and
addition is to be repeated increasing signaling overheadDirect Relation to
Drop Window
unnecessary softHO branches
remain undropped
+ Soft HOOverhead
too high
too low
too wide soft HOarea
- DL Troughput
frequent HOs + signallingoverhead
Figure 11 The impact of WindowDropRT
5123 Maximum Active Set Size
minus Abbreviated name MaxActiveSetSize
minus Parameter group HCConfiguration
minus Description Parameter determines the maximum number of cells which canparticipate in the softsofter handover
minus Range and step 1 3 step 1
minus Default value 3
The primary parameter controlling the addition of soft HO branch for RT traffic isAddition Window MaxActiveSetSize takes the secondary role by limiting the totalnumber of branches
When a MS already has enough number of soft HO branches the increase of softHO gain (reduction of target EbNo) due to addition of another branch can benegligible In that case addition of new branch means addition of Soft HO Overheadand DL interference This leads to the increase of DL Total Link Traffic andaccordingly the decrease of DL Total Call Traffic DL capacity reduction maynaturally cause UL capacity reduction
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Too small active set size may hinder necessary HOs Even a necessary soft HObranch might be added only when its power is stronger than that of the weakestexisting active branch by ComparisonThreshold This may require the increase of DLand UL transmission power tofrom the MS and thus decreasing DL and UL
Throughputs If the MS locates in a high pathloss area requiring high tx powerDLUL BLER Satisfaction Rate can rise due to power scarcity and possibly call dropwill happen See Figure 12
MaxActiveSetSize
unnecessary softHO branch
addition
hinder necessarysoft HO branch
addition
+ Soft HOOverhead
require highertransmit power to
a MS+ DL BLER + Call Drop Rate
too big
too small
require highertransmit power
from a MS+ UL BLER
- DL Troughput
- UL Troughput
Figure 12 The impact of MaxActiveSetSize
5124 Drop Time
minus Abbreviated name DropTime
minus Parameter group HCConfiguration
minus Description When an active set cell leaves the reporting range (drop window)the cell must continuously stay outside the reporting range for a given periodbefore the UE can send the Measurement Report to the RNC in order to removethe cell from the active set (event 1B) The period is controlled by the parameterDrop Time
minus Range and step 0 ms 10 ms 20 ms 40 ms 60 ms 80 ms 100 ms 120 ms160 ms 200 ms 240 ms 320 ms 640 ms 1280 ms 2560 ms 5000 ms
minus Default value 320 ms
Too long threshold may cause unnecessary SHO branch(es) to be active for a longtime ultimately increasing Soft HO Overhead and keeping unnecessary DL Txpower being transmitted This adds to DL loading of the cell and probably causes ACto block new call setups In that case DL Call Traffic will reduce
Too short threshold may introduce handover Ping-Pong phenomenon Thisphenomenon increases signaling overhead See Figure 13
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
cause unnecessayHO branch(es) tobe active for long
ping-pongphenominon
unnecessarytransmission of DL
power
DL loadingincrease
- Call SetupSuccess Rate
+ SignalingOverhead
too logn
too short
+ Soft HOOverhead
- DLUL Troughput
Figure 13 The impact of DropTimerRT
5125 Transmission power of the CPICH channel
minus Abbreviated name PtxPrimaryCPICH
minus Parameter group PCConfiguration
minus Description This is the transmission power of the primary common pilot channelwhich is used for neighbor measurements and MS channel and SIR estimationCritical for the network performance Default value is 5-10 of the maximumtransmitting power of WCDMA BTS with 43 dBmcarrier
minus Range and step -10 50 dBm step 01 dBm
minus Default value 30 dBm
minus Default valuersquos notes Default value should be checked
CPICH channel is used for neighbor cell measurements and SIR estimation in themobile and is transmitted 10 to 15dB below the total transmit power of WCDMA
BTS
5126 Replacement Window
minus Abbreviated name ReplacementWindow
minus Parameter group HCConfiguration
minus Description When the number of cells in the active set is the maximum and amonitored cell becomes better than an active set cell the UE shall transmit aMeasurement Report to the RNC in order to replace the active cell with themonitored cell (event 1C) The parameter Replacement Window determines themarging by which the CPICH EcNo measurement result of the monitored cell
must exceed the CPICH EcNo measurement result of the active cell before theUE can send the event 1C triggered Measurement Report to the RNC
minus Range and step 0 75 dB step 05 dB
minus Default value 2 dB
It is important to keep the elements of the Active Set being the best servers amongBSs
Too high threshold may prevent best serving BS from entering Active Set Active Setwhich is not being composed of the best servers requires transmission power from
each BSs and the MS as well Higher transmission power will increase UL and DL
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
loading and will cause AC to block new call setups Furthermore UL and DL carriedtraffic will decrease But we expect that the impact will be minimal
Too low threshold will cause frequent member changes of Active Set This will add tothe number of HOs increasing the signaling overhead See Figure 14
CompThresholdRT
prevent elementsof Active Setbeing optimal
execution ofunnecessary HOs
BS Tx powerincrease
DL load increase- Call Setup
Success Rate
+ SignalingOverhead
too high
too low
MS Tx powerincrease
UL load increase
- DLUL Total CallTraffic
+ Call Drop Rate
Figure 14 The impact of ReplacementWindow513 Parameter Relations
This chapter presents results from simulation in the dynamic network simulatorWALLU [8] In this simulations the relations between the parameters and SoftHandover Overhead has been investigated
The Soft Handover Overhead is always monitored during the simulation After thehandover parameters are changed some time is required to wait for the network tostabilize Figure 15 shows the variation of Soft Handover Overhead for the during thesimulation
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Figure 15 Effect of parameters to SHO Overhead (wadd=AdditionWindowwdrop=DropWindow ttdrop=DropTime Assize=MaxActiveSetSizeperchPower=CPICHTxPwr y-axe = 1+SHO Overhead)
From Figure 15 it can be observed that AdditionWindow (w_add) DropWindow(w_drop) and MaxActiveSetSize (assize) have obvious influence on SHOO Bydecreasing AdditionWindow and DropWindow by 15 dB (from 3 and 5 to 15 and 35respectively) SHO Overhead was decreased around 15 points Similarlydecreasing assize from 3 to 2 decreased the SHO Overhead further by 10 DropTimer (ttdrop) has very small influence on SHO Overhead The DropTimeincreases the residence time of a sector in the Active Set and thus has an effect toSHO Overhead When the Active Set Update Period is much larger than DropTimethen this effect is negligible The effect of PtxPrimaryCPICH (perchPower) on SHOOverhead is also very small However in the simulation the PtxPrimaryCPICH waschanged simultaneously for all cells in the network and the step size was also rathersmall These results are thus as expected It should be noted that changing thePtxPrimaryCPICH will also have a big impact on the coverage of the cell that is why
it should be the last parameter to be changed
514 Inter-area relations
In this chapter the relationships between different optimisation areas are discussedThe effects to Quality of Service Connection Quality Coverage and Capacity aredealt with
The improvement due to the decrease of SHOO is different for DL and UL Thedecrease of SHO Overhead degrades the performance at UL due to the degradationof macro diversity at UL However the DL can be improved by achieving the SHOcombining gain at smaller windows or the less overhead of DL powers
The SHO optimization is in fact an optimization of SHO at DL At UL the more SHOlinks is always preferred to increase the macro-diversity but will of course increase
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
occupation of BS resources A reasonably small SHO window size is important andhealthy to the network performance Large SHO window can increase interference atDL due to large power difference in the active set
It should be always noted that SHO performance depends on several factors
minus Channel properties and mobile speed
minus Power control
minus SHO measurement accuracy
This simulation used a pedestrian model with mobile speed of 3kmhour The SHOperformance and correspondent network performance of a circuit-switched dataservice (144 kbps rate) is investigated
Phase 0 1 2 3 4 5 6 7
Addition Window
(dB)
4 3 2 1 05 1 1 05
DropWindow (dB) 6 5 4 3 25 3 3 25
MaxActiveSetSize 3 3 3 3 3 3 2 2SHO Overhead()
877 801 683 550 492 572 434 399
Table 6 Parameters changes in the simulation
Figure 16 Variation in SHO Overhead in the second simulation(wadd=AdditionWindow wdrop=DropWindowAssize=MaxActiveSetSize)
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Figure 17 QoS in terms of Call Set-upSuccess rate and Call DropRate
P h a s e
A d d i t i on
Wi n d ow
D r o p
Wi n d ow
M ax A c t i v e
S e t S i z e
S H O
Ov er h e a d
0 4 6 3 877
1 3 5 3 8012 2 4 3 683
3 1 3 3 550
4 05 25 3 4925 1 3 3 572
6 1 3 2 434
7 05 25 2 399
A QoS index combining UL and DL performance is expressed as (CSR = Call Set-upSuccess Rate (service set-up ratio) CDR = Call Drop Rate p = coefficient here set to05
pCSR_DLCSR_UL+(1-p)(1-CDR_DL)(1-CDR_UL)
Note that the above formula is not an official Nokia KPI for the QoS it has beendeveloped and used only for simulation purposes From Figure 17 the phase 2 is thepreferred network state A degradation at phase 6 is observed It also shows the effectof SHO optimization at DL and UL is different QOS is improved at DL and is degradedat UL when SHOO is decreasing To find a balance point between DL and UL isimportant and that point might be the optimum point such as phase 2 here
Unfortunately in the real network separate measurements in UL and DL for the CSR andCDR are not available Instead we have to look at the KPIrsquos Service Set-up Ratio and
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
There is no significant changes in the UL FER However the DL FER has a tendency toincrease with lower SHOO This is due to some SHO gains in the DL that affectsdirectly the link performance
Observed from this graph phase 2 seems to be the optimum state of the network It
should be noted that at phase 6 (MaxActiveSetSize is changed from 3 to 2) FER has abig degradation (more than 15 at DL) The probability of always having best servingBS in the active set is smaller and may cause the degradation at link performance
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Functional flowchart of the Soft HO Overhead optimization is depicted in Figure 19see also the document on optimization procedures [9]
Addition Window is the first Parameter to be changed until it reaches the lower limitof 0 dB The MaxActiveSetSize can be lowered to 2 And the difference betweenAdditionWindow and DropWindow should be at least 1 dB The minimum value ofDropTime is 0ms The parameter limits are the technical limits [7] The step sizesused are found from simulations and 2G CDMA experience
START
Addition
Window gt 0 dB
Other KPIs
OK
SHO Overhead
optimized
END
Tune AdditionWindow andDropWindow
by -1dB
Yes
Yes
Yes
Restorepreviousvalue(s)
No
MaxActiveSetSi
ze gt 2
Other KPIs
OK
SHO Overhead
optimized
Tune MaxActiveSetSize by -1
Yes
Yes
Restorepreviousvalue(s)
No
No
Yes
NoNo
DropWindow gtAdditionWindow
+ 1dB
Other KPIs
OK
SHO Overhead
optimized
Tune DropWindowby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
DropTimer gt 0
ms
Other KPIs
OK
SHO Overhead
optimized
Tune DropTimerby -320 ms
Yes
Yes
Restorepreviousvalue(s)
No
No
No
No
No No
No
PTxPrimaryCPICH of
neighboringcells reducable
Other KPIs
OK
SHO Overhead
optimized
Tune PtxPrimaryCPICHT of a
neighboring cellby -1dB
Yes
Yes
Restorepreviousvalue(s)
No
YesYesYes
Figure 19 Functional flowchart of the Soft HO Overhead optimization
5152 Description
This procedure can be used to reduce the Soft Handover Overhead At this point a
procedure to increase the overhead will not be defined Based on 2G experiencesuch a need will very likely not occur
The most important parameters for optimizing the Soft HO overhead are AdditionWindow and Drop Window These are tuned first together Changing the Active SetSize will also have a considerable impact The maximum active set size in RAN 10is 3 therefore changing Assize has to be done very careful and only on cell basisThe value of Drop Timer has only a small effect to the overhead and should be setaccording the environment Finally one can tune CPICHTxPwr to change SHOOverhead This is however not recommended as it will affect also many otheraspects of the system This parameter has to be set to a correct value through thenetwork planning
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Check whether system is Capacity Limited or Coverage Limited Look at thedistributions of PrxTotal and PtxTotal Which link is operating near the upper limitsThis is the limiting link If the problem is in the downlink we usually have a capacitylimited system If the problem is in the uplink we usually have a coverage limitedsystem
Continue
Here we have to check if the performance of the system improved or degraded Thismeans the PtxTotal and PrxTotal compared to the DL and UL Throughput shouldhave gone down Especially in the downlink limited case the PtxTotal per DLThroughput is an important indicator and should decrease The Call Drop Rate andCall Set-up Success Rate are additional performance indicators These should haveimproved or remained stable
5162 Description
After reducing the Soft Handover Overhead to an acceptable level the optimizationof the Soft Handover Gain can start The acceptable level of Soft HandoverOverhead is that level where we do not need too much hardware for the SoftHandover An acceptable level of Soft Handover Overhead can be 50
In optimizing Soft Handover Gains there exist two distinct cases capacity limitedsystems and coverage limited systems See for the procedure Figure 20
Coverage limited
For coverage limited systems it is the uplink In the uplink a larger Soft HandoverOverhead is beneficial This does not require additional power but gives additionalgain So here we can increase the Soft Handover Overhead as much as possible
Capacity limited
For Capacity limited systems the limited link is usually the downlink In the downlinkexists a point where the UE experiences maximum combining gain At this point wecan find the optimal Soft Handover Gain To find this point we change the SoftHandover Overhead stepwise and at the same time check important PerformanceIndicators The important indicators are Call Drop Rate Call Set-up Success RatePtxTotal and PrxTotal As long as the network performs better after changing the
Soft Handover Overhead we continue to change At a certain point however thenetwork starts to degrade and then the procedure ends The optimum is found
52 CoverageCapacity Optimization
In this chapter it is explained the results coming from a study performed by NokiaKorea for updated information please check latest version of [21] In this simulationthe network has been highly overloaded in order to make the effects morenoticeable for instance in chapter 522 there are simulated so many call set upattempt that more than 60 of it are blocked
There are some parameters that have a close connection with the capacity and
therefore with coverage as in WCDMA capacity and coverage are coupled Theones taken into account in this study are
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
521 Offset of the primary CPICH transmission power and DL transmission power of referencecall
bull Abbreviated name CPICHtoRefRABoffset
bull Parameter group ACConfiguration
bull Description The parameter defines the offset of the primary CPICH transmissionpower and the maximum DL transmission power of the reference service channelin DL power allocation Maximum transmission power of the reference service isachieved (in dBm) by subtracting the value of the parameter from thetransmission power of the primary CPICH
bull Range and step -10 17 dB step 05 dB
bull Default value 5 dB for 122 kbits AMR speech service
The effect of changing CPICHToRefRabOffset has been simulated The results forthroughput and blocking dropping are shown respectively in Figure 21 and Figure22
3000
3500
4000
4500
0 2 4 6 8 10 12 14 16
CPICHToRefRABoffset (dB)
n u m b e r o
f c a l l s
DL ended calls 9000DL ended calls 6000
Figure 21 The number of successfully ended calls in the simulation asfunction of CPICHToRefRABoffset (for 9000 and 6000 users in thenetwork)
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Figure 22 The Call Drop Block Rate in relation to CPICHToRefRABoffset (for9000 and 6000 users in the network)
From Figure 23 it can be seen that a too high value will lead to an increase in the calldrop rate as explained previously in chapter 42
CPICHToRefRabOffset
higher estimationof DL power
increase
lower estimationof DL power
increase
unnecessary callrejections
- Call SetupSuccess Rate
call admissionover radiocapacity
system overload - DL FER
too low
too high
+ Call Drop Rate
Figure 23 The impact of CPICHToRefRabOffset
522 Target for received power
bull Abbreviated name PrxTarget
bull Parameter group ACConfiguration
bull Description Target for received total wideband interference power in a cell AnUL RT RAB is not admitted if the estimated non-controllable power exceeds thisthreshold PrxTarget is also used to calculate PrxTargetBS which is the firstoverload threshold for BSUL interference Value of the PrxTarget is relative to thesystem noise it gives an upper threshold for the noise rise ratio of the totalreceived UL power to system noise
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
The effect of changing PrxTarget has been simulated with Wallu again it should benoted that those graphs are coming from simulation and the dropping call cause inWallu it is different then the one in the real network more focus should be put in the
trend It can be seen that increasing the PrxTarget more calls will be admitted but atthe same time the number of bad quality calls will increase in a real network it isimportant to find the right balance between capacity and quality The results forthroughput and blocking dropping are shown respectively in Figure 24 and Figure25 It can be seen
10000
11000
12000
13000
14000
15000
16000
56 59 62 65 68 71 74
PrxTarget (dB)
N u m b e r o f c a l l s
Started
Ended
Linear (Started)
Linear (Ended)
Figure 24 Number of calls as function of PrxTarget
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Figure 25 Percentage of blockeddropped calls as a function of PrxTarget
The number of blocked calls is really high as in the simulation the network was fullyloaded and the number of call attempt was set to a high value
From Figure 26 it can be seen that this parameter is directly related to the Call Set-up Success Rate If the target is set too low calls will be sometimes rejected
unnecessarily meaning degradation of Call Set-up Success RateBut if the target is set too high RAN may easily move into an overloaded state In theoverload state uplink power control may not work accurately causing uplink FERincrease and possibly Call Drop Rate as well
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
bull Description Target for total transmitted power in a cell A real-time Radio AccessBearer is not admitted if the estimated non-controllable power exceeds thisthreshold
bull Range and step -10 50 dBm step 01 dBm
bull Default value Default value is 3dB below the Cell maximum transmission power
This parameter is directly related to the Call Set-up Success Rate If the target is settoo low calls will be sometimes rejected unnecessarily meaning degradation of CallSet-up Success Rate
But if the target is set too high RAN may easily move into an overloaded state In theoverload state downlink power control may not work accurately causing downlinkFER increase and possibly Call Drop Rate as well
The effect of changing PtxTarget has been simulated Wallu The results forthroughput and blocking dropping are shown respectively in Figure 27 and Figure28
9000
10000
11000
12000
13000
36 37 38 39 40 41 42 43
PtxTarget (dBm)
N u m b e r o f c a l l s
Started
Linear (Started)
Figure 27 Number of calls as function of PtxTarget
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
Figure 28 Percentage of blockeddropped calls as a function of PtxTarget
The effect of PtxTarget is similar as PrxTarget increasing the value will increase theoverall capacity of the network but at the same time it will degrade the quality
524 Coverage Optimization
Increasing the coverage it is a complicate task it is very difficult to achieve it bytuning only parameters Unlike the GSM system the coverage is not defined as areceived power RxLevel but as EcIo Therefore there are two ways to increase thecoverage either by increasing the Ec or by decreasing the Io
The Ec can be increased in two different ways increase the P-CPICH power oroptimizing downtilt and direction of the antenna The first solution has the drawbackof increasing the Soft handover area
The Io can also be decreased in two different ways decrease the P-CPICH power ofthe interfering cell or optimizing downtilt and direction of interfering cellrsquos antennaThis approach requires intensive studies in the network to find out which cell is
interfering with the serving cell
At this point there are no real network studies regarding this issue but somesimulation study is ongoing for further information refer to [22]
From experience it is suggested to first try to optimize through antenna changes andthen if there is no improvement start to change the P-CPICH power
In case none of this methods will give a reasonable improvement then the possibilityof diminishing the load with a hardware change should be taken into consideration Anew frequency could be add or increase the number of sectors or as the last chanceadding a site
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
53 Call setup success rate and call drop rate Optimization
Due to the implementation of Wallu the simulation regarding the set up success rateand the call drop rate will not be displayed in this document In Wallu it is notpossible to simulate yet the behavior of a real network for this particular study In thischapter only flowchart coming from theory and experience will be presented
531 Call Set Up Success Rate
In Figure 29 it is shown the flow chart relatively to the optimization of the call set upsuccess rate with call set up success rate it is meant an establishment of an RRCconnection and a bearer service which means meant that all the signaling shown inFigure 40 are successfully transmitted through the network elements
Figure 29 Call set up success rate flowchart
As can be seen from the figure above a low Call set up success rate can be for twodifferent reasons Capacity and Signaling The Signaling can be further divided intwo capacity and coverage of the common channels In this flowchart it is imply thatthe requested call is according to the planning ie in rural area the 384 Kbs is notplanned to be available at the cell edge
The capacity can be limited in Uplink or in Downlink if it is Uplink limited it is possibleto increase this KPI by increasing the PrxTarget or PrxOffset always keeping in mindthat PrxTarget is in direct relationship with the planned UL load and as it can be seen
from the previous chapter has a bad influence on the call quality If it is not possibleto increase those parameters because the quality will drop too much then the only
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
possibilities is to decrease the load of the cell by using SRC or MHA or increasingthe sectorisation of the BTS or by adding a carrier on a different frequency If it isdownlink limited the first parameters to tune are PtxTarget and PtxOffset If it is notpossible to increase those values because of the dropping of the quality then it could
be either increase the LPA power of the BTS or using transmission diversity (SRC)or add a new carrier or increase the sectorisation of the BTS Note that PtxTargetand PrxTarget will have effect on the call setup success rate of the RT calls while thePtxOffset and PrxOffset will effect only the NRT call set up success rate
If the problem is in the signaling then it could be either a coverage or a capacity ofthe signaling channels If the problem is in the coverage the only solution is toincrease the power of the problematic channel while if it is the capacity thendepending on the channel it is possible to increase the capacity of the FACH byincreasing the number of Secondary Common Control Channels Concerning theRACH it is possible to increase the number of access slot andor signaturesavailable if this is still not enough it can be decreased the RACH threshold
parameter shown in Table 3 In this way we decrease the amount of datatransmission in the common channels decreasing the probability of layer 1 collisionthe drawback is the decreasing of NRT call set up success rate as if the RACH loadis above that value the AC will reject any incoming NRT call
Call Drop Rate
As can be seen from Figure 30 high call drop rate value can be caused by lowhandover success rate or by lack of coverage
Figure 30 Call drop rate flowchart
There can be many reasons why the handover success rate is low either wronghandover triggering parameters or too high load in the target cell For the solution of
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
the first cause refer to chapter 51 while if the problem is the load in the target cellthen this load should be decreased by adding physical resources to the target cell asexplained in the previous sub-chapter
In WCDMA system the coverage is considered as a ratio between received signalcode power and interference in order to increase the coverage it is possible todecrease the interference or increase the received signal code power
Before starts to investigate into the network all the possible causes it should be firstchecked if the parameters marked in blue in Figure 30 are properly set A wrongvalue will change the planned cell radius leading to a coverage hole and to a highcall drop ratio
If the coverage is downlink limited then it is possible to increase the RSCP byoptimizing the antenna direction tilting or antenna type If it is not enough then thePtxPrimaryCPICH of the serving cell can be increased but paying attention on theside effect that this change will bring to the soft handover overhead Another solutionis to decrease the interference by optimizing the antenna direction tilting or antennatype of the interferer neighbor cell yet if this is not enough then thePtxPrimaryCPICH of the interferer cell can be lowered down paying particularattention to the possible creation of a coverage hole due to the diminished coveragearea In general it is highly recommended to not change the CPICH power as manyRRM functions are using it as input and a wrong value can have bad side effect ontothe network
If the coverage is uplink limited then the optimization is more complicated anddepends on the topology of the network Unlike the downlink in uplink it is possibleto act either on the pathloss or on the interference but not at the same time The
reason is that in uplink the interference is created by other mobile transmitting whichmeans it is not possible to control it in a optimal way The same applies for thepathloss
If the pathloss is too big we can not simply increase the UE Tx power because weassume that the UE it is already transmitting at the maximum power In theory theUE should never reach the maximum power because of the increase in the noiseraise in order to reduce the Tx power of the mobile we should move the UE in softhandover This can be done by changing the handover parameters like WindowAdd If this is not enough it is possible to achieve the same effect by by optimizingthe antennarsquos direction and tilting as shown in Figure 31
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
In Figure 32 instead it is shown how to decrease the interference The interference incell b is caused by two different mobiles which are powered controlled by cell a Withthis scenario the idea is to move the two interferer mobile phones under the cell b inthis way the cell b can use the power control in order to diminish the received powerof this two calls This can be done by changing the handover parameters likeWindow Add If this is not enough it is possible to achieve the same effect by byoptimizing the antennarsquos direction and tilting Of course the pathloss between thosetwo new mobiles and cell b should not be too high and cell b should not be highlyloaded
Figure 32 Uplink interference
It is not possible to say which one of this two solutions is the best one because itdepends on the network configuration cell location etc These are just examples itis the optimization engineer that with his experience can find the optimal solution ona case by case basis
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
In this chapter few test cases defined in the 3G FMF are described Those cases arebelonging to the family of Basic Test Cases and only the flow chart will be explainedin this document the list of all the test cases and more detailed information can befound in [10]
61 Cell Selection
In this test case the scope for the UE is to find the scrambling code of the cell withoutprevious knowledge of the frequency typical case is when the mobile is switched on
The UE should first find the primary SCH for TS synchronization once it has found itshould check the secondary SCH for frame synchronization The secondary SCHalso define the scrambling group of the cell The 512 DL scrambling codes aredivided in 64 groups each of them made by 8 scrambling codes Once the group isfound through the secondary SCH the UE has to check those 8 scrambling codesThe checking is done autocorrelating each of the 8 scrambling codes plus theknown channelisation code of CPICH with the received signal With this procedurethe UE should check only 8 codes instead of 512 In Figure 33 it is shown the flowchart for the cell selection
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
The paging procedure can be seen in Figure 34 The paging request comes from thecore network and in the BTS is started the layer 1 paging procedure First it iscalculate in which Paging indicator group the user belong Once this information isfound the corresponding Paging Indicator in the PICH channel is set to one Threetime slots later the information coming from the core network is broadcasted in theSecondary CCPCH After that the UE starts the RRC connection establishmentwhich is explained in the next chapter
UE BS RNC CN
RANAP PAGING
UE has no RRC connection
RRC connection establishment
Paging response
UE without RRCconnection -gtUE in idle mode
UE gets RRCconnection -gtUE in dedicatedmode
Paging isoriginated fromthe core network over the Iuinterface
The paging of the UE is initiated andscheduled by the RNC The RNC packspages to a L3 paging message (PCCH)and transmits them transparently over theIub
(FPAAL2PCCHPCHS-CCPCH) PAGING TYPE 1
Upon receipt of the paging messageand if access to the network isallowed the addressed UE initiatesthe RRC connection setup procedure
PICH
Figure 34 Paging procedure
63 RRC connection establishment
In this test case is explained the signaling during the RRC connection establishment
The RRC connection establishment procedure can be triggered either as an answerto a paging request or by a mobile originated call
From Figure 35 it can be seen that the UE sends the RRC connection requestthrough the RACH channel containing all the information regarding the UE identityand the reason for the connection request The network responds with the RRCconnection setup which contains all the physical layer information (scrambling codechannelisation code power etc) for the next signaling As can be seen in the redcircle the UE moves to cell DCH state to send the RRC connection setup completethis is a particularity of RAN 1 from RAN 2 the RRC connection setup complete canbe sent on a FACH state
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
In Figure 36 it is explained the flow chart for the RRC connection setup
T300 is the timer that is started when the RRC connection request and is stoppedwhen the UE receives the RRC connection setup In RAN 1 the range of theparameter T300 is from 100 ms to 8 seconds with a default value of 1 second
N300 is a parameter which set the maximum number of RRC connection attempt incase of no RRC connection setup message In RAN 1 the range is from 0 to 7 with adefault value of 3
The UE transmits RRCCONNECTION REQUEST
message (first one)
Reset Counter V300 Start timer T300set the RRC CONNECTION REQUEST message IE Establishment Cause set the IEInitial UE identity to the variable INITIAL_UE_IDENTITY set the protocol errorindicator to the value of the variable PROTOCOL_ERROR_INDICATOR includea measurement report in the IE measured results on RACH as specified in the IEintra-frequency reporting quantity fro RACH reporting and IE maximum numberof reported cells on RACH in system information block type 11
Reception of an RRCCONNECTION SETUP
by the UE
RRC CONNECTION SETUPmessage from RNC
no
yes
If cell reselection or expiry of T300 occurs
check the value of V300 (which is updatedevery time a new RRC CONNECTIONREQUEST MESSAGE is sent for thatparticular connection
V300 =lt N300
yes
no
Increment counter V300and restart timer T300
Transmit a new RRC CONNECTION REQUEST
MESSAGE
Enter in idle mode =gtthe end of procedure
UE compares the value of the IE initial UE identity in the received RRCCONNECTIONSETUP message with the value of the variable INITIAL_UE_IDENTITYIn case the values are different the UE ingnores the rest of the messageIf the values are identical the UE stops the timer T300 and act based on the receivedinformation and submit RRC CONNECTION SETUP COMPLETE message andenter to CELL_DCH state
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
The scope of this test case is to check that the Location update is done properlyThere are two kind of location update
One for the CS called LA update where the signaling goes from the UE to the 3GMSC Flow chart can be found in Figure 37 The timer T3210 indicates the expiringtime for the LA update In the LA update a CS service relate temporary identity CS-TMSI may be allocated to the UE this is unique within a LA It is formed as
LAI = MCC + MNC + LAC
UE Receives other LAI in MMregistrat Area Inf Broadcasted
No
UE sends LOCATION UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in LOCATION UPDATING INITIATED STATE
Start T3210
T3210expires
No
Yes
The LA update is only initiated by the UE whenthe UE is in state CS-IDLE
UE receives LOCATIONUPDATING ACCEPT
No
UE stores the new TMSI
UE receives new TMSI
UE stores the new LAI
Yes
UE sends to the Networka TMSI RELLOCATION COMPLETE
No
3G_MSCVLR release signalling connection
RRC Connection Release
UE receives LOCATIONUPDATING REJECT
No
UE in LOCATION UPDATING REJECT STATE
Yes
Yes
Stop T3210
The UE take dif Actions dependingon the received reject cause value
Stop T3210
Figure 37 Location Area update flow chart
The other for the PS called RA update in this case the signaling goes to the 3GSGSN The procedure is described in Figure 38 The timer T3330 indicates theexpiring time for the RA update In the RA update a PS service relate temporaryidentity PS-TMSI may be allocated to the UE this is unique within a RA It is formedas
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
In PS Idle-Mode UE Receives other RAIin MM registrat Area Inf Broadcasted
No
UE sends ROUTING UPDATEREQUEST Message to theNetwork
RRC Connection must beestablished
RRC Connectedmode
Yes
UE in ROUTING UPDATING INITIATED STATE
Start T3330
T3330expires
No
Yes
In PS Connected-Mode UE Receives(from the new SRNC) a new
MM system inf Indicating a new RAI
UE receives ROUTINGUPDATING ACCEPT
No
UE stores the new P-TMSI
UE receives new P-TMSI
UE stores the new RAI
Yes
UE sends to the Networka RA UPDATE COMPLETE
No
3G_SGS N release signalling connection RRC Connection Release
UE in ROUTINGUPDATING REJECT
STATE
Yes
Yes
Stop T3330
Stop T3330
The UE came RRC IdleMode
Yes
UE receives ROUTINGUPDATING REJECT
No
The UE take dif actionsdepending on the received
reject cause value
Figure 38 Routing Area update flow chart
The triggering for this procedure is the changing of the locationrouting area This
change can be seen by the mobile through the SIB 1 broadcasted in the BCCH(which is mapped in the P-CCPCH at the physical layer) Through a parameter it ispossible to enable the periodic location update in this case after the timer T3212 forLA and T3312 for RA expires the procedure is started
There is a third area called URA this is used when the UE is in URA PCH state TheURA area exists only inside the UTRAN the signaling goes only until the SRNC itwill not involve the core network
In UMTS network it is possible to define three different areas LA RA and URA areaThe relationship between those areas can be found in Figure 39
minus one RA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G SGSN
minus one LA consists of a number of cells belonging to RNCs that are connected tothe same CN node eg 3G MSC
minus one RA is a subset of one and only one LA meaning that an RA cannot spanmore than one LA
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
In Figure 40 it is explained the signaling exchanged between the UE the RNC andthe CN when there is a request for a service The only different between MobileTerminate all and Mobile Originated Call is the signaling marked in red at thebeginning of the figure That signal is present only in Mobile Terminated Call Formore detailed information regarding the content of each signal please refer to [19]
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
[18] Jochen Grandell (editor NET) Harri Holma (NET) Oscar Salonaho(NET) Kari Skog (NRC) David Soldani (NET) Achim Wacker (NET) rsquo SingleLink Measurement Campaign with the Nokia WCDMA Experimental SystemrsquoBMW03100doc
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