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WCDMA Mobility Troubleshooting
Studies and Enhancements
Serkan Kangal
Supervisor: Prof. Jyri Hmlinen
Instructor: Jukka Valtanen
This work is carried out in Nokia Siemens Networks
AALTO UNIVERSITY
School of Electrical Engineering
Department of Communications and Networking
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Agenda
Thesis Objective
Introduction to UMTS Radio Access NetworkArchitecture
Mobility in UMTS
Radio Network Controller
Troubleshooting Experiences
Conclusion
Future Work
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Thesis Objective
There are different types of challenges in WCDMAMobility part of the RNC software. From developersand testers point of view, it would be easier for them toinvestigate those issues by using a specially designed
troubleshooting tool or with improvements to theexisting tools.
Most of the existing troubleshooting approaches arebased on practical analysis which takes time and
usually hard to figure out the problem. This thesis willanalyze the existing challenges and propose bettersolutions to be implemented by modifying the existingsolution or in a new troubleshooting tool.
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UMTS Radio Access Network
Architecture
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Mobility in UMTS
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The task of Radio Resource Management (RRM)is to optimize the use of the available resources,
such as transmitter power and spreading codes,
in order to provide users with the largest
possible capacity for a specified coverage and
quality-of-service (QoS).
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Mobility in UMTS
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Radio Resource Management Admission Control
Load Control
Packet Scheduler
Resource Manager
Handover Control
Power Control
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Handover Types
Intra-System Intra - Frequency
Handover: Soft Handover(SHO)
Intra-System-Intra-Frequency Hard
Handover
Intra-System-Inter-Frequency Handover Inter-System Handover
Mobility in UMTS
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Handover Measurements
Neighbour cell definitions
Measurement reporting criteria
Intra-frequency measurements
Inter-frequency measurements
Inter-system measurements
UE internal measurements
Reporting of measurement results
Mobility in UMTS
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Management of terrestrial channels
Management of radio channel configurations in (RAN) Radio resource management
Telecom functionality
Transmission & transport features
Maintenance & operation
Radio Network Controller
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The key functions of the Radio Network Controller (RNC):
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Radio Network Controller
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The whole system can be seen as a network of responsibilities andservices.
The services become an interface to the process and the outside worldsees only the service interfaces.
The service model SW is divided into three levels:system blocksservice blocksprogram blocks
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Main task is to optimize the use of the available radioresources, such as transmitter power and the usage ofspreading codes in order to provide users with the largestpossible capacity for given coverage and quality-of-servicerequirements.
Radio Network Controller
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Handover Control Algorithm Program
Block has one master process and
several hand processes.
A Handover Control Algorithm hand iscreated in serving RNC together with
the radio resource control (RRC)
connection establishment for the UE
and it exists until the RRC connection is
released.
In drift RNC, Handover Control Algorithm hand is created when the first
radio link is established for diversity handover and it exists until last
radio link of the diversity handover is released.
Radio Network Controller
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Radio Network Controller
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Troubleshooting Experiences
In general, troubleshooting is done in 4 steps:
Fault Identification
Symptom Collection Symptom Analysis
Fault Repair
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Used for investigating different kinds of message monitoring
outputs and other log files.
Supports different software versions (different data types) and
products.
Provides profiles for different products and Software Program
Blocks, depending on the needs, for effective fault analysis
Troubleshooting Experiences
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EMIL
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Troubleshooting Experiences
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EMIL
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Troubleshooting Experiences
05.10.2011 17Serkan Kangal - WCDMA MobilityTroubleshooting Studies and Enhancements
There can be several problematic scenarios:
Radio Network Manager sends wrong data. Radio Network Manager sends correct data to a wrong ICSU.
Radio Network Manager sends correct data to ICSUs but, not to all of them.
Radio Network Manager sends correct data but, HC-master is unable to receive orprocess the data correctly.
Radio Network Manager does not notify the parameter changes to ICSUs.
RNW Database parameter consistency checking
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Troubleshooting Experiences
05.10.2011 18Serkan Kangal - WCDMA MobilityTroubleshooting Studies and Enhancements
In a regular consistency check approach :
1 - Correct parameters have to be read from the RNW Database Library.
2 - A parameter query has to be sent (broadcast) to every ICSU.
3 - Received parameters (from ICSU) have to be compared with the ones in the database.
4 - The differences need to be reported.
RNW Database parameter consistency checking
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Troubleshooting Experiences
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RNW Database parameter consistency checking
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Troubleshooting Experiences
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1 - Understandable view of the network topology is needed
2 - It is done by hand by using hundreds of network
modification messages3 - Required messages have to be collected and then processed
according to relations between cells.
4 - After data collection, required radio network topology canbe drawn.
Formatted printout of the RNW network topology
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Troubleshooting Experiences
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In the radio resource planning phase, some cellsneighbours are defined wrongly or with missing
information.
Solution: UEs detected cells measurements are sent toRNC and the troubleshooting tool can be used to informoperator about the unlisted but detected adjacent cells.
Missing neighbour cell definitions (ADJs)
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Troubleshooting Experiences
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Amount of information that is needed to analyze handoverproblems can be very huge (ICSU log files, parameter data andcounter data).
It would be good to have some tool which can be configured tosearch certain patterns which indicate some certain problems.
Handover Related Troubleshooting - Investigation oflarge ICSU-files
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Troubleshooting Experiences
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Solution: ICSU-logs have to be collected and thenprocessed in terms of important values to report.After doing required calculations, condensed values
can be reported in table or graphic format.Number of requests
Trigger cause for the request
Intra frequency measurement reports from UE
Handling Events 1A and 1CTarget cell
Number of ACKs for the request
Number of NACKs for the request
Failure cause of the request
Handover Related Troubleshooting - Investigation oflarge ICSU-files
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Troubleshooting Experiences
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KPIs have importance on indicating problems about the network.But time to time, there can also be problems about the KPIs itself.
With a new software release to the network elements, there can
be a change in the KPIs by %1 ~ %2 due to many reasons such asnew feature activations.
After software baseline upgrades, there can be KPI problems whichalso affect handover processes.
Solution : KPIs are calculated from counters, the raw data has to beread from counters and exact KPI values can be calculated fromthem. And the comparison has to be done to investigate wronglycalculated KPIs
Handover Related Troubleshooting - SHO KPI Problems
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Troubleshooting Experiences
05.10.2011 25Serkan Kangal - WCDMA MobilityTroubleshooting Studies and Enhancements
There is a huge traffic in the operator s livenetwork, it is difficult to find the root cause of
certain HSDPA or HSPA accessibility problemwithout proper tool which would easily show therequired information.
HSPA Related Troubleshooting - Investigation of largeICSU-files
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Troubleshooting Experiences
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Monitoring should be done cell based, responsiblecell and the target cell:
Number of requests
Trigger cause for the requestNumber of ACKs for the request
Number of NACKs for the request
Failure cause of the request
Solution: ICSU-logs have to be collected and thenprocessed in terms of important values to report. Afterdoing required calculations condensed values can bereported in table or graphic format.
HSPA Related Troubleshooting - Investigation of largeICSU-files
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Troubleshooting Experiences
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E_DCH operational state is used
by BTS to report to HSUPA
operational state of the cell.
HSPA Related Troubleshooting - HSPA Accessibility
Problems (Parameter Inconsistency)
In order to use HSUPA in a cell the BTS must have
reported HSUPA Operational state to be enabled in that
cell.Otherwise HSPA cannot be used in that cell.
HSDPAOperationalState and HSUPAOperationalState
indications are the most error prone and also the most
difficult one to catch from live network.
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Troubleshooting Experiences
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Radio Network Initiator has not always sent this information
correctly to Handover Control Algorithm or sometimes it has not
sent it at all.
Solution: The tool has to get the correct values of the
parameters from Radio Network Initiator and then compare with
the ones in Handover Control Algorithm and then it can:
Create alarms or warnings
Force Radio Network Initiator for parameter update
Force Handover Control Algorithm to ask for new set of
parameters.
HSPA Related Troubleshooting - HSPA Accessibility
Problems (Parameter Inconsistency)
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Troubleshooting Experiences
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UL SIRerror and periodical CPICH Ec/No values are used in
handover control algorithm decisions.
While investigating issues or problems in handover control
algorithm related to HS(D)PA functionality, those values has to be
analyzed in order to see if the algorithm works correctly and
utilizes correctly those inputs that are coming from UE and BTS.
Solution: The tool has to get the UL SIRerror and CPICH Ec/No
values from the ICSU-log. Then it will calculate the averaged UL
SIRerror and periodical CPICH Ec/No measurement results for
certain cell which is defined by the user.
HSPA Related Troubleshooting - Calculation of certain
Parameters related with HSPA
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Conclusion
The scope of this thesis was to analyze the existingtroubleshooting experiences in NSN-WCDMA-Control Plane-Handover Algorithm team and study the enhancementsopportunities to increase the efficiency of R&D engineers.
Study cases were chosen after long discussions to increasethe R&D engineers benefit from this work. The benefit of thisstudy will show itself in the long run.
In the future, it would be good to continue this type ofefficiency related studies for different troubleshooting casesand for different software platforms.
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Future Work
EMIL implementation can easily be done after thisthesis work.
In RNW Database parameter consistency checking:
Database consistency check feature can be added to theRNC software itself as an automated self-check tool.
In Formatted printout of the RNW network topology:New type of visualization objects can be added such as
downlink RF channel number, downlink scrambling code ofthe WCEL and Absolute radio frequency number.
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Future Work
In Missing neighbour cell definitionsThere can be an automated self-check in the RNC software
for neighbour cell definitions which is based on the reportsthat are received from UEs.
In Handover Related Troubleshooting:
There can be new parameters required to be in the filteredreport.
In HSPA Related Troubleshooting:Required parameters can be updated upon request in the
future.
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Thank you!
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Questions?