Handover Algorithm Complete and Detailed

Huawei Handover Algorithm

HUAWEI TECHNOLOGIES CO., LTD.

Huawei Handover Algorithm(GSM BSS)

6/05/2009


Table of Contents

1 Overview .............................................................................7

1.1 Background Introduction .................................................................................................. 7

1.2 Introduction to the Principles of Handover Algorithms ...................................................7

1.2.1 Procedures Related to Handover Algorithms ...................................................................7

1.2.2 MR Processing .................................................................................................................8

1.3 Handover Decision Algorithms ...................................................................................... 11

1.3.1 High-Speed Railway Fast Handover .............................................................................. 11

1.3.2 Emergency Handover .....................................................................................................12

1.3.3 Enhanced Dual-Band Handover .....................................................................................12

1.3.4 Load Handover ...............................................................................................................12

1.3.5 Normal Handover ...........................................................................................................12

1.3.6 No Downlink Measurement Report Handover ...............................................................15

1.3.7 Penalty Processing..........................................................................................................16

1.3.8 Triggering Conditions of Penalty ...................................................................................18

1.3.9 Penalty Processing..........................................................................................................18

1.3.10 Basic Queuing ................................................................................................................ 19

1.3.11 Network Characteristics Adjustment ..............................................................................23

1.3.12 Forced Handover ............................................................................................................27

1.3.13 Handover Decision .........................................................................................................28

1.3.14 Emergency Handover .....................................................................................................28

1.3.15 TA Handover ..................................................................................................................28

1.3.16 Interference Handover ....................................................................................................30

1.3.17 Quick Level Drop Handover ..........................................................................................32

1.3.18 Bad Quality Handover ....................................................................................................34

1.3.19 Load Handover...............................................................................................................37

1.3.20 Normal Handover ...........................................................................................................39

1.3.21 Edge Handover ...............................................................................................................40

1.3.22 Fast-Moving Micro-to-Macro Cell Handover ................................................................ 42

1.3.23 Hierarchical Handover ...................................................................................................44

1.3.24 PBGT Handover .............................................................................................................45

1.3.25 Concentric Cell Handover ..............................................................................................49

1.3.26 Normal Concentric Cell Algorithm ................................................................................ 49

1.3.27 Enhanced Concentric Cell Algorithm .............................................................................49

1.3.28 AMR Handover ..............................................................................................................53

1.3.29 Handover from TCHF to TCHH ....................................................................................54

1.3.30 Handover form TCHH to TCHF ....................................................................................54

1.3.31 Better 3G Cell Handover ................................................................................................ 55

1.3.32 Directed Retry ................................................................................................................ 57

1.3.33 Handover in Single-Signaling /SDCCH State................................................................ 57


1.3.34 Handover Implementation ..............................................................................................57

2 Parameters Involved in the Algorithms................................... 58

2.1 Parameters detail description..........................................................................................58

2.1.1 Co-BSC/MSC Adj ..........................................................................................................58

2.1.2 SDCCH HO Allowed .....................................................................................................58

2.1.3 Penalty Allowed .............................................................................................................59

2.1.4 MS Power Prediction after HO.......................................................................................59

2.1.5 Power Level for Direct Try ............................................................................................60

2.1.6 Allowed MR Number Lost .............................................................................................60

2.1.7 RscPenaltyTimer ............................................................................................................61

2.1.8 UmPenaltyTimer ............................................................................................................61

2.1.9 CfgPenaltyTimer ............................................................................................................61

2.1.10 MR Preprocessing ..........................................................................................................62

2.1.11 Transfer Original MR .....................................................................................................62

2.1.12 Transfer BS/MS Power Class .........................................................................................63

2.1.13 Sent Freq of Preprocessed MR .......................................................................................63

2.1.14 Report Type ....................................................................................................................64

2.1.15 DtxMeasUsed .................................................................................................................64

2.1.16 Allowed MR Number Lost .............................................................................................65

2.1.17 Filter Length for SDCCH Level .....................................................................................65

2.1.18 Filter Length for TCH Level ..........................................................................................65

2.1.19 Filter Length for SDCCH Qual ......................................................................................66

2.1.20 Filter Length for TCH Qual............................................................................................66

2.1.21 Filter Length for TA .......................................................................................................67

2.1.22 Filter Length for Ncell RX_LEV ...................................................................................67

2.1.23 Penalty Level after TA HO .............................................................................................68

2.1.24 Penalty Time after TA HO(s) ..........................................................................................68

2.1.25 Penalty Level after BQ HO ............................................................................................69

2.1.26 Penalty Time after BQ HO (s) ........................................................................................69

2.1.27 Penalty Level after HO Fail............................................................................................70

2.1.28 Penalty Time after HO Fail(s) ........................................................................................70

2.1.29 Penalty on MS Fast Moving HO ....................................................................................71

2.1.30 Penalty Time on Fast Moving HO..................................................................................71

2.1.31 Quick Handover Punish Value ........................................................................................72

2.1.32 Quick Handover Punish Time ........................................................................................72

2.1.33 Inter-BSC SDCCH HO Allowed ....................................................................................72

2.1.34 Min DL Level on Candidate Cell ...................................................................................73

2.1.35 HOCdCellMinUpPwr .....................................................................................................73

2.1.36 Min Access Level Offset ................................................................................................ 74

2.1.37 K Bias .............................................................................................................................74

2.1.38 UTRAN Cell Type..........................................................................................................75


2.1.39 FDD REP QUANT.........................................................................................................75

2.1.40 Min RSCP Threshold .....................................................................................................76

2.1.41 Min Ec/No Threshold .....................................................................................................76

2.1.42 RSCPOff.........................................................................................................................77

2.1.43 EcNoOff .........................................................................................................................77

2.1.44 Inter-layer HO Threshold ...............................................................................................77

2.1.45 Inter-layer HO Hysteresis...............................................................................................78

2.1.46 Inter-cell Handover Hysteresis .......................................................................................78

2.1.47 Min Interval for TCH Hos..............................................................................................79

2.1.48 Min Interval for SDCCH Hos ........................................................................................79

2.1.49 Min Interval for Consecutive Hos ..................................................................................80

2.1.50 Min Interval for Emerg Hos ...........................................................................................80

2.1.51 MS Fast-moving Time Threshold...................................................................................81

2.1.52 Max Consecutive HO Times ..........................................................................................81

2.1.53 Forbidden Time after Max Times ...................................................................................82

2.1.54 Interval for Consecutive HO Jud. ...................................................................................82

2.1.55 DtxMeasUsed .................................................................................................................83

2.1.56 Max Resend Times of Phy Info ......................................................................................83

2.1.57 T3105 (10ms) .................................................................................................................84

2.1.58 No Dl Mr. HO Allowed ..................................................................................................85

2.1.59 Cons. No Dl Mr. HO Allowed Limit ..............................................................................85

2.1.60 No Dl Mr. Ul Qual HO Limit .........................................................................................86

2.1.61 TA HO Allowed..............................................................................................................87

2.1.62 TA Threshold ..................................................................................................................87

2.1.63 Interference HO Allowed ...............................................................................................87

2.1.64 RXQUAL1 .....................................................................................................................88

2.1.65 RXQUAL2 .....................................................................................................................88

2.1.66 RXQUAL3 .....................................................................................................................88

2.1.67 RXQUAL4 .....................................................................................................................89

2.1.68 RXQUAL5 .....................................................................................................................89

2.1.69 RXQUAL6 .....................................................................................................................90

2.1.70 RXQUAL7 .....................................................................................................................90

2.1.71 RXQUAL8 .....................................................................................................................90

2.1.72 RXQUAL9 .....................................................................................................................91

2.1.73 RXQUAL10 ...................................................................................................................91

2.1.74 RXQUAL11 ...................................................................................................................92

2.1.75 RXQUAL12 ...................................................................................................................92

2.1.76 RXLEVOff .....................................................................................................................92

2.1.77 Intracell HO Allowed .....................................................................................................93

2.1.78 Rx_Level_Drop HO Allowed.........................................................................................93

2.1.79 Filter Parameter A1A8..................................................................................................93

2.1.80 Filter Parameter B ..........................................................................................................94


2.1.81 BQ HO Allowed .............................................................................................................94

2.1.82 DLQuaLimitAMRFR .....................................................................................................95

2.1.83 ULQuaLimitAMRFR .....................................................................................................95

2.1.84 DLQuaLimitAMRHR ....................................................................................................95

2.1.85 ULQuaLimitAMRHR ....................................................................................................96

2.1.86 DL Qual. Threshold ........................................................................................................ 96

2.1.87 UL Qual. Threshold ........................................................................................................ 97

2.1.88 BQ HO Margin ...............................................................................................................97

2.1.89 Load HO Allowed ..........................................................................................................97

2.1.90 System Flux Threshold for Load HO .............................................................................98

2.1.91 Load HO Threshold ........................................................................................................ 98

2.1.92 Load HO Step Period .....................................................................................................99

2.1.93 Load HO Step Level .......................................................................................................99

2.1.94 Load HO Bandwidth .................................................................................................... 100

2.1.95 Load Req. on Candidate Cell ....................................................................................... 100

2.1.96 Edge HO Allowed ........................................................................................................101

2.1.97 Edge HO UL RX_LEV Threshold................................................................................101

2.1.98 Edge HO DL RX_LEV Threshold................................................................................101

2.1.99 Edge HO Watch Time(s) .............................................................................................. 102

2.1.100 Edge HO Valid Time (s) ............................................................................................... 102

2.1.101 NC Edge HO Watch Time(s) ........................................................................................103

2.1.102 NC Edge HO Valid Time (s)......................................................................................... 103

2.1.103 MS Fast Moving HO Allowed ...................................................................................... 103

2.1.104 MS Fast-moving Watch Cells....................................................................................... 104

2.1.105 MS Fast-moving Valid Cells ........................................................................................104

2.1.106 PBGT HO Allowed ...................................................................................................... 105

2.1.107 PBGT HO Threshold.................................................................................................... 105

2.1.108 PBGT Watch Time (s) .................................................................................................. 106

2.1.109 PBGT Valid Time (s) .................................................................................................... 106

2.1.110 Intracell F-H HO Allowed ............................................................................................ 106

2.1.111 Penalty Time after AMR TCHF-H HO Fails(s)............................................................ 107

2.1.112 F2H HO th.................................................................................................................... 107

2.1.113 H2F HO th.................................................................................................................... 108

2.1.114 Intracell F-H HO State Time (s) ...................................................................................108

2.1.115 Intracell F-H HO State Time (s) ...................................................................................108

2.1.116 Outgoing-RAT HO Allowed......................................................................................... 109

2.1.117 Better 3G Cell HO Allowed ......................................................................................... 109

2.1.118 TDD Better 3G Cell HO Allowed ................................................................................110

2.1.119 RSCP Threshold for Better 3G CELL HO ...................................................................110

2.1.120 TDD RSCP Threshold for Better 3G CELL HO .......................................................... 110

2.1.121 Ec/No Threshold for Better 3G CELL HO ...................................................................111

2.1.122 3G Better Cell HO Valid Time ..................................................................................... 111


2.1.123 3G Better Cell HO Watch Time.................................................................................... 112

2.1.124 TDD 3G Better Cell HO Valid Time ............................................................................ 112

2.1.125 TDD 3G Better Cell HO Watch Time...........................................................................113

2.1.126 Inter-RAT HO Preference............................................................................................. 113

2.1.127 Inter-RAT HO Preference............................................................................................. 114

2.1.128 TDD Inter-RAT HO Preference.................................................................................... 114

2.1.129 HO Preference Threshold for 2G Cell .......................................................................... 115

2.1.130 TDD HO Preference Threshold for 2G Cell................................................................. 116


1 Overview

1.1 Background Introduction

The service area of the GSM is composed of the cells with continuous coverage. To enable the

users in move to communicate without interruption and to optimize the network performance, the

handover technique is introduced to the GSM system.

The handover in the GSM system involves the following entities: Mobile Station (MS), Base Station

Subsystem (BSS), and Mobile Switching Center (MSC). The MS and BTS in service measure the

uplink and downlink radio links respectively, assemble the measurement results into measurement

reports (MRs), and then send the MRs to the BSC. The handover algorithms in the BSC decide

whether to initiate handovers based on the measurement results and the actual network

performance. The algorithms also decide in which way to process the handover.

This document describes the technical aspects of handover in Huawei BSC6000 V900R008 in

terms of algorithm principles, applications, and parameters.

1.2 Introduction to the Principles of Handover Algorithms

1.2.1 Procedures Related to Handover Algorithms

The handover algorithms of the GSM system function in the following phases: measurement and

production of the MRs, MR processing, handover algorithm decision, and handover execution.

The measurement and the production of the MRs are performed by the MS andBTS. The MS measures and reports the downlink signal level of GSM cells,signal quality, and TA, whereas the BTS measures and reports the receive signallevel of the MS and its quality. The MR processing is performed by the BSC (the BTS can perform the task if the

processing functionality is assigned to the BTS). The BSC performs basicfunctions such as filtering and interpolation. The processed MRs are the basicinputs for the handover algorithms and serve as the basis for the handoveralgorithms taking decisions. The BSC select neighbor cells based on theBCCH/BSIC information in the downlink MRs. The cells with the sameBCCH/BSIC information are removed with only one neighbor cell is retained. If aneighbor cell is not found with respect to BCCH/BSIC, you can infer that theneighbor cell is illegal, and thus the measurement values are not processed. The handover algorithms evaluate the candidate cells based on the factors such

as radio signal quality, MS speed, traffic load, and requirements from the telecomoperator, and then determine the target cells. After the target cells are determined, the handover execution part performs

signaling interaction and handles the handover failures, rollback, or otherexceptions and, if necessary, forwards the result to the handover decisionmodule and tries other candidate cells.

The following figure shows the procedures related to GSM handover algorithms.


Procedures related to handover algorithms

MS entering connectionstate

Measurement andproduction of MRs

MR processing

Algorithms makinghandover decision

Handover execution

MS entering newconnection state

Figure1

1.2.2 MR Processing

The MR processing involves interpolation processing and filtering processing. The processing

procedure of the MRs is as follows:


Processing procedure of the MRs

Start (processesMR)

MR Preprocessing enabled?

End

UL/DL DTX once enabled?

TCH measurement ofthe serving cell

(SUBSET scheme)

MR serial numbercontinuous?

Performs linear interpolationof the MRs and then insert

latest MR value

End

No

Yes

No

Insert latest MRvaluesNumber of lost MRs

(serving cell) is less thanthe value of Allowed MR

Number Lost?

Discard former MRvalues and insert latest

MR values

Number of validbuffered MRs smaller

than values of the filterlength parameters?

Yes

No

Filtering processingof MRs

Filter length parameters:

Filter Length for SDCCH LevelFilter Length for TCH LevelFilter Length for SDCCH QualFilter Length for TCH QualFilter Length for TAFilter Length for Ncell RX_LEVFilter Length for SDCCH MEAN_BEPFilter Length for TCH MEAN_BEPFilter Length for SDCCH CV_BEPFilter Length for TCH CV_BEPFilter Length for SDCCH REP_QUANTFilter Length for TCH REP_QUANT

Filter Length for SDCCH NBR_RCVD_BLOCKFilter Length for TCH NBR_RCVD_BLOCK

Specifies the contents to bereported and the period toprovide the preprocessing

report based on theconfiguration parameters

Configuration parametersof pre-processed MRs:

Enhanced MR?

Interpretation ofnormal MR

Interpretation ofenhanced MR

MR type:Enhanced MR and normal

MR

Yes

DtxMeasUsed is set to TRUE?NoYes

UL/DL DTX enabled?

Switch for controlling the valuedetermination method of MR:

DtxMeasUsed

Allowed MR Number Lost

Yes

YesNo

No

No

No

Yes


(FULLSET scheme)

Yes

TCH measurement ofthe serving celll

(SUBSET scheme)


(FULLSET scheme)

MR Preprocessing

Transfer Original MR

Transfer BS/MS Power Class

Sent Freq of Preprocessed MR


The processing of the MRs involves interpolation processing and filtering processing. The

processing can be performed either on the BSC side or on the BTS side. In the BSC6000 LMT, set

MR Preprocessing to Yes, then you can set the parameters Transfer Original MR, Transfer

BS/MS Power Class, and Sent Freq of Preprocessed MR. These parameters specify the

contents of the MRs to be provided and the period during which the MRs are provided. In this way,

the signaling throughput on the Abis interface and the CPU usage of the BSC can be decreased.

If the BTS reports the measurement result information, then the information is processed according

to the interpolation and filtering procedures.

If the BTS reports the pre-processed measurement result information, then the information is used

for handover decision directly. Note if the pre-processed MRs result contains the original MRs, then

uplink link interpolation is performed.

Selection of the MR Data

Two types of MRs are available: enhanced MR and normal MR.

The enhanced MR is a new downlink MR, reported by the MS. Compared with the normal MR,

some new measurements are added, such as BER, FER, and so on. The enhanced MR provides

the measurement information of up to 15 neighbor GSM/WCDMA cells, whereas the normal MR

provides the measurement information of 6 neighbor GSM cells at most.

In the MR, the TCH measurement of the serving cell is classified into FULLSET and SUBSET. The

FULLSET measures the TCH channels (signal receive level and quality), whereas the SUBSET

measures the channels in DTX mode (signal receive level and quality). The MRs provided by the

MS and BTS indicate whether the DTX scheme is adopted.

If DtxMeasUsed is set to TRUE, then the FULLSET or SUBSET values should be taken according

to the DTX indication bit in the MR. That is, if the MR indicates that DTX is used, then the SUBSET

values should be selected; otherwise, the FULLSET values should be selected.

If DtxMeasUsed is set to FALSE and the MR indicates that DTX is not used, the FULLSET values

should be taken; if the MR indicates that DTX is used, then the SUBSET values should be taken. In

the latter case, the SUBSET values should be used irrespective how DTX is indicated in the MR.

Interpolation Processing of the MRs

If the latest two received MR are not continuous, that is, their serial numbers are not consecutive,

then apply the interpolation as follows:

For the serving cell, when the number of lost MRs is less than the value ofAllowed MR Number Lost, then the linear interpolation of the MRs must beperformed. For a neighbor cell, the worst interpolation value in accordance with protocols

should be applied for the lost signal level measurement values; that is, level 0(-110 dBm) should be applied. For the neighbor cell with low signal level and theMR not provided, the worst interpolation value is also applicable.


If the number of lost MRs is greater than the value of Allowed MR Number Lost, then the previous

measurement values should be discarded and the recalculation should be performed on receipt of

the MRs.

The interpolation scheme applies to the following objects:

Uplink TCHs of the serving cell: RXLEV, RXQUAL, and RQIDownlink TCHs of the serving cell: RXLEV and RXQUALMRs of the serving cell that contain the information of TADownlink transmit power of the serving cell: Poff_DLReceive level of the downlink BCCHs of neighbor GSM cells: RXLEVDownlink CPICH, RSCP, and Ec/No of neighbor 3G cells

Filtering Processing of MRs

After the MRs requiring interpolation are interpolated, if the number of buffered valid MRs is smaller

than the filter length (the filters correspond to different measurement objects, signaling channel, or

traffic channel), then the filtering is not applied.

The averaging should be applied to the filtering processing. Parameters with different filter lengths

should be used during filtering on the basis of the measured values and type of the channel being

occupied. The parameter Filter length for TCH Level applied to the filtering of the downlink

transmit power of the serving cell.

The filtering scheme applies to the following objects:

Uplink TCHs of the serving cell: RXLEV, RXQUAL, and RQIDownlink TCHs of the serving cell: RXLEV and RXQUALMRs of the serving cell that contain the information of TA (optional)Downlink transmit power of the serving cellReceive level of the downlink BCCHs of neighbor GSM cells: RXLEVDownlink CPICH, RSCP, and Ec/No of neighbor 3G cells

1.3 Handover Decision Algorithms

After MRs are processed, the handover decision procedure starts. This procedure involves the

actions related to initial access, including handover protection, penalty, 16-bit queuing, forced

handover, handover decision making, processing of target 2G/3G cells, and initiation of continuous

handover.

Five types of handovers are available in terms of the triggering conditions: high-speed railway fast

handover, emergency handover, enhanced dual-band network handover, load handover, and

normal handover.

1.3.1 High-Speed Railway Fast Handover

This handover algorithm applies mainly to railway areas. The algorithm is designed in accordance


with the railway features, and thus can guarantee precision and reliable handover along the railway.

High-speed railway fast handover consists of frequency offset handover and fast PBGT handover.

1.3.2 Emergency Handover

To maintain the conversations in emergent situations (risk of calls being dropped), the handover

conditions could be less evaluated to enable the handover decision procedure being executed

quickly and the overall handover delay being shortened. As the handover conditions are evaluated

in less degree, the emergency handover algorithm produces greater error in evaluating the target

cell than that produced by other handover algorithms. In normal network operation, frequent

emergency handovers should be avoided.

Emergency handovers consist of TA handover, interference handover, quick level drop handover,

bad quality handover, no downlink measurement report handover.

1.3.3 Enhanced Dual-Band Handover

In a dual-band network, the resources in the overlaid 1800M subcell and underlaid 900M subcell

can be shared during the assignment and handover procedures. That is, the calls in the high-traffic

900M subcell can be moved to the low-traffic 1800M subcell to achieve traffic balance.

1.3.4 Load Handover

In the coverage area where several cells are neighbors to each other, the traffic might be distributed

unevenly, causing one cell or several cells being congested or blocked while the neighbor cells still

having available free channels for use. In such case, load handover is applied. Through load

handover, some calls, especially those on the edge of the high-traffic cells are moved to the

neighbor cells with low traffic volume.

The main disadvantage of load handover is that the target cells are not selected in close to the

serving cell, which is preferred in network planning. Therefore, inter-cell interference increases and

ping-pong reselection occurs. Even the ping-pong symptom can be mitigated with the introduction

of the penalty scheme, it is still unavoidable.

1.3.5 Normal Handover

Normal handover is generally used in maintaining continuous conversations. Normal handover

consists of the following types in terms of handover target and handover principles: edge handover,

fast movement handover for microcell, hierarchical handover, PGBT handover, concentric handover,

AMR handover, better 3G cell handover, and tight BCCH handover.


The 2G-to-3G handovers supported at present include TA handover, BQ handover, quick level drop

handover, interference handover, and edge handover. The handover algorithms determine whether

there are eligible neighbor 2G cells first; if there are eligible neighbor 2G cells, the following

decisions are taken according to the 2G cell list and 3G cell list:

If Inter-RAT HO Preference is set to Pre_2G_Cell and there are no eligibleneighbor 2G cells but with eligible neighbor 3G cells, then a 3G cell is preferred;otherwise, a 2G cell is selected. If Inter-RAT HO Preference is set to Pre_3G_Cell, then a 3G cell is preferred. If Inter-RAT HO Preference is set to Pre_2G_CellThres and there are no

eligible neighbor 2G cells but with eligible neighbor 3G cells, then a 3G cell ispreferred; a 3G cell is also preferred if the receive level of the first candidate 2Gcell is lower than the value of HO Preference Threshold for 2G Cell.

Additionally, in the 3G better cell handover (2G-to-3G handover), if Better 3G Cell HO Allowed is

set to Yes, then a 3G cell is preferred.

The following figure shows procedure for the handover decision algorithms.


Procedure for the handover decision algorithms

Start

Interpolation and filteringprocessing of MRs

No downlink MRhandover decision-taking

Protection ofminimum handoverinterval triggered?

HOInterTimerprotection triggered forconsecutive handover

interval?

HOInitTimer protection triggered forminimum handover interval at initial

access phase

HOInitTimer:Min Interval for TCH HosMin Interval for SDCCH HosSDCCH HO Allowed

Penaltyprocessing

Basic queuing ofcandidate cells

Network characteristicstuning for candidate cells

Forced handover processing

Other handoverdecision-takings

HOInterTimer:Min Interval for Consecutive Hos

Determines targethandover cell basedon 2G/3GHOOPtSel

and 2GOrdThres

Starts consecutivehandover protectiontimer: HOInterTimer

End

High-speed railway fasthandover decision-taking

TA handover decision

Interference handoverdecision

Rapid level drophandover decision

Emergency handover

Min Interval forEmerg Hos triggered

Enhanced dual-bandhandover decision

Load handover decision

Edge handover decision

Hierarchicalhandover decision

PBGT handoverdecision

Concentrichandover decision

Normal handover

AMR handover decision

Better 3G cellhandover decision

Tight BCCHhandover decision

2G/3GHOOPtSe:FDD: Inter-RAT HO PreferenceTDD: TDD Inter-RAT HO Preference

2GOrdThres:FDD: HO Preference Threshold

for 2G CellTDD: TDD HO Preference

Threshold for 2G Cell

End

Yes

Yes

No

No

Fast-moving microcellhandover decision

Bad quality handoverdecision


1.3.6 No Downlink Measurement Report Handover

When the Um interface degrades, the MS might fail to send the downlink MRs due to bad uplink

quality, while it can still receive downlink signals because the downlink quality is acceptable. In such

emergent situations, the network initiates the handover and moves the MS to a neighbor cell to

avoid the call being dropped. The following figure shows the procedure for the handover decision:

No downlink measurement report handover procedure

No Dl Mr. HO Allowed isset to Yes?

At least one downlink MR is reported?

Number of consecutive lostMRs = value of

Filter Length for SDCCH/TCH Qual?

No downlink MRs in theavailable MRs?

Uplink quality after filtering >= valueof No Dl Mr. Ul Qual HO Limit?

Only one eligible candidate cell is available?

The candidate cell is the servingcell?

Consecutive intracell handoverprohibited?

If the serving cell belongs to thecandidate cells, the serving cell

should be removed.

Start

No

Yes

Filter lengths for signal quality:

Filter Length for SDCCH Qual

Filter Length for TCH Level

No

No

No

No

No

Yes

Yes

Yes

Yes

Yes

Yes

No

No

Yes

Yes

Yes

Intracell HO Allowed is set to Yes ?

Forbidden Time after Max Times

EndNo downlink

measurement reporthandover is triggered.

No

No

The handover decision is triggered if the following conditions are met:

No Dl Mr. HO Allowed is set to Yes.The number of lost MRs is smaller than the value of Cons. No Dl Mr. HO Allowed

Limit.


There are no downlink measurement values available in the current MR.For TCH, the number of saved MRs with uplink receive quality value is greater than

the value of Filter Length for TCH Qual; for SDCCH, the number of saved MRswith uplink receive quality value is greater than the value of Filter Length forSDCCH Qual.

Filtered uplink receive quality value >= value of the No Dl Mr. Ul Qual HO Limit

1.3.7 Penalty Processing

To avoid the occurrence of ping-pong reselection from different handovers, the penalty mechanism

is introduced to the handovers such as TA handover, UL/DL BQ handover, fast-moving

micro-to-macro cell handover, and concentric cell handover.


Procedure for penalty processing

Penalty processingprocedure starts

Penalty applied to all2G candidate cells is

completed?

End

No

The TA penalty timerfor the neighbor cell

has not expired?No

Yes

Yes

Acutal signal level of theneighbor cell = measured signal

level of the neighbor cell -ucSSTAPunish

Penalty applied to all3G candidate cells is

completed?

This is the neighbor cell towhich the latest handoverfails. The handover failure

penalty timer has not expired?

No Yes

No

Yes

ucSSTAPunish:Penalty Level after TA HO

TA penalty duration:Penalty Time after TA HO(s)

ucSSBQPunish:Penalty Level after BQ HOBQ penalty duration:

Penalty Time after BQ HO

ucFailSigStrPunish:Penalty Level after HO FailHandover failure penalty duration:

Penalty Time after HO Fail

ucSpeedPunish:Penalty on MS Fast Moving HO

Speed penalty duration:Penalty Time on Fast Moving HO

ucQuickHoPunishValue:Quick Handover Punish Value

Frequency offset handoverpenalty duration:

Quick Handover Punish Time

ucFailSigStrPunish:Penalty Level after HO FailHandover failure penalty duration:Penalty Time after HO Fail (s)

After frequency offsethandover succeeds, the

penalty timer for the old cellhas not expired.

No

Yes

The BQ penalty timerfor the neighbor cell

has not expired?No

Yes

This is the neighbor cell to whichthe latest handover fails. Thehandover failure penalty timer

has not expired?No

Yes

After fast movement handoversucceeds, the speed penaltytimer for the old cell has not

expired.No

Yes

Acutal signal level of the neighborcell = measured signal level of the

neighbor cell - ucSSBQPunish

Acutal signal level of the neighborcell = measured signal level of theneighbor cell - ucFailSigStrPunish

Actual signal level of the neighborcell= measured signal level of theneighbor cell - ucSpeedPunish.

Actual signal level of theneighbor cell= measured

signal level of the neighborcell - ucFailSigStrPunish

Actual signal level of the neighborcell= measured signal level of the

neighbor cell -ucQuickHoPunishValue


1.3.8 Triggering Conditions of Penalty

Provided that the periodic MRs are received, the penalty should be introduced when the latest

handover succeeds or fails and the penalty procedure should start before the penalty timer expires.

The penalty scheme applies to the following situations:

An emergency handover caused by higher TA value succeeds;An emergency handover caused by bad uplink quality succeeds;An emergency handover caused by bad downlink quality succeeds;Penalty after handover fails, including the handovers to 2G cells and the handovers to

3G cellsPenalty on the microcell from which a fast-moving MS is handed over to the

macrocell;A high-speed railway fast handover succeeds;An overlaid-to-underlaid handover succeeds;An overlaid-to-underlaid handover or underlaid-to-overlaid handover fails;

1.3.9 Penalty Processing

After the latest emergency handover is triggered due to higher TA value, the TApenalty timer is started, the duration being Penalty Time after TA HO(s). If theemergency handover succeeds, then the MS in the target cell (serving cell) shallqueue, within the penalty duration, the neighbor cells among which the actualreceive level of the old cell should be subtracted with the value of Penalty Levelafter TA HO. This enables the queuing priority of the old cell to be decreased. Ifthe emergency handover fails, then the MS in the current serving cell shall queue,within the penalty duration, the neighbor cells among which the actual receivelevel of the target cell should be subtracted with the value of Penalty Level afterTA HO. This enables the queuing priority of the target cell to be decreased andthus avoids unnecessary handover and handover failures.

After the latest UL/DL bad quality emergency handover (after an interferencehandover is triggered, the cause value is bad quality handover) or outgoing MSCforced handover is triggered, the bad quality penalty timer is started, the durationbeing Penalty Time after BQ HO (s). The MS in the target cell (serving cell) shallqueue, within the penalty duration, the neighbor cells among which the actualreceive level of the old cell should be subtracted with the value of Penalty Levelafter BQ HO. This enables the queuing priority of the old cell to be decreasedand thus avoids ping-pong handovers.

After the latest handover to a neighbor 2G or 3G cell fails, the 2G/3G handoverpenalty timer is started, the duration being Penalty Time after HO Fail(s). TheMS in the serving cell shall queue, within the penalty duration, the neighbor cellsamong which the actual receive level of the target cell should be subtracted withthe value of Penalty Level after HO Fail. This enables the queuing priority of thetarget cell to be decreased and avoids further handover failures.

If the serving cell belongs to the highest layer (layer 4) defined by Cell Layer, and thecause for the previous handover is fast-moving, then the speed penalty timer forthe neighbor cells is started, the duration being Penalty Time on Fast MovingHO. The MS in the serving cell shall queue, within the penalty duration, thenon-layer 4 neighbor cells whose actual receive level should be subtracted with


the value of Penalty on MS Fast Moving HO. This enables the queuing priorityof the target cell to be decreased and avoids handovers to microcells (non-layer 4neighbor cells).

If the latest handover is a high-speed railway fast handover, then the penalty timer isstarted, the duration being Quick Handover Punish Time. The MS in the targetcell (serving cell) shall queue, within the penalty duration, the neighbor cellsamong which the actual receive level of the old cell should be subtracted with theQuick Handover Punish Value. This enables the queuing priority of the old cell tobe decreased and avoids ping-pong handover.

If the latest overlaid-to-underlaid handover is triggered, then the penalty timer isstarted, the duration being Penalty Time of UtoO HO(s). Within the penaltyduration, the MS is not allowed to be handed over to the overlaid subcell. For theenhanced dual-band network, if the overlaid-to-underlaid handover is trigged withnormal handover cause or OtoU handover cause, then the penalty timer isstarted, the duration being Inn Out Cell HO Penalty Time. Within the penaltyduration, the underlaid-to-overlaid handover is not allowed.

If the latest overlaid-to-underlaid or underlaid-to-overlaid handover fails, then thehandover failure penalty timer is started, the duration being Penalty Time afterOtoU HO Fails(s)/Penalty Time after UtoO HO Fails(s). Within the penaltyduration, the overlaid-to-underlaid or underlaid-to-overlaid handover is notallowed.

1.3.10 Basic Queuing

The purpose of basic queuing is to produce the candidate cell list with the following information

taken into account: neighbor cell information after penalty processing, parameters contained in the

MRs, such as the signal level of the serving cell and neighbor cells, hysteresis, usage of TCHs in

the neighbor cells, and so on.

The basic queuing module functions in accordance with the M criterion and K criterion.


Processing procedure for the M criterion

Processing of Mcriterion starts.

Inter-BSC SDCCH HOAllowed is set to Yes?

Remove this cell fromthe candidate cell list.

Yes

Yes

Yes

No

No

This is a BSC external cell.The occupied channel is a

SDCCH?

No

Yes

Direct retry?

No

No

Whether the cell isoverloaded? If so, removethe cell from the candidate

cell list.

Downlink signal level of the candidate cell< HOCdCellMinDwPwr + MCriteriaOffset?

Remove the cellfrom the candidate

cell list.

Uplink signal level of the candidate cell =TrigThres

TrigThres: Load HO ThresholdAccThres: Load Req. onCandidate Cell

YES

Load bit of servingcell set to 1

NO

Load bit of servingcell set to 0

NO

Load of neighbor cell > =AccThres

YES NO

Load bit of neighborcell set to 1

Load bit of neighborcell set to 0

Co-BSC or not?YES NO

Co-MSC or not?YES NO

Different BSC: BIT 12set to 1

Different MSC: BIT 13set to 1

Serving cell or not?YES NO

DL RXLEV of the serving cell < ucLevThr -ucLevHyst

YES NO

Serving cell: BIT 14set to 1

BIT 5-13 set to 0

DL RXLEV of the neighbor cell = value of TA Threshold.

If the TA decision is allowed, the candidate cell selection is performed. The serving cell is removed. If the handover is triggered because the TA is too high, the co-site neighbor cells

that meet the following conditions are removed:


TA Threshold of the neighbor cell 3G handover, the 2G->3Ghandover is performed directly. If no eligible neighbor 3G cell available or if the 2G -> 3G handover is not allowed

because of the system parameter configuration and the MS capability, then thesubsequent decision on another emergency handover type is performed. If the TA handover decision is not allowed, then the subsequent decision on

another emergency handover type is performed.The following figure shows the procedure for the TA handover decision.


Procedure for the TA handover decision

s_TA: filtered TA of the serving cellTAlimit: TA Threshold

SYS_HO: Outgoing-RAT HOAllowed

Start

Whether a 2G/3G candidate cellexists?

NO

YES

TA_HO YES or NO?NO

s_TA>=TAlimit?

YES

End

NO

YES

Whether a 2G candidate cellexists?

NO

Eligible 2G target cellexists?

YES NO

SYS_HO is YES, a neighbor 3Gcell exists, and MS supports inter-

RAT handover?

End

NO

YES

YES

TA_HO: TA HO Allowed

TA handoverinitiation

Inter-RAThandover

Serving cell or not?YES

YES

NO

NO

Candidate cellqueue traverse

A co-site neighbor cell of which TAThreshold = AThe A of the AMR call and non-AMR call corresponds to different parameters:


AMR call: A is RXQUAL1 (n=1); RXQUALn + RXLEVOff (2n12)

Non-AMR call: A is RXQUALn (1n12)

If the uplink/downlink interference handover decision is allowed and if the numberof 2G candidate cells is not zero, then the candidate cell selection is performed. If Intracell HO Allowed is set to YES and if the intra-cell handover penalty timer

expires (when a certain number of consecutive intra-cell handovers occur, thetimer Forbidden Time after Max Times (s) starts to forbid the intra-cellhandover), then the serving cell can be the target cell. Otherwise, the serving cellis removed. The candidate neighbor cell (not the serving cell) must meet the following

conditions:Receive level on the BCCH of the neighbor cell after filtering and penalty >= Inter-layer HO

Threshold + Inter-layer HO Hysteresis of the neighbor cell

The following figure shows the procedure for the interference handover decision.


Procedure for the interference handover decision


Start


NO

YES

Interfere_HO is YES?NO

sULQual or sDLQual >= A?

YES

End

NOsULQual or sDLQual: UL or DL RX quality of theserving cellA:1. For a non-AMR call, A is RXQUAL1-12.2. For an AMR call, A is RXQUAL1-12 +RXLEVOff.


NO


YES NO

SYS_HO is YES, a neighbor 3G cellexists, and MS supports inter-RAT

handover?

YES

YES

End

NO

Interfere_HO: Interference HOAllowed

YES

Intra_HO: Intracell HO Allowed

Inter-RAThandover

ucLev: RXLEV on the BCCH of theneighbor cell

ucLevThr: Inter-layer HO Threshold ofthe neighbor cell

ucLevHyst: Inter-layer HO Hysteresis ofthe neighbor cell

Interferencehandover initiation

Serving cell or not?

Intra_HO is YES and thecell is not in penalty state?

NO

YES

ucLev>=ucLevThr+ucLevHyst?

NO

YES YES

Candidate cellqueue traverse

NO

1.3.17 Quick Level Drop Handover

If the TA/interference handover conditions are not met, Rx_Level_Drop HO Allowed is set to YES,

and if the neighbor cells are not in emergency handover penalty state, the quick level drop handover


decision is made according to the following rules. The level values in this decision are not filtered.

If the MR used for handover decision is a pre-processed MR, then the flag bit inthe MR is used for handover decision directly. If the MR is not pre-processed, then

SS_ULs_fm_f 3Ghandover, then the 2G -> 3G handover is performed directly. If no eligible neighbor 3G cell available or if the 2G -> 3G handover is not allowed

because of the system parameter configuration and the MS capability, then thesubsequent decision on another emergency handover type is performed. If the quick level drop handover decision is not allowed, then the subsequent

decision on another emergency handover type is performed.The following figure shows the procedure for the quick level drop handover decision.


Procedure for the quick level drop handover

Start


NO

YES

QuickFall_HO is YES?NO

SS_ULs_fm_f


If the BQ handover decision is allowed, the candidate cell selection is performed. If the candidate cells include the neighbor cells except the serving cell, and if the

neighbor cells meet the following formula:Filtered RXLEV_DL of the neighbor cell after penalty > Filtered RXLEV_DL of the serving cell +

Inter-cell Handover Hysteresis of the serving cell configured for the neighbor cell BQ HO Margin,

then the outgoing cell handover procedure is preferred.

If the number of candidate cells is 1, then the above condition for the neighbor cell isunnecessary. If the neighbor cells do not meet the above condition or if the candidate cell list

includes only the available serving cell, and if Intracell HO Allowed is set toYES and the serving cell is not in intra-cell handover penalty state, then thecandidate cell list keeps only the serving cell. The assignment strategy is differentfrequency bands, different frequencies set, different TRXs, and different timeslots(assignment priority: different frequency bands > different frequencies set >different TRXs > different timeslots). If the BQ decision is allowed but the number of candidate cells is zero: If there is an available 3G neighbor cell, and if the system parameter

(Outgoing-RAT HO Allowed) and the MS capability support the 2G -> 3Ghandover, then the 2G -> 3G handover is performed directly. If no eligible neighbor 3G cell available or if the 2G -> 3G handover is not allowed

because of the system parameter configuration and the MS capability, then thesubsequent decision on another emergency handover type is performed. If the BQ handover decision is not allowed, then the subsequent decision on

another emergency handover type is performed.The following figure shows the procedure for the BQ handover decision.


Procedure for the BQ handover decision

Start


NO

YES

BQ_HO is YES?NO

sULQual>=ULQuaLimit ORsDLQual>DLQuaLimit?

YES

End

NO

sULQual/sDLQual: UL/DL RX quality of theserving cellULQuaLimit/DLQuaLimit:1.UL/DL Qual. Threshold for a non-AMRcall2.ULQuaLimitAMRFR/DLQuaLimitAMRFR for an AMR FR call3.ULQuaLimitAMRHR/DLQuaLimitAMRHR for an AMR HR call


NO


YES NO

SYS_HO is YES, a neighbor 3G cellexists, and MS supports inter-RAT

handover?

YES

YES

End

NO

BQ_HO: BQ HO Allowed

YES

Inter-RAThandover


ucLev: filtered DL RXLEV of the neighborcellsLev: DL RXLEV of the serving cell (afterpower control)InterCellHyst: Inter-cell HandoverHysteresisBQMargin: BQ HO Margin

Candidate cell queuetraverse

Serving cell or not?

ucLev-sLev>InterCellHyst-

BQMargin?

Intra_HO is YES and thecandidate cell is not in

penalty state?

YESNO

NONO

YESYES

Intra_HO: Intracell HO Allowed

BQ emergencyhandover to theneighbor cell is

initiated preferentially.

1.3.19 Load Handover

The load handover is only for the 2G handover and cannot be used for 2G -> 3G

handover.The load handover decision is not performed even if the system load is

higher than System Flux Threshold for Load HO.

When the emergency handover and enhanced dual-band network handover are not

triggered and when Load Handover Allowed is set to YES, the load handover

decision is made according to the following rules:

The load handover is allowed only when the CPU usage of thecurrent system is smaller than or equal to System Flux Thresholdfor Load HO. Current load of the serving cell >= value of Load HO Threshold If the load handover decision is allowed, the hierarchical load

handover is performed. The calculation formula of the loadhandover strip is as follows:

1T

A StepPeriod

In this formula,

A is the width of the handover strip.

T is the timer of the load handover.

Period is Load HO Step Period (s).

Step is Load HO Step Level.

A cannot exceed the value of Load HO Bandwidth.

Power control compensation. The filtered downlink RXLEV on theTCH of the serving cell is compensated.

s_f_comp s_f s_f_ _ 2SS DL SS DL Poff_DL

In this formula,

SS_DLs_f_comp is the compensated RXLEV on the downlink TCH.

SS_DLs_f is the filtered RXLEV on the downlink TCH.

Poff_DLs_f is the power offset of the BTS transmit power compared with the

maximum transmit power on the downlink TCH after filtering. The offset level is 2 dB.

The system assigns the MS to different load handover strips basedon the downlink RX level so that the call is handed over out of thecell step by step.


Page 38

s_f_compClsHoStart _ ClsHoStart +ASS DL

In this formula,

ClsHoStart indicates Edge HO DL RX_LEV Threshold, which is the start of the

handover strip.

A is the handover strip using the above formula.

If the load handover strip decision formula is applied, the candidatecell selection is performed. The serving cell and external cell are removed. The candidate cell must meet the following formula:

_f layer layeriSS T H

In this formula,

SSi_f indicates the receive level on the downlink BCCH after filtering and penalty in

the neighbor cell.

Tlayer indicates Inter-layer HO Threshold.

Hlayer indicates Inter-layer HO Hysteresis.

The load of a candidate cell must meet the following formula:

iTloadLi _

In this formula,

Li indicates the current load of the neighbor cell i.

Tload_i indicates Load Req. on Candidate Cell of the neighbor cell i.

If the load handover decision is not allowed, then the subsequentdecision on another handover type is performed.

The following figure shows the procedure for the load handover decision.


Page 39

Procedure for the load handover decision

Start

Whether a neighbor 2Gcell exists?

NO

Load_HO is YES?

System flowSysFlowLev

NO Load_HO: Load HandoverAllowed

SysFlowLev: System FluxThreshold for Load HO

NO

Load of serving cellLoadTrigThres

LoadTrigThres: Load HOThreshold

NO

Timer of load handoverstarted?

A(T/Period+1)*Step

A: width of the load handover stripT: timer of the load handoverPeriod: Load HO Step PeriodStep: Load HO Step LevelOffset: Load HO Bandwidth

Start thetimer

ClsHoStart=Tlayer+ Hlayer?

YES NO

YES YES

NO

NO

End

Timer expires?

NO YES

AOffset

1.3.20 Normal Handover


Page 40

1.3.21 Edge Handover

If Fringe HO Allowed is set to Yes, the edge handover is allowed. If none of the

high-speed railway fast handover, emergency handover, enhanced dual-band

network handover, and load handover is triggered, the edge handover may be

triggered when all the following conditions are met:

Measured value of signal strength on the uplink TCH after filtering < value of Edge

HO UL RX_LEV Threshold; Measured value of signal strength on the downlink TCH

after filtering < value of Edge HO DL RX_LEV Threshold

According to the P/N criterion, if N reports out of the latest P MRsmeet the previous formulas, the uplink/downlink edge handover istriggered and the candidate cells are selected. Remove the serving cell from the candidate cell list Remove the neighbor cell whose 16-bit sequence number is

greater than the 16-bit sequence number of the serving cell. Ifthe sequence number is small, the priority of the cell is high.

The neighbor cells should meet the P/N (Edge HO Valid Time(s)/Edge HO Watch Time (s) criterion. If the edge handover decision is allowed but the number of

candidate 2G cells is zero, then:

If a neighbor 3G cell is available, the 2G -> 3G handover isperformed directly when the system parameter Outgoing-RATHO Allowed is set to Yes and the MS supports the 2G -> 3Ghandover.

If no neighbor 3G cell is available, or if the system parameterconfiguration and the MS do not support the 2G -> 3G handover,then the subsequent handover decision is performed.

The following figure shows the procedure for the edge handover decision.


Page 41

Procedure for the edge handover decision

Is Fringe HO Allowed set toYes?

For neighbor cell whose 16-bitpriority level is higher than serving cell,

update edge handover counter

Update UL levelbad counter

UL receive level < Edge HO ULRX_LEV Threshold?

Yes

Yes

End No

Bad UL level meets P/Ncriterion?

Update DL levelbad counter

DL receive level < Edge HO DLRX_LEV Threshold?

Yes

Bad DL level meets P/Ncriterion?

No

No

No

Do candidate 2Gneighbor cells exist?

Yes

No

End No

Trigger edgehandover

Fast-moving micro cellhandover decision

Whether to trigger fast-movingmicro-macro cell handover?

Yes

Trigger fast-movingmicro-macro cell

handoverYes

Filter candidate neighbor cells(edge handover counter forcandidate cells meets P/N

criterion

No

Trigger outgoingRAT handover

Start (MR input)

N: Edge HO Watch Time(s)P: Edge HO Valid Time (s)



Do candidate 3G neighbor cells existand is Outgoing-RAT HO Allowed

set to Yes?Yes

End

No

Do candidatecells exist?

Yes

No

Yes


Page 42

1.3.22 Fast-Moving Micro-to-Macro Cell Handover

If MS Fast Moving HO Allowed is set to Yes, the fast-moving micro-to-macro cellhandover is allowed. The fast-moving micro-to-macro cell handover is mainlyapplicable to the high-speed environment, such as highways. In the handover, twolayers of network coverage are involved: micro cell and macro cell.

If none of the high-speed railway fast handover, emergency handover, enhanced

dual-band network handover, load handover, and edge handover is triggered, the

fast-moving micro-to-macro cell handover decision is performed when the triggering

conditions of edge handover or PBGT handover are met. The decision conditions are

as follows:

If the duration for an MS to stay in the serving cell is less than the valueof MS Fast-moving Time Threshold (s) (the time threshold iscalculated based on the cell radius (r) and the velocity (v), that is, 2r/v),the number of fast-moving cells for the MS is calculated once.

The MS travels across a number of cells (the number is specifiedby MS Fast-moving Watch Cells) in sequence. Among thesecells, a small number of cells (the number is specified by MSFast-moving Valid Cells) are of fast movement. If the decision conditions are met and if the number of candidate

2G cells is not zero, then the candidate cells are selected. Penalty processing should be applied to neighbor cells

between the M sorting and the K sorting (see the sectioninvolving basic sorting). The target cell is a macro cell. In other words, the level of

the cell is 4. The candidate neighbor cells (not the serving cell) must

meet the following:

Receive level of the BCCH in neighbor cells after filtering and penalty value of

Inter-layer HO Threshold + value of Inter-layer HO Hysteresis

The neighbor cells have the smallest 16-bit sequence number.

The following figure shows the procedure for the fast-moving micro-to-macro cell

handover decision.


Page 43

Procedure for the fast-moving micro-to-macro cell handover decision

Is MS Fast MovingHO Allowed set to

Yes?

End

Start(MR input)

Is optimum neighborcell the serving cell?

Yes

Update fastmovement counter

Is neither optimum neighborcell nor serving cell the level-

4 cell?

Is optimum neighbor cellthe source cell of theprevious handover?

Is fast movement timertimed out?

Meet P/N criterion for fastmovement ?

Yes

No

No

No

No

No

Yes

Trigger fastmovementhandover

Yes

Yes

Yes

Choose a level-4 cellthat meets Inter-layer HO

Level Threshold

Does an elegiblelevel-4 cell exist?

Yes

No

No

The fast movement timer is used tomonitor the number of edge

handovers and PBGT handoverswithin TI_QUICKPASS after MSenters the cell. If the number of

handovers meets the P/N criterion,the MS is in fast-moving state.

P: MS Fast-moving Valid CellsN: MS Fast-moving Watch Cells


Page 44

1.3.23 Hierarchical Handover

If Level HO Allowed is set to Yes, the inter-layer handover is allowed. To enable the

handover between different priorities of cells at the same layer, you also need to set

this parameter to Yes. If none of the high-speed railway fast handover, emergency

handover, enhanced dual-band network handover, load handover, edge handover,

and fast-moving micro-to-macro cell handover is triggered, the hierarchical handover

may be triggered if all the following conditions are met:

The priority level of the neighbor cell is higher than the serving cell.

The receive level of the BCCH in neighbor cell i after filtering meets the following

formula: _f layer layeriSS T H

Where,

SSi_f indicates the receive level of the BCCH in the neighbor cell after filtering and

penalty.

Tlayer indicates Inter-layer HO Threshold.

Hlayer indicates Inter-layer HO Hysteresis.

The 16-bit sequence number of the neighbor cell is smaller thanthat of the serving cell. If the sequence number is small, the priorityof the cell is high.

If all these conditions are met during the period specified by Layer HO Valid Time(s)

within the latest Layer HO Watch Time(s), that is, if the P/N criterion is met, then the

hierarchical handover is triggered.

The following figure shows the procedure for the hierarchical handover decision.


Page 45

Procedure for the hierarchical handover decision

Start (MR input)

16-bit sequence number ofneighbor cell < that of serving

cell?

SSi_f>Tlayer+Hlayer andpriority of neighbor cell Margin

Update PBGTcounter

Yes

No

Meet conditons for PBGT handover

from enhanced dual-band cell to same

Yes

Yes No

No

Traversecomplete

Yes?

neighbor cells

group cell?

16-bit priority level of

serving cell have samepriority?

meets P/N criterion?

Conditions of PBGT handover from enhanceddual-band network cell to same group cell:

1) If MS in overlaid subcell and Out Cell

Load HO To Inn Cell Enable set to No

2) If MS in underlaid subcell and Out Cell

Load HO To Inn Cell Enable set to Noand enhanced dual-band network

overlaid-underlaid subcells handoverpenalty timer timed out or not started

Cell priority determinedby Layer of the Cell and

Cell Priority

SS_DLi_f: DL level of neighbor cell

SS_DLs_f: DL level of serving cell

Poff_DLs_f: BTS maximum TX power offset

Pms_i: MS maximum TX power in neighbor cell

Pms_s: MS maximum TX power in serving cellMargin: PBGT HO Thresho


Page 49

1.3.25 Concentric Cell Handover

The concentric cell handover is classified into normal concentric cell handover and

enhanced concentric cell handover. The current network mainly uses the enhanced

concentric cell handover and the ATCB algorithm applies to only the enhanced

concentric cell handover. Therefore, this part mainly describes the technology and

application of the enhanced concentric cell handover.

1.3.26 Normal Concentric Cell Algorithm

You can select the normal concentric cell handover or enhanced concentric cell

handover through Concentric Circles HO Allowed. If Concentric Circles HO Allowed

is set to NO, the normal concentric cell handover is enabled. At present, in the normal

concentric cell algorithm, the handover from the overlaid subcell to the underlaid

subcell is blind handover because the underlaid subcell level cannot be obtained.

Therefore, the handover success rate is low and this handover is rarely used for the

current network.

1.3.27 Enhanced Concentric Cell Algorithm

On the SDCCH If Assign Optimum Layer is set to No Priority, handle

the assignment procedure according to the assignmentprocedure in the access load module. If Assign Optimum Layer is set to Overlaid Subcell,

assign the TCHs to the overlaid subcell preferentially. If Assign Optimum Layer is set to Underlaid Subcell,

assign the TCHs to the underlaid subcell preferentially. If Assign Optimum Layer is set to System Optimization,

decide whether to assign TCHs to the overlaid subcellaccording to the uplink receive level and TA in the MRs from theSDCCH.

If the uplink receive level after filtering is greater than the value ofAssign-optimum-level Threshold and if the TA is smaller than the value of TAThreshold of Assignment Pref., assign the TCHs to the overlaid subcell.

On the TCH

The handover on the TCH is classified into the following: handover from the underlaid


Page 50

subcell to the overlaid subcell, handover from overlaid subcell to underlaid subcellcaused by low underlaid subcell load, and handover from the underlaid subcell to theoverlaid subcell due to MS movement.The triggering conditions are as follows:

None of the emergency handover, enhanced dual-band network handover, load

handover, edge handover, better cell handover, and PBGT handover is triggered.

The TCH is in the full-rate or half-rate state.

The attribute of the serving cell is concentric cell.

Handover from Underlaid Subcell to Overlaid Subcell The decision conditions are as follows:

1. The penalty timer with duration of Penalty Time of UL to OL HO is timed out or is

not started.

2. Number of Failed Handovers from Underlaid Subcell to Overlaid Subcell < value of

MaxRetry Time after UtoO Fail

3. If RX_LEV for UO HO Allowed is set to Yes, the downlink receive level after

power control compensation is greater than the value of UL to OL HO Received

Level Thrsh.

4. If ATCBHoSwitch is set to Yes, then (downlink receive level of the primary BCCHin the underlaid subcell - downlink receive level of the neighbor cell whose level is thehighest) > value of Distance Between Out And Inn Cell boundary.

5. If RX_QUAL for UO HO Allowed is set to Yes, the downlink receive quality of

underlaid subcell after filtering < value of RX_QUAL Thrsh..

6. If TA for UO HO Allowed is set to Yes, the TA of underlaid subcell after filtering Out Cell GeneralOverLoad Thred

Return

3. Cell load > Out Cell SeriousOverLoad Thred

4. For adaptation, value of Load HO StepPeriod decreases by 1 per second.The minimum is 1 and the step

remains unchanged

5. Adjust handover margin

based on handover period and

6. MS inhandovermargin?

7. MS initiateshandover

Return

Return

Configure LoadHO Step

Period to setvalue

No

Yes

Yes

No

Yes

No

U to O Traffic HOallowed?

No

Yes

load adjustment step

Procedure Description:

The TCH usage of the underlaid subcell is greater than the value of En Iuo Out CellGeneral OverLoad Thred, and the MSs that meet the handover conditions are withinthe handover margin. The handover margin is stepped from the maximum level (-47dBm) to the boundary of the overlaid and underlaid subcells level by level. The aim is


Page 52

to hand over the MSs near the BTS to the overlaid subcell. If the TCH usage of theunderlaid subcell is greater than the value of En Iuo Out Cell Serious OverLoadThred, the period specified by En Iuo In Cell Load classification HO Period shouldbe shortened to enable the faster handover of the MSs in the underlaid subcell to theoverlaid subcell.

Handover from Overlaid Subcell to Underlaid Subcell Caused byLow Underlaid Subcell Load

Handover Procedure

Start

1. Evaluate cell loadperiodically

(1s)

2. Cell load < Out Cell Low Load ThredL_Thdload

Return

3. Adjust handover margin based onhandover period andload adjustment step

4. MS inhandovermargin?

5. MS initiateshandover

Return

Return

Yes

No

Procedure Description:

If the load of the underlaid subcell is lower than the value of En Iuo Out Cell LowLoad Thred and if the MS is within the handover margin, the handover from theoverlaid subcell to the underlaid subcell is triggered. The maximum range of thehandover margin is from OL to UL HO Received Level Thrsh. to the maximum level(-47 dbm). If En Iuo In Cell Load classification HO Period of the handover margin


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is stepped to the BTS from OL to UL HO Received Level Thrsh. for En Iuo In CellLoad classification HO Step, the MSs on the overlaid subcell boundary arepreferentially handed over to the underlaid subcell.

Handover from the Overlaid Subcell to the Underlaid Subcell DueTo MS Movement Decision Conditions:

1. If RX_LEV for UO HO Allowed is set to Yes, the downlink receive level afterpower control compensation < value of OL to UL HO Received Level Thrsh.

2. If ATCBHoSwitch is set to Yes, (downlink receive level of the primary BCCH in the

underlaid subcell downlink receive level of the neighbor cell whose level is the

highest) < (Distance Between Out And Inn Cell boundary - Distance Hyst

Between Out And Inn Cell Boundary)

3. If RX_QUAL for UO HO Allowed is set to Yes, the downlink receive quality of the

underlaid subcell after filtering > RX_QUAL Thrsh.

4. If TA for UO HO Allowed is set to Yes, the TA of the underlaid subcell after

filtering > (TA Thrsh. + TA Hysteresis)

If any one of the previous conditions are met, the decision conditions of the handover

from the overlaid subcell to the underlaid subcell are met.

PN Criterion:

Within the period specified by UO HO Watch Time (s), the decision conditions are

met for the period specified by UO HO Valid Time (s), the conditions of the handover

from the overlaid subcell to the underlaid subcell are met.

Target Cell Selection:

The cell that has a favored 16-bit sequence ranking can be an underlaid subcell or a

neighbor cell.

1.3.28 AMR Handover


dual-band network handover, load handover, fast-moving micro-to-macro cell

handover, hierarchical handover, PBGT handover, concentric cell handover is

triggered, and if both Intracell HO Allowed and Intracell F-H HO Allowed are set to


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Yes, the AMR handover may be triggered if all the following conditions are met:

1.3.29 Handover from TCHF to TCHH

RQI/2 of the serving cell after filtering > value of F2H HO th

1.3.30 Handover form TCHH to TCHF

RQI/2 of the serving cell after filtering < value of H2F HO th

Within the period specified by Intracell F-H HO State Time, if the triggering

conditions are met for the period specified byIntracell F-H HO State Time, the P/N

criterion is met and the handover is triggered. Note: The previous two parameters are

also used for the handover from TCHH to TCHF.

The following figure shows the procedure for the handover:


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Procedure for the AMR handover

Start

Are both INTRAHO andINTRAFHHO set to Yes?

Handover triggered?

TCH and speech version 3?

INTRAHO: Intra-Cell Handover Allowed

INTRAFHHO: Intracell F-H HO Allowed

Full-rate TCH? andAMR TCH/H Prior Allowed?

and cell load lower than threshold?

Yes

Yes

Yes

AMR processing and concentriccell ping-pong handover

protection processing

No

Ping-pong protectionprotection for highly

loaded cell

Protectionprocessing in

underlaid subcell

RQI/2 of the serving cell afterfiltering > value of F2H HO th

Full-rate TCH? Half-rate TCH?

P/N criterion met?

Yes

Yes

Yes

RQI/2 of the servingcell after filtering >

value of H2F HO thh

Protection processingin overlaid subcell

Intra-cell AMRhandover istriggered.

End

Yes

Yes

No

No

No

No

No

Yes

Yes

No

End

No

P: Intracell F-H HO State TimeN: Intracell F-H HO State Time

The AMR handover failure timerhas not expired with the value

specified by Penalty Time afterAMR TCHF-H HO Fails?

1.3.31 Better 3G Cell Handover



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dual-band network handover, load handover, edge handover, fast-moving

micro-to-macro cell handover, hierarchical handover, PBGT handover, concentric cell

handover, and AMR handover is triggered, the procedure for the better 3G cell

handover is triggered, as shown in the following figure:

Procedure for the better 3G cell handover

Start

Handover triggered?

HOSYS is set to No?or are 3G better cell parameters set to 0?

FDD set to No?and TDD is set to No?

MTYPE is RSCP andRSCPi_f is greater than RSCP?

or MTYPE is Ec/N0 andEcNoi_f is greater than Ec/No?

FDD: Better 3G Cell HO Allowed

TDD: TDD Better 3G Cell HO Allowed

Processescandidate 3G

cell list

Current cell type is FDDand MS supports FDD

MTYPE:FDD REP QUANTRSCP: FDD RSCP Threshold for Better 3G CELL HO

RSCPi_f: measured value of FDD RSCP after filterinEc/N0: FDD Ec/No Threshold for Better 3G CELL HO

EcNoi_f: measured value of FDD Ec/No after filtering

TDDRSCP:TDD RSCP Threshold for Better 3G CELL HO

TDDRSCPi_f: measured value of TDD RSCP after filteringTDDRSCPi_fTDDRSCP

Current cell type is TDD?and MS supports TDD?

Are the FDD P/FDD criteriamet?

Are the TDD P/TDD Ncriteria met?

FDD P: 3G Better Cell HO Valid Time

FDD N: 3G Better Cell HO Watch Time

TDD P:T DD 3G Better Cell HO Valid Time

TDD N: TDD 3G Better Cell HO Watch Time

3G better cellhandover is

triggered.

End

End

No

No

Yes

No

Yes

No

No

No

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

HOSYS: Outgoing-RAT HO Allowed

For the FDD handover, whether to measure RSCP or Ec/No is selected on the basis

of FDD REP QUANT. The TDD supports only the measurement of the RSCP.

If the RSCP or Ec/No of a certain measurement period meets the conditions, one

valid measurement is calculated. If the persistent measurement results meet the P/N

criterion, the better 3G cell handover is triggered.


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1.3.32 Directed Retry

If the TCH assignment in the cell fails, the TCH assignment and handover procedure

is completed through the selection of new target cell via directed retry algorithm when

the MS has occupied the SDCCH (single signaling connection state) and Direct

Retry is set to Yes.

For directed retry, the procedure for selection of candidate cells is as follows: The

cells and serving cells that do not meet the necessary handover conditions based on

the handover type are removed from the cell queue after basic sorting. Then, the

directed retry procedure is initiated on the cell that has the smallest 16-bit sequence

number among the candidate cells.

1.3.33 Handover in Single-Signaling /SDCCH State

The handover decision for the MS that has occupied the SDCCH is the same as that

for the MS that has occupied the TCH. In other words, the TA handover, interference

handover, bad quality handover, quick drop handover, edge handover are allowed,

but the load handover, PBGT handover, concentric cell handover, and AMR

handover are prohibited. In addition, the parameters for the handover decision are

the same as TCH parameters. If SDCCH HO Allowed is set to Yes, the handover

between signaling channels is allowed. The measurement for the MS that has

occupied the SDCCH uses different filtering parameters from that for the MS that has

occupied the TCH.

1.3.34 Handover Implementation

In the handover implementation procedure, the Handover Power Boost Switch

parameter is used to determine whether the BTS of the serving cell uses the

maximum transmit power during the handover. If this parameter is set to Yes, the

transmit power of the BTS is set to the maximum value before the BSC sends the


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handover command to the MS. In addition, the BTS power is not adjusted during the

handover to ensure the success of the handover.

The handover implementation procedure uses the protocol procedure for the

standard interfaces.

2 Parameters Involved in the Algorithms

2.1 Parameters detail description

2.1.1 Co-BSC/MSC Adj

Description: This parameter determines whether the sequence of candidate cells is

adjusted. After the sequence is adjusted, the handover within the same BSC/MSC

takes priority.

Value range: Yes, No

Unit: none

Default value: Yes

Configuration policy: If this parameter is set to Yes, the target cell to which the MS is

handed over may not be the cell with the best signal quality.

Relevant algorithm: algorithms of all the handovers except intra-cell handovers,

such as the AMR handover and concentric cell handover

2.1.2 SDCCH HO Allowed

Description: This parameter determines whether a handover between signaling

channels is enabled.


Unit: none

Default value: No

Configuration policy: When the authentication and ciphering procedure is enabled,

this parameter can be set to Yes.


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Relevant algorithm: algorithms of all the handovers except the load handover,

PBGT handover, concentric cell handover, and AMR handover

2.1.3 Penalty Allowed

Description: This parameter determines whether a penalty is performed for the

target cell where a handover fails or for the serving cell where the TA is too great or

the signal quality is too bad.


Unit: none

Default value: Yes

Configuration policy: Huawei recommends that this parameter be set to Yes. If you

need to disable the penalty for a certain handover, set the related penalty time and

penalty level to 0.

Relevant algorithm: all algorithms

2.1.4 MS Power Prediction after HO

Description: This parameter determines whether an MS can use the optimum

transmit power instead of the maximum transmit power to gain access to the new

channel after a handover. The purpose is to reduce interference and improve the

service quality.


Unit: none

Default value: No

Configuration policy: If this parameter is set to Yes, the MS does not use the

maximum transmit power, and thus the handover success rate is decreased, but the

network interference is reduced.

Relevant algorithm: all algorithms


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2.1.5 Power Level for Direct Try

Description: This parameter is used to select the candidate cells during directed

retry.

Value range: 063

Unit

Date post:	14-Oct-2015
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Handover Algorithm Complete and Detailed

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