GSM RF Optim How To

8/6/2019 GSM RF Optim How To

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I. Background

1. Introduction2. Causes that inspire carrying out the RN optimization

3. Inputs for Radio Network optimization4. KPI

i. Drive test dataii. Tracing call data

iii. Performance measurement dataiv. Configuration data

II. Radio Network Optimization Activities

1. Flow Chart for Network Optimization2. Radio Network Optimization Start Up

i. Organization of Radio Optimization teamii. Determination of the Optimization acceptance counters

iii. Preparation of Radio Network Optimization tool

3. Single Site Verification

iv. Preparation for Single Site Testv. Single Site Test and Troubleshooting

4. RF Optimization

vi. Preparation for RF Optimization Testvii. Collection of RF Optimization data

viii. Analysis of RF Optimization data

1. Analysis of Coverage Problemsa. Common problems that affect coverage

b. Parameters that affect coverage areas

2. Analysis of Interference Problems3. Analysis of Hardware Faults4. Analysis of end-to-end network element interoperation.

ix. Implementation RF Optimization


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5. KPI Optimization

a. Collection of KPI data

1. Drive Test data2. Call Tracing data3. Traffic Measurement data4. Configuration data

b. Analysis of KPI data

i. Analysis of Access Counter Optimization

Common Access problem Solutions to Common Access problem

ii. Analysis of congestion Counter Optimization

1. Congestion Caused by High Traffic Volume2. Congestion Caused by Burst Traffic3. Congestion Caused by TRX Failure4. Congestion Caused by Interference5. Congestion caused by Channel Assignment Failure due to

Inconsistent Coverage.6. Congestion Caused by Inappropriate Data Configuration

iii. Analysis of Handover Counter Optimization

1. Unsuccessful handover 2. Handover Problems Caused by Hardware Failure3. Handover Problem Caused Inappropriate Data Configuration

iv. Analysis of Call Drop Counter Optimization

Causes of Common Call Drops

1. Coverage Related Call Drops2. Handover related Call drops3. Interference-related Call Drops4. Antenna System- related Call Drops5. Transmission-related Call Drops6. Parameter related Call Drops


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c. Implementation of KPI Optimization

6. Optimization Reports

1. Project background2. Networking modes3. Optimization process, content and progress4. Optimization counters5. Conclusion6. RF Optimization7. KPI Optimization8. Comparison of Traffic measurement KPI before and after

optimization9. Conclusion and analysis of KPI optimization

10. Analysis of remaining problems11. Network development suggestion12. Appendix

7. Optimization tools


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RADIO NETWORK OPTIMIZATION

I. Background

1. Introduction

Radio network optimization is carried out in order to improve the network performancewith the existing resources. The main purpose is to increase the utilization of the network resources, solve the existing and potential problems on the network and identify the

probable solutions for future network planning.

Through Radio Network Optimization, the service quality and resources usage of thenetwork are greatly improved and the balance among coverage, capacity and quality is

achieved.

In general, the following steps are followed during the Radio Network Optimization:

Data Collection and verification Data analysis Parameter and hardware adjustment Optimization result confirmation and reporting.

Due to the mobility of subscribers and complexity of the radio wave propagation, most of network problems are caused by increasing subscribers and the changing environment.Radio Network Optimization is a continuous process that is required as the network evolves.

2. Causes that inspire carrying out the RN optimization:

New network or expansion on the existing network The network quality decreased seriously and there are many complaints from

subscribers. An event occurs suddenly which affects the network performance seriously. The number of subscribers increased and affects the network performance

gradually.

3. Inputs for optimization

Traffic statistics Drive test Customer complaints


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4. Key Performance Indicators KPI

The KPI indicates the overall service performance of the network over a period of time to

meet the acceptance requirements.The KPI data is obtained from:

Drive test data

This data collected from the filed and is associated with the Mobile Station. Thefollowing aspects should be taken into during the drive test:

- Test service: speech and data- Test methods: continuous conversation, call set up and network access , handover, etc

Call tracing data

This data is collected from the network equipment side. It consists of the following:

- User signaling messages- Cell signaling messages- Standard interface signaling messages- LAC data- Real-time performance monitoring data.

Performance measurement data

The performance measurement data indicates the radio performance on the network leveland cell level. BSS performance data consists of the following:

- Access data- Call drop data- Handover data- Traffic volume- Congestion data

Configuration data

Configuration script file collected from the BSC are normally used for problem analysisand location.


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II. Radio Network Optimization Activities

1. Flow chart for network optimization

Network Statistics Drive Test Call tracing

KPI target

Propose Action Plan

Frequency, parameter, configuration and hardware changes

Implement action plan

Achieved KPI

End


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2. Radio optimization Start up

Organization of radio Optimization team

The team to carry out the Radio Optimization activities is shown below

Determination of optimization acceptance counters

These are targets for the Network optimization. The key counters that indicate thenetwork quality include the coverage rate, call drop rate, call setup success rate,congestion rate. The counters are of two types:a) Drive test counters mainly for network with comparatively few subscribers

b) Traffic measurement Preparation of radio network optimization tool

The tools for RN optimization have to be made ready. The list of tools is indicated on page 18

3. Single Site Verification

This is a self-test associated with equipment in each site and each cell. Its purpose is toverify the basic functions such as access, call and handover of each site and each cell inthe area to be optimized.

1 Radio Network Optimization Team Leader

2 Radio Network Optimization Engineers

1 Field MeasurementTechnician

1 Field MeasurementTechnicians


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Preparation for single site test

Site status and site configuration data are checked. Test places or routines and debugs testinstruments are also selected.

Single site test and troubleshooting

It aims to locate the problems associated with the installation and functionality of equipment. It looks at the following aspects:

- Check whether the ARFCNs are the same as planned- Check whether the LAI are the same as planned- Check whether the configuration of neighbor cell is complete and whether

the handover parameters are normal.

For abnormal sites, adjust the related parameter or rectifying the hardware faults to solvethe problem.

- Check problems related to power amplification, improper antenna systemconnection, and blockage due to environmental change, inconsistentantenna tilt and azimuth.

- Perform Call Quality Test to check whether the access and conversation of the speech are normal through dialing test.

.

4. RF Optimization

It aims to optimize the signal coverage, mitigate the interference and ensure the evendistribution and normal coverage of the radio signal after the service parameters areoptimized.

Following aspects are followed:

Preparation for RF optimization test

It involves the following points:

- Determine the optimization target so that the network can operate as planned and the KPIs meet the acceptance requirements.

- Since the coverage, capacity and quality of the GSM network are relatedto each other, categorize the clusters. RF optimization should performed incluster instead of individual BTSs

- Determine the drive test route.


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- Prepare the documents and tools

Collection of RF optimization data

The RF optimization data can be collected through:

- Drive test- Call Quality Test for indoor areas and pre-selected required areas.

The collected data together with the BSC call tracing data and configuration data providereference for the problem location. This data helps to check whether the network operatesin accordance with specifications.

Analysis of RF optimization data

Through the analysis of RF optimization data, problems related to coverage, interference,

hardware failure, and interoperability of network elements can be located and thenappropriate adjustments can be made.

a) Analysis of coverage problems

It mainly focuses on signal distribution. Common items to be checked:

1. If the coverage area becomes smaller after the BTS starts services, check thefollowing items:

- Ambient environment of the BTS antennas

- Changes in the propagation environment- Whether there are VSWR alarms and diversity receive alarms on the SiteMaintenance Terminal System

- Whether VSWR is less than 1.5- Whether TMA is operational- Antenna tilt and azimuth- BTS transmit power - Whether BTS receive sensitivity is normal- Whether the parameter associated to coverage are set properly- Whether noise floor is high due to interference and poor electromagnetic

environment.

2. If the coverage problems are caused by expansion of the BTS capacity, check thefollowing items:

- Whether the configuration of combiners changes after capacity expansion- Whether appropriate antennas are selected- Whether new antennas are installed in accordance with the requirements


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- The location of the BCCH transmit antenna of the omnidirectional doubletransmit antennas.

- For directional double transmit antennas, whether the pitch and theazimuth of the antenna are consistent

- The output power on top of the cabinet for different TRXs when the

maximum coverage configuration is used.

3. If the coverage problems are caused by swapping or new construction, check thefollowing items:

- Whether the azimuth and height of the antennas is the same as those before swapping

- Whether the tilt of the directional antenna is the same as that beforeswapping

- Whether the power on top of the cabinet for the BTS before and after

swapping are consistent.- Whether the BTS receiver sensitivity is normal.- Whether the noise floor is high due interference and poor electromagnetic

environment- Whether there are VSWR alarms and main diversity receive alarms on the

Site Maintenance Terminal System- Whether the parameters associated with coverage are set properly.- Check whether the antennas are installed in accordance with the

requirements after the BTS is put into operation or after new construction.- Whether appropriate antenna are selected- That there are inverse connections in the antenna system- Whether the TMA is operational- The power on top of the cabinet for different TRXs when maximum

coverage configuration is used.

Common problems that affect coverage

1. Water running into antennas2. Passive intermodulation antennas3. Inappropriate antenna types4. Tower influence on the omnidirectional antennas5. Inappropriate installation of the directional antennas

6. Inappropriate installation of the omnidirectional antennas7. Problems associated with connection of the antenna systems, combiners anddividers, and CDU.

8. TMA problems9. BTS front-end module fault (Isolator, duplexer, filters,)

Parameters that affect coverage areas


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TRX power level, TMA power attenuation factor, MS maximum transmit power controllevel, MS minimum receive signal level, and RACH minimum access level

b) Analysis of Interference problems

It greatly affects the speech quality and handover. Call drop or congestion may be alsocaused. Its analysis involves:- Uplink interference analysis: when the traffic volume is low compared

with the interference band- Downlink interference analysis: If the Received Signal Quality is lower

(RXQUAL) than the predefined threshold and Receive Signal level(RXLEV) is higher than the predefined threshold. If RXQUAL andRXLEV are lower than the predefined thresholds.

The interference sources of the GSM network are:

1. Intra-network interference2. interference from repeaters3. interference from other high-power communication equipment4. Hardware faults.

The location and troubleshooting are:

1. Determine the cells that have interference on the basis of KPIs2. Check the OMC alarms3. Check the frequency planning4. Check the cell parameter setting5. Perform drive test6. Eliminate the interference based on analysis and check the results.

c) Analysis of hardware faults

Hardware faults affect the normal operation of the network or disrupt the network. Theyconsist of network elements faults and transmission link faults. The type of the faults can

be determined by checking hardware alarms and analyzing the traffic measurementresults.

d) Analysis of end-to-end network elements interoperation.

Check the normal operation of BTS, BSC, and MSC. Interoperation problem refer to problems in interface protocols, version matching, A and Abis interface dataconfiguration, and interface signaling compatibility.


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Implementation of RF optimization

To meet the KPI requirements, adjust the cell engineering parameters based on the data

analysis. Consider the optimization cost when replacing the antennas, adding TMA andadding BTSs. The following engineering parameters can be adjusted:

- Antenna tilt- Antenna height- Antenna height- Antenna location- Adding TMA- Replacing the site type- Adjusting the site location- Adding sites.

5. KPI optimization

It involves finding and solving the problems that do not meet the acceptance requirementthrough the analysis of drive test data and the traffic measurement data. It also involvesthe counter such as call setup success rate, call completion rate, call drop rate, handover success rate and congestion rate.

5.1. Collection of KPI data

The data consist of:

a) Drive Test data

It is associated with the MS and it has to be more detailed. It involves:- Test service: speech and data- Test methods: continuous conversation, dialing test and automatic test.

b) Call tracing Data

It is collected from the network element and contains:

- User signaling messages- Cell signaling messages- Standard interface signaling messages- LAC data


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- Real-time performance monitoring data

c) Traffic Measurement data

It indicates the radio performance on the network level and cell level. It consists:- Access data- Call drop data- Handover data- Traffic volume- Congestion data

d) Configuration data

Scripts files collected in the BSC

5.2. Analysis KPI optimization data

The analysis of the KPI optimization data helps solve the remaining equipment andcoverage problems after the previous actions mainly associated with call access,congestion, handover, and call drops.

5.2.1. Analysis of Access Counter optimization

- Access specifications (drive test): calling part completion rate, called part completion

rate and access delay of the CS and PS services.- Access specification (traffic measurements): paging success rate and call setupsuccess rate.

Common access problem are:

- Paging problem- Assignment problem- Authentication and encryption problems- Equipment problems

Solution to access problems

- Cell resection parameters: reselection start threshold, reselection delay, reselectionhysteresis and cell offset.

- Random access parameters: RACH minimum access threshold, MS minimum accesslevel and RACH error threshold.


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5.2.2. Analysis of Congestion Counter optimization

The congestion in the GSM network refers to the SDCCH congestion ant TCH

congestion.

Common congestion and troubleshooting:

1) Congestion caused by high traffic volume Check from the performance measurement results whether the traffic volume of SDCCHand TCH exceeds the specification. In this case capacity expansion or traffic sharing can

be applied to mitigate congestion.

2) Congestion caused by burst traffic

If the SDCCH congestion rate and the traffic volume are high while the TCH trafficvolumes is normal, configure more SDCCH or enable SDCCH-TCH dynamicconversation function.

3) Congestion caused by TRX failure

If there is a TRX fault, replace the faulty unit. It is also important to check the cables inthe antennas systems and whether the VSWR

4) Congestion caused by interference

Interference on Um interference.

5) Congestion caused by channel assignment failure due to inconsistent coverage

The causes are:

- The transmit power of the TRXs are not the same- The coverage areas of the transmit antennas in a cell are not the same- The transmit and receive antennas are not on the same horizontal plane or their tilts

are not the same.

6) Congestion caused by inappropriate data configuration

- Planning of location areas reasonably to decrease the SDCCH congestion.- Enable SDCCH dynamic allocation function to decrease SDCCH congestion.- For dual dual-band network, set the corresponding parameters appropriately to

decrease SDCCH congestion: CRO, CBA, CBQ and Cell reselection Hysteresis


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- Timer setting: T3101, T3103, T3107, T3122, T3212 and T3111

5.2.3. Analysis of Handover Counter optimization

It aims to make sure that the drive test and traffic measurement data meet specifications.

Common handover problems:

1) Unsuccessful handover

The MS fails to initiate a handover when the signal in the cell is weak or signal quality is poor. Take the following into consideration:

- Handover conditions are met- There is a candidate cell that meets the handover conditions.

Adjust the relevant parameters based on the following causes:

- The handover thresholds are set too low- No neighboring cell relation is set- Handover hysteresis is set inappropriately.- The BTS clock expires

2) Handover problems caused by hardware failure

Replace the faulty hardware.

3) Handover problems caused by inappropriate data configuration.

- In independent MSC networking mode, check whether the signaling settings areconsistent in the local and the peer MSCs- In the co-MSC networking mode, check whether the signaling settings are consistent

in the BSCs from different manufacturers.- If the handover failure applies to only one cell, then analyze the problems base on the

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

How to locate the handover problems

1) Check whether the fault lies in one cell or in all cells (the faulty cells are

neighboring cells of a cell or the faulty cells a BSC or an MSC).2) Check whether the configuration data is adjusted before the problem occurs3) Check whether the problem is caused by hardware faults.4) Register handover performance measurement counters and TCH performance

measurement counters.5) Perform drive test in the faulty cell and analyze the signaling.


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5.2.4. Analysis of Call drop Counter optimization

Call drops are associated with coverage, handover, interference, antenna system,transmission and parameter setting.

The causes of common call drops are:

1) Coverage related call drops are caused by:

- Discontinuous coverage with blind areas : weak and poor quality signals at the edgeof the isolated BTS which cause calls to drop because they cannot be handed over toother cells

- Bad indoor coverage: densely distributed buildings and thick walls cause greatattenuation and low indoor level which causes call drops.

- Cross-area coverage.

2) Handover-related call drop3) Interference-related call drop4) Antenna system-related call drop5) Transmission-related call drops6) Parameter-related call drops

- radio link timeout- SACCH multi-frame- Access control parameters

- Timer T3101 and T3107

In addition, check the following:

- A interface failure during the TCH seizure- TCH availability- Call drops due to terrestrial link interruption.

5.3. Implementation KPI optimization

Radio configuration parameters are adjusted to enhance the service performance.

Before adjusting the radio configuration parameter, perform the following:

1. Make a detailed parameter adjustment plan- Adjustment objectives- Version of the network equipment and instructions- Adjustment procedures


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- Adjustment details (the parameter values before and after adjustment should berecorder).

- Operation time.- Troubleshooting

2. Review the adjustment plan of the parameter in large size and that are of a highsecurity level.3. Submit the application for the network operation to the customer with the

following items:- Operation content- Operation purpose- Operational time- Required resources such as personal, vehicles and SIM cards- Abnormal results that may occur and their troubleshooting measures- Operation impacts on the services (impacts on traffic counters).

After adjusting the radio configuration parameters, perform the following:

1. Back up the latest data file and record the date2. Verify that the BTSs and cells are operating normally after the adjustment.

Conduct dialing test and ensure all services are normal.3. Check the traffic measurement results such as access success rate, congestion rate,

call drop rate and handover rate.4. Record the adjustment and its effects for future check.

6. Optimization reports

The optimization report should content the following:

1. Project background2. Networking modes3. Optimization process, content and progress4. Optimization counters (drive test counter and performance counters)5. Conclusion6. RF Optimization

Test methodComparison of coverage data before and after optimization

7. KPI optimization

Test methodComparison of the drive test KPI before and after optimization

8. Comparison of the traffic measurement KPI before and after optimization

Analysis of access counters


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Analysis of retainability countersAnalysis of mobility counters

9. Conclusion and analysis of the PKI optimization

List of problemsList of solutionList of the remaining problems

10. Analysis of remaining problem11. Network development suggestions12. Appendix:

List of the engineering parameters after optimizationList of the system parameters optimization

7. Network optimization tools Network optimization tools are used for data collection, data analysis, and simulationanalysis. These are:

1. LAPTOP WITH TERMS INVESTIGATION 8.0 or NEMO2. CAR to carry out the Drive Test3. FULL DRIVE TEST KIT4. DIGITAL CAMERA5. GPS6. RECHARGEABLE BATTERIES and THE CHARGER

7. MAPS

Documents

GSM RF Optim How To