handover algorithm complete and detailed
DESCRIPTION
Handover AlgorithmTRANSCRIPT
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Huawei Handover Algorithm
HUAWEI TECHNOLOGIES CO., LTD.
Huawei Handover Algorithm(GSM BSS)
6/05/2009
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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:
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Huawei Handover Algorithm
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
TCH measurement ofthe serving cell
(FULLSET scheme)
Yes
TCH measurement ofthe serving celll
(SUBSET scheme)
TCH measurement ofthe serving cell
(FULLSET scheme)
MR Preprocessing
Transfer Original MR
Transfer BS/MS Power Class
Sent Freq of Preprocessed MR
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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:
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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:
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
Procedure for the interference handover decision
SYS_HO: Outgoing-RAT HOAllowed
Start
Whether a 2G/3G candidate cellexists?
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.
Whether a 2G candidate cellexists?
NO
Eligible 2G target cellexists?
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
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
Procedure for the quick level drop handover
Start
Whether a 2G/3G candidate cellexists?
NO
YES
QuickFall_HO is YES?NO
SS_ULs_fm_f
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
Procedure for the BQ handover decision
Start
Whether a 2G/3G candidate cellexists?
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
Whether a 2G candidate cellexists?
NO
Eligible 2G target cellexists?
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
SYS_HO: Outgoing-RAT HOAllowed
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.
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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)
N: Edge HO Watch Time(s)P: Edge HO Valid Time (s)
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
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Huawei Handover Algorithm
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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.
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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.
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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
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Huawei Handover Algorithm
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
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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
If none of the high-speed railway fast handover, emergency handover, enhanced
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
If none of the high-speed railway fast handover, emergency handover, enhanced
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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.
Value range: Yes, No
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.
Value range: Yes, No
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.
Value range: Yes, No
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