Guide to CDMA 1X Traffic Statistic Analysis-20030710a-A-1.3

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Guide to CDMA1X Traffic Statistic

Analysis

Prepared by:

RadioResourceManagementAnalysis &ApplicationTeam

Date: 2002-10-15

Reviewedby:

Date:

Reviewedby:

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Approvedby:

Date:

Huawei Technologies Co., Ltd.

All rights reserved


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Revision RecordDate Revised version Author Description

2002-11-15 1.00 Tang

Chunmei

Complete the first draft

2003-01-13 1.01 TangChunmei

Add the inter-BS hard handoff functionsubset table and supplement thedescription of call drop ratio


Modify the description of call drop ratioand supplement the descriptions of trafficand Eb/Nt


Describe the restrictions of the trafficstatistic item registration, the RSSI testmethod and the soft handoff ratio, addthe description of disqualified forwardtransmit power measurement andforward load measurement, and modifythe errors in the description of Eb/Nt


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Table of Contents

1 Explanatory Notes......................................................................................................................... 2

2 Introduction to Traffic Statistic .................................................................................................... 2 2.1 Function of Traffic Statistic in Network Optimization ............................................................ 2

2.2 Traffic Statistic Function of M2000 ....................................................................................... 2

3 Traffic Statistic Analysis............................................................................................................... 3 3.1 Traffic Statistic Task Registration......................................................................................... 3

3.1.1 Basic Traffic Statistic Tasks ....................................................................................... 3 3.1.2 Other Traffic Statistic Tasks....................................................................................... 5 3.1.3 System Tasks............................................................................................................. 5

3.2 Traffic Statistic Analysis........................................................................................................ 5 3.2.1 Acquisition of Basic Network Information................................................................... 5 3.2.2 Major Measurement Items ......................................................................................... 6 3.2.3 Analysis Preparations ................................................................................................ 7 3.2.4 Precautions for Traffic Statistic Analysis.................................................................... 7 3.2.5 Other Auxiliary Methods............................................................................................. 8

4 Introduction to Major Traffic Statistic Items............................................................................. 10

4.1 Call Setup Success Ratio ................................................................................................... 10 4.1.1 Calculation Formula ................................................................................................. 10 4.1.2 Meaning.................................................................................................................... 10 4.1.3 Description of Measurement Items in Function Subset ........................................... 11 4.1.4 Measurement Item Analysis..................................................................................... 11

4.2 Call Drop Ratio.................................................................................................................... 12 4.2.1 Calculation Formula ................................................................................................. 13 4.2.2 Meaning.................................................................................................................... 13 4.2.3 Description of Measurement Items in Function Subset ........................................... 13 4.2.4 Measurement Item Analysis..................................................................................... 13 4.2.5 Possible Causes for a High Call Drop Ratio ............................................................ 16 4.2.6 Examples of Call Drop ............................................................................................. 17

4.2.7 Traffic Call Drop Ratio.............................................................................................. 18

4.3 Traffic Channel Congestion Ratio....................................................................................... 19 4.3.1 Calculation Formula ................................................................................................. 19 4.3.2 Meaning.................................................................................................................... 19 4.3.3 Description of Measurement Items in Function Subset ........................................... 19 4.3.4 Measurement Item Analysis..................................................................................... 19 4.3.5 Possible Causes for Traffic Channel Congestion .................................................... 21

4.4 Traffic .................................................................................................................................. 22 4.4.1 Calculation Formula ................................................................................................. 22 4.4.2 Meaning.................................................................................................................... 22 4.4.3 Description of Measurement Items in Function Subset ........................................... 22 4.4.4 Measurement Item Analysis..................................................................................... 22

4.5 Soft Handoff........................................................................................................................ 23 4.5.1 Calculation Formula ................................................................................................. 23

4.5.2 Meaning.................................................................................................................... 24 4.5.3 Description of Measurement Items in Function Subset ........................................... 24 4.5.4 Measurement Item Analysis..................................................................................... 24 4.5.5 Possible Causes for Soft Handoff Failure ................................................................ 25

4.6 Hard handoff ....................................................................................................................... 26 4.6.1 Calculation Formula: ................................................................................................ 26 4.6.2 Meaning.................................................................................................................... 26 4.6.3 Description of Measurement Item in Function Subset ............................................. 26 4.6.4 Measurement Item Analysis..................................................................................... 26 4.6.5 Possible Causes for Hard Handoff Failure............................................................... 27

4.7 Carrier Power Control Measurement.................................................................................. 28 4.7.1 Description of Measurement Item ............................................................................ 28 4.7.2 Judgment of Reverse Interference........................................................................... 29


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Guide to CDMA1X Traffic Measurement Analysis _V1.02 Confidential

4

4.7.3 Querying RSSI in Telnet Mode ................................................................................ 29

5 Analysis of Causes Affecting Measurement Items.................................................................. 30 5.1 Imbalance between Forward Link and Reverse Link.......................................................... 30 5.2 Pilot Pollution ...................................................................................................................... 32

5.3 Improper Setting of Handoff Parameter.............................................................................. 34

5.4 Improper Adjacency............................................................................................................ 35 5.5 Improper Setting of Search Window................................................................................... 36

6 Recording Problems in Traffic Measurement........................................................................... 37

7 References ................................................................................................................................... 37


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Guide to CDMA1X Traffic Statistic Analysis

Keywords: M2000, traffic Statistic, measurement item, call drop ratio, call setup success ratio,

congestion ratio, soft handoff and hard handoff

Abstract: This document introduces the methods and procedures to analyze the network

symptoms and carry out the network optimization by using M2000 traffic Statistic

function. It points out the position of the traffic Statistic in the network optimization. It also

gives the signalling measurement points of the major measurement items, optimization

analyses and suggestions. This document provides reference methods or clues for the

network optimization engineers when they solve problems by means of traffic Statistic.

Abbreviations:

References:

References

Name Author No. Release date Source of information Publisher

Guide to CDMA 1XM2000 TrafficStatistic (V 1.0)

Gu Xinyu 2002/08/22

Specifications forCDMA2000 BSCPerformanceMeasurement DataCollectionRequirements

Wang Yifeng, QiuJianjun, Cui Yaleiand Liu Aihua

2002-06-29

Description of CBSCTraffic Statistic Items

1


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2.1

2.2

Explanatory Notes

Version of the corresponding M2000 of this first draft: iManagerM2000V100R003B01D204SP02. Version of the corresponding BSC:BSC6600V100R001B02D305.

This document introduces how to analyze network symptoms, locate problems andoptimize networks by means of the traffic Statistic results. It provides a referencemethod or clue for network optimizers based on a prior good plan and effectiveimplementation of it.

The compilation of this document is limited to the knowledge available currently. Dueto the complexity of networks, there will inevitably exist some deficiencies in thisdocument, but they will be amended in the later versions as the network knowledgegets enriched.

This document is only intended for Huawei engineers.

Introduction to Traffic Statistic

Function of Traffic Statistic in Network Optimization

The traffic statistic data and drive test data are the objective basis of the network

optimization, while the human perception is the subjective basis. It is necessary totrace and analyze signalling messages to locate problems before these problems aresolved. It is obvious that the traffic statistic data provide a very important means tolearn the network performances. Especially when there is traffic in the network, thetraffic statistic data provide important references and guidelines for the networkoptimization. The integrity and accuracy of the measurement items and theconvenience of operations will directly affect the efficiency of network optimization.Meanwhile, the grade of measurement items is also a very important factor tomeasure the effect of network optimization.

On the other hand, network operators set much store by the traffic statistic data. Thedecision-making level of network operators usually learns and judges the runningstatus of networks according to the visual data obtained from traffic statistic. These

visual traffic statistic data also provide an important basis for the future networkcapacity expansion.

Traffic Statistic Function of M2000

Huawei iManager M2000 is an integrated network management system in the mobiletelecommunication field. With an integrated platform, iManager M2000 performs themanagement of Network Elements (NEs). It also supports the network managementfunction, including centralized configuration management, centralized faultmanagement and centralized performance management. The centralizedperformance management module provides the network traffic statistic function and isclosely related to the network optimization. The centralized performance management

module provides a visual, comprehensive operational environment for network

2


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3.1

3.1.1

operators to perform the system performance management. Network operators canmonitor the status of networks, NEs or communication equipment, locate faults andevaluate the status of communication equipment and efficiency of networks or NEs bycollecting various traffic statistic data of NEs, such as BSC and MSC. The

performance management module provides a basis of network optimization. Itconsists of the performance adapter, the performance server and the performanceclient end (PM NWS).

Performance tasks of different NEs can be registered at the centralized performanceconsole (PM-NWS) of the client end (Remote ws) of the M2000 system. Theperformance tasks are assigned by Adapter to BAM of the corresponding NE andthen transferred to the host. The task results are transferred to the performanceserver via BAM and Adapter and are saved in the database. The task results can bequeried by selecting a task and inputting the query condition at the centralizedperformance console (PM-NWS) of the client end (Remote ws).

Traffic Statistic Analysis

Traffic Statistic Task Registration

Basic Traffic Statistic Tasks

Note:

The basic traffic statistic tasks must be registered at the beginning of the equipmentdeployment and saved during the system optimization period and maintenanceperiod.

Caution !

1) Be careful that the reporting capability of RMU will overrun so that somemeasurement items may be lost when too many measurement items are registered,especially when too many carriers are configured in the sector.For the versions below D302, a maximum of 160 carriers (i.e., measurement objects)can be registered in each measurement set if the twelve carrier-level measurement

sets are registered. More than 150 carriers can be registered in each measurementset if other measurement sets such as BSC overall performance measurement setare registered. If the four seldom-used carrier-level measurement sets (i.e., the fourmeasurement sets related to the hard handoff) among the twelve measurement setsare not registered, a maximum of 240 carriers can be registered in eachmeasurement set.To solve the above problem, a patch is designed for D302 to improve the reportingcapability of RMU, which supports the measurement of 240 carriers or so when thetwelve measurement sets are registered. 2) The maximum number of measurement objects in a carrier-level measurement setis 200 carriers. If there are more than 200 carriers, it is necessary to register twotasks.


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The basic traffic statistic tasks are registered at the beginning of the equipmentdeployment and saved all the time.

1. BSC overall performance measurement and carrier performance measurement,with a measurement period of 1 hour and 24 hours respectively. All function sets andmeasurement items are selected.

To cope with the unexpected accidents at the stage of network optimization, the BSCoverall performance measurement and carrier performance measurement can beregistered in a shorter measurement period, such as 15 minutes. But themeasurement in a short period is little useful and there are large amounts of data.Therefore, measurement tasks with a measurement period of 15 minutes can becancelled after the system runs stably.

The call drop ratio, call setup success ratio, congestion ratio and handoff successratio are the main measurement items that are used to appraise the network quality.This guide mainly analyzes these measurement items. Other measurement tasks,such as carrier power control measurement and carrier channel performance

measurement are mainly used for problem analysis.

2. Carrier power control measurement with a measurement period of 5 minutes. Thefour measurement items are all selected.

The carrier power control measurement can be used to measure the link information,including the parameters of average carrier transmit power, Eb/Nt, RSSI and FER.The RSSI can help to tell the reverse interference. The average carrier transmit power,Eb/Nt and FER can be used to judge whether a balance is achieved between theforward and reverse links, so they are very helpful to the network optimization. For themeasurement item RSSI in the task, if the measurement period is too long, the datawill be so averaged that it is difficult to observe the exception. Therefore, the shortestmeasurement period of 5 minutes should be selected. For the introduction of RSSI,please refer 4.7.

3. Channel load measurement in carrier channel performance measurement. Themeasurement period is 60 minutes. The four measurement items are all selected.

The channel load measurement item can help the network optimizers learn theforward and reverse loads of the network. Currently, only the forward load can bemeasured, but the reverse load can not yet and it will be “0” in the traffic statisticresults.

The channel load measurement covers the measurement of bandwidth occupied bydata service. The bandwidth measurement is only based on the forward SCH. Thebandwidth is measured at the end of each measurement period. The occupiedbandwidth multiplied by the duration of the measurement period is the throughput of

the data service. The bandwidth is not an average value.

Specific operations: Select the NE of CBSC, and select overall performancemeasurement, carrier performance measurement, carrier power control measurementand carrier channel performance measurement from function sets. Select allmeasurement items in all function subsets for the three measurements other than thecarrier channel measurement. Select only the function subset of channel loadmeasurement and all measurement items in it for the carrier channel performancemeasurement. The measurement time segment is 0 ~ 24 hours. The measurementtype is semi-permanent. The measurement mode is measurement by day. Thestorage period is recommended to be above 7 days.


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Note:

1) The current version supports a maximum of 120 objects in the same traffic statistictask and a maximum of 128 measurement items.

2) If the storage period of the traffic measurement task is 7 days, the data before 7days can not be viewed. But too long a storage period will increase the load of thesystem. So it is recommended to output the complete traffic statistic results of the dayto an .xls file and save them during the network optimization for the sake of acomparison in the future.

3.1.2

3.1.3

3.2

3.2.1

Other Traffic Statistic Tasks

After the basic traffic statistic tasks are registered, other new traffic statistic tasks canbe added according to the actual situation of the network.

The number of channels, total number of carrier control channels and the percentage

of traffic channels in good condition can be measured through the carrier channelperformance measurement. The carrier channel performance measurement can helpto check whether the data configuration is reasonable and to learn the running statusof the network. It can also be registered at the beginning of the equipmentdeployment.

The broken Abis signalling link measurement, A1 interface performance measurement, A2 interface performance measurement, SCCP-related measurement, MTP signallinglink measurement, MTP signalling link set measurement, MTP signalling pointmeasurement, PCF call processing measurement, PCF data processingmeasurement and CPU load measurement of CSPU can help to monitor the links,interfaces and the load of the system for a definite purpose. These measurementtasks can be registered according to the actual situation.

If necessary, the self-defined measurement items can be applied. The newmeasurement items can be calculated from the existing measurement items of thesystem.

System Tasks

The system tasks refer to those necessary for the system to run. They areindependent of the network optimization. There are four system tasks, which aremainly used to provide performance data for the performance measurement reporttemplate of the customized report tool of the M2000 system. Since the data sourcenecessary for the report is the result table of the system task, the user must register

the system measurement task before using the prepared template in the intelligentreport system. Only the administrator in the entire network and the superadministrator can register a system measurement task.

Traffic Statistic Analysis

Acquisition of Basic Network Information

The network problem analysis by means of traffic statistic data is based on theacquisition of the basic information of the network.


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3.2.2

I.

II.

First, it is necessary to get familiar with the early network planning and obtain thedocuments about the early network planning, such as the planning report,engineering parameter table, network topology and cell parameter designspecifications, so as to have a general idea of the network and find some obvious

problems.

Secondly, it is necessary to learn the current engineering construction progress, suchas, the completion status of BTS installation, the modification of planning, especiallythe engineering parameter planning, BTS commissioning and simple drive tests.Special attention should be paid to network defects caused by engineering installationquality or the construction progress. For example, the uncompleted or wronginstallation of some BTS will cause handoff problems in a large area in a city.

The objective of the network optimization can be defined effectively only after thebasic information of network is obtained. Different optimization strategies andoptimization objectives should be established for different coverage areas andapplication environments.

Major Measurement Items

Major appraisal measurement items of China Unicom

Call setup success ratio C2.5: 92%Call drop ratio of radio system C2.4: 1%.Traffic call drop ratio C2.11: 90Paging success ratio C4.6: 86%.Call completion ratio of system C4.4: 50%.Call completion ratio of MSC C4.5: 80%.

The above appraisal measurement items make sense only when the system is busy.

The values of the last three measurement items are measured at MSC. This guidefocuses on the first three measurement items. The paging success ratio is not onlyrelated to the radio signals, but also the paging strategy of MSC. The problems of lowcall setup success ratio and high call drop ratio of radio system are solved in thisguide. The problems that affect the paging success ratio are also basically solved.Later, emphasis is placed on the cooperation between BSC parameters and thepaging strategy of MSC.

It should be noted that the above measurement items are only required by someoperator and are given only for reference. These measurement items may vary withthe operator and the frequency band. The measurement items of different localnetworks of the same network operator may also vary and should be optimizedaccording to the local requirements.

Major traffic statistic items

The running status of the network is learnt from the following traffic statistic items. Forthe explanations of these measurement items, see 4 Introduction to Major TrafficStatistic Items.

Call setup success ratio

Learn the number of originated calls, major causes for call failure and call setupsuccess ratio.

Call drop ratio

Learn the cause for call drop and the call drop ratio.

Soft handoff


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3.2.3

3.2.4

Learn common soft handoff success ratio, softer handoff success ratio and the totalsoft handoff success ratio and learn whether the soft handoff ratio is normal.

Traffic

Learn the traffic without handoffs.

Congestion ratio

Learn whether there exists congestion and the major causes for the congestion.

Hard handoff

If the hard handoff takes place between BSCs of different manufacturers, first learnthe call handoff (out) success ratio & the cause for handoff failure, and then the callhandoff (in) success ratio & the cause for handoff failure.

Analysis Preparations

After the network starts to work, first confirm the following before the network

optimization:

1) Check the versions of the software and hardware used by the equipment arecorrect, the versions of BTSs and BSC are matched, the versions used are the moststable ones, the versions in the entire network are uniform, and all BTSs adopt thesame version.

2) Confirm the calibration test and sensitivity test have been carried out for each BTS.

3) Confirm the no-load test and loading test have been carried out for each BTS.

4) Confirm the VSWR test has been carried out for the antenna.

5) Confirm the dialling test has been carried out for each BTS after it is activated, andthe engineering installation is correct. During the dialling test, observe whether thecall can be accessed normally, the call quality is good, and the handoff can take placenormally. Make sure that the antenna feeder is not connected inversely. View the PNfrom the DEBUG window of the MS under the BTS. (If the PN is consistent with theplanned one, the antenna feeder is correctly connected.)

6) After the above problems are all eliminated, check the difference between theactual coverage and the expected coverage of each sector. If the coverage isexceptional, check whether the azimuth and downtilt of the antenna are consistentwith the planned ones. If they agree with the planned ones, but the coverage issignificantly different from the expected coverage or the coverage is overlapped, it isnecessary to adjust the downtilt or azimuth of the antenna. When the antenna isadjusted, do not adjust the coverage of an individual sector only, but the whole areaaround should be taken into consideration. If necessary, the antennas of several

sectors should be adjusted altogether.

7) Check whether any sensitive radio function (such as load control, cell breath,special handoff algorithms, special channel assignment algorithms, special powercontrol algorithms) has been applied. If so, the traffic measurement analysis may bedifferent from below. Therefore, a special analysis is required.

Precautions for Traffic Statistic Analysis

When analyzing the traffic statistic items, first study BSC overall performancemeasurement items to learn the general situation of the network operation. Thenanalyze the carrier performance measurement.


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3.2.5

I.

The filtering method is adopted during the traffic statistic analysis. First analyze thecell whose measurement items are obviously exceptional. It may be the version,hardware, transmission equipment, antenna feeder (including GPS) or data that leadsto the exception. In combination with the alarm information, check the

above-mentioned points. If there is no obvious exception, measure and sort thecarriers of each sector according to the measurement items and make a list of cellswhose major measurement items are poor so as to analyze them.

Be careful of the parameter modification. Modify the parameters after everything isfully considered. For example, when the timer is modified, be sure that the length ofthe timer can not be set too large. If so, the system load will become so heavy thatother problems will occur.

If it is necessary to adjust the antenna feeder or modify the parameters during thenetwork optimization, it is better to observe the measurement items for a period aftera measure is taken. After the effect of the measure is known, go on with the next step.Doing so can provide protection against any accident on the one hand, and help toaccumulate experiences on the other hand. In practice, the measurement items of the

network fluctuate much, with great randomness. If the measurement items are verypoor one hour before the parameter modification, but they become good shortly afterthe modification, it does not mean the parameter modification is highly effective,because the measurement items may become poor one hour later. It is preferred toobserve the measurement items for more than one day after the parametermodification. Compare these measurement items with those in the same timesegment before the modification (It is better to compare them with those in the sametime segment of the same day in the previous week). Only in this way, can a preciseconclusion be drawn. In addition, keep a close eye on the alarm information in thistime segment.

When observing the measurement items, you should not only concern the absolutevalues of the measurement items, but their relative values. Only when the statistical

magnitude for a measurement item is big enough, can the measurement item provideguiding significance. For example, a call drop ratio of 50% does not mean a poornetwork quality. Only when the absolute values of call attempts, call successes andtotal call drops have the statistical significance, will this call drop ratio make sense

It should be noted that these measurement items do not exist independently, but theyrelate to each other. For example, the interference and coverage will affect manymeasurement items. Vice versa, if the problem of a low handoff success ratio issolved, the problem of a high call drop ratio will be improved to some extent.Therefore, you should take other measurement items into consideration whenfocusing on analyzing a specific measurement item in practice.

Other Auxiliary Methods

The traffic measurement data only provide an important basis for the networkoptimization, so it is necessary to take other measures and methods to solve networkproblems.

Drive test

It is a direct, accurate method of learning the network quality and finding networkproblems. If you want to learn the radio network coverage, then the drive test willhave the irreplaceable advantage over the traffic measurement and other methods.You can use the drive test to learn whether the area is covered, whether there is anycoverage blind area, whether there is any imbalance between the forward link and

reverse link, and whether the antenna feeder is installed inversely that signals of the


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II.

III.

IV.

corresponding PN carrier appear where they should not. Especially after parameters,such as the power ratio, are modified or the coverage area is changed by adjustingthe antenna feeder, it is necessary to perform a drive test to learn whether theexpected results have been achieved.

The drive test can be used to solve a specific problem, but it has its own limitations.Limited to the test path and time, it is impossible to obtain the complete network data.For example, it is very difficult to find a call drop and to further analyze the cause forthe call drop by means of the drive test. Suppose the call drop ratio is 3%, namely,only three calls out of 100 are dropped, it is very difficult to find where a call isdropped, let alone the cause for the call drop.

The drive test can be used to learn the radio network structure and the quality of theengineering installation. The detailed analysis of the measurement items in the trafficmeasurement will provide a way of improving the measurement items. Only thecombination of macro traffic measurement with a particular test can effectively solvethe problem.

Signalling message tracing and signalling message printing ofdebugging console

These methods are usually used to solve difficult problems.

The AirBridge service maintenance system can trace signalling messages of differentinterfaces. The Um interface and Abis interface can trace signalling messages of asingle subscriber. If you encounter a complicated problem, you can trace thesignalling messages of interfaces (especially the Um interface) of the test MS as youperform a drive test, and then analyze the signalling flow to locate the problem.

The exceptional signalling message printing of debugging console of CBSC can helpyou to locate problems. From the signalling message printing of the debugging

console, you can find problems, such as, absent configuration of pilot and improperadjacent cell planning.

Alarm information

The alarm information of equipment can reflect the real-time running status of theequipment in the whole-network, so enough attention should be paid to the alarminformation. The exception of some measurement item in the traffic measurementmay be likely related to the alarm occurrence to the equipment. When different alarmsare distinguished and they are related to the measurement items, no time will bewasted blindly. The alarm information of equipment can be viewed in the centralizedfault management system of M2000 or at the alarm console of AirBridge.

M2000 also provides the task-based performance alarm function. It defines theperformance measurement items. If a measurement item exceeds the set threshold, itwill send a performance alarm to the alarm server. The alarm information can beviewed at the centralized alarm workstation.

Traffic statistic function provided by the AirBridge performancemanagement module

The AirBridge performance management module can provide the traffic statisticfunction, too. New tasks can be created and the measurement results can be queried.The measurement items are just the same as those in M2000. But the measurementresults can only be displayed in the form of text, so they are not so visual as those inM2000. The traffic measurement tasks registered in M2000 can also be queried on


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AirBridge. The traffic measurement tasks with “NM task” behind names are thoseregistered in M2000 Network Management (NM) system.

Introduction to Major Traffic Statistic Items

This section introduces the major measurement items in M2000 traffic statistic, andsubdivided measurement items and signalling measurement points in the functionsubsets. It also analyzes the measurement items based on the experiences of acommercial network in Cangzhou, and points out the causes for the exceptionalmeasurement items.

For the analysis of causes for the exceptional measurement items, see 4.1.4.

Note:

1) The causes for the exceptional measurement items and the analyses given in thisguide are not very perfect. These causes may vary greatly with operationalenvironments of networks. So we need to accumulate experiences in practice toperfect our theory.2) For the parameter configurations and modifications involved in this guide, seeCDMA1X BSS Network Planning Parameter Configuration Recommendations.3) The following measurement items except those in 4.7 Carrier Power ControlMeasurement are all measurement items in the function sets of BSC overallperformance measurement and carrier performance measurement. Unless otherwisespecified, the subdivided measurement items in the function sets in this guide applyto both the BSC overall performance measurement and the carrier performancemeasurement.4) At present there are some indefinite signalling measurement points for themeasurement items or their meanings are not clear. They will be improved in laterversions.

4.1

4.1.1

4.1.2

Call Setup Success Ratio

Calculation Formula

Call setup success ratio = [Call setup successes/call attempts]*100%

Meaning

Ratio of successful traffic channel (TCH) assignment times of BSC to the total callattempts in mobile originated calls without handoffs, mobile terminated calls withouthandoffs, and the receiving & transmitting of SMS on TCH.


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4.1.3

4.1.4

I.

II.

III.

Description of Measurement Items in Function Subset

Measurement Item Analysis

When the call setup success ratio is low, find the major cause that leads to themaximum call setup failures. If the number of call setup failures resulting fromdifferent causes is basically equal, find the causes for the MS reverse servicepreamble capture failure and waiting-for-MS-response timeout.

MSC denial

MSC will deny calls when some invalid subscribers continuously make calls. If thenumber of denials is not too large, they can be ignored temporarily. If the number isexceptionally large, check whether the setting of CCM_T_WT_ASSG_REQ timer isproper, and whether the link connection of A interface is normal. Then make a further

analysis of MSC.

Early release

It is normal that this cause value appears, because the measured calls are those thatare normally cleared before the assignment is completed. If the early release isexceptional, you can also analyze MSC to locate the problem.

MS reverse service frame preamble capture failure

In terms of the signalling flow, one failure cause may be that the forward signal qualityis so poor that the MS fails to receive the Enhanced Channel Assignment Message(ECAM) or the MS can not successfully demodulate the forward traffic channel.

Another failure cause may be that the reverse signal quality is so poor that the BTScan not receive the TCH preamble after the MS sends it. The third failure cause maybe the wait timeout of the timer of the BTS.

If this failure frequently occurs in the actual network, the possible causes include:

Imbalance between the forward link and reverse link

It is necessary to adjust the radio coverage or modify the system parameters in thiscase (See 5.1).

Improper setting of power control parameters

On the one hand, a low initial forward transmit power may make it difficult for MS toaccess the network and thus lead to the call failure. In this case, check the settings ofthe initial transmit power and maximum transmit power of the forward traffic channel.Note that the forward power control parameters of IS-95 MSs and CDMA2000 MSsare configured in the PWRPARA table and the FWDPWRPARA table, respectively.On the other hand, the improper setting of the reverse access parameters may causethe access failure. The related reverse access parameters include NOM_PWR,INIT_PWR and PWR_STEP

Improper setting of access parameters

The access parameters include NUM_STEP, ACC_TMO, PAM_SZ and MINPAMSZconfigured in BTS. For the parameter settings, see CDMA1X BSS Network PlanningParameter Configuration Recommendations.

Improper setting of CCM_T_WT_TCH_PREAMBLE timerToo few assignment message resending times

Reverse service frame capture failure due to improper setting of traffic channelresearch window of BTS


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IV.

V.

4.2

External interferencePilot pollution

See 5.1

Waiting-for-MS response timeout

The causes for waiting-for-MS-response timeout are similar to those for MS reverseservice frame capture failure. At this time, the closed power control has started in thereverse link. If the BTS has already demodulated the reverse traffic channel, thepower control will also start in the forward link. The possible causes include:

Imbalance between forward link and reverse linkImproper setting of power control parameters

The same as that for MS reverse service frame capture failure. Not only the reversepower control step REV_FCH_FER in the reverse link, but also the settings ofparameters of power control step and frequency in the forward link can be checked.

Improper settings of timers of CCM_T_WT_MS_ACK_ORD,CCM_T_WT_SRV_CONN_CMP_MSG and CCM_T_WT_STATUS_RSP_MSGImproper setting of traffic channel research window of BTSExternal interference.Pilot pollution.

The measurement item “traffic channel congestion ratio” is added in the versionsabove D405. It refers to the congestion ratio of calls.

Others

Causes for the exception of equipment or causes that are not mentioned above. Ifthere is any exception, it is necessary to make an in-depth analysis in combinationwith the signalling alarm messages.

Besides, the access failure may be caused by the conflict between access andhandoff.

If the signal quality in the serving cell is poor during the access, the MS needs to behanded off to a new cell where the signal quality is good. However, no handoff ispermitted during the access period. There are two cases during the access.

1) The Ec/Io of the pilot in the serving cell decreases quickly (5-6dB/S) while the Ec/Ioof the pilot in the new cell is quite large. In this case, if the handoff region is too small,the MS may be dropped off the network during the access.

2) The access is too slow. The Ec/Io of the pilot in the serving cell decreases veryslowly and the Ec/Io of the pilot in the new cell is quite large. If the MS moves quickly,

it stays in the good coverage area at the very beginning of access, but it soon entersthe coverage border. It will be dropped off the network because the handoff fails.

The parameters ACCESS_HO (access handoff allowed) and ACCESS_PROBE_HO(access probe handoff allowed) are configured to allow a handoff during the access.But these parameters are not recommended.

Call Drop Ratio

The call drop ratio is classified into the call drop ratio of radio system and the call dropratio of system. The call drops of system refer to the total call drops resulting fromdifferent causes in the whole network system, including call drops resulting from the

radio system or other causes. Since the majority of call drops are related to the radio


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4.2.1

4.2.2

4.2.3

4.2.4

I.

system, the call drop ratio of radio system should be the highlight. What is mentionedin the traffic measurement is just the call drop ratio of radio system. There should belittle difference between the call drop ratio of system and the call drop ratio of radiosystem. If necessary, the call drop ratio of system can be defined in the traffic

measurement.

Calculation Formula

China Unicom: Call drop ratio of radio system = [Total call drops of radio system/Callsetup successes]*100%

Huawei: Call drop ratio of radio system = [Total call drops of radio system/Call setupsuccesses + Successful inter-BS hard handoffs (in)]*100%

Meaning

The call drop ratio refers to the ratio of calls exceptionally released due to radio link tothe call setup successes. The total call drops of radio system refer to the call dropscaused by radio signal quality degrade and handoffs.



When the call drop happens to the link branches of other BSCs without exception, thecall drop will not be measured at the local BSC or at the target BSC.

It should be noted that, for the carrier-level call drop ratio measurement in the currenttraffic measurement, if the call drop takes place in the soft handoff state, it will only bemeasured for one time and be considered happening to the link branch on which thecurrent call is first established.

It should be noted that the carrier-level call drop measurement in the current trafficmeasurement is described as below if there are multiple branches: When the originalaccess cell is still in the current active set, the call drop, if it happens, will beconsidered happening to the access cell. When the access cell is not in the currentactive set, all branches occupied by the MS can be searched by virtue of a function,and then the call drop will be considered happening to the branch (sector carrier)which is first searched. The call drop measurement is not an average value and thebranch search is random.

Radio link causes

One cause is that the BTS is blocked and CCM directly releases the resource. Thecall drop seldom happens in this case. This cause can be judged and solved byquerying the status of the BTS. The other cause is that a high frame error rate (FER)results from the poor radio signal quality. The call drop resulting from a high frameerror is very common. FMR will report TCH ERR to CCM due to the high frame errorrate and the call drop will happen when CCM releases it. FMR will report TCH ERRwith the following cause values. Only after TCH ERR whose cause value is 4, 5 and 6is reported to CCM, CCM will release the call. The cause value 2 is only for the softhandoff link branch which will be cleared by CCM.

Cause value 5


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After all link branches in FMR are merged, more than 270 out of the 300 reverseframes are erasure frames. For the cause, refer to the analysis below. The Erasureframe ratio and Erasure frame threshold can be modified on AirBridge by using thecommand MOD SDUMDC. The frame information can be queried by using the

command LST FRMINFO.Cause value 4

300 idle frames are received in the reverse link. In the version above D302, if thedelay between two handoff link branches exceeds the length of the reverse framecombination timer, FMR will be unable to combine the frames of the two branches,but send them to the voice subrack. At this time, if the new branch fails to capture thereverse service frame, the CP of BTS will report idle frames and idle frames will bemeasured by FMR. But all branches share the same idle frame counter and thereading of the counter will be cleared only after the idle frames reach 300 and thecounter reports TCH ERR. In this way, a call drop may happen during the soft handoffbecause of too many idle frames. If a call drop happens during the soft handoff, theexceptional signalling message printing of the debugging console will show too many

idle frames. The transmission delay of one branch is so long that the frames of thetwo branches can not be aligned. Therefore, errors will occur when the frames arecombined on FMR. FMR will consider the call drop is caused by the idle frames. Thethreshold of idle frame counter can be modified on AirBridge by using the commandMOD SDUMDC. The frame information can be queried by using the command LSTFRMINFO

Cause value 6

Too high a markov FER. The system will compare the received frames with thoselocally generated. If the received frame is different from the locally generated one, itwill be considered as an erasure frame. The markov FER refers to the ratio of theerasure frames to the total received frames. When the system fails to receive the

frame sent from the opposite party, this frame will also be considered as an erasureframe. By default, if 95% of 500 frames in 10 seconds are erasure frames, TCH ERRwill be reported. The markov FER can be set at the debugging console..


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II.

III.

4) Cause value 2: One branch does not receive any frame within 80ms. The length ofthe reverse frame receiving timer can be modified on AirBridge by using thecommand MOD SDUMDC. Note that the length of timer is in millisecond. The frameinformation can be queried by using the command LST FRMINFO. Due to this cause,

the soft handoff link branch is very likely deleted just when the Ec/Io of the pilot of thislink branch is very large. After the deletion, the MS will soon report PSMM andrequest BSC to add the branch, so the link branch is frequently deleted and addedduring the soft handoff. In this case, the length of the reverse frame receiving timercan be set a little larger, because no signal on one branch will not affect the frameselection of FMR. The possible causes for Cause Value 5 and Cause Value 6 includethe following cases:

1) The poor reverse signal quality leads to a high FER.

2) The poor forward signal quality leads to a high FER. From the angle of MS, themechanism of call drop is described as follows:

A. If the MS receives 12 (N2m) successive erasure frames, the MS will switch off the

transmitter, but it still receives frames in the forward link. If two (N3m) successivegood frames are received within 5 seconds (Fade Timer), the MS will restart thetransmitter. Otherwise, the MS will be reinitialized.

B. The MS fails to receive the response message. If the MS still does not receive anyresponse after N1m successive times of transmission, it will be reinitialized. (N1m isthe maximum times that the MS resends a response request message on the reversetraffic channel. It's a protocol value. For IS-95A, it is 3, for IS-95B, it is 9, and IS2000,it is 13.)

If the forward signal quality is poor, the MS will switch off the transmitter. In this case,FMR considers there are erasure frames, so a call drop happens.

3) Abis link fault, such as broken optical fiber. In this case, FMR considers there are

erasure frames, so a call drop happens.

For the possible radio link causes for the call drop, see 4.2.5.

Abis interface

1) It can be seen from the signalling measurement point that when Abis interface isexceptionally interrupted (for example, the optical fiber is broken), the call drop willnot be considered resulting from Abis interface cause. When Abis interface issuddenly interrupted, BSC does not know it but only knows that FMR does notreceive the data frames, so Abis interface cause will be considered as a radio linkcause. In this case, it can be easily learnt from the alarm console that Abis interface isexceptionally interrupted.

2) In the case of BTS fault, the BTS will automatically report “Abis BTS releaserequest” only when it finds problems in its internal processing. In this case, the calldrop will be considered resulting from this cause and the alarm information of theequipment will also appear at the alarm console.

A interface

The possible A interface causes include:


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IV.

V.

4.2.5

I.

II.

1) During the conversation, MSC itself sends or MSC is made to send the A interfacereset command.

2) A interface is temporarily faulty or the link is broken. In this case, if FMR does notreceive the EVC frame sent from MSC within a certain period, it will send “TRAUERR” to CCM and CCM will release the resource. Problems on transmission can besolved in combination with the alarm information, such as E1/T1 alarm. If thetransmission of A interface is normal, the problem may lie in the equipment, includingMSC and BSC.

3) If FMR does not receive the EVC frame, but A interface is normal, the problem maylie in the internal processing or the transmission of the equipment.

Transmission link from BSC to PCF

1) PDSN is abnormal.

2) PPU or A8/A9 interface in BSC is abnormal.

3) When Huawei BSC is connected to PCF of other manufacturers, PCF or A8/A9interface or the transmission equipment of other manufacturers is abnormal.

Others

It is difficult to locate the other causes for the failure. When there are exceptions,problems can be analyzed from the equipment in combination with the alarminformation and the signalling message printing of debug console.

Possible Causes for a High Call Drop Ratio

Low Ec/Io of the forward link

If the forward link can not be demodulated, the MS will switch off the transmitter so asto lead to a call drop.

The Ec/Io of the forward link can be obtained from the MS and the drive testequipment. The receiving level can also be taken into consideration during the causeanalysis. If the Ec/Io is small and the receiving level is low, the coverage will be poor.The possible cause may be that the MS is far away from the BTS, or there is a largebarrier in the way of the propagation. This problem can be solved by adjusting theantenna of the BTS to improve the coverage. If Ec/Io is small while the receiving levelis high, strong interference will exist in the forward link. The forward interferenceincludes the inter-BTS interference and the external interference. The forward

interference will make Ec/Io decrease. The forward interference data can be obtainedby means of some instruments, such as YBT250.

High FER in the reverse link

The FER data in the reverse link can be obtained from the carrier power controlmeasurement. The possible causes for a high FER in the reverse link include:


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III.

IV.

V.

VI.

4.2.6

I.

II.

1) Too high a propagation attenuation in the reverse link leads to a high FER in thereverse link. If the FER in the forward link is also high at this time, it indicates that thepropagation attenuation of the BTS is too large. The cause for this symptom is thatthe MS is far away from the BTS. To solve the problem, more BTSs should be added.

2) If the signal level in the forward link is high enough, but only the FER in the reverselink is high, it indicates the coverage of the BTS is good. It is possible that the highFER is caused by the low power in the reverse link. To solve the problem, the systemparameters, such as the reverse power control threshold Eb/Nt, can be modified.However, the modification of Eb/Nt will only function within a certain range becausethe maximum transmit power of the MS is limited. If the transmit power of the MSreaches the maximum and the modification of the Eb/Nt is useless, it shows the MS isalready on the border of the reverse coverage.

3) The reverse power does not reach the maximum, but the FER in the reverse linkincreases. The symptom is usually caused by the fast fading. It shows there is nostable master pilot where the MS is located.

4) Dense subscribers and strong reverse interference may also lead to a high FER inthe reverse link.

Imbalance between the forward and reverse links

See 5.1.

No master pilot coverage

See 5.2.

Improper setting of handoff parameters

See 5.3.

Improper adjacency

See 5.4 Measurement Item Analysis.

Examples of Call Drop

Call drop caused by conflict between access and handoff

If the system does not support the handoff during the access, but a handoff is

required when the MS originates a call on the border, the MS has to wait for thehandoff. If it takes a long time for the MS to access the network, the call may bedropped before the handoff process is completed. In this case, the Ec/Io observed onthe MS will decrease while the receiver power (Rx) of the MS will increase. Thatmeans interference is caused by a new strong pilot and a handoff is necessary.Furthermore, the MS will reselect the new pilot after the call drop.

Call drop caused by traffic channel power restriction

The power of the traffic channel is usually controlled by the settings of Eb/Nt of theforward and reverse links. If the setting of the maximum transmit power of the trafficchannel is improper, a call drop may happen when the power is not high enough tomaintain the link connection, even though the Ec/Io of the pilot is very large.

Forward link failure


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III.

IV.

4.2.7

In this case, it can be seen from the MS that the Ec/Io of the pilot and the receiverpower (Rx) of the MS are both above the threshold (for example, Ec/Io is greater than-15dB, and Rx greater than -100dBm). If the TX_GAIN_ADJ of the MS remainsunchanged within 5 seconds (Fade Timer of the MS) and the MS then is reinitialized,

it shows the MS switches off the transmitter because it fails to receive the forwardtraffic channel frames. In addition, since the Ec/Io of the original serving pilot is large,the MS will reselect this pilot after the call drop. It shows the call drop is very likelycaused by the low power of the forward traffic channel.

Reverse link failure

The power of the reverse traffic channel is controlled by the setting of Eb/No. If thepower of the reverse traffic channel is not high enough to reach the BTS, the BTS willrelease the call when it detects 270 erasure frames out of 300.

Call drop caused by forward interference

If it can be seen from the MS that the Ec/Io of the pilot decreases while the receiver

power (Rx) of the MS increases, it shows there exists interference in the forward link.Due to the interference, the Ec/Io of the pilot will decrease. If the forward link can notbe demodulated, the MS will switch off the transmitter. If the forward interference lastslonger than the length (5s) of the Fade Timer of the MS, the MS will be reinitializedwhen the Fade Timer is reset.

The possible interference causes include:

1) The CDMA interference may lead to a handoff failure. If the MS selects a new pilotafter the re-initialization, the call drop is contributed to the handoff failure. In this case,the call drop is very likely caused by the forward link interference.

2) There is another special case. When a blocked BTS is suddenly unblocked, strongforward interference will occur to the BTSs around, so call drops may happen to those

BTSs..

3) External interference. If the MS stays in the search state for a long time (more than10 second), the call drop may be caused by a high FER due to the existence of aninterference source (e.g., AMPS system and microwave emission) that is useless tothe MS.

Call drop caused by a heavy forward load

If the load of the BTS is heavy and the transmit power is 20W above the maximumtransmit power, the self-protection mechanism of the BTS will automatically decreasethe transmit power of each channel so that the Ec/Io of the pilot is lowered and thetransmit power of the traffic channel drops. In this way, the forward link can not be

demodulated. Especially, it is very likely that call drops will happen to MSs on theborder of coverage. Meanwhile, the call setup success ratio will decrease.

Traffic Call Drop Ratio

Traffic call drop ratio = Traffic (without handoff) over traffic channel * 60/total calldrops of radio system

China Unicom is much concerned about this measurement item. It is closely relatedto the traffic. However, for the traffic in a non-populated urban area, the traffic calldrop ratio can meet the requirement as long as the call drop ratio is up to standard.


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4.3

4.3.1

4.3.2

4.3.3

4.3.4

I.

II.

Traffic Channel Congestion Ratio

Calculation Formula

Traffic channel congestion ratio = [Traffic channel congestion times/Traffic channelrequest times]*100%

Meaning

In mobile originated calls, mobile terminated calls, handoffs, and the receiving &transmitting of SMS on TCH, traffic channels can not be successfully assigned due tothe insufficient Walsh codes, power, traffic channels, encoders or transmission linksfrom BTS to BSC. The traffic channel congestion ration refers to the ratio of the totaltraffic channel assignment failures to the total traffic channel requests.


The traffic channel congestion ratio contains five function subsets, which are call,inter-BS hard handoff (in), intra-BS hard handoff (in), inter-BS soft handoff (in) andintra-BS soft handoff (in), respectively.


The congestion ratio is a measurement item that the operator is concerned about. It isalso the basis of network capacity expansion.

Insufficient Walsh codes

In the normal case, there are sufficient Walsh codes. The Walsh codes may beinsufficient when a data service is requested.

Insufficient forward power

1) The forward common channel occupies too much of the power.

Check the power configuration of the forward channel. The pilot power should notoccupy too much of the power (The pilot power usually accounts for 20% of the totalforward power) and the initial transmit powers and maximum transmit powers of

paging channel, synchronization channel and forward traffic channel should be set inproper proportion to the pilot power.

2) So many subscribers that the forward power is used up.

From the forward and reverse load data in the channel load measurement, thereverse load will be heavy when there are many subscribers or when the forwardpower is insufficient. In this case, the system capacity will not be large enough if thecall quality is guaranteed. If only the capacity of a single sector is not large enough,you can adjust the height and downtilt of the antenna in the sector or change thetransmit power of the MS and the sector to share the traffic with adjacent sectors. Youcan also modify the parameters to relieve the congestion. For example, increase thehandoff threshold of the congested cell and reduce the handoff threshold of adjacent

cells. If the capacity in the whole coverage area is insufficient in different timesegments, it is necessary to expand the capacity.


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III.

IV.

V.

Insufficient reverse power

When the channel is assigned, the system will judge whether the reverse power issufficient. Since the measurement of the reverse load is not accurate, the admission

control will be applied in the reverse channels according to the equivalent number ofsubscribers.

The different RC voice and data subscribers will be converted into the equivalent RC3voice subscribers. When the system assigns channels, it will first predict the totalequivalent RC3 voice subscribers, and then judge if the number of the total RC3 voicesubscribers exceeds REV_MAX_USER (reverse subscriber admission threshold). Ifso, the channel assignment will fail and the system will be considered the reversepower is insufficient in the traffic measurement. The REV_MAX_USER is configuredin the CH_INFO (channel information) table. Other data, such as, equivalent RC3voice subscribers of RC2 voice subscribers can be configured in this table. For thedata configuration, see CDMA BSS Network Planning Parameter ConfigurationRecommendations.

If the reverse power is insufficient in the traffic measurement, it is possible that thereare too many subscribers. If there are too many subscribers, the forward power willbe insufficient, too. Besides, you can check whether the parameters of reverseadmission control in the CH_INFO table are properly configured.

Insufficient channels

In the normal case, there are sufficient channels unless

1) The channels are not well planned that they can not meet the capacity requirementof the operator. But the probability of this case is very low.

2) The channel planning meets the capacity requirement, but the real number of

subscribers goes beyond the capacity. This is a case of insufficient system capacityand the capacity needs to be expanded. This case seldom happens at the earlyoperation stage of the network.

3) The soft handoff ratio is so high that too many CEs are occupied. The soft handoffratio is by far greater than the planned redundancy. So it should be reduced.

4) For the intra-BS soft handoff and the inter-BS soft handoff, the insufficient channelsin the traffic measurement may also result from the CCM wait timer timeout andunsuccessful resource assignment due to other exceptional causes. You can checkwhether the setting of the CCM_T_WT_RL_CNF timer is proper.

A interface transmission link establishment failure

A interface includes A1/A2 interface between BSC and MSC. For the intra-BS softhandoff, the A interface includes A8/A9 interface between BSC and PCF. According toDescription of CBSC Traffic Measurement Items, the intra-BS hard handoff dataservices are not measured.


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VI.

VII.

4.3.5

I.

II.

III.

1) Insufficient capacity of A interface links: When the network load does not exceedthe network capacity, this problem can be avoided if the A interface link is properlycalculated. If the network load exceeds the network capacity, the capacity of Ainterface transmission links should be expanded.

2) Transmission fault. You can query the alarm information to solve transmissionproblems.

3) Timer timeout. The timers of calls and inter-BS hard handoff areCCM_T_WT_BOOK_CIC_CNF, CCM_T_WT_PIE_RES_APPLY_CNF,CCM_T_WT_PIE_RES_AFFIRM_CNF and CCM_T_WT_A9_CONN_A8. The timer ofthe intra-BS hard handoff is CCM_T_WT_HO_RES_CNF..

4) Other exceptions.

Abis interface transmission link establishment failure

1) Insufficient capacity of Abis interface links.

The same as A interface.

2) Abis transmission link fault. You can query the alarm information to solvetransmission problems.

3) The timer expires when CCM requests Abis link resource. Check whether thesettings of timers of CCM_T_WT_TCH_SETUP_CNF, CCM_T_WT_BOOK_BIE_CNF,CCM_T_WT_ABIS_BTS_SETUP_ACK and CCM_T_WT_SETUP_LEG_ACK areproper.

A3 interface transmission link establishment failure

During the inter-BS soft handoff, the target BSC needs to connect A3 interface and Abis interface to realize the service transmission between MS and BSC afterreceiving the A7-Handoff Request message at A7 interface. The failure may becaused by the improper setting of CCM_T_WT_BOOK_TIE_CNF timer or thetransmission link fault.

Possible Causes for Traffic Channel Congestion

Insufficient system capacity

Compare the busy hour traffic of the congested cell with the planned capacity. When itis sure that the system capacity is insufficient, capacity expansion is recommended.

The probability of insufficient system capacity is very low at the early stage of networkoptimization.

Interference

If the system capacity is sufficient, but failure often occurs after the command isissued, the failure may be caused by interference. The interference can be analyzedaccording to the carrier power control measurement. See 4.7.

Insufficient allocated power of traffic channel

The common channel occupies too much of the forward power so that the forwardpower will be insufficient in the traffic measurement. In consideration of the coverage


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IV.

V.

4.4

4.4.1

4.4.2

4.4.3

4.4.4

and the capacity balance, the power reduction of the common channel can relieve thecongestion.

Improper setting of handoff parameters

If the handoff threshold of the congested cell is too low while that of the destinationcell is too high, the MS can not be successfully handed off to the destination cell. Inthis case, properly add more adjacent cells according to the actual situation or modifythe handoff parameters to relieve the congestion. See 5.3.

Improper adjacency

See 5.4.

Traffic

Calculation Formula

Traffic over TCH (with handoff) = TCH seizure duration (with handoff)/Measurementperiod (Second)

Traffic over TCH (without handoff) = TCH seizure duration (withouthandoff)/Measurement period (Second)

Meaning

The measurement item is the traffic over TCH (including traffic with handoff and trafficwithout handoff). That is, the traffic measurement with handoff is the seizure durationof all call branches, while the traffic measurement without handoff is the actual trafficof the user.


The BSC overall performance measurement item includes soft handoff ratio. Thecarrier performance measurement includes the handoff duration and handoff traffic.


The traffic without handoff is the essential item for understanding of network bearer.Through the traffic measurement, we can grasp the pattern of subscriber behavior;understand the network position to work out corresponding optimization solutions andstrategies. Only the item with large traffic in overall performance measurement item issignificant for traffic measurement. The item with small traffic is often unreliable. Weshould attach importance on the sector with large traffic and take precedence ofsolving the problems in sector with large traffic.

Soft handoff ratio: At current, the measurement result includes the softer handoff ratio.

Calculation formula = Traffic (with handoff) – Traffic (without handoff)/Traffic (withhandoff).

The specification of China Unicom includes 3 types of traffic measurement: actualtraffic, CE traffic, and WALSH traffic.


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I.

II.

III.

4.5

4.5.1

Accordingly, other vendors should conform to the traffic measurement of above threetypes. The formula for soft handoff ratio is (CE traffic—actual traffic)/ CE traffic, andthe measurement value obtained is generally within 30% and 40%. However, inHuawei the CE traffic is not independent from the traffic measurement, now the CE

traffic and WALSH traffic are the same. Therefore, the soft handoff ratio of Huawei isa little high (i.e. about 50%). Actually, the soft handoff ratio of Huawei is about 33%,i.e., a rational value, if it is calculated in the same way as other vendors (the CE trafficis generally about 75% of the WALSH traffic).

The CE traffic will become independent of the traffic measurement in later versions ofBSC ROO2B03D003 so that the soft handoff ratio displayed in traffic measurementequals the actual soft handoff ratio.

The soft handoff makes use of multiple sectors to generate diversity gain for one callto improve the link quality in cell border overlap area. The power control of softhandoff also helps reduce the interference of MS on its adjacent cells. Therefore,appropriate handoff can improve the quality of call, widen the coverage area, expandthe system capacity and improve the performance. But high soft handoff ratio will

increase the probability of call drops on the one hand, and result in heavy signalingload, occupy CE and impact the forward capacity of the system on the other hand.The venders generally hold different opinions about soft handoff ratio, but it is theunanimous viewpoint that the acceptable soft handoff ratio without softer handoffshould be about 30%~40%.

The factors leading to exceptional soft handoff ratio include:

Excessive handoff region

The excessive region with overlapped coverage on the border of adjacent cells leadsto frequent soft handoff. The soft handoff region can be located through the drive test.The size of soft handoff region can be controlled by adjusting antenna height, downtilt

and azimuth instead of modification of power control.


See 5.2

Improper setting of handoff threshold

See 5.3.

Soft Handoff

Calculation Formula

The soft handoff success ratio= [(Intra-BS soft handoff successes + inter-BS softhandoff successes)/(Intra-BC soft handoff requests + Inter-BS soft handoffrequests)]*100%.

Note:

The successes and requests here are only related to the soft handoffs (out).


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4.5.2

4.5.3

4.5.4

I.

II.

Meaning

It refers to the intra-BSC and inter-BSC handoff (out) success ratios, includingcommon soft handoff and softer handoff.


Intra-BS and inter-BS soft handoffs are included.

Perform measurement of softer handoff if softer relation exists between new linkbranch and original active set branches (i.e. they are located in the same cell),otherwise, perform measurement of soft handoffs.


Though soft handoff success ratio aims at the handoff (out), the handoff (in) dataused for calculation of congestion ratio is also of great help for analysis of soft handoffsuccess ratio. Both intra-BS and inter-BS soft handoffs are originated by Huaweiequipment due to unavailability of A3 and A7 interfaces. The congestion upon handoff(in) corresponds to the soft handoff (out) failure.

Adding a branch

Better carrier

After detecting that Ec/Io of certain PN is large, the MS will sends a PSMM to theBSC. The BSC sends an EHDM to the MS to add a soft handoff branch after judgingthe Ec/Io.

Network optimizationThe soft handoff due to poor coverage is specified in consideration of the specialrequirements during network optimization. Currently, measurement of this item is notperformed.

Others

It refers to manual execution of command of adding soft handoff branch via networkmanagement system, or other causes except those above.

Deleting soft handoff branch

Normal handoff branch deletion

If the Ec/Io of a certain branch decreases, the MS will send a PSMM to the BSC. The

BSC sends an EHDM to the MS to delete a soft handoff branch after judging theEc/Io.

Forward link quality

The precondition for the FMR reporting TCH ERR to the CCM is that this branch failsto receive the frame within 80ms. Upon receipt of the TCH ERR containing the causevalue, the CCM will report it to the RMM to request for disconnection of this branch.

A7 interface reset

For inter-BSC soft handoff, the call management is performed at the original BSCside. The target BSC should send the received reverse signal to the original BSC forprocessing via A3/A7 link. A7 interface functions as a signaling interface between theoriginal BSC and target BSC. The measurement of this item can only be performedafter A7 interface is reset and "A7 Reset" message is sent to the BSC. That the FMRfails to receive the reverse frame of this branch will be reported to the original BSC in


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III.

4.5.5

case of broken A3/A7 link. In this case, the measurement of branch deletion will fallinto the measurement of branch deletion caused by forward link quality. Currently thismeasurement is unavailable.

Soft handoff failure

Radio resource unavailable

It corresponds to radio resource request failure of incoming party, and specific failurecause can be located through analysis of handoff (in) congestion.

Requested terrestrial resource unavailable

The establishment of link with BTS terrestrial resource fails, corresponding to handoff(in) Abis interface setup failure.

Radio interface failure

Waiting for “Handoff Complete MSG” from the MS times out. The probability of thisfailure is great.

1) Poor radio link including both forward and reverse links: the cause is that the MSfails to receive the handoff command, or the BTS fails to receive the handoff completemessage from the MS. For details, see 4.5.5.

2) Improper timer setting. Please check the CCM_T_WT_MS_HO_CMP timer.

MS denial

The MS cannot identify the received handoff command and reject it. This probability islow unless the MS does not comply with protocol specifications to support handoffmessage. Currently measurement value of it is 0 due to unavailability. If the MSrejects the EHDM indeed, this cause will incorrectly fall into other cause in the trafficmeasurement.

A3 link setup failure

Upon receipt of A7-Handoff Request via A7 interface, the target BSC should establishthe connection of A3 and Abis interfaces for service transmission between the MSand original BSC. Analysis of transmission can be performed based on alarminformation.

Others

On the one hand, there are exceptional causes other than mentioned above, such ascode exception and incorrect status, which are hard to locate. Generally the judgmentresult can be displayed at the debug console.

On the other hand, timer of RRM waiting for handoff completion expires:

1) If the timer of CCM waiting for handoff completion also expires, i.e., a soft handofffailure is counted in the measurement of soft handoff failures caused by radiointerface failure, it must be the cause of poor radio link.

2) Check the setting in TT_HO_REQ (timer duration of handoff request), and thisvalue should be larger than the timer duration of CCM waiting for handoff completion.For details, see CDMA1X BSS Network Planning Parameter ConfigurationRecommendations.

3) If the timer duration of RRM is longer than that of CCM, and CCM timer does notexpire, it must be the problem of communication between equipment modules.

Possible Causes for Soft Handoff Failure



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4.6

4.6.1

See 5.2.

Incorrect setting of handoff threshold and parameter

See 5.3.

Absent configuration of adjacencySee 5.4.

Improper adjacent cell priority

See 5.4.

Improper setting of search window

See 5.5.

Imbalance between forward and reverse links

See 5.1.

CongestionPoor coverage

Hard handoff

Calculation Formula:

Hard handoff success ratio= [Intra-BS hard handoff successes+ inter-BS hard handoffsuccesses/ Intra-BS hard handoff requests+ inter-BS hard handoff requests]*100%

Note:

The successes and requests are only related to the handoffs (out).

4.6.2

4.6.3

4.6.4

Meaning

Success ratios of intra-BSC and inter-BSC hard handoff (out), including co-frequencyand inter-frequency hard handoffs

Description of Measurement Item in Function Subset

Intra-BS hard handoff and inter-BS hard handoff are included.


Hard handoff measurement covers the co-frequency, inter-frequency, intra-BSC andinter-BSC hard handoffs. The hard handoff success ratio refers to the success ratio ofall hard handoffs (out). The measurement of hard handoff involving multipleequipment suppliers requires the coordination of the client.

As there are many hard handoff algorithms, different optimization targets andmeasures should be developed for different algorithms during the optimizationprocess. Attention should be given to the co-frequency hard handoff, as it is hard toachieve a satisfying handoff success ratio due to co-channel interference. Take thecommercial network in Cangzhou for example, the success ratio of 80% is acceptedby the client. The relative low handoff success ratio will definitely affect other

measurement items, such as the call-drop rate. With the maturity of technology,


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4.6.5

clients will ask for a higher co-frequency hard handoff success ratio. More experienceis also required for the analysis of inter-frequency hard handoff.

A lot of measurement items of hard handoff are similar with those of soft handoff. Forthe same measurement items, see the relevant description of soft handoffmeasurement items.

Better pilot

When MS detects that the Ec/Io of a certain PN is stronger than the serving one, it willreport PSMM message. BSC sends EHDM message according to the Ec/Io

Network optimization

It refers to the load-balance hard handoff. At present, this item is not measured.

Border cell

It refers to the handoff target cell is border cell. At present, this item is notunavailability.

Pseudo-pilot

It is measured when the handoff target is the pseudo-pilot.

Returning to source channel

The cause is not unclear yet. At present, it is treated as the successful return to thesource channel after the MS fails to be handed off to the target carrier.

Others

The hard handoff measurement does not cover the radio interface fault measurement.However, the measurement item includes the radio interface measurement and othercauses in the soft handoff.

Possible Causes for Hard Handoff Failure

Improper configuration of adjacency

During the preliminary planning of hard handoff adjacency, the adjacency isconfigured as much as possible. In this way, ping-pong handoff occurs on the borderof the cell. In addition, as the system has to monitor the changes of the MS pilotsignals in a lot of border cells, the system load increases. The drive test can becarried out to get the information about BTSs really and directly adjacent to HuaweiBTSs. In this way, the unnecessary or unimportant adjacency can be removed toreduce the ping-pong handoffs and call drops, and increase the handoff successratio.

Poor coverageImproper settings of handoff threshold and related parameters

In the co-frequency hard handoff, the signal on the boarder of handoff regionfluctuates seriously and fades quickly due to the signal interference of two cells. If therelative hard handoff threshold is too low, it is easy to trigger the handoff, whichcauses ping-pong handoffs. When a hard handoff occurs, the hard handoff may endup with failure due to the change of signal and fading of target pilot. In this case, therelative hard handoff threshold can be increased to reduce the times of hard handoffattempts and increase the success ratio.

However, the threshold cannot be too high. Otherwise, it could be too late to triggerthe hard handoff. When the hard handoff is triggered, the fading of the forward link ofHuawei BTS may be too serious for MS to receive the HDM message from the sourcecarrier.

Improper setting of search window

Improper setting of access parameters


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4.7

4.7.1

Improper setting of power

If the pilot power of destination cell is greater than the source cell, the handoff regionwill lean towards the source cell. If MS is far away from the destination cell, it is hardfor MS to capture the destination cell. This situation can be improved by adjusting the

powers of both cells.

If the hard handoff fails because the MS sends a candidate frequency search reportto the source carrier and then returns to the source channel, the failure cause is the“failure of capturing target channel”. There are two methods to solve this problem.One is to increase the transmit power of the initial traffic channel of the destinationcell. The other is to increase the MS search window.

Carrier Power Control Measurement

Description of Measurement Item

1) It is a sector-specific measurement item. Please note that:

All measurement items are average values of all subscribers in this sector. TakeRSSI for instance, the RSSI in the Common Measurement Report sent by BTS isaverage of RSSI every second. If the measurement period is 5 minutes, themeasurement

Date post:	07-Aug-2018
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Guide to CDMA 1X Traffic Statistic Analysis-20030710a-A-1.3

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