Radio Network Optimization

I.

Background 1. 2. 3. 4.

Introduction Causes that inspire carrying out the RN optimization Inputs for Radio Network optimization KPI i. ii. iii. iv.

II.

Drive test data Tracing call data Performance measurement data Configuration data

Radio Network Optimization Activities 1. Flow Chart for Network Optimization 2. Radio Network Optimization Start Up i. Organization of Radio Optimization team ii. Determination of the Optimization acceptance counters iii. Preparation of Radio Network Optimization tool

3. Single Site Verification iv. Preparation for Single Site Test v. Single Site Test and Troubleshooting

4. RF Optimization vi. Preparation for RF Optimization Test vii. Collection of RF Optimization data viii. Analysis of RF Optimization data 1. Analysis of Coverage Problems a. Common problems that affect coverage b. Parameters that affect coverage areas 2. Analysis of Interference Problems 3. Analysis of Hardware Faults 4. Analysis of end-to-end network element interoperation. ix. Implementation RF Optimization

5. KPI Optimization a. Collection of KPI data 1. 2. 3. 4.

Drive Test data Call Tracing data Traffic Measurement data 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. 2. 3. 4. 5.

Congestion Caused by High Traffic Volume Congestion Caused by Burst Traffic Congestion Caused by TRX Failure Congestion Caused by Interference 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 Failure 3. Handover Problem Caused Inappropriate Data Configuration iv. Analysis of Call Drop Counter Optimization •

Causes of Common Call Drops 1. 2. 3. 4. 5. 6.

Coverage Related Call Drops Handover related Call drops Interference-related Call Drops Antenna System- related Call Drops Transmission-related Call Drops Parameter related Call Drops

c. Implementation of KPI Optimization

6. Optimization Reports 1. 2. 3. 4. 5. 6. 7. 8.

Project background Networking modes Optimization process, content and progress Optimization counters Conclusion RF Optimization KPI Optimization Comparison of Traffic measurement KPI before and after optimization 9. Conclusion and analysis of KPI optimization 10. Analysis of remaining problems 11. Network development suggestion 12. Appendix

7. Optimization tools

RADIO NETWORK OPTIMIZATION I.

Background

1. Introduction Radio network optimization is carried out in order to improve the network performance with 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 the network 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

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. The following 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 level and 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 analysis and location.

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

2. Radio optimization Start up •

Organization of radio Optimization team

The team to carry out the Radio Optimization activities is shown below 1 Radio Network Optimization Team Leader

2 Radio Network Optimization Engineers

1 Field Measurement Technician

•

1 Field Measurement Technicians

Determination of optimization acceptance counters

These are targets for the Network optimization. The key counters that indicate the network 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 to verify the basic functions such as access, call and handover of each site and each cell in the area to be optimized.

•

Preparation for single site test

Site status and site configuration data are checked. Test places or routines and debugs test instruments 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 solve the problem. -

Check problems related to power amplification, improper antenna system connection, and blockage due to environmental change, inconsistent antenna tilt and azimuth. Perform Call Quality Test to check whether the access and conversation of the speech are normal through dialing test.

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4. RF Optimization It aims to optimize the signal coverage, mitigate the interference and ensure the even distribution and normal coverage of the radio signal after the service parameters are optimized. 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 related to each other, categorize the clusters. RF optimization should performed in cluster instead of individual BTSs Determine the drive test route.

•

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 provide reference for the problem location. This data helps to check whether the network operates in 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 then appropriate 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 the following items: - Ambient environment of the BTS antennas - Changes in the propagation environment - Whether there are VSWR alarms and diversity receive alarms on the Site Maintenance 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 the following 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 double transmit antennas. For directional double transmit antennas, whether the pitch and the azimuth 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 the following 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 before swapping 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. 2. 3. 4. 5. 6. 7.

Water running into antennas Passive intermodulation antennas Inappropriate antenna types Tower influence on the omnidirectional antennas Inappropriate installation of the directional antennas Inappropriate installation of the omnidirectional antennas Problems associated with connection of the antenna systems, combiners and dividers, and CDU. 8. TMA problems 9. BTS front-end module fault (Isolator, duplexer, filters,…) Parameters that affect coverage areas

TRX power level, TMA power attenuation factor, MS maximum transmit power control level, 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 also caused. 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 and RXLEV are lower than the predefined thresholds. The interference sources of the GSM network are: 1. Intra-network interference 2. interference from repeaters 3. interference from other high-power communication equipment 4. Hardware faults. The location and troubleshooting are: 1. 2. 3. 4. 5. 6.

Determine the cells that have interference on the basis of KPIs Check the OMC alarms Check the frequency planning Check the cell parameter setting Perform drive test 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. They consist of network elements faults and transmission link faults. The type of the faults can be determined by checking hardware alarms and analyzing the traffic measurement results. 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 data configuration, and interface signaling compatibility.

•

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 and adding 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 requirement through the analysis of drive test data and the traffic measurement data. It also involves the 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 and coverage 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 setup success 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, reselection hysteresis and cell offset. Random access parameters: RACH minimum access threshold, MS minimum access level and RACH error threshold.

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 SDCCH and 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 traffic volumes is normal, configure more SDCCH or enable SDCCH-TCH dynamic conversation 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 in the 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 are consistent 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 occurs 3) 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.

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 edge of the isolated BTS which cause calls to drop because they cannot be handed over to other cells Bad indoor coverage: densely distributed buildings and thick walls cause great attenuation and low indoor level which causes call drops. Cross-area coverage. 2) 3) 4) 5) 6)

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Handover-related call drop Interference-related call drop Antenna system-related call drop Transmission-related call drops 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 be recorder). Operation time. Troubleshooting

2. Review the adjustment plan of the parameter in large size and that are of a high security 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 date 2. 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. 2. 3. 4. 5. 6.

Project background Networking modes Optimization process, content and progress Optimization counters (drive test counter and performance counters) Conclusion RF Optimization  

Test method Comparison of coverage data before and after optimization

7. KPI optimization  

Test method Comparison of the drive test KPI before and after optimization

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

Analysis of access counters

 

Analysis of retainability counters Analysis of mobility counters

9. Conclusion and analysis of the PKI optimization   

List of problems List of solution List of the remaining problems

10. Analysis of remaining problem 11. Network development suggestions 12. Appendix:  List of the engineering parameters after optimization  List of the system parameters optimization

7. Network optimization tools Network optimization tools are used for data collection, data analysis, and simulation analysis. These are: 1. 2. 3. 4. 5. 6. 7.

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