16 GSM BSS Network KPI (Inter-RAT Handover Success Rate) Optimization Manual[1].Doc

GSM BSS Network KPI (Inter-RAT Handover Success Rate) Optimization Manual INTERNAL

Product Name Confidentiality Level

G3BSC INTERNAL

Product Version Total 25 pages

GSM BSS Network KPI (Inter-RAT Handover Success Rate) Optimization Manual

(For internal use only)

Prepared by Zhao Kang, WCDMA&GSM Network Performance Research Dept.

Date

2009-03-24

Reviewed by Date

Reviewed by Date

Granted by Date

Huawei Technologies Co., Ltd.All rights reserved

2023-4-8 Huawei Technologies Proprietary Page 1 of 25


Contents

1 Definition of the Inter-RAT Handover Success Rate..........................51.1 Definition...........................................................................................................................................................5

1.2 Recommended Formulas...................................................................................................................................5

1.2.1 Success Rate of Incoming Inter-RAT Inter-Cell Radio Handover...........................................................5

1.2.2 Success Rate of Outgoing Inter-RAT Inter-Cell Radio Handover............................................................6

1.3 Signaling Procedure and Measurement Points..................................................................................................6

2 Influencing Factors........................................................................82.1 Hardware Failure...............................................................................................................................................8

2.2 Transmission Problems......................................................................................................................................8

2.3 Version Upgrade.................................................................................................................................................8

2.4 MS Problems......................................................................................................................................................9

2.5 Improper Parameter Settings.............................................................................................................................9

2.6 Unbalanced Traffic Volume.............................................................................................................................11

2.7 Intra-Network and Inter-Network Interference................................................................................................12

2.8 Coverage Problems..........................................................................................................................................12

3 Analysis Process and Optimization Method...................................133.1 Analysis Process..............................................................................................................................................13

3.2 Problem Location and Optimization Methods.................................................................................................14

3.2.1 Checking the Hardware Status of the Cells with High Inter-RAT Handover Success Rate...................14

3.2.2 Checking the Transmission in the Cells with High Inter-RAT Handover Success Rate........................15

3.2.3 Checking the Problems Caused by BSC Version Upgrade and BTS Version Upgrade..........................16

3.2.4 Checking the Parameter Settings in the Cells with High Inter-RAT Handover Success Rate...............16

3.2.5 Checking the Interference in the Cells with High Inter-RAT Handover Success Rate..........................17

3.2.6 Checking the Conditions of Coverage, Antenna, and Balance Between Uplink and Downlink in the Cells with High Inter-RAT Handover Success Rate........................................................................................18

3.2.7 Checking the Repeaters in the Cells with Low Inter-RAT Handover Success Rate..............................19

4 Test Methods...............................................................................20

5 Optimization Cases......................................................................215.1 Case 1: Data Configuration..............................................................................................................................21

5.2 Case 2: Inter-RAT Handover Success Rate Decreasing Caused by Data Configuration.................................22

6 Information Feedback.....................................................................................23





Revision Record

Date Version Description Author

2008-12-25 V10 Initial draft Zhao Kang

References

SN Document Author Date

1 GSM BSS Network KPI (Inter-RAT Handover Success Rate) Baseline

Wu Zhen

Zhao Jinjin



Network KPI (Inter-RAT Handover Success Rate) Optimization Manual

Keywords: Inter-RAT handover success rate

Abstract: This document introduces the definition, test methods, and optimization methods of the inter-RAT handover success rate.

Acronyms and Abbreviations:

Abbreviation Full Spelling



1 Definition of the Inter-RAT

Handover Success Rate

1.1 DefinitionThe success rate of incoming inter-RAT inter-cell radio handover refers to the ratio of the total number of successful handovers from 3G cell to 2G cell triggered by all causes to the total number of handover requests from 3G cell to 2G cell triggered by all causes.

The success rate of outgoing inter-RAT inter-cell radio handover refers to the ratio of the total number of successful handovers from 2G cell to 3G cell triggered by all causes to the total number of handover commands from 2G cell to 3G cell triggered by all causes.

Both the success rate of incoming inter-RAT inter-cell radio handover and the success rate of outgoing inter-RAT inter-cell radio handover are important retainability KPIs. The KPIs directly affect the experience of 2G/3G users and are most significant KPIs for the operators to appraise the 2G/3G network interoperability.

1.2 Recommended Formulas

1.2.1 Success Rate of Incoming Inter-RAT Inter-Cell Radio Handover

The success rate of incoming inter-RAT inter-cell radio handover is obtained on the basis of the traffic measurement. The recommended formula is as follows:

Number of successful incoming inter-RAT inter-cell handovers/Number of incoming inter-RAT inter-cell handover responses.In the BSC6000, the recommended formula is as follows:

Success rate of incoming inter-RAT inter-cell radio handover = Number of successful incoming inter-RAT inter-cell handovers/Number of Incoming inter-RAT inter-cell handover responses x 100% = CH363/CH361 x 100%



1.2.2 Success Rate of Outgoing Inter-RAT Inter-Cell Radio Handover

The success rate of outgoing inter-RAT inter-cell radio handover is obtained on the basis of the traffic measurement. The recommended formula is as follows: Number of successful outgoing inter-RAT inter-cell handovers/Number of outgoing inter-RAT inter-cell handovers.In the BSC6000, the recommended formula is as follows:

Success rate of outgoing inter-RAT inter-cell radio handover = Number of successful outgoing inter-RAT inter-cell handovers/Number of outgoing inter-RAT inter-cell handovers x 100% = CH353/CH351 x 100%

For details, refer to the GSM BSS Network KPI (2G/3G Interoperability) Baseline.

1.3 Signaling Procedure and Measurement Points

Where:A1 – Number of incoming inter-RAT inter-cell handover requests

B1 – Number of incoming inter-RAT inter-cell handover responses

C1 – Number of successful incoming inter-RAT inter-cell handovers


h00121471, 06/19/09,

图1 系统间入小区切换过程：Figure 1 Incoming inter-RAT inter-cell handover procedure


Where:

A2 - Number of outgoing inter-RAT inter-cell handover requests

B2 – Number of outgoing inter-RAT inter-cell handovers

C2 – Number of successful outgoing inter-RAT inter-cell handovers

The measurement points of 2G/3G interoperability KPIs are presented as follows:

Success rate of incoming inter-RAT inter-cell radio handover: C1/B1

Success rate of outgoing inter-RAT inter-cell radio handover: C2/B2



2 Influencing Factors

According to user complaints and network optimization experience, the major factors that affect the inter-RAT handover success rate are as follows:

Hardware failure

Transmission problems

Version upgrade

MS problems

Improper parameter settings

Unbalanced traffic volume

Intra-network and inter-network interference

Coverage problems

2.1 Hardware FailureDuring the test, when a large number of terrestrial resources are unavailable or devices are faulty, seizing the TCH becomes difficult. As a result, the inter-RAT handover success rate decreases.

2.2 Transmission ProblemsThe inter-RAT handover success rate decreases in any of the following conditions: (1) The transmission quality is bad on the A or Abis interface due to various reasons. (2) Transmission links are unstable.

2.3 Version UpgradeAll the current versions of the BSC6000 of Huawei support the handover between the GSM and the 3G UTRAN FDD system. The initial field trial release and later versions, that is, the BSC6000V9R3 and later versions, support the handover between the GSM and the 3G UTRAN TDD system. However, if the following restrictions exist, that is, a version does not support the inter-RAT handover in FFD or TDD mode, the inter-RAT handover may fail. As a result, the inter-RAT handover success rate decreases.



2.4 MS ProblemsNow, many operators take the sales strategy of presenting an MS for free after a subscriber subscribes to 3G network services. Thus, most MSs are customized multi-mode MSs. To implement special functions and features of operators, operators add and reduce some functions from the MSs. In the network, when a type of MS always incurs handover failure, the failure can be located through the MS-related support capability and parameter settings.

2.5 Improper Parameter SettingsThe settings of some parameters of BSC and MSC also affect the inter-RAT handover success rate. The main parameters include:

3G System Information Data Table

3G Search PRIO: Indicates whether the BISC is allowed to search for a 3G cell when the BISC must be decoded. Default value: Yes

Qsearch C: Indicates the signal level threshold for cell search in connection mode. When the signal level in the serving cell is below (0–7) or above (8–15), the MS starts to search for 3G cells.

Serving Band Reporting: Indicates the number of cells that are contained in the best cell list in the current serving band.

FDD MULTIRAT Reporting: Indicates the number of UTRAN FDD cells that are contained in the measurement report.

3G BA2 Table Provides the frequencies, scrambling codes, and diversity indication of 3G UTRAN FDD neighboring cells, and the basis for sorting 3G cells. If the parameter is not set, the handover to 3G cell is impacted.

Early Classmark Sending Control (ECSC)

Indicates whether the MSs in a cell use early classmark sending. You can send classmark 3 with the MS to determine whether the MS supports 3G.

3G HO Data table

Inter-RAT In BSC Handover Enable/Inter-RAT Out BSC Handover Enable: Indicates whether the handover from 2G to 3G is allowed. Recommended value during the 2G/3G interoperability: Yes

Better 3G Cell HO Allowed: Indicates whether the better 3G cell handover algorithm is allowed. Yes indicates the handover algorithm is allowed, and No indicates the handover algorithm is not allowed. Recommended value during the 2G/3G interoperability: Yes

Inter-RAT HO Preference: Indicates whether an MS is preferentially handed over to a 2G cell or a 3G cell.

HO Preference Threshold for 2G Cell: If the Inter-RAT HO Preference parameter is set to Preference for 2G Cell By Threshold, and if the receive level of the first candidate cell among 2G candidate cells is lower than or equal to the HO Preference Threshold for 2G Cell, the 3G cell handover is preferred; otherwise, the 2G cell handover is preferred.

RSCP Threshold for Better 3G Cell HO: If Outgoing-RAT HO Allowed is set to Yes and Better 3G Cell HO Allowed is also set to Yes, a better 3G cell handover is triggered when the RSCP of a



neighboring 3G cell is greater than RSCP Threshold for Better 3G Cell HO. Default value: 50

Ec/No Threshold for Better 3G Cell HO: If Outgoing-RAT HO Allowed is set to Yes and Better 3G Cell HO Allowed is also set to Yes, a better 3G cell handover is triggered when the Ec/No of a neighboring 3G cell is greater than Ec/No Threshold for Better 3G Cell HO. Default value: 35

3G External Cell

Indicates how to configure a 3G external cell and the neighboring cell relation between the cell and a 2G cell.

During the 2G/3G interoperability, improper parameter settings affect cell reselection. As a result, the subscriber distribution is impacted.

The parameters that affect the 2G/3G inter-RAT cell reselection are as follows:

Parameter Parameter Configuration

Inter-RAT Cell Reselection Enable

Inter-RAT Cell Reselection Enable: Indicates whether the reselection from a 2G cell to a 3G cell is allowed. Recommended value during the 2G/3G interoperability: Yes

Equivalent PLMN Table Equivalent PLMN refers to the PLMN that can provide the same services to subscribers as the current network does. This parameter is set on the core network side. Set the peer PLMNs of both 2G core network and 3G core network to Equivalent PLMN.

3G BA1 Table To implement 2G/3G inter-RAT cell reselection, add the corresponding cells to the neighboring cell table, and configure the neighboring relation. The settings include the downlink frequency, whose value ranges from 0 to 16383, of the neighboring 3G cell, the scrambling code, whose value ranges from 0 to 511, of the neighboring 3G cell, and the diversity indication, whose value ranges from 0 to 1, of the neighboring 3G cell. This parameter is set in the advanced idle parameter table.

3G System Information Data Table

MSC Version Information: Indicates the protocol version of the MSC that works with the BSC. The supported signaling varies with the protocol versions. Value range: R98 or R98 below and R99 or R99 above. Default value: R98 or R98 below.

This parameter is set in the advanced call-control parameter table according to the actual MSC protocol version.



Parameter Parameter Configuration

Qsearch I: When the parameter is set to 0–7, the MS starts to search for 3G cells if the signal level of the current serving cell is lower than the level corresponding to the parameter. When the parameter is set to 8–15, the MS starts to search for 3G cells if the signal level of the current serving cell is higher than the level corresponding to the parameter. If this parameter is set to 7, the MS searches for 3G cells all the time. If this parameter is set to 15, the MS does not search for 3G cells at all. The values 0 to 6 map to the following signal levels respectively: –98 dBm, –94 dBm, –90 dBm, –86 dBm, –82 dBm, –78 dBm, and –74 dBm. The values 8 to 14 map to the following signal levels respectively: –78 dBm, –74 dBm, –70 dBm, –66 dBm, –62 dBm, –58 dBm, and –54 dBm.

Qsearch C Initial: Specifies the mode in which an MS searches for 3G cells. Value range: Always, Use Qsearch_I. If this parameter is set to Always, an MS always searches for neighboring 3G cells. If this parameter is set to Use Qsearch_I, an MS starts to search for neighboring 3G cells only when it meets the Qsearch I. Default value: Use Qsearch_I

FDD Q Offset: Indicates that a 3G cell can become a candidate cell for reselection only when the average receive level of the 3G cell is FDD Q Offset greater than the average receive level of the current serving cell. Value range: 0–15. If the parameter is set to 0, it indicates that the reselection is allowed as long as the FDD neighboring cell exists. The values 1 to 15 correspond to the following levels respectively: –28 dB, –24 dB, –20 dB, –16 dB, –12 dB, –8 dB, –4 dB, 0 dB, 4 dB, 8 dB, 12 dB, 16 dB, 20 dB, 24 dB, and 28 dB. Default value: 0

FDD Qmin: Indicates that a 3G cell can become a candidate cell for reselection only when the receive level of the 3G cell is greater than FDD_Qmin. Value range: 0–7. The values 0 to 7 map to the following levels respectively: –20 dB, -19 dB, –18 dB, -17 dB, –16 dB, -15 dB, –14 dB, and -13 dB. Default value: 0 (-20 dB).

2.6 Unbalanced Traffic VolumeTraffic volume is unevenly distributed in the network in the test environment, such as burst traffic. This causes the 3G or 2G network congestion. As a result, the inter-RAT handover success rate decreases.



2.7 Intra-Network and Inter-Network Interference

If inter-network interference and repeater interference exist, or if severe intra-network interference occurs because of tight frequency reuse, call drops may occur on SD or TCH channels due to bad QoS. This affects the inter-RAT handover success rate.

The following types of interference may occur:

1. Inter-network interference from scramblers or privately installed antennas

2. Repeater interference

3. Intermodulation interference from BTSs

4. Intra-network co-channel and adjacent-channel interference

5. Three-phrase intermodulation interference from other inter-network systems

2.8 Coverage ProblemsThe following coverage problems may affect the inter-RAT handover success rate:

1. Discontinuous coverage (blind areas)

In complex terrains covered by 3G BTSs and complex radio transmission environment, and at the early construction stage of the 3G network, the inter-RAT handover success rate decreases because of the discontinuous coverage of 3G signals.

2. Poor indoor coverage

Densely distributed buildings and thick walls cause great attenuation. In addition, the 2G and 3G signal loss difference causes 2G and 3G signal coverage difference. As a result, the inter-RAT handover success rate decreases during a call.

3. Insufficient coverage

At the late construction stage of the 3G network, if the site is selected incorrectly, the signals from antennas are blocked or the BCCH TRX is faulty. As a result, the inter-RAT handover success rate decreases because of discontinuous coverage.



3 Analysis Process and

Optimization Method

3.1 Analysis Process


A problem in the whole network?

Antenna faulty? Adjust the antenna.

Add coverage optimization RF indexes.

Locate interference source.

Replace the version or install a patch.

Start

Data configuration problem?

Interference exists?

No

Yes

否

Insufficient coverage or blind area?

Transmission problem or hardware fault?

Adjust handover parameters

Solve the problem.

Yes

Traffic unevenly distributed? Optimize handover reselection parameters

Yes

End

Yes

Caused by version upgrade?

No

No

No

N

o

Yes

Yes

Yes

Yes


3.2 Problem Location and Optimization Methods

General ideas

To analyze an inter-RAT handover success rate problem, determine whether the problem exists in a cell or in the whole network first of all. If the problem of low handover success rate exists in the whole network, the relevant parameter may be set incorrectly. You must check the parameter settings.

First, determine whether the problem is an outgoing inter-RAT handover problem or an incoming inter-RAT handover problem through the analysis of traffic measurement. Preliminarily find the handover failure causes through the analysis of the traffic statistics.

Secondly, if the problem exists in some cells in a certain area, you need to find the detailed causes. Check whether the software version supports the 3G inter-RAT handover. Or view the product release description of inter-RAT handover. Rectify the problems caused by the defective software, version upgrade or version itself.

After rectifying the preceding problems, check whether the hardware and transmission in these cells incur error, whether relevant alarms are generated, and whether these cells are in normal status.

Check whether the traffic volume bursts or is congested. In this way, rectify the antenna problem, insufficient coverage problem, and interference problem. Thus, finally rectify the inter-RAT handover success rate problem.

Specific analysis methods and ideas

First, determine the handover failure scope through the analysis of traffic measurement. If the inter-RAT handover success rate is low in all the cells, you need to rectify the problem by checking the inter-RAT handover characteristics parameters, circuits on the A interface, and BSC clock.

Secondly, classify the cells into the cells with low inter-RAT handover success rate and TOPN cells, and then perform the following steps to rectify the problem.

Thirdly, check the success rate of outgoing inter-RAT inter-cell handover and success rate of incoming inter-RAT inter-cell handover in the inter-RAT handover measurement. Subsequently, analyze the outgoing/incoming inter-RAT inter-cell handover measurement of faulty cells to find the cells to which handover failure occurs. Analyze the failure causes, and make statistics of the distribution of these causes.

Fourthly, check the TRX availability of faulty cells to determine whether the failure is caused by faulty devices.

Fifthly, check the number of A interface failures during TCH seizure and the number of terrestrial link disconnections to determine whether the failure is caused by faulty terrestrial link devices.



3.2.1 Checking the Hardware Status of the Cells with High Inter-RAT Handover Success Rate

If a TRX or a combiner is faulty or if an RF cable is incorrectly connected, seizing the SDCCH becomes difficult, and thus the inter-RAT handover success rate decreases.

You can check whether hardware is faulty by viewing BTS alarms or viewing the hardware state on the Site Device Panel of the LMT. The following table lists the major BSC alarms related to hardware failures:

Alarm ID Alarm Name

1000 LAPD_OML fault

2204 TRX communication alarm

4414 TRX VSWR alarm

3606 DRU hardware alarm

In addition, you can locate the fault by checking the traffic measurement related to hardware failures, as shown in the following table.

Cause BSC Level Cell Level

Equipment faults

BSC Measurement -> Access measurement per BSC -> Congestion Ratio on SDCCH per BSCSDCCH Availability per BSC

Channel Measurement ->

Analyzed Measurement of Available Channels (SDCCH)

Call Measurement -> Call Drop Measurement

Call Drops due to Equipment Failure (Signaling Channel)

3.2.2 Checking the Transmission in the Cells with High Inter-RAT Handover Success Rate

Poor transmission quality, unstable transmission links, or insufficient resources on the Abis and A interfaces may lead to the decrease of the inter-RAT handover success rate. You can check the transmission conditions by viewing the alarms related to transmission. If a large number of transmission alarms are generated, you can infer that transmission failures occur. Then, you should check the transmission connections.

The following table lists the BSC alarms related to transmission failures:

Alarm ID Alarm Name

1000 LAPD_OML fault

11270 LAPD alarm



11278 E1 local alarm

11280 E1 remote alarm

20081 Loss of E1/T1 signals (LOS)

20082 Loss of E1/T1 frames (LOF)

In addition, you can locate the fault by checking the traffic measurement related to transmission failures, as shown in the following table.

Cause BSC Level Cell Level

Transmission failure

BSC Measurement -> LAPD Measurement

Call Measurement -> Channel Activation Measurement ->

CHAN ACTIV NACK Messages Sent by BTS

Channel Activation TimeoutsCall Measurement -> Call Drop Measurement

Measurement of Call Drops Due to Abis Link Failure

3.2.3 Checking the Problems Caused by BSC Version Upgrade and BTS Version Upgrade

If the inter-RAT handover success rate drops greatly after the BSC version or BTS version is upgraded, you should check whether the BTS version is compatible with the BSC version and whether the parameters and algorithms in the new version are changed.

To locate the problem, you can check the version description document and the related documents, or provide the feedback to the Maintenance Team to learn whether the new version has known defects. If the new version has defects, you should replace it with another version or install a patch.

3.2.4 Checking the Parameter Settings in the Cells with High Inter-RAT Handover Success Rate

The parameter settings on the BSC side and MSC side may affect the inter-RAT handover success rate. You should check the settings of the following parameters for a faulty cell:

Outgoing-RAT HO Allowed: Indicates whether the outgoing system handover from 2G to 3G is allowed. Recommended value during the 2G/3G interoperability: Yes

Better 3G Cell HO Allowed: Indicates whether the better 3G cell handover algorithm is allowed. Yes indicates the handover algorithm is allowed, and No indicates the handover algorithm is not allowed. Recommended value during the 2G/3G interoperability: Yes

Inter RAN Load Information Allowed: Indicates whether to use the information about the load of 3G neighboring cells for load handover decision.



Recommended value during the 2G/3G interoperability: Yes

Inter-RAT HO Preference: Indicates whether an MS is preferentially handed over to a 2G cell or a 3G cell.

HO Preference Threshold for 2G Cell: If Inter-RAT HO Preference is set to HO Preference Threshold for 2G Cell, and if the receive level of the first candidate cell among 2G candidate cells is less than or equal to Pre_2G_CellThres, the 3G cell handover is preferred; otherwise, the 2G cell handover is preferred.

RSCP Threshold for Better 3G Cell HO: If Outgoing-RAT HO Allowed is set to Yes and Better 3G Cell HO Allowed is also set to Yes, a better 3G cell handover is triggered when the RSCP of a neighboring 3G cell is greater than RSCP Threshold for Better 3G Cell HO. Default value: 50

Ec/No Threshold for Better 3G Cell HO: If Outgoing-RAT HO Allowed is set to Yes and Better 3G Cell HO Allowed is also set to Yes, a better 3G cell handover is triggered when the Ec/No of a neighboring 3G cell is greater than Ec/No Threshold for Better 3G Cell HO. Default value: 35

3G Search PRIO: Indicates whether the BISC is allowed to search for a 3G cell when the BISC must be decoded. Default value: Yes

QSearch C: Indicates the signal level threshold for cell search in connection mode. When the signal level in the serving cell is below (0–7) or above (8–15), the MS starts to search for 3G cells.

Serving Band Reporting: Indicates the number of cells that are contained in the best cell list in the current serving band.

FDD MULTIRAT Reporting: Indicates the number of UTRAN FDD cells that are contained in the measurement report.

3.2.5 Checking the Interference in the Cells with High Inter-RAT Handover Success Rate

If inter-network interference and repeater interference exist, or if severe intra-network interference occurs because of tight frequency reuse, call drops may occur on SD or TCH channels due to bad QoS. This affects the inter-RAT handover success rate.

The uplink interference information can be obtained on the basis of the interference band distribution in the traffic measurement results. A large proportion of interference levels belong to interference bands 3–5, you can infer that the uplink has strong interference. In this case, you can view the interference band distribution at the TRX level based on the SD or TCH measurement report.

The interference elimination can be classified into intra-network interference elimination and inter-network interference elimination. For details about interference elimination, see the G-Guide to Eliminating Interference.



Cause TRX Level

Interference

MR Measurement ->

Interference Band Measurement ->

Mean Number of SDCCHs in Interference Band 1Mean Number of SDCCHs in Interference Band 2Mean Number of SDCCHs in Interference Band 3Mean Number of SDCCHs in Interference Band 4Mean Number of SDCCHs in Interference Band 5

MR Measurement ->


Mean Number of TCHFs in Interference Band 1Mean Number of TCHFs in Interference Band 2Mean Number of TCHFs in Interference Band 3Mean Number of TCHFs in Interference Band 4Mean Number of TCHFs in Interference Band 5

MR Measurement ->


Mean Number of TCHHs in Interference Band 1Mean Number of TCHHs in Interference Band 2Mean Number of TCHHs in Interference Band 3Mean Number of TCHHs in Interference Band 4Mean Number of TCHHs in Interference Band 5

3.2.6 Checking the Conditions of Coverage, Antenna, and Balance Between Uplink and Downlink in the Cells with High Inter-RAT Handover Success Rate

In the cells with high inter-RAT handover success rate, you can check the network coverage through DT and CQT. Coverage problems or imbalance problems between UL and DL exist if the following phenomena occurs: DL receive level is low; the difference between the UL level and DL level is large in the measurement report viewed through the signaling, level quality deteriorates gradually, the DL measurement report is lost, and call access is performed for a long time.

In the cell where the preceding problems exist, the call establishment success rate and handover success rate are impacted. The deteriorated receive quality is also reflected in the quality traffic measurement. In addition, you can analyze the cell coverage based on the drive test route and geographical condition, and troubleshoot the antenna system based on a fault symptom. Some cell coverage problems and imbalance problems between UL and DL are caused by the coverage direction and tilt angle of antennas, and damage, water penetration, and loose connector of antenna feeders.

To rectify the preceding problems, see the following documents: GSM BSS Network KPI (Coverage) Optimization Manual and GSM BSS Network KPI (Uplink and Downlink Balance) Optimization Manual.



3.2.7 Checking the Repeaters in the Cells with Low Inter-RAT Handover Success Rate

Check whether the parameter Directly Magnifier Site Flag is set to Yes in the data configuration on the LMT and whether the signaling channel handover is enabled. If this parameter is set to Yes, you can infer that the cell is configured with repeaters. If this parameter is set to No, you should check whether other operators' repeaters are installed near the cell.

If repeaters are installed, check whether the type, operating frequency band and operating bandwidth (broadband or narrowband) of the repeaters impact the inter-RAT handover success rate. If it is, check whether the UL/DL magnifying coefficient is excessively high. If it is, reduce the coefficient. If the impact is serious, disable the repeater.

In addition, you should check whether a repeater is faulty and whether the uplink/downlink gain is set to a too great/small value. If this problem exists, the actual coverage area of the BTS may different from the planed coverage area. Thus, the call drop rate increases.

If repeater problems exist in a cell, the TA distribution varies greatly in the traffic measurement results. The following table lists the traffic measurement counters related to repeaters.

Cause Cell Level TRX Level

Repeater None

MR Measurement ->

Number of MRs Based on TA



4 Test Methods

The inter-RAT handover success rate can be obtained through the registration or reporting of the related traffic measurement counters. Because the 3G system belongs to different manufacturers, the inter-RAT handover may have cooperation problems. Thus, you need to adjust the relevant parameters of the 3G system, and troubleshoot the 2G system based on the preceding check.



5 Optimization Cases

5.1 Case 1: Data ConfigurationProblem description: In a site, the GSM network and UMTS network coexist. A customer requires enabling the reselection from a 2G cell to a 3G cell, and disabling the handover from the 2G cell to the 3G cell.

Problem analysis and handling: Based on the preceding analysis, set the BSC-related parameters as follows:

1. Make a 3G external neighboring cell datasheet, and then import the datasheet to the BSC through the mass import function of the LMT.

2. Set Inter-System Handover Enable to Yes.

3. Set the relevant parameters in the parameter table that is displayed by choosing Call Control -> UTRAN System Message, thus ensuring the reselection from a 2G cell to a 3G cell. The parameters related to cell reselection contain Qsearch I, FDD Q Offset, and FDD Qmin. The specific value can be set as required and the operation is beyond the scope of this document.

The preceding settings ensure the reselection from a 2G cell to a 3G cell. Then, we disable the handover from a 2G cell to a 3G cell:

4. Set Qsearch C to 15, which indicates that no 3G cell is searched in connection mode.

5. Set Inter-RAT HO Preference in the UTRAN FDD handover datasheet to Preference for 2G Cell. That is, a 2G neighboring cell is selected preferentially in accordance with the handover strategy.

6. Set the parameters in the 3G external neighboring table as follows: Min RSCP Threshold = 63 Min Ec/No Threshold = 49 RSCP Threshold for Layer Of 3G Cell = 63 Ec/No Threshold for Layer Of 3G Cell = 49

Setting the RSCP threshold to 63 (maximum value) indicates that a 3G neighboring cell cannot become a candidate neighboring cell until its receive level is greater than 63, that is, -25 dBm. Setting the Ec/No threshold to 49 (maximum value) indicates that a 3G neighboring cell cannot become a candidate neighboring cell until its signal-to-noise ratio is greater than 0 dB. In this way, the handover from a 2G cell to a 3G cell is disabled, because no 3G neighboring cell can meet so rigid RSCP and Ec/No thresholds in practice. Then, by viewing the outgoing handover traffic measurement from a GSM cell to a UMTS cell for a week, you can find that no handover request from a 2G cell to a



cell 3G cell is initiated. It indicates that the preceding settings make us achieve expected objectives.

5.2 Case 2: Inter-RAT Handover Success Rate Decreasing Caused by Data Configuration

Problem description: The operator M in S country had used Huawei 2G equipment for two years in Al kharj area. The network run normally and the network KPIs were stable. On March 16, 2008, we suddenly found that the incoming BSC handover success rate of the BSC132 had decreased drastically from 97% to 40% during KPI statistics.

Problem analysis and handling: After communicating with M's optimization department, we find that the competitor A has deployed and powered on its 3G equipment in the area without informing Huawei in advance, resulting in high failure rate of Huawei inter-BSC handover. Huawei equipment version in the existing network:BSC version:G3BSC32V300R002C13SP54BTS version:BTS : GBT312G3BTS32V302R007C07B001In the existing network, Huawei BSC132 is mounted on the MSC102 of competitor E, and the RNC16 of competitor A is mounted on the MSC104 of competitor E. As a result, the inter-RAT interoperability problem occurs between two systems of three manufacturers. Upon coordination, three manufacturers performed the first combined DT on March 20, and drove from a 2G/3G co-sited cell to a 2G coverage area. In addition, Huawei OMC was required to trace signaling on the A interface and user plane at the same time. In the test process, we found that the 3G UE sent a 2D event to the system and requested the handover when the RSCP was weak, but the UE receives no response until the call was dropped. Through analysis, it was found that Huawei BSC did not respond to the handover request. After location, we found that the problem was concentrated on data configuration.

To check the data configuration of the BSC, first check the following aspects:1. Encryption algorithm2. MSC version supported by the BSC3. Configuration of the external LAC4. Enabling state of inter-RAT handoverAfter confirmation between Huawei and engineers of competitors A and E, we found that the 3G system adopted A5/1 algorithm, the current MSC version was R99, and the external LAC had been added. Finally, the problem was concentrated on the setting of the inter system HO allowed parameter in the Modify BSC Interface Phase ID table. After the parameter was set to Yes, the inter-RAT handover was normal. Through CN signaling trace, the MSC104 received the handover complete message from the MSC102, and the success rate of Huawei inter-BSC handover increases to the normal level.



6 Information Feedback

If the call drop rate is high and technical support is required, fill in the following form:

Information Remarks Purpose

Software version Software versions of the BSC and BTS

Check whether the software version is defective.

Data configuration table

*.dat files Check the network optimization parameters and power configuration.

Alarm information

Alarm information related to hardware, clock, and transmission (self-check)

Check whether such alarms are generated in the faulty cell. Such alarms should be cleared.

Traffic measurement

Causes of inter-RAT handover failure

Incoming/outgoing inter-RAT handover measurement

Signaling RSL signaling tracing data Check the causes of call drops.

DT data *.log (*.CELL) files or *.ant files Based on the drive test data, determine whether interference or coverage problems exist.

Others Engineering parameter tables and e-maps

Facilitate the checking of the geographical information by the NASTAR tool.


Documents

16 GSM BSS Network KPI (Inter-RAT Handover Success Rate) Optimization Manual[1].Doc