01-05 KPI Optimization

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5KPI OptimizationAbout This Chapter

KPI optimization refers to optimizing the service performance of the network to meet the

acceptance requirements. During KPI optimization, the network optimization engineers find and

solve the problems that do not meet the acceptance requirements through the analysis of the

drive test data and the performance measurement data.

KPI optimization involves the counters such as the call-completion rate, call drop rate, handover

success rate, and congestion rate.

Figure 5-1shows the KPI optimization process.

HUAWEI BSC6000 Base Station Subsystem

BSS Radio Network Opimization Guidelines 5 KPI Optimization

Issue 01 (2007-09-05) Huawei Technologies Proprietary 5-1


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Figure 5-1KPI optimization process

No

Yes

Start

RF optimization

Data collection:

Configuration data

Drive test data

Performance

measurement data

Call trace data

End

Are the

optimization results

satisfactory?

Data analysis

Are the

optimization results

satisfactory?

Yes

Data analysis

and processing

No

Discuss solutions

Make solutions

5.1 KPI Optimization Data Collection

The data collected during KPI optimization data collection is the drive test data, call trace data,

performance measurement data, and configurationdata.

5.2 KPI Optimization Data Analysis

Single site verification focuses on equipment-related problems, and RF optimization focuses on

coverage-related problems. Therefore, KPI optimization needs only to focus on KPI-related

problems. However, the unsolved equipment-related and coverage-related problems, if any,

must be solved during KPI optimization. Common KPI-related problems are related to access,

congestion, handover, and call drop.

5.3 KPI Optimization Implementation

During KPI optimization implementation, you can adjust the radio configuration parameters to

enhance the service performance.

5 KPI Optimization


BSS Radio Network Opimization Guidelines

5-2 Huawei Technologies Proprietary Issue 01 (2007-09-05)


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5.1 KPI Optimization Data Collection

The data collected during KPI optimization data collection is the drive test data, call trace data,

performance measurement data, and configuration data.

Drive Test Data Collection

The data collected during drive test data collection is the MS data. The drive test in KPI

optimization is more complete than that in RF optimization.

l Service tested: voice and data services

l Test method: continuous conversation, dialing test, and automatic test

Call Trace Data Collection

The data collected in call trace data collection is the call trace data on the network equipment

side. It consists of the following:

l User signaling message trace data

l Cell signaling message trace data

l Standard interface signaling message trace data

l LAC data

l Real-time performance monitoring data

Performance Measurement Data CollectionThe performance measurement data comprehensively indicates the radio performance on the

network level and the cell level. GBSS performance data consists of the following:

l Access data

l Call drop data

l Handover data

l Traffic volume data

l Congestion data

Configuration Data Collection

Configuration data collection is to obtain the BSC configuration script files for problem analysis

and location.

5.2 KPI Optimization Data Analysis

Single site verification focuses on equipment-related problems, and RF optimization focuses on

coverage-related problems. Therefore, KPI optimization needs only to focus on KPI-related

problems. However, the unsolved equipment-related and coverage-related problems, if any,

must be solved during KPI optimization. Common KPI-related problems are related to access,

congestion, handover, and call drop.





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5.2.1 Access Analysis

Access analysis refers to checking whether the access counters during the drive test and the

performance measurement meet the acceptance requirements.

5.2.2 Congestion Analysis

GSM network congestion mainly refers to SDCCH congestion and TCH congestion. SDCCHcongestion refers to no available channels for SDCCH seizure. TCH congestion consists of two

situations. One is no available channels for TCH seizure, which leads to channel request failures.

The other is TCH assignment failures.

5.2.3 Handover Analysis

Handover analysis involves the drive test data and the performance measurement data. It refers

to checking whether the handover counters tested during the drive test and the performance

measurement meet the acceptance requirements. Before performing related optimization, judge

whether the handover problem is related to the BSS network elements.

5.2.4 Call Drop Analysis

Call drops are caused by problems in coverage, handover, interference, antenna system,transmission, and parameter setting.

5.2.1 Access Analysis

Access analysis refers to checking whether the access counters during the drive test and the

performance measurement meet the acceptance requirements.

l Access counters (drive test): calling party completion ratio, called party completion ratio,

and access delay of the CS and the PS services

l Access counters (performance measurement): paging success ratio and call setup success

ratio The common access problems are related to the following:

Paging

Assignment

Authentication and encryption

Hardware

Solve the access problems by adjusting the antenna configuration parameters that are as follows:

l Cell reselection parameters: reselection start threshold, reselection delay, reselection

hysteresis, and cell offset

l Random access parameters: RACH minimum access threshold, BS-PA-MFRAMS, MS

minimum access level, and RACH error threshold

5.2.2 Congestion Analysis

GSM network congestion mainly refers to SDCCH congestion and TCH congestion. SDCCH

congestion refers to no available channels for SDCCH seizure. TCH congestion consists of two

situations. One is no available channels for TCH seizure, which leads to channel request failures.

The other is TCH assignment failures.

The commoncongestion problems and troubleshooting are as follows:

l High traffic

Check the performance measurement results to see whether the traffic volume of theSDCCHand the TCH exceed the thresholds. Capacity expansion is the best way to solve

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the congestion caused by high traffic. Traffic sharing measures is another way to mitigate

congestion.

l SDCCH burst traffic

If the SDCCH congestion rate and the traffic volume is high while the TCH traffic volume

is normal, the SDCCH congestion may be caused by a traffic burst. To mitigate the SDCCHcongestion, modify the SDCCH configuration or enable the SDCCH-TCH dynamic

adjustment function.

l TRX fault

In a cell of multiple TRXs, if a faulty TRX is out of service, congestion may be caused.

Replace the faulty TRX. If you are not sure whether the fault lies in the TRX or not, check

whether the cables in the antenna system are properly connected and whether the VSWR

is normal. If the cables in the antenna system are properly connected and the VSWR is

normal, replace the TRX and then check whether the services recover.

l Interference

Interference also causes congestion. Mitigate the congestion by solving the interferenceproblems.

l Channel assignment failure caused by inconsistent coverage

The causes are as follows:

The transmit power of the TRXs in a cell are not consistent. Check the connections of

the combiner, divider, CDU, and SCU.

The coverage areas of the transmit antennas in a cell are not consistent. Modify the

engineering parameters.

The transmit and receive antennas are not in a horizontal plane or are of different tilts.

Adjust the antennas.

l Inappropriate data configuration. To reduce SDCCH congestion rate, troubleshoot asfollows:

Appropriately plan the location areas

Enable the SDCCH dynamic allocation function

Appropriately set the dualband network parameters, for example, the CRO, CBA, and

CBQ.

Appropriately set the timers, for example, the T3101, T3103, T3107, T3122, T3212,

and T3111

5.2.3 Handover Analysis

Handover analysis involves the drive test data and the performance measurement data. It refers

to checking whether the handover counters tested during the drive test and the performance

measurement meet the acceptance requirements. Before performing related optimization, judge

whether the handover problem is related to the BSS network elements.

The common handover problems and troubleshooting are as follows:

l Unable to initiate a handover

The MS cannot initiate a handover when the signals are weak. Check the following:

Whether the handover conditions are met

Whether there is a candidate cell that meets the handover conditions

The problem may lie in the following:





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The handover thresholds are set too low.

No adjacent cell relation is set.

The handover hysteresis is not set appropriately.

The best cell measurement time P/N is not set appropriately. N is a continuous lengthof time. P is the length of time when the conditions are met.

The BTS clock times out.

l Hardware faults

If the data of the faulty cell and its neighbor cell is not modified recently, check whether

the problem is caused by hardware faults. If yes, replace the faulty hardware.

l Inappropriate data configuration. Troubleshoot as follows:

In MSC independent networking mode, if the incoming or outgoing MSC handover is

abnormal, check whether the signaling of the local MSC and the peer MSC is consistent

and whether the data of the local MSC and the peer MSC is modified.

In co-MSC networking mode, if the inter-BSC handover is abnormal, check firstwhether signaling of the local BSC and the peer BSC is consistent and whether the data

of the local BSC and the peer BSC is modified.

If the handover of a certain cell is abnormal, analyze the problem based on the actual

situations.

Check the handover-related timers such as the T3105, Ny1, T3103, and T3124.

To locate the handover problems, do as follows:

1. Check whether the fault lies in a certain cell or in all the cells. Check also the features of

the faulty cells. For example, the faulty cells are neighbor cells of a certain cell or the faulty

cells share a BSC or MSC.

2. Check whether the data is modified before the problem occurred.

3. Check whether the problem is caused by hardware faults.

4. Register the related performance measurement counters such as handover performance

measurement counters and TCH performance measurement counters.

5. Perform a drive test in the faulty cell and analyze the signaling.

5.2.4 Call Drop Analysis

Call drops are caused by problems in coverage, handover, interference, antenna system,

transmission, and parameter setting.

The causes and troubleshooting of common call drops are as follows:

l Coverage-related call drops are caused by the following:

Discontinuous coverage with dead zones

At the edge of the coverage area of an isolated BTS, the signals are weak and are of bad

quality, which causes handover unavailability. In complex landforms, for example,

mountainsides, the transmission of the signals is blocked and discontinuous, which

causes call drops.

Bad indoor coverage

Densely distributed buildings and thick walls cause great attenuation and low indoor

level, which lead to call drops.

Cross-area coverage (isolated island)

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Cell B is the neighbor cell of cell A, but cell C is not. If the MS roams from cell A to

cell C and still seizes the signals of cell A, when a handover is initiated from cell A to

cell B, the MS will not find a suitable target cell and a call drop is caused. See Figure

5-2.

Figure 5-2Call drops due to overlarge coverage

Cell A

Cell B

Cell C

Can't find next cell

cause call drop

Expected Coverage

Actual Coverage

Oversmall coverage

If the hardware of a cell is faulty, for example, the radiator of the antenna is blocked or

the BCCH is faulty, call drops may be caused.

In this case, find the areas with insufficient coverage through the drive test and ensure

indoor coverage. For details about how to rectify the hardware faults and about how to

modify inappropriate adjacent cell relations, refer to 4 RF Optimization.

l

Handover-related call dropsFor details about the causes and troubleshooting of handover-related call drops, refer to

5.2.3 Handover Analysis.

l Interference-related call drops

For details about the causes and troubleshooting of interference-related call drops, refer to

4.3.2 Interference Analysis.

l Antenna system-related call drops

For details about the causes and troubleshooting of antenna system-related call drops, refer

to 4 RF Optimization.

l Transmission-related call drops

For details about the causes and troubleshooting of transmission-related call drops, refer

to 4 RF Optimization. In addition, analyze the following counters:

TCH performance measurement: A interface failures during TCH seizure

TCH performance measurement: TCH availability

TCH performance measurement: Call drops due to interruption of terrestrial links

l Parameter-related call drops

Check whether the call-drop related parameters are set appropriately. The parameters are

as follows:

Radio link failure counter

SACCH multiframe number



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Access control parameters

T3101 and T3107 parameters

T200 and N200 parameters

5.3 KPI Optimization Implementation

During KPI optimization implementation, you can adjust the radio configuration parameters to

enhance the service performance.

Perform the following preparations:

l Make a detailed adjustment plan, which has the following contents:

Adjustment objectives

Version of the network equipment and instructions

Adjustment procedure Adjustment details including the changes of the parameter values

Operation time: determined by the network security and the operation impacts on the

services Perform the adjustment at midnight (after 24:00) when the traffic volume is

low. Do not perform dynamic adjustment during peak hours.

Troubleshooting

l Pre-review the adjustment plan. Pre-review the adjustment plan of the parameters that cover

a large area and that are of a high security level.

l Submit theApplication for Network Operationto the customer. The application includes

at least the following items:

Operation content

Operation purpose

Operation time

Resources prepared by the customers: personnel, vehicles, and SIM

Abnormal results and troubleshooting

Operation impacts on services including the performance measurement counters

l Back up the original data and record the date before every operation.

Check the following after the adjustment:

l Back up the latest data file on the BAM and record the date.

l Check whether the BTSs and cells are operational after the adjustment. Conduct a dialup

test to ensure that the services are normal.

l Check the performance measurement results after the adjustment. The performance

measurement counters include the access success rate, congestion rate, call drop rate, and

handover rate. Troubleshoot in time to ensure normal operation of the equipment.

l Record the adjustment and its effects for future check.

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