16 GSM BSS Network KPI (Inter-RAT Handover Success Rate) Optimization Manual_2

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

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Product Name

G3BSC

Product Version

GSM BSS Network KPI (Inter-RAT Handover

Success Rate) Optimization Manual

Prepared by Date

Reviewed by Date

Reviewed by Date

Granted by Date


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Contents

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

1.1 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 ....................................................................................................................... 8

2.1 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 ......................................................................... 13

3.1 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..................................................................................................................... 21

5.1 Case 1: Data Configuration ............................................................................................................................ 21

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

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


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Revision Record

Date Version Description Author

References

SN Document Author Date


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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


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1 Definition of the Inter-RAT Handover Success Rate

1.1 Definition

The 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%


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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

UE NodeBRNC

ServingCN MSC BSC BTS

1Relocation RQD

2Prepare HO

3HO REQ

4HO REQACK

5Prepare HOResponse

6RelocationCMD

7Inter System HO CMD

8HO Detect

9 HO CMP

10 HO CMP

11Send EndSignal REQ

12Iu REL CMD

13IU REL CMP

14Send EndSignal Response

A1

B1

C1

图1 系统间入小区切换流程

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


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UE NodeBRNC

ServingCN MSC BSC BTS

1HO RQD

5Prepare HOResponse

7 HO CMD

11Send EndSignal REQ

14Send EndSignal Response

2Prepare HO

3Relocation REQ

4Relocation REQACK

6HO CMD

8RelocationDetect

9 HO CMP

10RelocationCMP

12Clear CMD

13Clear CMP

A2

B2

C2

Outgoing 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


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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 Failure

During 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 Problems

The 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 Upgrade

All 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.


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2.4 MS Problems

Now, 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 Settings

The 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


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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.


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.


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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 Volume

Traffic 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.


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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 Problems

The 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.


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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?

N

o

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?

N

o

N

o

N

o

N

o

Yes

Yes

Yes

Yes


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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:


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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

BSC

SDCCH 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.


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Cause BSC Level Cell Level

Transmis

sion

failure

BSC Measurement -> LAPD

Measurement

Call Measurement -> Channel Activation

Measurement ->

CHAN ACTIV NACK Messages Sent by BTS

Channel Activation Timeouts

Call 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.


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


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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.


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Cause TRX Level

Interference

MR Measurement ->

Interference Band Measurement ->

Mean Number of SDCCHs in Interference Band 1





MR Measurement ->


Mean Number of TCHFs in Interference Band 1





MR Measurement ->


Mean Number of TCHHs in Interference Band 1





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.


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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


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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.


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5 Optimization Cases

5.1 Case 1: Data Configuration

Problem 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.


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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:

G3BSC32V300R002C13SP54

BTS version:

BTS : GBT312G3BTS32V302R007C07B001

In 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 algorithm

2. MSC version supported by the BSC

3. Configuration of the external LAC

4. Enabling state of inter-RAT handover

After 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.


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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.

16 GSM BSS Network KPI (Inter-RAT Handover Success Rate) Optimization Manual_2

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