Handover(GBSS14.0)

GSM BSSGBSS14.0

Handover Feature ParameterDescription

Issue 02Date 2012-12-31

HUAWEI TECHNOLOGIES CO., LTD.

Copyright Huawei Technologies Co., Ltd. 2013. All rights reserved.No part of this document may be reproduced or transmitted in any form or by any means without prior writtenconsent of Huawei Technologies Co., Ltd. Trademarks and Permissions

and other Huawei trademarks are trademarks of Huawei Technologies Co., Ltd.All other trademarks and trade names mentioned in this document are the property of their respective holders. NoticeThe purchased products, services and features are stipulated by the contract made between Huawei and thecustomer. All or part of the products, services and features described in this document may not be within thepurchase scope or the usage scope. Unless otherwise specified in the contract, all statements, information,and recommendations in this document are provided "AS IS" without warranties, guarantees or representationsof any kind, either express or implied.

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Bantian, LonggangShenzhen 518129People's Republic of China

Website: http://www.huawei.comEmail: [email protected]

Issue 02 (2012-12-31) Huawei Proprietary and ConfidentialCopyright Huawei Technologies Co., Ltd.

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Contents

1 Introduction....................................................................................................................................11.1 Scope..................................................................................................................................................................11.2 Intended Audience..............................................................................................................................................11.3 Change History...................................................................................................................................................1

2 Overview.........................................................................................................................................63 Technical Description.................................................................................................................13

3.1 Measurement Report Processing......................................................................................................................133.2 Handover Preprocessing...................................................................................................................................153.3 Forced Handover..............................................................................................................................................183.4 Handover Decision Based on Handover Algorithm I.......................................................................................20

3.4.1 Quick Handover.......................................................................................................................................203.4.2 TA Handover...........................................................................................................................................223.4.3 BQ Handover...........................................................................................................................................233.4.4 Rapid Level Drop Handover....................................................................................................................253.4.5 Interference Handover.............................................................................................................................253.4.6 Handover Due to No Downlink Measurement Report............................................................................273.4.7 Enhanced Dual-Band Network Handover...............................................................................................283.4.8 Load Handover........................................................................................................................................313.4.9 Enhanced Load Handover.......................................................................................................................343.4.10 Edge Handover......................................................................................................................................353.4.11 Fast-Moving Micro Cell Handover.......................................................................................................363.4.12 Inter-Layer Handover............................................................................................................................383.4.13 PBGT Handover....................................................................................................................................403.4.14 AMR Handover.....................................................................................................................................413.4.15 SDCCH Handover.................................................................................................................................433.4.16 Other Handovers....................................................................................................................................43

3.5 Handover Decision Based on Handover Algorithm II.....................................................................................433.5.1 Quick Handover.......................................................................................................................................453.5.2 TA Handover...........................................................................................................................................473.5.3 BQ Handover...........................................................................................................................................483.5.4 Interference Handover.............................................................................................................................493.5.5 Handover Due to No Downlink Measurement Report............................................................................51

GSM BSSHandover Feature Parameter Description Contents


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3.5.6 Enhanced Dual-Band Network Handover...............................................................................................513.5.7 Load Handover........................................................................................................................................543.5.8 Edge Handover........................................................................................................................................543.5.9 Fast-Moving Micro Cell Handover.........................................................................................................563.5.10 Better-Cell Handover.............................................................................................................................583.5.11 Handover Between a Full-Rate TCH and a Half-Rate TCH.................................................................593.5.12 SDCCH Handover.................................................................................................................................623.5.13 Other Handovers....................................................................................................................................62

4 Related Features...........................................................................................................................635 Impact on the Network...............................................................................................................66

5.1 HUAWEI I Handover and HUAWEI II Handover...........................................................................................665.2 Direct Retry......................................................................................................................................................665.3 SDCCH Handover............................................................................................................................................665.4 Processing of Measurement Report..................................................................................................................675.5 Pre-processing of Measurement Report...........................................................................................................675.6 Fast Move Handover........................................................................................................................................675.7 Chain Cell Handover........................................................................................................................................675.8 BTS power lift for handover.............................................................................................................................685.9 Dynamic HR/FR Adaptation............................................................................................................................685.10 AMR FR/HR Dynamic Adjustment...............................................................................................................68

6 Engineering Guidelines.............................................................................................................696.1 When to Use Handover.....................................................................................................................................69

6.1.1 HUAWEI I Handover..............................................................................................................................696.1.2 HUAWEI II Handover.............................................................................................................................696.1.3 Direct Retry.............................................................................................................................................696.1.4 SDCCH Handover...................................................................................................................................696.1.5 Processing of Measurement Report.........................................................................................................696.1.6 Pre-processing of Measurement Report..................................................................................................696.1.7 Fast Move Handover...............................................................................................................................706.1.8 Chain Cell Handover...............................................................................................................................706.1.9 BTS power lift for handover....................................................................................................................706.1.10 Dynamic HR/FR Adaptation.................................................................................................................706.1.11 AMR FR/HR Dynamic Adjustment......................................................................................................70

6.2 Information to Be Collected.............................................................................................................................706.2.1 HUAWEI I Handover..............................................................................................................................706.2.2 HUAWEI II Handover.............................................................................................................................706.2.3 Direct Retry.............................................................................................................................................706.2.4 SDCCH Handover...................................................................................................................................706.2.5 Processing of Measurement Report.........................................................................................................716.2.6 Pre-processing of Measurement Report..................................................................................................716.2.7 Fast Move Handover...............................................................................................................................71



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6.2.8 Chain Cell Handover...............................................................................................................................716.2.9 BTS power lift for handover....................................................................................................................716.2.10 Dynamic HR/FR Adaptation.................................................................................................................716.2.11 AMR FR/HR Dynamic Adjustment......................................................................................................71

6.3 Network Planning.............................................................................................................................................716.4 HUAWEI I Handover Feature Deployment.....................................................................................................716.5 HUAWEI II Handover Feature Deployment....................................................................................................716.6 Direct Retry Feature Deployment.....................................................................................................................726.7 Pre-processing of Measurement Report Feature Deployment..........................................................................726.8 Fast Move Handover Feature Deployment.......................................................................................................726.9 Chain Cell Handover Feature Deployment......................................................................................................726.10 BTS power lift for handover Feature Deployment.........................................................................................726.11 Dynamic HR/FR Adaptation Feature Deployment........................................................................................726.12 AMR FR/HR Dynamic Feature Deployment.................................................................................................72

7 Parameters.....................................................................................................................................738 Counters......................................................................................................................................2839 Glossary.......................................................................................................................................43210 Reference Documents.............................................................................................................433



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1 Introduction1.1 Scope

This document describes the Handover feature, including its working principles, featuredependencies, network impact, and engineering guidelines. It also introduces the overallprocedure of Huawei handover algorithms and describes the handover decision algorithms.

1.2 Intended AudienceThis document is intended for:l Personnel who need to understand the Handover featurel Personnel who work with Huawei GSM products

1.3 Change HistoryThe section provides information about the changes in different document versions.There are two types of changes, which are defined as follows:l Feature change: refers to a change in the Handover feature of a specific product version.l Editorial change: refers to a change in wording or the addition of information that was not

described in the earlier version.

Document IssuesThe document issues are as follows:l 02(2012-12-31)l 01(2012-4-28)l Draft A (2012-02-15)

02(2012-12-31)This is the second official release of GBSS14.0.

GSM BSSHandover Feature Parameter Description 1 Introduction


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Compared with 01 (2012-04-28), issue 02 (2012-12-31) of GBSS14.0 incorporates the changesdescribed in the following table.

Change Type Change Description Parameter ChangeFeature change Deleted descriptions about

the Load handover penaltyinheritance function in theHandover Decision Based onHandover Algorithm Ifeature.

None

Editorial change None None

01(2012-04-28)This is the first official release of GBSS14.0.Compared with draft A (2012-2-15), issue 01 (2012-04-28) of GBSS14.0 incorporates thechanges described in the following table.

Change Type Change Description Parameter ChangeFeature change None NoneEditorial change l Optimized the description

about networkcharacteristicsadjustment. For details,see section 3.2 HandoverPreprocessing

l Added the flowchart forthe interference handoverprocess. For details, seesection 3.4.5Interference Handover

l Added the formula forcalculating the TCHusage and flowchart forthe load handoverprocess. For details, seesection 3.4.8 LoadHandover

l Added the flowchart forthe inter-layer handoverprocess. For details, seesection 3.4.12 Inter-Layer Handover

None



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Draft A (2012-02-15)This is a draft.Compared with issue 03 (2011-10-30) of GBSS13.0, draft A (2012-02-15) of GBSS14.0incorporates the changes described in the following table.



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Change Type

ChangeDescription

Parameter Change

Featurechange

l Optimized theDynamic HR/FRAdaptationfeature. Afteroptimization, thisfeature can be usedwith HUAWEI IHandover andHUAWEI IIHandover. Fordetails, see section3.5.11 HandoverBetween a Full-Rate TCH and aHalf-Rate TCH

l Added handoverpenaltyinheritancesupported by theload handover. Fordetails, see section3.4.8 LoadHandoverand3.5.7 LoadHandover

l Optimized theinterferencehandover inHUAWEI IHandover. Fordetails, see section3.4.5 InterferenceHandover3.4.5"InterferenceHandover."

l Optimized triggerconditions for thequick handover.For details, seesections3.4.1QuickHandover and3.5.1 QuickHandover

l Added the value HOBASECAPANDQUAL(HOBASECAPANDQUAL) for theINTRACELLFHHOEN parameter.

l Added the following parameters: LoadHoPunishInheritSwitch INTERHOOPTALLOW QUICKPBGTHOEN ADJHOOFFSET



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Change Type

ChangeDescription

Parameter Change

Editorial change

Added the followingchapters:l Chapter 4 4

Related Featuresl Chapter 5 5

Impact on theNetwork

l Chapter 6 6EngineeringGuidelines

None



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2 OverviewThe GSM network comprises of multiple cells with continuous coverage. The handovertechnique is introduced into the GSM system to enable users who are in motion to continue theircurren calls without interruption, optimizing the network performance.During a handover, the MS and BTS in service measur the conditions of uplink and downlinkradio links respectively, record the measurement results into measurement reports (MRs), andthen send the MRs to the BSC. The BSC determines whether to trigger a handover based on theMRs and the actual conditions of the radio network.Huawei handover algorithms (handover algorithm I and handover algorithm II) involvemeasurement and MR reporting, MR processing, handover decision, and handover execution.

NOTE

Huawei handover algorithms apply to handovers on TCHs as well as handovers on SDCCHs.

The handover algorithm used for a cell is determined by the HOCTRLSWITCH parameter.Figure 2-1 shows the procedure for performing Huawei handoveralgorithms (includinghandover algorithm I and handover algorithmII ).

GSM BSSHandover Feature Parameter Description 2 Overview


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Figure 2-1 Procedure for performing Huawei handover algorithms

Handover Decision Based on Handover Algorithm IFigure 2-2 shows the procedure of handover decisionbased on handover algorithm I.



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Figure 2-2 Procedure of handover decision based on handover algorithm I

In handover algorithm I, five types of handover decisions are defined:l Quick handover (including quick PBGT handover and frequency offset handover): Good

and stable services can be provided when the voice quality deteriorates during the fastmovement of an MS. Quick handover mainly applies to the railway scenario.

l Emergency handover: Ensures the call continuity when the radio condition severelydeteriorates. Theoretically, an emergency handover has a bigger deviation than other



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handovers in terms of the selection of the target cell. In a normal cell, frequent emergencyhandovers should be avoided.

l Enhanced dual-band network handover: In an enhanced dual-band network, the resourcesin the overlaid (OL) DCS1800 cell and underlaid (UL) GSM900 cell can be shared duringthe assignment and handover procedures. That is, the calls in the high-traffic GSM900 cellcan be handed over to the low-traffic DCS1800 cell to balance traffic.

l Load handover: Balances system load among multiple cells so that the system performancecan be ensured.

l Normal handover: Ensures good service quality when an MS is moving.Figure 2-3 shows the handovers provided in Figure 2-2 and their priorities in handoveralgorithm I.



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Figure 2-3 Handover decisions based on handover algorithm I



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Handover Decision Based on Handover Algorithm IIFigure 2-4 shows the procedure of handover decision based on handover algorithm II.

Figure 2-4 Procedure of handover decision based on handover algorithm II

In handover algorithm II, three types of handover decisions are defined, as shown in Figure2-5.



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Figure 2-5 Handover decisions based on handover algorithm II

Handover ExecutionThe BTS power lift for handover function determines whether the BTS of the serving celltransmits signals at the maximum power during a handover. The BSC maximizes the transmitpower of the BTS before sending a handover command to the MS. The BSC maintains the BTSpower during the handover to ensure the success of the handover. (GBFD-117101 BTS powerlift for handover)

Synchronous Handover and Asynchronous HandoverThe BSC supports both synchronous handovers and asynchronous handovers. Generally, theBSC performs synchronous handovers for intra-BTS inter-cell or intra-cell handovers andperforms asynchronous handovers for inter-BTS handovers. However, the BSC also performsasynchronous handovers for intra-BTS inter-cell handovers when the following conditions aremet:l DIRMAGANSITEFLAG is set toYES(Yes). That is, a repeater is configured for the source

cell or target cell.l FRAMEOFFSETis set to a value other than0 or 255. That is, frame offset is configured

for the source cell or target cell.l The source cell or target cell is a multi-site cell.



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3 Technical Description3.1 Measurement Report Processing

This section describes the features GBFD-110801 Processing of Measurement Report andGBFD-110802 Pre-processing of Measurement Report.Measurement report processing involves measurement report interpolation and filtering.

NE Selection for Measurement Report ProcessingThe processing can be performed either on the BSC side or on the BTS side.l If BTSMESRPTPREPROC is set to BSC_Preprocessing(BSC preprocessing), the

processing is performed on the BSC side.l If BTSMESRPTPREPROC is set to BTS_Preprocessing(BTS preprocessing), the

processing is performed on the BTS side. By setting the parameters PRIMMESPPT,BSMSPWRLEV, and MRPREPROCFREQ, you can specify the contents of the MRs tobe provided and the period during which the MRs are provided. This decreases the signalingtraffic on the Abis interface and the traffic volume processed by the BSC.

Data Selection for Measurement ReportMRs can be classified into enhanced MRs and normal MRs. The parameter MEASURETYPEdetermines the type to be used.In an MR, the TCH measurement of the serving cell is classified into FULL SET and SUB SET.

Measurement Report InterpolationThe neighboring cell indexes are found on the basis of the BCCH ARFCNs and BSICs providedby the MS. Then, the uplink and downlink measurement results are obtained from the MRs.l If MRs are issued continuously, they are directly added to the MR list.l If MRs are not issued continuously and the number of lost MRs is less than the value of

MRMISSCOUNT, the system performs operations as follows: If MrIntrplOptSwitch is set to NO(No): For the serving cell, handover algorithm I

performs the linear interpolation for the MRs. The lowest values are applied to the

GSM BSSHandover Feature Parameter Description 3 Technical Description


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interpolation of MRs by handover algorithm II according to the protocols; that is, level0 (110 dBm) and quality 7 are applied in the interpolation. For a neighboring cell,handover algorithm I and handover algorithm II use the lowest values stipulated in theprotocols for the lost signal level; that is, level 0 (110 dBm) is used in the interpolation. If MrIntrplOptSwitch is set to YES(Yes): For the serving cell, handover algorithm I

and handover algorithm II perform the linear interpolation for the MRs. For aneighboring cell, handover algorithm I and handover algorithm II perform the linearinterpolation for the MRs.

l If MRs are not issued continuously and the number of lost MRs is greater than the valueof MRMISSCOUNT, the previous MRs are discarded. When new MRs are issued,calculation is done again.

Measurement Report FilteringFiltering is performed on MRs obtained continuously from the MR list. Averaging is performedon uplink/downlink receive level, uplink/downlink receive quality, Timing Advance (TA),Radio Quality Indication (RQI), BTS power, neighboring 2G cell level, Common Pilot Channel(CPICH), received signal code power (RSCP), and Ec/No of neighboring 3G cell. The averagingminimizes the effect on the result of handover decision due to sudden changes in themeasurement values.Power control compensation needs to be performed for the downlink receive level of the servingcell by the handover algorithm II. If you compare the receive level of the serving cell after thepower control with that of all BCCH TRXs of the neighboring cell, there is no mapping betweenthem. In situations where the cells overlap severely, the handover is easily triggered, causingthe ping-pong handover. After the power control compensation is performed, the receive levelof the serving cell can reflect the coverage condition of the BCCH TRX of the serving cell. Thepower control compensation of the serving cell is performed after the interpolation processingand before the filtering processing. In general, the compensation of power control is calculatedby adding the downlink receive level of the serving cell and twice the current downlink transmitPOWL of the BTS.The number of consecutive MRs required for filtering is determined by the measurement objectand channel type. See Table 3-1 for details.

Table 3-1 Parameters related to the number of MRsMeasurement Object Channel Type ParameterReceive level of the servingcell

SDCCH NSIGSTRFLTLENTCH SSLENSD

Quality of the serving cell SDCCH QLENSITCH DATAQUAFLTLEN

TA of the serving cell TCH TAFLTLENSDCCH TASIGSTRFLTLEN

Receive level of theneighboring cell

BCCH NCELLFLTLENSDCCH NSIGSTRFLTLEN



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Measurement Object Channel Type ParameterPower of the BTS in theserving cell

TCH DATASTRFLTLEN

RQI TCH QLENSD

If consecutive MRs are insufficient, the filtering fails. The handover decision is not performed.

3.2 Handover PreprocessingHandover Penalty

According to the neighboring cell information in an MR and the parameters, the system performshandover preprocessing and adjusts the priorities of neighboring cells.The handover penalty is performed after successful fast-moving micro cell handover, timingadvance (TA) handover, Bad Quality (BQ) handover, fast-moving micro cell handover, OLsubcell to UL subcell handover within an enhanced concentric cell, and after the handoverfailures.In handover algorithm II, in addition to the situations mentioned above, the handover penalty isalso performed after successful or failed load handover and interference handover.

NOTE

In the handover decision procedure of handover algorithm II, the handover penalty is performed after thenetwork characteristics adjustment and before the emergency handover decision.Handover penalty inheritance enables an MS to inherit its penalty state after the MS is successfully handedover to another cell.

l After a quick handover, TA handover, BQ handover, or load handover (in handoveralgorithm II) is successfully performed, the penalty level is subtracted from the actualreceive level of the original cell during the penalty period. Table 3-2 lists the parametersrelated to handover penalty.

Table 3-2 Parameters related to handover penaltyHandover ParameterQuick handover TIMEPUNISH

HOPUNISHVALUETA Handover SSTAPUNISH

TIMETAPUNISHBQ Handover SSBQPUNISH

TIMEBQPUNISH



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Handover ParameterLoad handover (handover algorithm II) LOADHOPENTIME

LOADHOPENVALUELoadHoPunishInheritSwitch

l After a fast-moving micro cell handover is successfully performed, penalty is performed

on all the neighboring cells of the micro cell. Related parameters are SDPUNVAL andSPEEDPUNISHT.

l If an MS fails to initiate an intra-cell adaptive multirate (AMR) TCHF to TCHH handover,it cannot initiate another intra-cell AMR TCHF to TCHH handover withinTIMEAMRFHPUNISH.

l In handover algorithm II, after the interference handover is initiated, initiating this handoveragain is not allowed within INTERFEREHOPENTIME regardless of whether thehandover is successful or not.

l After an OL subcell to UL subcell handover within an enhanced concentric cell issuccessful, the handover from UL subcell to OL subcell is not allowed withinUTOOHOPENTIME.

l After an OL cell to UL cell handover in the enhanced dual-band network is successful, thehandover from UL cell to OL cell is not allowed within HOPENALTYTIME.

l After a handover fails, different penalties are performed on the target cell based on thecauses: If a handover to a neighboring 2G or 3G cell fails, the actual receive level of the target

cell is subtracted by FAILSIGSTRPUNISH for neighboring cell ranking during thepenalty.

NOTE

Based on the handover failure cause, the penalty time could be UMPENALTYTIMER,RSCPENALTYTIMER, or PENALTYTIMER.

l If an OL subcell to UL subcell handover within a concentric cell fails, the handover fromOL subcell to UL subcell is not allowed within TIMEOTOUFAILPUN.

l If a UL subcell to OL subcell handover within a concentric cell fails, the handover fromUL subcell to OL subcell is not allowed within TIMEUTOOFAILPUN.

Basic RankingBasic ranking is performed after handover penalty to generate a candidate cell list in descendingorder taking the following information into account: receive levels of the serving cell andneighboring cells carried in the MRs, hysteresis, usage of TCHs in the neighboring cells, and soon.l In the case of non-directed retry, if an MS in an external BSC cell occupies an SDCCH and

INRBSCSDHOEN is set to NO(No), this cell should be removed from the candidate celllist. In other words, the handover to this external BSC cell is prohibited.

l If a neighboring 2G cell and the serving cell are controlled by the same BSC and the TCHusage of the neighboring cell is 100%, the neighboring cell should be removed from thecandidate cell list; that is, the handover to this neighboring cell is prohibited.



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l If the downlink receive level of a neighboring 2G cell is smaller than the sum ofHOCDCMINDWPWR and MINOFFSET, the neighboring cell should be removed fromthe candidate cell list; that is, the handover to this neighboring cell is prohibited.

l If the uplink receive level of a neighboring 2G cell is smaller than the sum ofHOCDCMINUPPWR and MINOFFSET, the neighboring cell should be removed fromthe candidate cell list; that is, the handover to this neighboring cell is prohibited.

l If a neighboring 3G cell is a frequency division duplex (FDD) cell, the cell is processedaccording to FDDREP: If FDDREP is set to EcN0(Ec/N0), and the Ec/No of a neighboring cell is smaller than

MINECNOTHRES, the neighboring cell should be removed from the candidate celllist; that is, the handover to this neighboring cell is prohibited. If FDDREP is set to RSCP(RSCP), and the received signal code power (RSCP) of a

neighboring cell is smaller than MINRSCPTHRES, the neighboring cell should beremoved from the candidate cell list; that is, the handover to this neighboring cell isprohibited.

l If a neighboring 3G cell is a time division duplex(TDD) cell and the RSCP after penalty issmaller than the MINRSCPTHRES, the neighboring cell should be removed from thecandidate cell list; that is, the handover to this neighboring cell is prohibited.

l Calculate the difference between the downlink receive level of the neighboring cells andthe downlink receive level of the serving cell. Based on the difference, rank the neighboringcells in descending order.

Network Characteristics AdjustmentFactors considered during network characteristics adjustment have higher priorities than thoseconsidered during basic ranking.During network characteristic adjustment, the following factors are considered based on theirpriorities from high to low:l Whether the serving cell and a neighboring cell share the same BSC or MSCl Load in a celll Layer where a cell is locatedAfter performing basic ranking on all candidate cells based on their priorities, the BSC ranksthese cells again to determine their comprehensive priorities.After network characteristics adjustment, the BSC generates a final candidate cell list (includingthe serving cell and neighboring cells). The candidate cells are ranked based on their prioritiesfrom high to low. Then, the BSC starts the handover decision procedure.If HOPRIOMODEN is set to NO(No): In handover algorithm II, the emergency handoverdecision is made before network characteristics adjustment and forced handover and afterhandover penalty (except load handover penalty) and basic ranking. Load handover penalty isperformed before network characteristics adjustment and after an emergency handover. Afterthe emergency handover decision, LOADHOPENVALUE is subtracted from the signal level ofthe original cell within the time specified by LOADHOPENTIME if the load handover issuccessful. After load handover penalty, the signal level of the target cell changes. Therefore,the network characteristics need to be readjusted.If HOPRIOMODEN is set to YES(Yes): In handover algorithm II, all handover decisions aremade after handover penalty, basic ranking, network characteristics adjustment, and forced



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handovers. In handover algorithm I, all handover decisions are made after handover penalty,basic ranking, and network characteristics adjustment.

3.3 Forced HandoverA forced handover does not require a handover decision.A forced handover is triggered in the following scenarios:l If no TCH is available in the serving cell which the MS attempts to access and

DIRECTRYEN is set to YES(Yes), the BSC triggers a directed retry procedure.l When a BTS is under maintenance, the MSs served by the BTS should be handed over to

the cells controlled by a functional BTS. This ensures that no call drop occurs during theBTS maintenance.

Directed RetryWhen the MS initiates a call, after the BSC receives an ASSIGN REQ message from the MSC,the BSC determines an assignment mode based on the load of the serving cell.

NOTE

Assignment mode is categorized into normal assignment procedure, mode modification procedure, anddirected retry procedure. The commands issued by the BSC vary according to the procedure.l For a normal assignment procedure, the BSC activates a channel and issues a channel assignment

command.l For a mode modification procedure, the BSC issues a mode modification command.l For a directed retry procedure, the BSC issues a handover command.

If the serving cell is so overloaded that new calls cannot be admitted or admitting new calls willaffect ongoing services, the BSC triggers a directed retry procedure. By using the directed retry,the MS is handed over to the target cell and part of the traffic in the serving cell is distributedto the target cell. This avoids traffic congestion in the serving cell. (GBFD-110607 DirectedRetry)Figure 3-1 shows the procedure for a directed retry decision.



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Figure 3-1 Procedure for a directed retry decision

When ASSLOADJUDGEEN is set to DISABLE(Disable), the BSC triggers a directed retryprocedure after completing basic ranking if the load of the serving cell exceeds 100%.As shown in Figure 3-1, directed retry is categorized into enhanced dual-band network directedretry and normal directed retry.l Enhanced Dual-Band Network Directed Retry

In an enhanced dual-band network, two cells form a group and the MS camps on one ofthe two cells. After the directed retry is triggered, the MS is handed over to the other cell.For details on the conditions of triggering an enhanced dual-band network directed retry,



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see sections 3.4.7 Enhanced Dual-Band Network Handover and 3.5.6 Enhanced Dual-Band Network Handover.

l Target Cell Selection in a Normal Directed Retry ProcedureThe target cell must have the highest priority in the candidate cell list after handoverpreprocessing. In addition, the target cell must meet the following conditions:

l The serving cell does not function as a target cell.l Load of the candidate neighboring cells DTLOADTHREDl In handover algorithm II, serving cell level < receive level of neighboring cells < serving

cell level + DRHOLEVRANGE.l In handover algorithm I, receive level of neighboring cells MINPWRLEVDIRTRY.If DRTAGCELLSEL is set to YES(Yes), the MS can be handed over to one of multiple candidatecells by using directed retry. If DRTAGCELLSEL is set to NO(No), the MS can be handed overto only one target cell. The number of available candidate cells is controlled by HOTRYCNT.

3.4 Handover Decision Based on Handover Algorithm IThis section describes the feature GBFD-110601 HUAWEI I Handover.According to the emergency condition of an MS in the network, the handover decision basedon handover algorithm I is made in the following order: quick handover, emergency handover,enhanced dual-band network handover, load handover, and normal handover.Handover decision based on handover algorithm I involves the following procedures:l Determines whether the serving cell meets the trigger conditions.l Selects corresponding candidate cells.In handover algorithm I, HOOPTSEL specifies whether a neighboring 2G cell or a neighboring3G cell is preferred.l When HOOPTSEL is set to Pre_2G_Cell(Preference for 2G cell):

A neighboring 2G cell is preferred. If the candidate cell list contains suitable neighboring3G cells but no suitable neighboring 2G cells, a neighboring 3G cell is selected.

l When HOOPTSEL is set to Pre_3G_Cell(Preference for 3G cell):A neighboring 3G cell is preferred. If the candidate cell list contains suitable neighboring2G cells but no suitable neighboring 3G cells, a neighboring 2G cell is selected.

l When HOOPTSEL is set to Pre_2G_CellThres(Preference 2G cell by thresh):If the receive level of a candidate 2G cell is smaller than or equal to HOPRETH2G, aneighboring 3G cell is preferred.

If the trigger conditions for an emergency handover are met and there is at least one candidatecell, the emergency handover timer NEWURGHOMININTV is started. Another emergencyhandover decision can be performed only when NEWURGHOMININTV times out.

3.4.1 Quick HandoverThis section describes the features GBFD-510103 Chain Cell Handover and GBFD-510102 FastMove Handover.



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Quick handover aims to increase the handover success rate of an MS moving at a high speedand to ensure the call continuity and low call drop rate. Quick handover applies to the scenariowhere an MS moves fast along an urban backbone road, a selected route, or a high-speed railroad.

Quick Handover TypesQuick handover consists of frequency offset handover and quick PBGT handover.l Frequency offset handover

Whether the MS moves away from the serving cell is determined based on the frequencyoffset information provided by an MS moving at a high speed. Frequency offset handoverdecision is made according to the uplink/downlink receive level of the serving cell and thepath loss of neighboring cells.

l Quick PBGT handoverQuick PBGT handover decision is made according to the path loss of neighboring cells.

For quick handover, the handover response speed is enhanced by:l Accurately calculating the move speed of the MSl Lifting the restriction on the interval between handover decisionsl Reducing the number of MRs for the handover decisionl Introducing the alpha filtering

Quick Handover PreparationThe preparation for quick handover involves the following aspects:l Frequency offset is decoded from the MR.

Frequency offset of the MS is obtained from the uplink MR that the BTS sends to the BSC.l Alpha filtering is performed on the MR.

Trigger ConditionsDuring the handover decision, it is first determined whether the trigger conditions for a frequencyoffset handover are met. When the BTS cannot send the frequency offset information or thereported frequency offset information is invalid, a fast move handover is triggered, providedthat other conditions for a frequency offset handover are met.If QUICKHOEN is set to YES(Yes), the trigger conditions for a quick handover are as follows:l The MS moves away from the serving cell (the frequency offset in the measurement result

is a negative value) and the move speed of the MS is greater thanMOVESPEEDTHRES.

l The filtered uplink level of the serving cell is less than HOUPTRIGE.l The compensated downlink level of the serving cell is less than HODOWNTRIGE.l The difference between the path loss of a chain neighboring cell and that of the serving cell

is greater than the predefined threshold. The threshold is equal to the value ofHOOFFSET (in the SET GCELLHOFAST command for an internal neighboring cell orin the MOD GEXT2GCELL command for an external neighboring cell) plus the value ofADJHOOFFSET for the serving cell.

The trigger conditions for a quick handover are as follows:



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l If all the last three conditions are met, the handover decision is made as follows: If the first condition is met, a frequency offset handover is triggered. If QUICKPBGTHOEN is set to YES(Yes) and the first condition is not met, a quick

PBGT handover is triggered. If QUICKPBGTHOEN is set toNO(No), a quick PBGT handover is not triggered.

l If all the last three conditions are not met, a quick handover is not triggered.

Target Cell SelectionThe target cell must be a chain neighboring cell of the serving cell. The target cell can be obtainedthrough the setting of ISCHAINNCELL. If HODIRFORECASTEN is set to YES(Yes), aneighboring cell in the moving direction of the MS is selected preferentially.To forecast the moving direction of the MS, the direction of a chain neighboring cell (A or B)compared with the serving cell is specified by CHAINNCELLTYPE. If the number of timesthat the MS is handed over to neighboring cells in the same direction (B for example) is greaterthan or equal to HODIRLASTTIME when the handover time reaches HODIRSTATIME, theMS is inferred to be moving towards the B direction. Subsequently, the MS is preferentiallyhanded over to the neighboring cell whose CHAINNCELLTYPE is B.

LimitationsThe limitations on quick handover are as follows:l The serving cell cannot be selected as the target cell.l The candidate cells for quick handover must be chain neighboring cells of the serving cell.l After a quick handover is successful, the penalty is performed on the original cell during

the penalty time to prevent an immediate handover back to the original cell. The penaltytime and penalty value are specified by TIMEPUNISH and HOPUNISHVALUErespectively.

3.4.2 TA HandoverTA handover is a type of emergency handover. The TA handover decision is made accordingto the TA value reported by the MS.The TA value of a normal cell ranges from 0 to 63 and that of an extended cell ranges from 0 to229. The TA can be stepped up or down in steps of 553.5 m. The TA value of 63 correspondsto a distance of 35 km.

Trigger ConditionsTA handover is triggered when the following conditions are met:l TAHOEN is set to YES(Yes).l Filtered TA value in the MR provided by the MS is greater than or equal to TALIMIT.

NOTE

From the perspective of the trigger conditions for a TA handover, TA can be regarded as a limitation tothe size of a cell.



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Target Cell SelectionThe target cell must have the highest priority in the candidate cell list after handoverpreprocessing. In addition, the target cell must meet the following conditions:l The serving cell cannot be selected as the target cell.l If TALIMIT of a co-site neighboring cell is smaller than or equal to the TALIMIT of the

serving cell, a handover to the neighboring cell is prohibited.If the trigger conditions for a TA handover are met but the candidate 2G cells are not suitable,the following operations are performed:l If a neighboring 3G cell is available, if INTERRATOUTBSCHOEN is set to YES(Yes),

and if the MS supports the 2G/3G inter-RAT handover, the 2G/3G inter-RAT handover isperformed.

l If no neighboring 3G cell is available, if INTERRATOUTBSCHOEN is set to NO(No),or if the MS does not support the 2G/3G inter-RAT handover, the decision on whether toinitiate another type of emergency handover is made.

LimitationsAfter the TA handover is successful, the penalty is performed on the original cell. DuringTIMETAPUNISH, SSTAPUNISH is subtracted from the level of the original cell to preventan immediate handover back to the original cell.

3.4.3 BQ HandoverBQ handover is a type of emergency handover in which the system makes the decision basedon the uplink/downlink receive quality on the Um interface.The receive quality is measured in bit error rate (BER). The BSC measures the quality of a radiolink based on the quality band in the MR. The probable cause of an increase in BER is that thesignal power is too low or the channel interference increases.

Trigger ConditionsIf BQHOEN is set to YES(Yes), the BQ handover is triggered when either of the followingconditions are met:l The uplink receive quality is greater than or equal to the uplink receive quality threshold

of the serving cell.l The downlink receive quality is greater than or equal to the downlink receive quality

threshold of the serving cell.The parameters for specifying the uplink and downlink receive quality thresholds are as follows:l For non-AMR calls, the parameter for specifying the uplink receive quality threshold is

ULQUALIMIT and the parameter for specifying the downlink receive quality threshold isDLQUALIMIT.

l For AMR FR calls, the parameter for specifying the uplink receive quality threshold isULQUALIMITAMRFR and the parameter for specifying the downlink receive qualitythreshold is DLQUALIMITAMRFR.



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l For AMR HR calls, the parameter for specifying the uplink receive quality threshold isULQUALIMITAMRHR and the parameter for specifying the downlink receive qualitythreshold is DLQUALIMITAMRHR.

Target Cell SelectionThe target cell must have the highest priority in the candidate cell list after handoverpreprocessing. In addition, the target cell must meet the following conditions:l If the target cell is a neighboring cell, the receive level of the target cell must meet the

following condition:l Filtered downlink receive level of the target cell > Filtered downlink receive level of the

serving cell after compensation + (INTERCELLHYST of the serving cell configured forthe neighboring cell 64) (BQMARGIN 64)

NOTEl In handover algorithm I, if there is only one cell in the candidate cell list and the cell is a neighboring

cell, the preceding condition does not need to be met.l If INTRACELLSINUSEREN is set to NO(No), no intra-cell handover is allowed within the time

specified by BANTIME when multiple intra-cell handovers are performed consecutively.l If INTRACELLSINUSEREN is set to YES(Yes), no quality-related intra-cell handovers (such as BQ

handover, interference handover, TCHH-to-TCHH handover, and tight BCCH handover) is allowedwithin the time specified by BANTIME whenthe same MS consecutively performs multiple such typesof handovers.

l An MS is handed over to the serving cell when the following conditions are met:l Handover algorithm I is used.l There is no neighboring cell.l INTRACELLHOEN is set to YES(Yes).l BADQUALHOOPTALLOW is set to NO(No).l The serving cell is not in the intra-cell handover penalty state.

Specifically, the MS is preferentially handed over to a channel with a different frequencyband, different frequency, different TRX, or different timeslot (handover priority: channelwith a different frequency band > channel with a different frequency > channel with adifferent TRX > channel with a different timeslot).An MS is not handed over to the serving cell if both INTRACELLHOEN andBADQUALHOOPTALLOW are set to YES(Yes) or if INTRACELLHOEN is set to NO(No).

l If the trigger conditions for a BQ handover are met but the candidate 2G cells are notsuitable, the following operations are performed:

l If a neighboring 3G cell is available, if INTERRATOUTBSCHOEN is set to YES(Yes),and if the MS supports the 2G/3G inter-RAT handover, the 2G/3G inter-RAT handover isperformed.


LimitationsAfter the BQ handover is successful, the penalty is performed on the original cell. DuringTIMEBQPUNISH, SSBQPUNISH is subtracted from the level of the original cell to preventan immediate handover back to the original cell.



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3.4.4 Rapid Level Drop HandoverRapid level drop handover is a type of emergency handover.In edge handover and PBGT handover, the mean value filtering and P/N decision methods arenot responsive to short-period rapid level drop. Therefore, to solve the rapid level drop problem,the finite impact response filtering can be performed on the original receive level. This filteringmethod is responsive to the rapid level drop based on the drop slope of the original receive level.

Trigger ConditionsIf RXQCKFALLHOEN is set to YES(Yes), the trigger conditions for a rapid level drop handoverare as follows:l Filtered uplink level < ULEDGETHRESl A1 x C(nt) + A2 x C(nt - t) + A3 x C(nt - 2t) + + A8 x C(nt - 7t) < B

where, A1 indicates FLTPARAA1. A2 indicates FLTPARAA2. A3 indicates FLTPARAA3. A4 indicates FLTPARAA4. A5 indicates FLTPARAA5. A6 indicates FLTPARAA6. A7 indicates FLTPARAA7. A8 indicates FLTPARAA8. B indicates FLTPARAB.

Target Cell SelectionThe target cell must have the highest priority in the candidate cell list after handoverpreprocessing. In addition, the target cell must meet the following conditions:l The target cell has a higher priority than the serving cell.l The serving cell cannot be selected as the target cell.If the trigger conditions for a rapid level drop handover are met but the candidate 2G cells arenot suitable, the following operations are performed:l If a neighboring 3G cell is available, if INTERRATOUTBSCHOEN is set to YES(Yes),

and if the MS supports the 2G/3G inter-RAT handover, the 2G/3G inter-RAT handover isperformed.


3.4.5 Interference HandoverIn handover algorithm I, if INTERHOOPTALLOW is set toNO(No), interference handover isregarded as a type of emergency handover; if INTERHOOPTALLOW is set toYES(Yes),interference handover is not regarded as a type of emergency handover and the decision oninterference handover is made after a decision on AMR handover is made.



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Interference handover helps protect calls affected by interference and reduce networkinterference. It is applicable in scenarios with interference.In handover algorithm I, the difference between interference handover and BQ handover is asfollows: In BQ handover, the bad signal quality resulting from both coverage and interferenceis checked. In interference handover, the bad signal quality resulting from coverage is notchecked.

Trigger ConditionsIf INTERFHOEN is set to YES(Yes), the interference handover is triggered when either of thefollowing conditions are met:l The filtered value of uplink receive quality is greater than or equal to the specified receive

quality threshold at the current uplink receive level.l The filtered value of downlink receive quality is greater than or equal to the specified

receive quality threshold at the current downlink receive level.The parameters for specifying the uplink and downlink receive quality thresholds are as follows:l For non-AMR FR calls, the parameter for specifying the receive quality threshold is

RXQUALn, where 1 n 12.l For AMR FR calls, the parameters for specifying the receive quality threshold are

RXQUALn (1 n 12) and RXLEVOFF. If n = 1, the receive quality threshold is RXQUAL1. If 2 n 12, the receive quality threshold is RXQUALn + RXLEVOFF.

Target Cell SelectionIn handover algorithm I, the target cell must have the highest priority in the candidate cell list.In addition, the target cell must meet the following conditions:l If INTRACELLHOEN is set to YES(Yes) and the intra-cell handover penalty timer

expires, the serving cell can be selected as the target cell.l If both INTRACELLHOEN and INTERHOOPTALLOW are set to YES(Yes), only the

serving cell can be selected as the target cell.l If INTRACELLHOEN is set to YES(Yes) and INTERHOOPTALLOW is set to NO

(No), either the serving cell or a neighboring cell can be selected as the target cell. IfINTRACELLHOEN is set to NO(No), the serving cell cannot be selected as the target cell.

NOTE

l If INTRACELLSINUSEREN is set to NO(No), no intra-cell handover is allowed within the timespecified by BANTIME when multiple intra-cell handovers are performed consecutively.

l If INTRACELLSINUSEREN is set to YES(Yes), no quality-related intra-cell handovers (such as BQhandover, interference handover, TCHH-to-TCHH handover, and tight BCCH handover) is allowedwithin the time specified by BANTIMEwhenthe same MS consecutively performs multiple such typesof handovers.

l If the filtered level of a neighboring cell after handover penalty HOTHRES of the neighboring cell+ INTELEVHOHYST 64, this neighboring cell can serve as the target cell.

If the trigger conditions for an interference handover are met but the candidate 2G cells are notsuitable, the following operations need to be performed:



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l If a neighboring 3G cell is available, if INTERRATOUTBSCHOEN is set to YES(Yes),and if the MS supports the 2G/3G inter-RAT handover, the 2G/3G inter-RAT handover isperformed.


l

Interference Handover ProcessFigure 3-2 shows the interference handover process.

Figure 3-2 Interference handover process

NOTEIn Figure 3-2, "A" indicates the receive quality threshold under the current uplink or downlink signal level.l For non-AMR FR calls, "A" ranges from RXQUAL1 to RXQUAL12.l For AMR FR calls, "A" equals RXQUAL1or the sum of a value from RXQUAL2 to RXQUAL12

and RXLEVOFF.

3.4.6 Handover Due to No Downlink Measurement ReportHandover due to no downlink measurement report is performed on the basis of the uplink quality.The purpose is to ensure the call continuity and minimize the possibility of call drops.



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Handover due to no downlink measurement report is generally caused by adverse radioenvironment on the uplink. In this case, the requirements of the filtering algorithm cannot bemet, so other handover decisions cannot be performed.

Trigger ConditionsIn handover algorithm I, the trigger conditions for a handover due to no downlink measurementreport are as follows:l NODLMRHOEN is set to YES(Yes).l There is no downlink information in the MR of the call.l The filtered value of uplink quality is greater than or equal to

NODLMRHOQUALLIMIT.l The number of lost downlink MRs is smaller than NODLMRHOALLOWLIMIT.l For TCH, the number of saved MRs with uplink quality value is greater than

DATAQUAFLTLEN; for SDCCH, the number of saved MRs with uplink quality value isgreater than QLENSI.

l In addition, the BSC triggers a handover due to no downlink measurement report whenMRs of the serving cell keep lost for NODLMRHOLASTTIME withinNODLMRHOSTATTIME.

Target Cell SelectionIn handover algorithm I, the conditions for selecting the target cell are as follows:l The ranked neighboring cells recorded in the last complete MR are saved as candidate cells.l A neighboring cell is preferentially selected as the target cell. If

BADQUALHOOPTALLOW is set to YES(Yes), only a neighboring cell can be selectedas the target cell.

l If no neighboring cell is available, or if BADQUALHOOPTALLOW is set to NO(No), theserving cell is selected as the target cell.

3.4.7 Enhanced Dual-Band Network HandoverEnhanced dual-band network handover is performed based on the traffic volume of the OL andUL cells and based on the receive level.Enhanced dual-band network handover is classified into the following types:l Handover due to high load in the UL celll Handover due to low load in the UL celll Handover due to MS movement to the border of the OL cell

Trigger Conditions for a Handover Due to High Load in the Underlaid CellThe trigger conditions for a handover due to high load in the UL cell are as follows:l The two cells are in the enhanced dual-band network and OUTLOADHOENABLE is set

to YES(Yes).l The MS supports the frequency band on which the OL cell operates.l The handover due to high load in the UL cell is performed only on TCHs.



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l The load in the UL cell is greater than or equal to OUTGENOVERLDTHRED.l The load in the OL cell is smaller than INNSERIOVERLDTHRED.l The system traffic volume is smaller than or equal to EDBSYSFLOWLEV.l The current call is within the handover margin, and the INTOINNREXLEVTHRED plus

the handover margin is greater than or equal to the receive level, which is also greater thanor equal to the INTOINNREXLEVTHRED.

l The current call is within the handover margin, and the sum of the receive level in theoverlaid subcell and that in the underlaid subcell is greater than or equal toINTOINNREXLEVTHRED.

l The receive level in the underlaid subcell minus the receive level of the optimal neighboringcell is greater than the sum of ATCBTHRED and ATCBHYST.

When all the preceding conditions are met, the handover due to high load in the UL cell istriggered.If the load of the UL subcell in the cell is greater than or equal toOUTSERIOVERLDTHRED, the handover margin is adjusted in a period ofOUTLOADHOPERIOD subtracted by OUTLOADHOMODPERI. The step length forhandover margin adjustment is specified by OUTLOADHOSTEP.

Trigger Conditions for a Handover Due to Low Load in the Underlaid CellThe trigger conditions for a handover due to low load in the UL cell are as follows:l The load in the UL cell is smaller than OUTLOWLOADTHRED.l The system traffic volume is smaller than or equal to EDBSYSFLOWLEV.l The current call is within the handover margin and the receive level is greater than or equal

to OUTINNREXLEVTHRED.When all the preceding conditions are met, the handover due to low load in the UL cell istriggered.If the load of the UL subcell in the cell is smaller than OUTLOWLOADTHRED for a specifiedperiod, the handover margin is adjusted in a period of INNLOADHOPERI. The step length forhandover margin adjustment is specified by INNLOADHOSTEP.

Trigger Conditions for a Handover Due to MS Movement to the Border of theOverlaid Cell

The trigger conditions for a handover due to MS movement to the border of the OL cell are asfollows:l SS(s) < Thdouterl SS(u) SS(n) < ATCB_THRD ATCB_HYST

where, SS(s): specifies the filtering compensated downlink receive level in the serving cell. Thdouter: specifies OUTINNREXLEVTHRED. SS(u): specifies the downlink level (power compensation is performed on the downlink

level based on the measurement) of the UL subcell where the call is originated. If theSS(u) value cannot be obtained, the decision of enhanced dual-band network handoveris not performed and the decision condition is met by default.



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SS(n): The best neighboring cell is the one whose measured BCCH level is the highestamong neighboring cells. SS(n) is the signal level of the best neighboring cell that workson the same frequency band, locates at the same layer, and has the same priority as theUL cell but is not co-sited with the UL cell. If such a neighboring cell is not available,the value of SS(n) is 110 dBm. ATCB_THRD: specifies ATCBTHRED. ATCB_HYST: specifies ATCBHYST.

Handover due to MS movement to the border of the OL cell is triggered if either of thepreceding conditions is met.

NOTEl In the Adapter distance To Cell Border (ATCB) handover algorithm, the border between the OL and

UL subcells is determined according to the signal strength of the serving cell and that of neighboringcells. If SS(s) = SS(n), the system considers that the MS is located at the border of the UL cell. If SS(s) SS(n) > ATCB_THRD, the system considers that the MS is located in the coverage area of theOL subcell. The coverage area of the OL subcell is determined according to different networking andcoverage conditions of the existing network. In addition, the OL subcell of the serving cell and the OLsubcell of the neighboring cells will not overlap regardless of the distance between BTSs.

l The handover margin specifies the range of signal level. In the case of OL/UL load handover on theenhanced dual-band network, the MSs whose downlink levels are within the handover margin arehanded over level by level.

Target Cell SelectionThe requirements for target cell selection in the enhanced dual-band network are as follows:l For the handover due to high load in the UL cell, the MS must be handed over to the OL

cell.l For the handover due to low load in the UL cell, the MS must be handed over to the UL

cell.l For the handover due to MS movement to the border of the OL cell, the MS is handed over

to the neighboring cell that ranks first among neighboring cells. The MS should not behanded over to the cell that ranks after the serving cell. Generally, the target cell is the ULcell. The target cell can also be another neighboring cell.

LimitationsThe limitations on the handover due to high load in the UL cell are as follows:l If the cell where the call is located is on an enhanced dual-band network, CELLINEXTP

is set to Extra(Extra).l The OUTLOADHOENABLE parameter should be set.l The maximum range of the handover margin is from 63 to INTOINNREXLEVTHRED.

The MS with the highest receive level is handed over first.The limitations on the handover due to low load in the UL cell are as follows:l If the cell where the call is located is on the enhanced dual-band network,

CELLINEXTP is set to Inner(Inner).l The INNLOADHOEN parameter should be set.l The maximum range of the handover margin is from 63 to OUTINNREXLEVTHRED.

The MS with the lowest receive level is handed over first.The limitations on the handover due to MS movement to the border of the OL cell are as follows:



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l If the cell where the call is located is on the enhanced dual-band network,CELLINEXTP is set to Inner(Inner).

Impact of the Enhanced Dual-Band Network Handover on the Existing AlgorithmThe impact of the enhanced dual-band network handover on the existing algorithm is as follows:l On the enhanced dual-band network, the MS should not be handed over to a cell in the

same UL/OL cell group when the load handovers between the OL cell and the UL cell(specified by OUTLOADHOENABLE and INNLOADHOEN) are allowed. This is toprevent a load handover of a normal cell from colliding with a load handover between theOL cell and the UL cell on the network.

l The PBGT handover algorithm may cause inter-cell handovers. Therefore, to avoid ping-pong handovers, PBGT handovers are restricted in either of the following conditions: When INNLOADHOEN is set to YES(Yes), PBGT handovers from the underlaid

subcell to the overlaid subcell are prohibited. When OUTLOADHOENABLE is set to YES(Yes), PBGT handovers from the overlaid

subcell to the underlaid subcell are prohibited.

3.4.8 Load HandoverIn the network, some cells carry heavy load whereas the overlapping upper-layer cells and theneighboring cells may carry light load. The load handover is required to balance the load of thesecells.In a load handover procedure, some load in heavy-load cells is switched to light-load cells.Meanwhile, the load in neighboring cells is not switched to heavy-load cells.Load handover can be performed between cells at different layers. Figure 3-3 shows the details.

NOTEFor details about the inter-RAT load handover, see theInteroperability Between GSM and WCDMAFeature Parameter Description.

Figure 3-3 Load h.andover between cells

To perform load sharing, increase DLEDGETHRES so that the load at the border of a cell isswitched to a neighboring cell with light load.Whether a cell carries heavy load or light load is determined by the traffic volume in the cell,that is whether the traffic volume (generally TCH usage) in the cell exceeds the preset threshold.



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The TCH usage is calculated using the following formula:TCH usage = (Number of occupied TCHFs x 2 + Number of occupied TCHHs)/(Number ofavailable TCHFs x 2 + Number of available TCHHs)whereNumber of available TCHHs is the sum of idle and occupied TCHHs.Number of available TCHFs is the sum of idle and occupied TCHFs.l If the traffic volume in a cell is greater than TRIGTHRES, the load in this cell is heavy.

The load handover algorithm needs to be enabled.l If the traffic volume in a cell is smaller than LoadAccThres, the load in this cell is light

and the cell can receive load from the heavy-load cells.Load handover may lead to many handovers. Therefore, the load of the system CPU should beconsidered before load handover is performed. In other words, the system traffic volume shouldbe taken into account. In addition, to prevent too many MSs from being handed over at a time,load handover is performed step by step. In other words, the edge handover threshold is increasedon the basis of LOADHOSTEP (CLS_Ramp) and LOADHOPERIOD (CLS_Period). When theincrease in the edge handover threshold equals LOADOFFSET (CLS_Offset), the edgehandover threshold is not increased any more. See Figure 3-4 for details.

Figure 3-4 Load handover

Trigger ConditionsIf LoadHoEn is set to YES(Yes), the trigger conditions for a load handover are as follows:l The CPU usage of the system is less than or equal to SYSFLOWLEV.l The current load of the serving cell is greater than or equal to TRIGTHRES.

Target Cell SelectionThe conditions for selecting the target cell are as follows:l Filtered receive level after handover penalty HOTHRES + INTELEVHOHYST 64l The serving cell cannot be selected as the target cell.l If the target cell and the serving cell are in the same BSC, a load handover is performed

when the current load of the target cell is smaller than LoadAccThres.



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l If the target cell and the serving cell are not in the same BSC, a load handover is performedwhen the load of the target cell is smaller than LoadAccThres and OutBscLoadHoEn isset to YES(Yes).

Load Handover ProcessFigure 3-5 shows the load handover process.

Figure 3-5 Load handover process

ExamplesThe system assigns MSs to different load handover margins based on the downlink receive level.The load handover algorithm is used to hand over the MSs out of a cell step by step.



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1. The MSs in load handover margin 1 are handed over to the neighboring cells. Load handovermargin 1 specifies the area where the downlink level ranges from DLEDGETHRES to thesum of DLEDGETHRES and LOADHOSTEP.

2. After a LOADHOPERIOD elapses, the MSs in load handover margin 2 are handed overto the neighboring cells. Load handover margin 2 specifies the area where the downlinklevel ranges from DLEDGETHRES to the sum of DLEDGETHRES and (2 xLOADHOSTEP).

3. The load handover stops when the traffic volume in the cell is less than or equal toTRIGTHRES.

The load handover is performed step by step to prevent call drops caused by a sudden increasein CPU load or the congestion in the target cell.

3.4.9 Enhanced Load HandoverLike the load handover, the enhanced load handover is used to balance load of cells in a network.Unlike the load handover, the enhanced load handover considers the handover quality and theload in the target cell before the handover is performed. In this way, the possibility of low leveland congestion due to heavy load in the target cell after the handover is minimized. The enhancedload handover is applicable to the scenario where multiple base stations are located at the sameplace.

Trigger Conditions for an Enhanced Load HandoverIf LOADHOAD is set to YES(YES), the trigger conditions for an enhanced load handover areas follows:l The CPU usage of the current system is smaller than or equal to SYSFLOWLEV.l The load of the serving cell is greater than TRIGTHRES.Here, the load of the serving cell is expressed in the percentage of the channels that are occupied.If the built-in PCU is used, the calculation method of the cell load depends on the setting ofLOADSTATYPE. The setting of the parameter determines whether the dynamic PDCHs thatcan be preempted are considered as occupied channels.l When LOADSTATYPE is set to NODYNPDCH(Not count dynamic PDCH), the

dynamic PDCHs that can be preempted are not considered in the cell load.l When LOADSTATYPE is set to DYNPDCHASOCCUPY(Count dynamic PDCH

(Occupy)), the dynamic PDCHs that can be preempted are considered as occupied TCHsin the cell load.

l When LOADSTATYPE is set to DYNPDCHASIDLE(Count dynamic PDCH(Idle)), thedynamic PDCHs that can be preempted are considered as idle TCHs in the cell load.

The number of the dynamic PDCHs that can be preempted depends on the number of dynamicPDCHs and DYNCHNPREEMPTLEV. The number of dynamic PDCHs is the total number ofchannels whose CHTYPE is set to FULLTCH.If the external PCU is used, the number of the dynamic PDCHs that can be preempted is alwayszero. The setting of LOADSTATYPE is irrelevant to calculation of the cell load.

Target Cell SelectionWhen a candidate cell satisfying the following conditions is found and not a single MS withinthe range specified by LOADHOUSRRATIO is handed over to the target cell, further search of



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the target cell is stopped and current traffic is handed over to the candidate cell. The detailedconditions for selecting the target cell are as follows:l The value of LOADHOPBGTMARGIN is not 0 and the path loss in the serving cell minus

that in the target cell is larger than LOADHOPBGTMARGIN.l The load of the target cell is smaller than LoadAccThres.l The receive level of the target cell is greater than HOTHRES of the target cell plus

INTELEVHOHYST of the handover from the serving cell to the target cell.l Of all the MSs that are within the range specified by LOADHOUSRRATIO and meet the

preceding conditions, only one MS can initiate the handover at a time. This regulationprevents too many MSs from being handed over to the target cell at one time and avoidscongestion in the target cell.

3.4.10 Edge HandoverEdge handover is performed on the basis of receive level.To trigger an edge handover, the receive level of the target cell should be at least one hysteresisvalue (specified by INTERCELLHYST 64) greater than the receive level of the serving cell.

Trigger ConditionsIf FRINGEHOEN is set to YES(Yes) and EDOUTHOADEN is set to NO(No), the triggerconditions for an edge handover are as follows:l Either of the following conditions is met:

The filtered downlink receive level of the serving cell after compensation is smallerthan DLEDGETHRES. The filtered uplink receive level of the serving cell after compensation is smaller than

ULEDGETHRES.l Filtered d ownlink receive level of a neighboring cell after power control compensation >

Receive level of the serving cell + (INTERCELLHYST 64).An edge handover is triggered when the P/N criterion is met, that is, when the previous conditionsare met for EDGELAST1 within EDGESTAT1.If both FRINGEHOEN and EDOUTHOADEN are set to YES(Yes), the trigger conditions foran edge handover are as follows:l Either of the following conditions is met:

Filtered downlink receive level of the serving cell after compensation PBGT_HO_MARGINwhere, RXLEV_DL: indicates the filtered downlink receive level of the serving cell. MS_TXPWR_MAX: indicates the maximum allowed transmit power of an MS in the

serving cell. MS_TXPWR_MAX (n): indicates the maximum allowed transmit power of an MS in

neighboring cell n. RxLev_NCELL (n): indicates the downlink receive level in neighboring cell n. PWR_DIFF: indicates the difference between the maximum downlink transmit power

in the serving cell due to power control and the actual downlink transmit power in theserving cell. P: indicates the maximum transmit power of an MS. PBGT_HO_MARGIN: indicates the PBGTMARGIN of the serving cell configured for

neighboring cells minus 64.If NCELLPUNEN is set to NO(No) for the target cell, a PBGT handover is triggered when theprevious conditions are met.If NCELLPUNEN is set to YES(Yes) for the target cell, the timer NCELLPUNTM is startedwhen the previous conditions are met. After the timer is started, the value ofNCELLPUNLEV is subtracted from the filtered receive level of the target cell. If the timerexpires, a PBGT handover is triggered. If the timer stops, no PBGT handover is triggered. Thetimer stops in either of the following cases:l If the filtered BCCH receive level of the target cell is smaller than the value of

NCELLPUNSTPTH, the timer stops for the target cell.l If the trigger conditions for a BQ handover are met, the timer for all handover candidate

cells stops.

Target Cell SelectionThe target cell must meet the following conditions:l The target cell and the serving cell are at the same layer and have the same priority.l The serving cell cannot be selected as the target cell.l The target cell has the highest priority in the candidate cell list.

3.4.14 AMR HandoverThis section describes the feature GBFD-115504 AMR FR/HR Dynamic Adjustment.The AMR handover in handover I algorithm consists of the AMR TCHF-TCHH handover andAMR TCHH-TCHF handover algorithm. The AMR TCHF-TCHH handover is conducted basedon cell load and RQI, whereas the AMR TCHH-TCHF handover is conducted based on RQI.The conversion formula between RQI and C/I is RQI = 2 x C/I.The handover I algorithm also supports dynamic adjustment between TCHFs and TCHHs. Fordetails, see section 3.5.11 "Handover Between a Full-Rate TCH and a Half-Rate TCH." Thissection describes the AMR handover in handover I algorithm.



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Trigger Conditions for an AMR TCHF-TCHH HandoverThe trigger conditions for an AMR TCHF-TCHH handover are as follows:l INTRACELLFHHOEN is set to YES(Yes).l The target call is an AMR call.l The half-rate function must be enabled in the cell where the call is initiated.l The full-rate speech version 3 and half-rate speech version 3 must be supported by the cell

where the call is initiated.l The type of channel specified by the MSC during a call can be changed during a handover.l For AMR FR calls, if the parameter AMRTCHHPRIORALLOW is set to ON(On), TCHF-

to-TCHH handover is triggered when the cell load is greater than the value for the parameterAMRTCHHPRIORLOAD and the proportion of AMR HR users is smaller than the valuefor the parameter ALLOWAMRHALFRATEUSERPERC.

l For AMR FR calls, if the parameter AMRTCHHPRIORALLOW is set to OFF(Off),TCHF-to-TCHH handover is triggered when the proportion of AMR HR users is smallerthan the value for the parameter ALLOWAMRHALFRATEUSERPERC.

l The call occupies the full-rate TCH, and the RQI/2 is greater than INHOF2HTH.For an AMR FR call, the AMR TCHF-TCHH handover can be performed if the precedingconditions are met for INFHHOLAST within INFHHOSTAT.

Trigger Conditions for an AMR TCHH-TCHF HandoverThe trigger conditions for an AMR TCHH-TCHF handover are as follows:l INTRACELLFHHOEN is set to YES(Yes).l The target call is an AMR call.l The half-rate function must be enabled in the cell where the call is initiated.l The full-rate speech version 3 and half-rate speech version 3 must be supported by the cell

where the call is initiated.l The type of channel specified by the MSC during a call can be changed during a handover.l The call occupies the half-rate TCH, and the RQI/2 is smaller than INHOH2FTH.For an AMR HR call, the AMR TCHH-TCHF handover can be performed if the precedingconditions are met for INFHHOLAST within INFHHOSTAT.

NOTE

l If INTRACELLSINUSEREN is set to NO(No), no intra-cell handover is allowed within the timespecified by BANTIME when multiple intra-cell handovers are performed consecutively.

l If INTRACELLSINUSEREN is set to YES(Yes), no quality-related intra-cell handovers (such as BQhandover, interference handover, TCHH-to-TCHH handover, and tight BCCH handover) is allowedwithin the time specified by BANTIME whenthe same MS consecutively performs multiple such typesof handovers.

Target Cell SelectionThe AMR handover is an intra-cell handover. Therefore, only the serving cell can be selectedas the target cell.



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3.4.15 SDCCH HandoverThis section describes the feature GBFD-110608 SDCCH Handover.SDCCH handover is a process in which the MS is handed over from an SDCCH to anotherSDCCH in an immediate assignment. SDCCH handover helps improve the access success rateof the MSs on the edge of the network, improving the network QoS.The principle of SDCCH handover is the same as that of TCH handover. Regarding procedure,an SDCCH handover involves measurement and MR reporting, MR processing, handoverdecision, and handover execution.Whether an SDCCH handover can be performed is controlled by the SIGCHANHOENparameter. If an inter-BSC SDCCH handover is required, both SIGCHANHOEN andINRBSCSDHOEN should be set to YES(Yes).The handover decision algorithm for SDCCH handover is different from that for TCH handoverin the following ways:l The algorithms for the following handovers support SDCCH handover:

Quick handover, TA handover, BQ handover, rapid level drop handover, interferencehandover, handover due to no downlink measurement report, Inter-layer handover ,edgehandover, and fast-moving micro cell handover

l The algorithms for the following handovers do not support SDCCH handover:Dual-band network handover, load handover, PBGT handover, AMR handover, better 3Gcell handover, concentric cell handover, and tight BCCH handover

3.4.16 Other HandoversOther handovers here refer to better 3G cell handover and tight BCCH handover.

Better 3G Cell HandoverSee the Interoperability Between GSM and WCDMA Feature Parameter Description

Tight BCCH HandoverSee the BCCH Dense Frequency Multiplexing Feature Parameter Description

3.5 Handover Decision Based on Handover Algorithm IIThis section describes the feature GBFD-510501 HUAWEI II Handover.Handover decision based on handover algorithm II is made in the following order: forcedhandover, emergency handover, intra-cell handover, and inter-cell handover.Handover decision based on handover algorithm II involves the following procedures:l Determines whether the serving cell meets the trigger conditions.l Selects corresponding candidate cell list for each handover type.l Performs the comprehensive decision and determining the candidate neighboring cells.The procedure for performing comprehensive decision based on handover results anddetermining the candidate neighboring cells is as follows:



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1. The BSC selects a handover type with the highest priority from all the handovers that canbe performed on each neighboring cell.The handover priority is as follows:l Forced handover, emergency handover, and interference handover have a high priority.

Figure 3-10 shows the details.

Figure 3-10 Handovers with high priority

NOTE

Quick handover is classified into frequency offset handover and quick PBGT handover. Frequencyoffset handover has a higher priorit

Handover(GBSS14.0)

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