15 GSM BSS Network KPI (RxQuality) Optimization Manual_2.doc

GSM BSS Network KPI (RxQuality) Optimization Manual

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GSM BSS

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V00R01

GSM BSS Network KPI (RxQuality) Optimization

Manual

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2023-04-21 Page 1 of 17


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GSM BSS Network KPI (RxQuality) Optimization

Manual

Keyword: RxQuality

Abstract:

This document analyzes factors that affect the downlink RxQuality on the BSS side. Based on the analysis, some methods are elaborated to quickly improve the downlink RxQuality. The Um quality is also to be improved to avoid poor RxQuality failure, call drop, and frame deletion resulted from the voice decoding decrease in the call. Some measures for optimizing this KPI are provided in this document to help field engineers address quality problems. This document targets at optimizing network KPIs and improving network quality so as to make sound preparations for the final network delivery.

Keyword: RxQuality (Downlink)

List of abbreviations:

Abbreviations

Full spelling

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Contents

1 Basic Principle................................................................51.1 Definition................................................................................................................................5

1.2 Theory Introduction.................................................................................................................5

1.3 Recommended Formula..........................................................................................................5

1.4 Signaling Procedure and Statistical Point...............................................................................5

2 Influencing Factors..........................................................6

3 Analysis Process and Optimization Methods.....................73.1 Analysis Process......................................................................................................................7

3.1.1 Procedures for RxQuality Problem Location.................................................................7

3.2 RxQuality Optimization Methods...........................................................................................8

3.2.1 Poor RxQuality on Entire Network................................................................................9

3.2.2 Passive Intermodulation...............................................................................................10

3.2.3 Intra-Network Interference..........................................................................................11

3.2.4 Inter-Network Interference..........................................................................................12

3.2.5 Hardware Fault.............................................................................................................12

3.2.6 Huawei Anti-Interference Technology.........................................................................14

3.2.7 Test Tool and Recommendations.................................................................................15

3.2.8 Recommendations for Configuration and Test............................................................15

4 RxQuality Optimization Cases........................................164.1 Low RxQuality in Kenya......................................................................................................16

4.2 Enabling Idle Burst Causing Interference Increase and Low RxQuality..............................16

5 Information Feedback....................................................175.1 TEMS Test Log of Faulty Cell..............................................................................................17

5.2 Requirements for Existing Network Configuration Data and Traffic Measurement............17

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1 Basic Principle

1.1 DefinitionThe RxQuality is an informal KPI. It identifies the Bit Error Rate (BER) on the Um interface based on the proportions of downlink RxQuality at various levels. The RxQuality can reflect the entire network quality. When the RxQuality is good and no major bug exists in voice processing, you can infer that the voice quality on the network is good.

1.2 Theory IntroductionIn theory, two measures can be taken to improve the RxQuality. One is to improve the RxQuality and demodulation performance (decoding the BER) with the same signals. The other is to decrease interference. In practice, the latter is an optimization method for improving the RxQuality.

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1.3 Recommended FormulaNone.

1.4 Signaling Procedure and Statistical Point

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2 Influencing Factors

According to cases and experiences in solving this problem, the following factors affect the downlink RxQuality:

Network planning

Data configuration

Frequency planning

Coverage

Interference

Power control

Interference-Based Channel Assignment (IBCA)

UISS

ICC

These preceding factors are described in Chapter 3 .

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3 Analysis Process and

Optimization Methods

This section aims to provide baseline recommendations for data configuration. In addition, it highlights some methods for improving the RxQuality on the premise that the project is clear of major problems and the coverage is good.

3.1 Analysis ProcessThe RxQuality reflects the network quality from two perspectives. The first is TRX-based counters, and the second is drive test or customer complaints. The RxQuality is improved mainly by eliminating or reducing interference. The interference is eliminated through interference source investigation to reduce intermodulation, proper planning of network frequency, frequency hopping check, and replacement of aged RF hardware. The interference is reduced by decreasing the transmit power of RF components while ensuring the quality, and intelligently choosing the frequencies or timeslots with little interference for channel assignment. The quality and capacity are contradictory. When the BTS configuration exceeds a specific limit, the quality is affected.

3.1.1 Procedures for RxQuality Problem Location

The common procedures for RxQuality problem location are described as follows:

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3.2 RxQuality Optimization MethodsThe poor RxQuality may be caused by the following factors:

Hardware transmission fault (faulty TRX and antenna system in combination mode)

Improper data configuration

Intra- network interference

Inter-network interference

Clock fault

Coverage and uplink-downlink imbalance

Improper power control settings

When the RxQuality is poor, the reasons for poor RxQuality are classified in terms of the preceding factors. Then, the RxQuality is improved from two perspectives. Check whether the poor RxQuality occurs on the entire network or only in some cells or BTSs. If poor RxQuality occurs on the entire network, causes are investigated in terms of internal network interference and external network interference. If poor RxQuality only occurs in some cells or BTSs, the procedures in section 3.1 are taken to investigate the causes. The RxQuality is improved by examining interference, modifying data configuration, replacing some hardware, cleaning feeder and jumper connectors, and replacing aged feeders.

3.2.1 Poor RxQuality on Entire NetworkAccording to statistics of traffic measurement counters, if the poor RxQuality occurs on the entire network, it cannot be optimized through optimization in only some cells or BTSs. You are advised to follow the procedures described in section 3.2.1.1.

3.2.1.1 Processing Methods

For the poor RxQuality of the entire network, check the frequency planning. In scenarios of S4/4/4 or above with low band (5 MHz) and a certain frequency hopping (1x3), the noise floor of the entire network is high. In addition, the cell coverage is not well controlled in the network planning. The inter-cell coverage therefore causes co-channel and adjacent-channel frequency collisions. The interference is comparatively large, which causes poor RxQuality. On the network with non-synchronized frequency hopping in sequence, the continuous frequencies may cause continuous collisions, which may also affect the RxQuality.

In summary, the poor RxQuality occurs in narrow band with large configurations. You are advised to take measures to control the coverage of each cell to avoid inter-cell coverage that may cause co-channel or adjacent-

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channel interference. The random frequency hopping instead is adopted to avoid low RxQuality. In the optimal solution, you need to decrease the BTS configuration and site distance or divide cells, and plan the network properly.

Besides, on the network with high noise floor, the RxQuality can be greatly improved by reducing the network noise floor and interference through the power control.

If the preceding adjustments still cannot solve the problem, the latest R&D results of the Performance Dept are applied. These R&D results include synchronization network, ICC technology, and IBCA. The RxQuality is improved without reducing the network capacity.

The maximum RxQuality is not the ultimate aim of the network optimization. The ultimate goal is to enrich the customer experience according to different bandwidths, capacity requirements, traffic models, and network scenarios.

3.2.1.2 Traffic Measurement Analysis

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3.2.1.3 Alarm Analysis

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3.2.2 Passive Intermodulation


When two RF signals are transmitted to a nonlinear component, or transmitted through a discontinuous transmission medium, a series of new frequency components are generated. These frequency components satisfy the following formulas. Suppose the frequencies of these two signals are f1 and f2 (absolute frequencies).

Fn = mf1 + nf2, and Fn = mf1 – nf2

The most common types are third-order, five-order, and seven-order intermodulations. The RxQuality of the system is affected when the intermodulation components are transmitted to the Rx band and the level exceeds a specific limit.

The intermodulation interference is generated mainly because the frequency interval is short. In this case, the interference can be eliminated by increasing the cell frequency intervals.

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[m–n] = 1, m + n = x, in which x stands for x order.


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3.2.3 Intra-Network Interference


The intra-network interference is classified into two categories: co-channel interference and adjacent-channel interference.

The frequency reuse is adopted on the GSM network. When the frequency reuse radius of two cells in the same frequency or adjacent frequencies is improperly small, the co-channel or adjacent-channel interference is easy to generate.

The following methods are used for addressing the intra-network interference. Check whether the frequency planning, especially the co-channel and adjacent-channel frequency reuse, is proper.

Besides, the coverage of each cell is controlled in accordance with practical situations. It is important especially for the network with heavy traffic and less frequency resources to control the coverage and maintain proper co-channel and adjacent-channel frequency reuses.

The data should be configured accurately. The proportions of inter-cell co-channel and adjacent-channel frequencies should be proper in the data configuration.

The intra-network interference can be solved through frequency optimization, antenna adjustment, and coverage control. In addition, tools such as Nastar can be used for frequency optimization. Check the co-channel and adjacent-channel frequencies and recommended frequencies by entering engineering parameters. The frequencies with severe interference are replaced to greatly improve the RxQuality.

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None.


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3.2.4 Inter-Network Interference


The inter-network interferences can be classified into the following three categories:

Repeater interference: It can be solved by communication with repeater vendors.

Inter-RAT interference: The filter is added to filter out interference. In addition to frequency modification, the co-site BTSs do not use the E-GSM frequencies. Besides, the gains of two antennas can be reduced by increasing the space between two antennas or antenna tilt.

Security equipment interference: Information about the BTSs with interferences is collected. You are advised to replace the security equipment with the recommended Interference Unit (IU).


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3.2.5 Hardware Fault


The interference caused by hardware fault is mostly due to the passive intermodulation interference.

To solve this problem, multiple hardware operations are required. Due to frequency reuse in the network operation, difficult problem location, and multiply faulty cells, a special team is established to solve this problem quickly.

The idle burst authentication is transmitted through the LMT.

Check the data of interference band level 3 to level 5 according to the traffic measurement. Check whether the interference bands follow some rules and whether the interference bands are related to time, traffic, weather, and cell location. Check whether similar interference band problems used to occur. Finally, perform comprehensive analysis.

If the interference band persists, the interference band is enhanced with the traffic increase, or the external BTS interference is excluded by replacing the frequencies, you can infer that it is internal BTS interference. Take the following measures:

Check whether the TRX or Combining and Distribution Unit (CDU) fault causes the inter-network interference by blocking and replacing boards.

Check whether the jumpers are connected to the cabinet top outlet and feeder properly. If the ports do not match, the front end circuit of the BTS may be unstable. In this case, the spontaneous vibrations may generate to bring interference to the internal bandwidth.

Check whether the antenna system generates the passive intermodulation by disabling some TCH TRXs or exchanging antenna systems. In this case, you can determine whether the interference is caused by antenna intermodulation.

The interference is eliminated mainly through RF optimization. For details, see the GSM Interference Analysis Guide.


None.

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Three types of alarms need to be observed: antenna alarm, TRX alarm, and BTS clock alarm.

If any one of the following alarms is reported, see the BSS Alarm Reference for specific processing methods.

Alarm ID and Name

4154 TRX main clock alarm

4156 TRX slave clock alarm

4184 TRX clock critical alarm

4708 Clock Reference Abnormal Alarm

4732 TMU clock critical alarm

4734 Master TMU clock alarm

4760 13M Maintenance Alarm

4102 LAPD Alarm

4104 TRX configuration Alarm

4108 Radio link critical Alarm

4114 TRX interior I/O alarm

4136 TRX Hardware alarm

4144 TRX VSWR alarm

4192 TRX communication alarm

4714 E1 Local Alarm

5286 CDU VSWR Level 1 Alarm

5284 CDU VSWR Level 2 Alarm

5326 Level 1 VSWR Alarm

5328 Level 2 VSWR Alarm

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3.2.6 Huawei Anti-Interference Technology


Huawei has the following anti-interference technologies. These technologies facilitate the reduction in network interference and improvement in the RxQuality to enrich the end user experience.

List of Huawei anti-interference technologies:

UISS

IBCA

Flexible MAIO (FLEX MAIO)

Power Control, DTX


None.


None.

3.2.7 Test Tool and RecommendationsThe TEMS that is accepted by the industry and widely used serves as the test tool. The drive test is required for the cell with low RxQuality. The low RxQuality in some cells or BTSs can be detected and solved by drive test.

3.2.8 Recommendations for Configuration and Test

For network configurations, see the latest GSM BSC6000 Performance Parameter Baseline (V900R008) V2.0. The configurations are performed according to different scenarios. When the RxQuality is low, you need to check the data configuration that is greatly different from the parameter baseline.

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4 RxQuality Optimization

Cases

4.1 Low RxQuality in KenyaIn Kenya, the configuration of existing network has multiple sites in S8/8/8 configuration, which is very large. The entire network uses 1*3 RF frequency hopping. The RxQuality is not satisfactory. According to check results, the existing network uses the latest BSC version. The power control parameters, however, are set according to second generation power control algorithm rather than the parameter configuration baselines. After the parameters are set by using the third generation power control algorithm, the proportion of RxQualtiy 0–3 is increased by 12% compared to that by using the second generation algorithm.

4.2 Enabling Idle Burst Causing Interference Increase and Low RxQuality

After the site is swapped, the network quality is decreased by 3% to 4% according to the drive test results. The hardware, frequency planning, and inter-cell engineering are proper. The RxQuality is decreased by 2% to 3% compared with that of the existing network. Other KPIs are proper.

According to analysis, after the idle bursts are enabled, they cannot be automatically disabled. In this case, the idle TRX timeslots are transmitted in full power, and the BER is increased, thus, the RxQuality deteriorates. When the idle burst is disabled manually, the Um quality of the entire network is greatly improved. The RxQuality is improved by 2%, which is almost the same as that of the original network.

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5 Information Feedback

5.1 TEMS Test Log of Faulty CellThe cell information table in .cel format of the TEMS test is sent back with the log.

5.2 Requirements for Existing Network Configuration Data and Traffic Measurement

The latest data configuration and engineering parameter list on the network are specified. Provide the traffic measurement counters of continuous two days. The traffic measurement counters are described as follows:

MR Measurement > Receive Quality Measurement per TRX

MR Measurement > Interference Band Measurement per TRX

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15 GSM BSS Network KPI (RxQuality) Optimization Manual_2.doc