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GSM Handover Algorithm N-1
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Copyright 2008 Huawei Technologies Co., Ltd. All rights reserved.
GSM HandoverAlgorithm
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GSM Handover Algorithm N-2
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Foreword
Handover is a key technology of mobile communication system and
make continued conversation possible.
Handover algorithm in Huawei product is flexible and powerful.
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GSM Handover Algorithm N-3
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Objectives
Upon completion of this course, you will be able to:
Outline the types of handover
Master handover judgment flow
Understand algorithm of different handovers
Explain HO data configuration
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GSM Handover Algorithm N-4
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Contents
1. Introduction of Handover
2. HO Algorithm Process
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GSM Handover Algorithm N-5
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Contents
1. Introduction of Handover
2. HO Algorithm Process
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GSM Handover Algorithm N-6
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Purposes of HO
To keep a continuous communication with a moving MS
To improve network service performance
To reduce the call drop rate
To reduce the congestion rate
Handover can maintain the communication continuity of MS which moves across different
cells and lower the call drop rate and provide better communication service.
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GSM Handover Algorithm N-7
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Classification by Reason
No DL MR Emergency HOTiming Advance (TA) HO
Interference HO
Rx_Level_Drop HO
Bad Quality (BQ) HO
Emergency HO
Enhanced Dual Band HO
Load HO
Normal HO
1
2
3
4
Classification
by
ReasonEDGE HO
PBGT HO
Layer HO
MS Fast Moving HO
Concentric Cell HO
AMR HO
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GSM Handover Algorithm N-8
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Classification by Synchronization
CELL
Case 1
Synchronous Handover: the target BTS shall not send PHY INFO message
Case 2
Asynchronous Handover: the target BTS shall send PHY INFO message
Case 3 Case 4Case 5
MSC
BSC
BTS
BSC BSC
MSC
BTS BTSBTS
BTS
NSS Network
Synchronous handover: source and target cell belong the same BTS
Asynchronous handover: source and target cell belong the different
BTS
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GSM Handover Algorithm N-9
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Classification by Equipment and
Channel
SDCCHSDCCH TCHTCH
(Direct Retry)(Direct Retry)
SDCCHSDCCH SDCCHSDCCH
IntraIntra Cell HOCell HO ((HRHRFRFR))
InterInter Cell HOCell HO
IntraIntra BSC HOBSC HO
IntraIntra MSC HOMSC HO
InterInter MSC HOMSC HO
TCHTCH TCHTCH
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GSM Handover Algorithm N-10
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Contents
1. Introduction of Handover
2. HO Algorithm Process
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GSM Handover Algorithm N-11
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Contents
2. HO Algorithm Process
2.1 General HO Process
2.2 Measure and Measurement Result Report
2.3 Measurement Report Preprocessing
2.4 Handover Judgment
2.5 Handover Implementation
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GSM Handover Algorithm N-12
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General HO Process
MS Goes into New Dedicated Mode
MS Goes into Dedicated Mode
Measure and Measurement Result Report1
Measurement Report Preprocessing2
Handover Judgment3
Handover Implementation4
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GSM Handover Algorithm N-13
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General HO Process
MS Goes into New Dedicated Mode
MS Goes into Dedicated Mode
Measure and Measurement Result Report1
Measurement Report Preprocessing2
Handover Judgment3
Handover Implementation4
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GSM Handover Algorithm N-14
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The downlink measurement reportof the neighbor cell (BCCH)
Measurement Report
Uplink MR includes uplink receiving level and quality.
Downlink MR includes downlink receiving level, downlink
receiving quality of the serving cell and other downlink receiving
levels from the neighbor cells.
Serving cell
Neighbor cell
The uplink MR
The downlink MR
In dedicated mode, the system performs handover and power control judgment based on
measurement reports. The downlink MR are reported to the network via uplink SACCH
channel.
Downlink--In dedicated mode, MS reports MR via uplink SACCH channel periodically. The
report includes the receiving level, received quality, TA, power class and whether DTX isused. At the same time, MS will perform pre-synchronization to neighbor cell defined by the
system to obtain BCCH frequencies and BSIC, measure their received signal level and
report the six max. neighbor cells with the highest received signal level.
Uplink--The uplink measurement report is measured by BTS, including the receiving level
and receiving quality from the MS.
Both parts are sent by BTS to BSC for further processing at the same time.
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GSM Handover Algorithm N-15
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Measurement Report
There are two values in the measurement report: FULL MR and SUB MR.
FULL--Averaging 100 TCH bursts (except the four idle frames in the four 26-multiframes)
SUB--Averaging 12 bursts (four SACCH bursts and eight TCH bursts in specific position).
SUB should be selected when the Discontinuous Transmission (DTX) function is activated.
RXQUAL level in MR Huawei value BER behind
0 0 Less than 0.2%
1 10 0.2% ~ 0.4%
2 20 0.4% ~ 0.8%
3 30 0.8% ~ 1.6%
4 40 1.6% ~ 3.2%
5 50 3.2% ~ 6.4%6 60 6.4% ~ 12.8%
7 70 Greater than 12.8%
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GSM Handover Algorithm N-16
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Period of Measurement Report
The downlink MR is sent to BTS in SACCH uplink
The interval is 480ms/per time when MS is on TCH
The interval is 470ms/per time when MS is on SDCCH
12TCH 12TCH1SACCH 1 Idle
480ms 4 TCH Multi-frames
SACCH is a bidirectional channel.
It sends the downlink measurement report to BTS in uplink SACCH.
It sends SYS.INFO. 5 and SYS. INFO. 6 to MS in downlink SACCH.
1. The SACCH measurement report period varies with the channel
occupied by MS in dedicated mode.
2. When associated with SDCCH, SACCH measurement period is 470ms,
this is because there is an entire SACCH message block in 2 SDCCH
51-multiframes.
3. When associated with TCH, SACCH measurement period is 480ms, this
is because there is an entire SACCH message block in 4 TCH 26-
multiframes
A complete measurement report is formed by four consecutive SACCH bursts. In SDCCH
channel the four bursts are transmitted continuously. In TCH channel there is only oneSACCH burst in each 26-multiframe, therefore only four 26-multiframe can constitute a
complete measurement report.
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GSM Handover Algorithm N-17
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General HO Process
MS Goes into New Dedicated Mode
MS Goes into Dedicated Mode
Measurement Report Preprocessing
Handover Judgment3
Handover Implementation4
Measure and Measurement Result Report1
2
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GSM Handover Algorithm N-18
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MR Preprocessing
MR Preprocessing
Interpolation
Recover the lost
measurement report
Filtering
Smooth the instantaneous
fading point
MR preprocessing consists of two steps: interpolation and filtering.
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GSM Handover Algorithm N-19
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MR Interpolation
MR
MR
No. n
No. n+4
Continu
ousMRFlow
MRMR
MR
Missing by
some reasons
MR Interpolation recover the lost measurement report
BTS may fail to receive the MR from MS, and it needs to recover the lost measurement reports. If the
lost MR amount is within the allowed range (Allowed MR Number Lost), then recovers the lost MR
according to the specific algorithm.
Service cell: linear algorithm
Neighboring cell: the lowest value defined in GSM specification (-110dBm)
The continuity of measurement report is judged by measurement report number. Each
measurement report has a serial number. If the serial numbers of received measurement
reports are not consecutive, there must be missing measurement reports, and the system
will make them up according to the interpolation algorithm.
As shown in the diagram, the network receives measurement reports n and n+4, whose
serial numbers are not consecutive, so the system will make up for the missing
measurement reports n+1, n+2 and n+3 with a certain algorithm.
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GSM Handover Algorithm N-20
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MR Filtering
MR
MRCon
tinuous
MRFlo
w
MRMR
MR
Filter----Average severalconsecutive MRs
MR
Filteringsmooth the instantaneous fading point
Calculate the average value within the filter window
When the network receives the measurement report, it can not judge the current condition of
MS according to just one measurement report due to the signal fluctuation. Therefore,
filtering, a more suitable method is applied.
Different filters are applied in receiving level, receiving quality and TA of uplink and downlink.
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GSM Handover Algorithm N-21
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Data Configuration of MR
Preprocessing
[MR Preprocessing]
Value Range: Yes, No
Default Value: No
Description: This parameter indicates whether the BTS pre-processes the MR.
This parameter determines the location where power control is performed. If this parameteris set to Yes, power control is performed by the BTS. Otherwise, the power control is
performed by the BSC.
When this parameter is set to No, the MR is processed by the BSC, in which case, both
Transfer original MR, Transfer BS/MS power class and Sent Freq of preprocessed MR are
invalid.
When this parameter is set to Yes, the load over Abis interface and that over the BSC are
reduced, thus shortening the response time and improving the network performance.
[Transfer Original MR]
Value Range: Yes, No
Default Value: No
Description: This parameter indicates whether the original MR is transferred to the BSCafter the BTS pre-processes the MR.
When the parameter is set to Yes, the BTS transfers to the BSC both the processed MR and
the original MR.
Remarks:In case of 4:1 configuration, this parameter must be set to No if SDCCH/8 isgreater than 2.
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GSM Handover Algorithm N-22
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Data Configuration of MR
Preprocessing
[Transfer BS/MS Power Class]
Value Range: Yes, No
Default Value: Yes
Description: This parameter indicates whether the original BS/MS power class is transferred
to the BSC.
Remarks:When MR pre-processing is enabled, uplink and downlink balance measurement is
affected if this parameter is set to No. In addition, power compensation handovers, such as
PBGT handovers, load handovers, and Concentric Cell handovers, may become abnormal.
[Sent Freq of Preprocessed MR]
Value Range: Do not Report, Twice every second, Once every second, Once every two
seconds, Once every four seconds
Default Value: Twice every second
Description: This parameter indicates the frequency that the BTS transfers the preprocessed
MR to the BSC. After the MR is preprocessed by BTS, the BTS transfers the preprocessed
MR to the BSC. For example, if this parameter is set to Twice every second, the BTS
transfers the preprocessed MR to the BSC twice per 0.5 second.
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GSM Handover Algorithm N-23
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Data Configuration of MR
Preprocessing
[Allowed MR Number Lost]
Value Range: 0~31
Default Value: 4
Description: This parameter indicates the number of MRs allowed to be lost in succession. When thisthreshold is not reached, the lost MR is estimated via the linear interpolation basing on the first and the
last MRs received. When this threshold is reached, all previous MRs are discarded, and calculations are
made again when new MRs are received.
Remarks: MRs fail to be decoded correctly when the signal strength in the serving cell is poor. Whenthis threshold is reached, all previous MRs are discarded and handover may fail. Thus, it is advised to
assign this parameter with a greater value to enable emergency handover.
[Filter Length for TCH Level]
Value Range: 1~31
Default Value: 4
Description: This parameter indicates the number of MRs used for averaging the TCH signal strength.
This parameter helps to avoid sharp drop of signal levels caused by Raileigh Fading and to ensure
correct handover decisions.
Remarks: When this parameter is too large, the impact of sudden changes is reduced, and the responseis delayed, thus affecting the network performance.
[Filter Length for TCH Qual]
Value Range: 1~31
Default Value: 4
Description: This parameter indicates the number of MRs used for averaging the TCH signal quality.
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GSM Handover Algorithm N-24
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Data Configuration of MR
Preprocessing
[Filter Length for SDCCH Level]
Value Range: 1~31
Default Value: 2
Description: This parameter indicates the number of MRs used for averaging the SDCCH signal strength.
It is recommended that you assign this parameter with a lower value because the SDCCH occupation
time is shorter than the TCH occupation time.
[Filter Length for SDCCH Qual]
Value Range: 1~31
Default Value: 2
Description: This parameter indicates the number of MRs used for averaging the SDCCH signal quality.
It is recommended that you assign this parameter with a lower value because the SDCCH occupation
time is shorter than the TCH occupation time.
[Filter Length for Ncell RX_LEV]
Value Range: 1~31
Default Value: 4
Description: This parameter indicates the number of MRs used for averaging the signal strength in neighboring cells.
This parameter helps to avoid sharp drop of signal levels and to ensure correct handover decisions.
Remarks: When this parameter is too large, the impact of sudden changes is reduced, and the response is delayed,thus affecting the network performance.
[Filter Length for TA]
Value Range: 1~31
Default Value: 4
Description: This parameter indicates the number of MRs used for TA averaging.
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GSM Handover Algorithm N-25
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General HO Process
MS Goes into New
Dedicated Mode
MS Goes into
Dedicated Mode
Measure and MeasurementResult Report
1
MR. Preprocessing2
Handover Judgment3
Handover Implementation4
TA HO
Interference HO
Rx_Level_Drop HO
Bad Quality HO
Load HO
Edge HO
Layer HO
PBGT HO
AMR HO
No DL MR HO
Concentric Cell HO
MS Fast Moving HO
Enhanced Dual Band HO
Penalty Processing
Ranking Processing
OM Forced HO
Direct Retry
Emergency HO
Normal HO
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GSM Handover Algorithm N-26
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Penalty Processing
Intra-cellHO
HO FailsEmergency(TA&BQ)HO
MS FastMoving
HO
ConcentricCell HO
Penalty
Punish on the
target cell
Punish on the
original cell
Punish on other high
priority layer cells
AMR HO
Fails
There are several kinds of penalty process
Penalty on target cell when a HO fails.
Penalty on source cell when an emergency HO (BQ and TA ) is performed.
Penalty on other high priority layer cells after fast moving HO is performed.
Penalty for concentric cell HO
Penalty for intra-cell HO
Penalty for AMR HO
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GSM Handover Algorithm N-27
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Penalty for Handover Failure
Punish the target cell when a HO fails.
This is to avoid the MS to select this cell again in next HO judgment.
Cell A
BTS
HO Fail
BSC
Cell B
BTS
When MS fails to handover to a target cell, a penalty will be given on the signal level of this
target cell during a so called handover failure penalty time period. That is, when ranking the
neighbor cells in the cell list, the corresponding neighbor cell with a failure record within the
penalty time will be penalized by cutting certain value on the reported signal level.
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GSM Handover Algorithm N-28
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Data Configuration of Penalty for
Handover Failure
[Penalty Level after HO Fail]
Value Range: 0~63
Unit: dB
Default Value: 30
Description: This parameter indicates the penalty level given to a target cell.
A penalty level is given to a target cell to avoid further attempts when a
handover fails due to any of the following reasons:
Cell congestion
A message indicating internal handover refusal is received.
A message indicating Um interface handover failure is received during out-going
BSC handover.
A message indicating Um interface handover failure is received during internal
handover.
Remarks: This parameter is valid only before the penalty time of handover
failure expires.
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GSM Handover Algorithm N-30
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Cell A
Cell B
BTSBQ&TA HO
BSC
Penalty for Emergency Handover
Punish the original cell when an emergency HO ( due to BQ andTA) occurs.
In case of BQ emergency handover, the original serving cell will be penalized (called signal
level penalty by BQ HO ), during BQ HO penalty time, to avoid MS to be handed back to the
original serving cell again within certain time.
It is the same for TA handover, i.e. the original serving cell is penalized (signal level penalty
by TA HO ) during TA HO penalty time.
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GSM Handover Algorithm N-31
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Data Configuration of Penalty for
Emergency Handover
[Penalty Level after BQ HO]
Value Range: 0~63
Unit: dB
Default Value: 63
Description: This parameter indicates the penalty level given to the original serving cell where emergency handoveris performed due to bad quality. After emergency handover is performed due to bad quality, the receive level of the
original serving cell is decreased by the penalty level. Thus, other cells are given higher priority and handover to theoriginal serving cell is not allowed.
Remarks: This parameter is valid only before the penalty time of handover due to bad quality expires.
[Penalty Time after BQ HO (s)]
Value Range: 0~255
Unit: Seconds
Default Value: 15
Description: This parameter indicates the penalty time given to the original serving cell where emergency handoveris performed due to bad quality. During the penalty time, the receive level of the original serving cell is decreased by
the penalty level. Thus, other cells are given higher priority and handover to the original serving cell is not allowed.
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GSM Handover Algorithm N-32
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Data Configuration of Penalty for
Emergency Handover
[Penalty Level after TA HO]
Value Range: 0~63
Unit: dB
Default Value: 63
Description: This parameter indicates the penalty level given to the original serving cell
where emergency handover is performed due to TA. After emergency handover is performed
due to TA, the receive level of the original serving cell is decreased by the penalty level.
Thus, other cells are given higher priority and handover to the original serving cell is not
allowed. This parameter is valid only before the penalty time of handover due to TA expires.
[Penalty Time after TA HO(s)]
Value Range: 0~255
Unit: Seconds
Default Value:30
Description: This parameter indicates the penalty time given to the original serving cell
where emergency handover is performed due to TA. During the penalty time, the receive
level of the original serving cell is decreased by the penalty level. Thus, other cells are given
higher priority and handover to the original serving cell is not allowed.
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GSM Handover Algorithm N-33
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Back? No way!Back? No way!
Umbrella
Micro cell
Penalty for MS Fast-moving Handover
Giving penalty on the other three layers(Non-umbrella Layer ) after MS
handovers to Umbrella cell by fast-moving-HO.
This is to keep MS staying in the umbrella cell and avoid frequent HO.
Purpose of such penalty: When MS crosses continuously several micro cells, it handover to
the umbrella cell with lower hierarchical priority level, to avoid too frequent handovers which
will affect the communication quality between those cells. At the same time, penalty is
started to avoid handover back to original cell again. A possible example is that a fast
moving car is running on a highway.
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GSM Handover Algorithm N-34
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Data Configuration of Penalty for MS
Fast-moving Handover
[Penalty on MS Fast Moving HO]
Value Range: 0~63
Unit: dB
Default Value:30
Description: This parameter indicates the penalty given to the level in a neighboring cell
when an MS is moving fast. Only the cells in the umbrella layer can give penalty to the cells
in other three layers.
Remarks: This parameter is valid only before the penalty time of fast moving expires.
[Penalty Time on Fast Moving HO]
Value Range: 0~255
Unit: Seconds
Default Value: 40
Description: This parameter indicates the period during which penalty is performed on the
neighboring cells of the fast moving MS. During this period, penalty on the neighboring cells
(on only the other three layers except the umbrella layer) of fast moving MS is valid.
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GSM Handover Algorithm N-35
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Underlaid
Overlaid Do not attemptagain duringpenalty time
after one failedHO(O->U)!
Penalty for Concentric Cell
A new concentric cell HO is prohibited within a penalty time after a
concentric cell HO failure.
Do notattempt againafter N failedHO(U->O)!
Huawei concentric cell HO failure means the failure of handover from the Underlaid to the
Overlaid, or from the Overlaid to the Underlaid.
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GSM Handover Algorithm N-36
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Data Configuration of Penalty for
Concentric Cell
[Penalty Time after UtoO HO Fails(s)]
Value Range: 10~255 Unit: Seconds Default Value: 40
Description: After a UL to OL handover fails, no UL to OL handover
request is allowed before the penalty time expires.
[Penalty Time after OtoU HO Fails(s)]
Value Range: 0~255 Unit: Seconds Default Value: 10
Description: After an OL to UL handover fails, no OL to UL handover
request is allowed before the penalty time expires.
[MaxRetry Time after UtoO Fail]
Value Range: 0~8 Default Value: 3
Description: This parameter indicates the threshold of UL to OL handover
failures. UL to OL handover is not allowed if the number of handover
failures reaches this threshold.
Remarks: When this parameter is set to 0, not this threshold but the penalty
time restricts the permission of handover.
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GSM Handover Algorithm N-37
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Underlaid
OverlaidDo not
attempt backtoo fast!
Penalty for Enhanced Concentric Cell
A new UO HO is prohibited within a penalty time after a
OU HO is performed successfully.
This penalty is valid only for Enhanced Concentric Cell.
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GSM Handover Algorithm N-38
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Data Configuration of Penalty for
Enhanced Concentric Cell
[Penalty Time of UtoO HO(s)]
Value Range: 0~255
Unit: Seconds
Default Value: 10
Description: This parameter indicates the penalty time for forbidding ping-
pong handovers. After an OL to UL handover is performed, UL to OL
handover is not allowed before the penalty time expires. If this parameter is
set to 0, a UL to OL handover is allowed when required.
Remarks: This parameter is valid only when Enhanced Concentric Cell is
allowed.
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GSM Handover Algorithm N-40
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Data Configuration of Penalty for
Intra-cell HO
[Max Consecutive HO Times]
Value Range:1~20
Default Value: 3
Description: This parameter indicates the maximum number of consecutive intra-cellhandovers allowed. If the interval of two continuous intra-cell handovers is less than a
specified threshold, the two handovers are regarded as consecutive handovers.Intra-cell
handover is forbidden if the number of consecutive handovers exceeds this threshold.
[Forbidden Time after Max Times]
Value Range: 1~200
Unit: Seconds
Default Value: 20
Description: This parameter indicates the timer that starts when the threshold of maximumconsecutive intra-cell handovers is reached. Intra-cell handovers is allowed only when the
timer expires.
[Interval for Consecutive HO Jud.]
Value Range: 1~200
Unit: Seconds
Default Value: 6
Description: This parameter indicates the period for judging whether two continuous intra-cell handovers are consecutive.
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GSM Handover Algorithm N-41
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Data Configuration of Penalty for AMR
FRHR Handover Failure
[Penalty Time after AMR TCHF-H HO Fails(s)]
Value Range: 0~255
Unit: Seconds
Default Value: 30
Description: This parameter indicates the penalty time for AMR full rate to
half rate (FR-to-HR) handovers. Before the timer expires, no AMR FR-to-HR
handover request is allowed if the previous full-half handover fails due to
channel unavailability or channel mismatch.
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GSM Handover Algorithm N-42
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General HO Process
MS Goes into New
Dedicated Mode
MS Goes into
Dedicated Mode
Measure and MeasurementResult Report
1
MR. Preprocessing2
Handover Judgment3
Handover Implementation4
TA HO
Interference HO
Rx_Level_Drop HO
Bad Quality HO
Load HO
Edge HO
Layer HO
PBGT HO
AMR HO
No DL MR HO
Concentric Cell HO
MS Fast Moving HO
Enhanced Dual Band HO
Penalty Processing
Ranking Processing
OM Forced HO
Direct Retry
Emergency HO
Normal HO
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GSM Handover Algorithm N-43
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Ranking Processing
M rule
K rule
Basic ranking
16 bits ranking
Network feature adjustment
The ranking result: target cell selection of handover
Ranking processing of cells are major parts of the HO judgment.
The ranking result is used for target cell selection of handover.
The ranking processing includes:
Basic ranking
M rule
K rule
Network feature adjustment
16 bits ranking
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GSM Handover Algorithm N-44
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M RuleBegin
Finish to allneighbor cells?
An BSC external neighboringcell& the current channel is
SDCCH ?
No
Yes
Direct retry? [Inter-BSC SDCCH HOAllowed] is Yes?
Delete the cell from
the cell list?
If the cell flow is overload ?
Yes No
Yes
No
RX_LEV_DL(n) < [Min DL Power
on HO Candidate Cell](n)+
[Min Access Level Offset](s)?
RX_LEV_UL(n) < [Min UP Power on HO
Candidate Cell](s)+
[Min Access Level Offset](s)?
Delete this cell from
the cell list
Yes
No
No
No
No
Yes
End
For service cell:
Min Access Level Offset=0M rule will remove the neighbor
cells from the candidate cell listaccording to the flow.
Yes
Yes
M rule will remove the cells from the candidate cell list according to the
following conditions:
Under the condition of non-direct retry, if Inter-BSC SDCCH HO Allowed isNo, and
this is an external neighboring cell, and the current channel is SDCCH
If the cell is overload
RX_LEV_DL < Min DL Power on HO Candidate Cell + Min Access Level Offset
RX_LEV_UL < Min UL Power on HO Candidate Cell + Min Access Level Offset
For service cell:Min Access Level Offset is 0.
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GSM Handover Algorithm N-45
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Data Configuration of M Rule
[Inter-BSC SDCCH HO Allowed]
Value Range: Yes, No
Default Value: No
Description: This parameter indicates whether an inter-BSC SDCCH
handover is allowed. An inter-BSC SDCCH handover is triggered when an
MS succeeds in requesting SDCCH but fails to request TCH in a BSC.
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GSM Handover Algorithm N-46
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Data Configuration of M Rule
[Min UP Power on HO Candidate Cell]
Value Range: 0~63 (-110 dBm to -47 dBm) Default Value: 10
Description: The M criterion supports the minimum value constraint of uplink received level of the
neighbor cell. Expected uplink level of the neighbor cell >= (the minimum uplink power of the
candidate cell for handover + the minimum access level offset)The M criterion is satisfied only when
the expected downlink level of the neighbor cell >= (the minimum downlink power of the candidate
cell for handover + the minimum access level offset).0-63 with 0 indicating -110 dBm and 63
indicating -47 dBm.
[Min DL Level on Candidate Cell]
Value Range: 0~63 (-110 dBm to -47 dBm) Default Value: 15
Description: This parameter indicates the lower threshold of downlink receive level when a cell
becomes a candidate cell.
Remarks: This parameter must be appropriately specified. If it is too high, some desired cells may be
excluded from the candidate cells. If it is too low, an unwanted cell may become the target cell, thus
leading to handover failures or call drops. A cell can become a candidate cell only when the receive
level minus this parameter is greater than the minimum access level offset.
[Min Access Level Offset]
Value Range: 0~63 Unit: dB Default Value: 0
Description: This offset is based on the Min DL level on Candidate Cell. For different adjacent cells,
different offsets can be defined. Only when the receiving level of an adjacent cell > Min DL Level on
Candidate Cell + Min Access Level Offset, then this cell become a candidate cell.
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GSM Handover Algorithm N-47
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K Rule Flow of calculating K value.
Begin
Finish to calculatevalue K to all cells?
Serving cell?
K=0
No
K = RX_LEV (n) RX_LEV (s)
Yes
End
No
Yes
All the candidate cells are ranked in descending order according to the K value
A
F
E
D BC
Serving
Cell
Receiving
Level
Cell
Serving Cell
Cell ACell B
Cell C
Cell D
Cell E
Cell F
After the M rule , all the candidate cells are ranked in descending order
according to the K value
Service cell: K = 0
Neighboring cell: K = RX_LEV (n)RX_LEV (s)
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GSM Handover Algorithm N-48
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Network Feature Adjustment
After network feature adjustment, all the candidate cells have their
own 16 bits value.
The smaller the value is, the higher the handover priority and
position of the cell are in the candidate cell list, then it is possible to
be the candidate cell.
TheLowest
Weight
TheHighest
Weight 16 15 14 13 1
2 11 10 9
8 7 6 5
4 3 2
1
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GSM Handover Algorithm N-49
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Network Feature Adjustment
The 1st~3rd bits
The bit value indicates the priority of downlink receiving level
according to the cell signal level and the penalty process taking place
beforehand.
The values come from max. 6 candidate cells and 1 serving cell
according to the level ranges from 000~110. The value for the cell
with the strongest signal level is 000.
141516 12345678910111213
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GSM Handover Algorithm N-50
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Network Feature Adjustment
The 4th bit: Inter-cell HO hysteresis bit.
Note: In PBGT HO, whichever the greater of the inter-cell ( of the
same layer ) hysteresis and PBGT threshold, that value will be used
in the PBGT HO.
141516 12345678910111213
Is serving cell?
Always set to 0
No
RX_LEV_DL (n) >=
RX_LEV_DL (s) +
[Inter-cell HO hysteresis]
Yes
Set to 0Yes
Set to1
No
Service cell: always 0
Neighboring cell: when RX_LEV_DL (n) >= RX_LEV_DL (s) + Inter-
cell HO hysteresis, bit 4th is set to 0. Otherwise, set to 1
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GSM Handover Algorithm N-51
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Data Configuration of Inter-cell HO Hysteresis
[Inter-cell HO Hysteresis]
Value Range: 0~63
Unit: dB
Default Value: 5
Description: This parameter indicates the handover hysteresis between
adjacent cells of the same layer. The purpose of setting this parameter is to
reduce the "Ping-Pong" handovers. The value of this parameter is invalid if
cells are not on the same layer. 4 dB for populous urban areas and 8 dB for
suburbs.
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GSM Handover Algorithm N-52
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Network Feature Adjustment
The 5th~10th bits
The bit value is decided according to their position in Huawei
hierarchical network structure.
Huawei cell layers can be divided into 4 layers and each layer can be
further divided into 16 different priorities.
So there are 64 different priorities in Huawei hierarchical cell structure.
141516 12345678910111213
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GSM Handover Algorithm N-53
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Hierarchical Cell Structure
GSM900 Cell
Micro Cell
Umbrella Cell GSM 900
GSM1800 GSM1800GSM1800
GSM 900
GSM900GSM900
GSM1800GSM1800
GSM1800 Cell
GSM 900
GSM900GSM900
GSM1800GSM1800
Layer 4low
Layer 3
Layer 2
Layer 1high
The handover algorithm of Huawei divides the whole network into four
layers, each of which further divided into 16 levels. The lower the layer
is, the higher the handover priority level will be. The Micro Cell layer
has the highest priority level.
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GSM Handover Algorithm N-54
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Data Configuration of Cell HierarchicalNetwork Structure
[Cell Layer]
Value Range:1~4 (mapping to the PICO layer, the MICRO layer, the MACRO layer, and the
UMBRELLA layer)
Unit: Layer
Default Value: 3
Description: The framework of Huawei network is divided into four layers: Umbrella layer, Macro
layer, Micro layer, and Pico layer. Each layer is designed with 16 priorities. The Umbrella layer refers
to the GSM900 layer with a large coverage area. It implements the high-layer coverage and the
connection of MSs moving at a high speed. The Macro layer carries most traffic on the GSM900 band.
The Micro layer carries most traffic on the DCS1800 band. It solves the problem of insufficient
resources. The Micro layer is a main cell layer for dual-band MSs in the future. The Pico layer is a
microcell layer on the GSM900 and DCS1800 bands. It meets the requirements for the provisioning of
traffic at hot spots and dead zones.
Remarks: You can set multiple priorities (a maximum of 16 priorities) for each layer. From the aspect
of traffic priority, if the layer and level of a cell is low, the priority is high.
[Cell Priority]
Value Range:1~16
Unit: Level
Default Value:1
Description: This parameter controls handover between cells at the same layer. Generally, the cells at
the same layer have the same priority. If the cells at the same layer have different priorities, the cell
with a smaller value has a higher priority.
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GSM Handover Algorithm N-55
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Network Feature Adjustment
The 11th bit: The bit value is decided by cell-load-sharing criterion.
This bit is affected by 14th bit.
141516 12345678910111213
System load>=[System Flux Threshold for Load HO] or[Load HO Allowed ] =No ?
Yes 11th bit is
turned off
Is serving cell?
set to 0
NoYes
Cell load >= [Load
HO T hreshold](s)?
set to 1 set to 1
cell load >=[ Load Rep.
on Candidate Cell](n)?
set to 0
Yes
No
Yes
No
No
The 11th bit: bit value is decided by cell-load-sharing criterion. And this bit
will be turned off when the system load is higher than System Flux
Threshold for Load HO orLoad HO Allowedis set toNO
Service cell: if cell load >=Load HO Threshold, bit 11th is set to 1.
Otherwise, set to 0
Neighboring cell: if cell load >=Load Rep. on Candidate Cell, bit 11th is set
to 1. Otherwise, set to 0
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GSM Handover Algorithm N-57
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Data Configuration of Cell-load-sharing
[Load HO Threshold]
Value Range: 0~100(%)
Default Value: 85
Description: When the load handover is switched on, it is recommended that the Load HO
Threshold is set to 85.The cell load refers to TCH usage. When the cell load exceeds thevalue of Load HO Threshold, the BSC starts the load handover. That is, the BSC starts the
load handover after the TCH in the cell are proportionally occupied.
Remarks: Even if the Load HO Allowed is set to Yes, the Load HO Threshold and Load
Req. on Candidate Cell affect the queuing of the candidate cell handover. Therefore, when
the cell is overloaded, the handovers such as PBGT cannot be performed if this parameter
is not properly set.
[Load Req. on Candidate Cell]
Value Range: 0~100(%)
Default Value: 75
Description: If the cell load is lower than the value of this parameter, the cell accepts users
that are handed over to the cell due to their cell load. If the cell load is not lower than the
value of this parameter, the cell refuses the users.
Remarks: The same as that of Load HO Threshold
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GSM Handover Algorithm N-58
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Network Feature Adjustment 12th bit and 13th bit: Whether share the same BSC or MSC.
141516 12345678910111213
Is serving cell?NoYes
Both 12th and 13th set to 0
Different BSC:12th set to 113th set to 0
Is [Co-BSC/MSCAdj] yes?
See 14th bit
Yes
No
Co-BSC?
Co-MSC?
No
Yes
Different MSC:12th set to 013th set to 1
No
Yes
Turn off
12th &13th bit
The same BSC:12th set to 013th set to 0
12th bit: if neighbor cell is co-BSC with the serving cell, 12 th bit is set to 0. Otherwise,
set to 1
13th bit: if neighbor cell is co-MSC with the serving cell, 13 th bit is set to 0.
Otherwise, set to 1
Service cell: is always set to 0
These two bits will be turned off when Co-BSC/MSC Adj. is set toNO
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GSM Handover Algorithm N-59
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Data Configuration of Co-BSC&MSC
[Co-BSC/MSC Adj]
Value Range: Yes, No
Default Value: Yes
Description: This parameter indicates whether the sequence of candidate
cells is adjusted. After the sequence is adjusted, the handover within the same
BSC/MSC takes priority.
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GSM Handover Algorithm N-60
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The 14th bit: Layer HO threshold adjustment bit.
Network Feature Adjustment
141516 12345678910111213
The 15th/16th bits are reserved
Is serving cell?
set to 0
NoYes
Bit 14th set to 1, and bit
5th ~13th are turned off set to 0
Yes YesRX_LEV_DL >= [Inter-layer HOThreshold][Inter-layer HO Hysteresis]?
RX_LEV_DL >= [Inter-layer HOThreshold] + [Inter-layer HO Hysteresis]?
No No
The 14th bit: Layer HO threshold adjustment bit
Serving cell: RX_LEV_DL >=Inter-layer HO ThresholdInter-layer HO
Hysteresis, bit 14th is set to 0
Neighboring cell: RX_LEV_DL >=Inter-layer HO Threshold+Inter-layer HO
Hysteresis, bit 14th is set to 0.
If the above criterion is not met, then bit 14th is set to 1.
At the same time, bit 5th- 13th bits are turned off.
The 15th/16th bits are reserved
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GSM Handover Algorithm N-61
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Data Configuration of Layer HO
Threshold Adjustment
[Inter-layer HO Threshold]
Value Range: 0~63(-110 dBm to -47 dBm)
Default Value: 25
Description: In BSC handover algorithm, the M criterion is used to rank the handover
candidate cells. The M criterion includes 16 bits. This parameter is one bit of the 16 bits andit affects the rank of a candidate cell. When the downlink level of a cell is lower than this
threshold, the cell takes low priority as far as comprehensive sequence is concerned.
Remarks: Make sure that the receive level of the destination cell is higher than this threshold
in inter-layer handover or load handover. Otherwise, the MS may be handed from a cell with
heavy load and high level (high priority cell) to a cell with light load and low level (low
priority cell), thus leading to call drops.
[Inter-layer HO Hysteresis]
Value Range: 0~63
Unit: dB
Default Value: 3
Description: This parameter indicates the hysteresis of an inter-layer or inter-priority
handover. It is used to avoid inter-layer ping-pong handovers. Actual Inter-layer HO
Threshold of a serving cell = Inter-layer HO Threshold C Inter-layer HO hysteresis Actual
Inter-layer HO Threshold of a neighboring cell = Inter-layer HO Threshold + Inter-layer HO
hysteresis
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GSM Handover Algorithm N-62
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General HO Process
MS Goes into New
Dedicated Mode
MS Goes into
Dedicated Mode
Measure and MeasurementResult Report
1
MR. Preprocessing2
Handover Judgment3
Handover Implementation4
TA HO
Interference HO
Rx_Level_Drop HO
Bad Quality HO
Load HO
Edge HO
Layer HO
PBGT HO
AMR HO
No DL MR HO
Concentric Cell HO
MS Fast Moving HO
Enhanced Dual Band HO
Penalty Processing
Ranking Processing
OM Forced HO
Direct Retry
Emergency HO
Normal HO
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GSM Handover Algorithm N-63
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No DL MR HO
Serving Cell Neighboring Cell
When the quality of Um interface become worse and worse, it is
for the worse uplink quality that MS can not deliver downlink MR,
while the downlink quality is not bad enough for MS to receive the
downlink message normally.
Baduplinkquality
When the quality of Um interface become worse and worse, it is for the worse uplink
quality that MS can not deliver downlink MR, while the downlink quality is not bad
enough for MS to receive the downlink message normally. Under this kind of
urgency condition, in order to save this call, the network send handover command to
MS.
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GSM Handover Algorithm N-64
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Position of No DL MR HO
MS Goes into NewDedicated Mode
MS Goes into
Dedicated Mode
Measure and Measurement
Result Report1
MR. Preprocessing2
Handover Judgment3
Handover Implementation4
TA HO
Interference HO
Rx_Level_Drop HO
Bad Quality HO
Load HO
Edge HO
Layer HO
PBGT HO
AMR HO
Concentric Cell HO
MS Fast Moving HO
Enhanced Dual Band HO
Penalty Processing
Ranking Processing
OM Forced HO
Direct Retry
Emergency HO
Normal HO
No DL MR HO
Attention: After MR. Preprocessing, the No DL MR handover is triggered if trigger condition is satisfied.
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GSM Handover Algorithm N-65
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No DL MR HOBegin
Report 1 DL MR at lease?
Is [No Dl Mr. HOAllowed] Yes ?
= signal quality
filter length?
Yes
signal quality filter length:
For TCH:[Filter Length for TCH Qual]
For SDCCH:[Filter Length for SDCCH Qual]
No Dl Mr. in
current Mr.?
Yes
UL_Qua. (after filering)
>=[No Dl Mr.Ul QualHO Limit]?
Yes
Only one
cadidate cell?
>=[Forbidden timeafter MAX Times]?
Yes
No
No
No
Yes
Yes
No
No
[Intrecell HOAllowed]?
Yes
No
Triggering condition
No DL information in current MR
Stored UL Rx_Qual Value Number >=Rx_Qual Filter Length
UL Rx_Qual >=No DL MR HO UL Rx_Qual Threshold
Number of Lost DL MR < Cons. No DL MR HO Allowed Limit
Object cell selection
Prefer neighboring cell
If choose the service cell, it cannot in the penalty time for intra-cell handover.
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GSM Handover Algorithm N-66
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Data Configuration of No DL MR HO
[No Dl Mr. HO Allowed]
Value Range: Yes, No
Default Value: No
Description: This parameter is used to control the handover algorithm without downlink measurementreport. If this parameter is set to 0, the no handover algorithm without downlink measurement report is
disabled. Therefore, handover decision without downlink measurement report is not allowed in this cell.
If this parameter is set to 1, the no downlink measurement report handover algorithm is enabled.
Therefore, handover decision without downlink measurement report is allowed in this cell.
[No Dl Mr. Ul Qual HO Limit]
Value Range: 0~70 (mapping to RQ (0~7)10)
Default Value: 60
Description: This parameter indicates the uplink receive quality threshold of triggering an emergencyhandover when no measurement result on downlink channels is contained in the MR. The emergency
handover is allowed only when the filtered uplink receive quality crossed this threshold. When an
emergency handover is triggered, inter-cell handover takes priority. Intra-cell handover, however, is
triggered if no candidate cell is available and intra-cell handovers are allowed.
[Cons. No Dl Mr. HO Allowed Limit]
Value Range: 0~64
Default Value: 8
Description: This parameter indicates the upper threshold of consecutive MRs containing no downlinkmeasurement result for a call. Each call is configured with a global timer, which counts the number of
consecutive MRs containing no downlink measurement. When the timer exceeds this threshold, the
handover is disabled and the timer is reset.
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GSM Handover Algorithm N-67
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TA(Time Advance) HO
Serving Cell Neighboring Cell
TA Threshold(s)
Time
TA(s)
HandoverTriggering
TA Threshold(n)
or
Handover Triggering ZoneTA(n)
Because a MS is far away from its serving BTS, the practice TA value is
more than TA threshold configured in data configuration, TA handover is
triggered.
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GSM Handover Algorithm N-68
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TA(Time Advance) HO
Trigger
TA handover
Begin
The actual TA >=
[TA Threshold]?
Is [TA HO Allowed]
Yes ?
Any neighbour cell
exist?
Is serving cell?
Select the cell with the
highest priority in the
cadidate cell list
TA(n is in the same BTS)= TA Threshold
Object cell selection
The cell must be of the highest priority in the candidate cell sequence and meet
the following restrictions.
Restriction
The service cell cannot be the object cell.
HO is not allowed when TA Threshold of the neighboring cell with the same BTS
is equal or smaller than that of the service cell.
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GSM Handover Algorithm N-69
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Data Configuration of TA HO
[TA HO Allowed]
Value Range: Yes, No
Default Value: Yes
Description: The parameter indicates whether a Timing Advance (TA)
handover is allowed. A TA handover is triggered when the TA is higher than
the triggering threshold. TA is calculated based on the distance between the
MS and the BTS. The longer the distance is, the greater the TA is.
[TA Threshold]
Value Range: 0~255
Unit: Bit period (A bit period corresponds to 0.55 km.)
Default Value: 255
Description: This parameter indicates the TA threshold of triggering
emergency handover. Emergency handover is triggered when TA is equal to
or greater than this threshold.
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GSM Handover Algorithm N-70
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Interference Handover
Lev_Thr
Rx_Qual
RX_Lev
Qual_Thr
InterferenceOrigin
Serving Cell Neighboring Cell
Handover Triggering
Zone
For a MS or a BTS, when the receiving quality is lower than the interference
quality threshold and receiving level is higher than the interference level
threshold, it is considered that interference exists in serving cell, so
interference handover is triggered.
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GSM Handover Algorithm N-71
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Interference HOBegin
UL or DL receiving
Quality(s)>=A?
Is [Interference HO
Allowed] Yes ?
Any neighbour cell
exist?
Is serving cell?
Select the cell with thehighest priority in the
cadidate cell list
Rx_Level(n)>=[Inter-layer HO Threshold](n) +
[Inter-layer HO Hysteresis](n)?
Yes
No
End
No
No
Yes No
NoYes
None AMR FR:
A = RXQUALn, 1 RXQUAL8
9. Rx_lev is within [53,55], and Rx_qual > RXQUAL9
10. Rx_lev is within [56,58], and Rx_qual > RXQUAL10
11. Rx_lev is within [59,62], and Rx_qual > RXQUAL11
12. Rx_lev >= 63, and Rx_qual > RXQUAL12
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GSM Handover Algorithm N-72
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Data Configuration of Interference HO
50>=63RXQUAL12
5159~62RXQUAL11
5256~58RXQUAL10
5353~55RXQUAL9
5449~52RXQUAL8
5546~48RXQUAL7
4042~45RXQUAL6
5739~41RXQUAL5
5836~38RXQUAL4
5932~35RXQUAL3
60=31RXQUAL2
70
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Data Configuration of Interference HO
[Interference HO Allowed]
Value Range: Yes, No
Default Value: Yes
Description: The parameter indicates whether an interference handover is allowed. An
interference handover is triggered when the receive level is higher than the receive threshold,
but the transmission quality is lower than the handover triggering threshold.
Remarks: Both downlink and uplink interference is judged, and inter-cell handover takes
priority. If no target cell is available, intra-cell interference handover can be implemented in
the serving cell if intra-cell handovers are allowed.
[RXQUAL1] ~ [RXQUAL12]
Value Range: 0~70
Description: Quality threshold 1~12 for the interference handover of nonCAMR FR voice
services. The value corresponds to (quality level 0~7) x 10.See the next slide
[RXLEVOff]
Value Range: 0~70
Default Value: 5
Description: The quality level offset of the interface handover of the AMR FR service
relative to non-AMR services or the AMR HR service (x 10).
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GSM Handover Algorithm N-74
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Rx_Level_Drop HO
Rx_Level_Drop HO will be triggered when receiving level drops fast
because of barrier such as high building.
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GSM Handover Algorithm N-76
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Data Configuration of Rx_Level_Drop HO
[Rx_Level_Drop HO Allowed]
Value Range: Yes, No Default Value: No
Description: The parameter indicates whether the emergency handover algorithm is allowed. The emergency handover algorithm isused to prevent call drops when the receive level of the MS drops rapidly. Generally this algorithm is not enabled until the
conditions are met. To enable this algorithm, original MR is required for the BSC.
[Filter Parameter A1~A8]
Value Range: 0~20 Default Value: 10
Description: Filter Parameter A1~A8 and Filter Parameter B work together to decide whether the rapid drop of the receive levelmust be reflected in one or multiple MRs. The conditions to trigger a rapid level dropping handover are as follows; In the algorithm
above, X1, X2, X3, X4, X5, X6, X7, and X8 indicate the uplink receive levels of the last eight MRs in the queue. Filter Parameter
A1~A8 must meet the following conditions: A1+A2+A3+A4+A5+A6+A7+A8=80. For example, if you want to reflect the rapid
drop of the cell level in a MR, you can set A3-A8 to greater than 10, A1 to 0, and A2 to 20.
[Filter Parameter B]
Value Range: 0~200 Default Value: 0
Description: This is one of the parameters that determine whether a handover is required due to fast dropping levels.This parameter
indicates the drop trend of the receive level within a period. The greater the parameter B is, a more rapid level drop is required for
triggering a rapid level dropping handover.See Filter Parameter A1-A8.
[Edge HO UL RX_LEV Threshold]
Value Range: 0~63 (-110 dBm to -47 dBm) Default Value: 10
Description: The parameter indicates the uplink receive level threshold of an edge handover. An edge handover will be triggered ifthe uplink receive level is constantly lower than "Edge HO UL RX_LEV Thrsh." for a period longer than Edge HO Valid Time(s)
within Edge HO Watch Time(s). If PBGT handover is enabled, the corresponding edge handover threshold can be lowered. If
PBGT handover is disabled, this parameter must be properly specified to avoid overlapping coverage and channel interference. This
parameter should be adjusted based on the performance statistics and actual networks to achieve uplink-downlink balance.
Remarks: Edge handover uplink/downlink receive level threshold < Uplink/downlink signal strength lower limit of HUAWEI IIpower control
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GSM Handover Algorithm N-77
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BQ(Bad Quality) HO
Begin
Is [BQ HO Allowed]
Yes ?
Any neighbour cell
exist?
Is serving cell?
Select the cell with the
highest priority in the
cadidate cell list
Yes
No
End
No
No
Yes
NoYes
Yes
UL_Rx_Q(s)>=[UL Qual.
Threshold]or DL_Rx_Q(s)
>=[DL Qual. T hreshold]?
RX_LEV_DL (n) >RX_LEV_DL (s)
+ Inter-cell HO hysteresis(s)
-BQ HO Margin(s) ?
[IntracellHO Allowed] yes
& cell notpunished?
Suitable cell
exist?
Trigger
BQ handover
Yes
Yes
Yes
No
No No
When the receiving level of a MS or a BTS is lower than the quality
threshold, bad quality handover will be triggered.
Triggering condition
UL receiving quality >= UL Qual. Threshold
OR DL receiving quality >= DL Qual. Threshold
For AMR call, the quality threshold is DL/UL Qual. Limit AMR FR/HR
Object cell selection
The cells must be of the highest priority in the candidate cell sequence and meet
the following restrictions.
Restriction
Prefer neighboring cell. If the number of neighboring cell is more than one, it is
required that RX_LEV_DL (n) > RX_LEV_DL (s) + Inter-cell HO hysteresis -
BQ HO Zone
If there is no neighboring cell, handover can occur to the service cell, and the
channel at different frequency band, different MA, different TRX or different
channel (from left to right) is preference.
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GSM Handover Algorithm N-78
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Data Configuration of BQ HO
[BQ HO Allowed]
Value Range: Yes, No
Default Value: Yes
Description: The parameter indicates whether a Bad Quality (BQ) handover is allowed. BQ handover is triggeredwhen Bit Error Ratio (BER) over uplink/downlink channels is higher than the triggering threshold. If BER rises, or
signal strength drops, suspect that the signal power is low or channel interference increases.
Remarks: Inter-cell BQ handover is preferentially performed. If no target cell is available, intra-cell BQ handovercan be implemented in the serving cell if intra-cell handovers are allowed.
[DL Qual. Threshold]
Value Range: 0~70 (RQ (0~7) 10)
Default Value: 60
Description: This parameter indicates the downlink receive quality threshold of triggering an emergency handover.When the receive quality of the downlink is greater than DL Qual Threshold, an emergency handover is triggered.
When frequency hopping or DTX of the cell is enabled, it is recommended that you set this parameter to 70. When
an emergency handover is triggered, inter-cell handover takes priority. An intra-cell handover, however, is triggered
if no candidate cell is available and intra-cell handovers are allowed.
[UL Qual. Threshold]
Value Range: 0~70 (RQ (0~7)10)
Default Value: 60
Description: This parameter indicates the uplink receive quality threshold of triggering an emergency handover.When the receive quality of the uplink is greater than UL Qual Threshold, an emergency handover is triggered due to
bad quality. When frequency hopping or DTX of the cell is enabled, it is recommended that you set this parameter to
70.When an emergency handover is triggered, inter-cell handover takes priority. An intra-cell handover, however, is
triggered if no candidate cell is available and intra-cell handovers are allowed.
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GSM Handover Algorithm N-79
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Data Configuration of BQ HO
[DL/UL QuaLimitAMRFR]
Value Range: 0~70
Default Value: 65
Description: This parameter indicates the urgent switchover downlink/uplink quality controlfor the AMR FR service. The values of this parameter match quality levels 0-7 multiplying
10. The urgent switchover is triggered only when the downlink/uplink receiving quality of
the MS is greater than the switchover threshold, that is, the receiving quality is poor.
[DL/UL QuaLimitAMRHR]
Value Range: 0~70
Default Value: 60
Description: This parameter indicates the urgent switchover downlink quality control for theAMR HR service. The values of this parameter match quality levels 0-7 multiplying 10. The
urgent switchover is triggered only when the downlink receiving quality of the MS is greater
than the switchover threshold, that is, the receiving quality is poor.
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GSM Handover Algorithm N-80
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Data Configuration of BQ HO
[BQ HO Margin]
Value Range: 0~127 (-64 dB to +63 dB)
Default Value: 69
Description: A Margin in BQ handover algorithm used to judge whether to
perform BQ handover. When BQ Handover Allowed is set to Yes and Inter-
cell HO Hysteresis > "Inter-cell HO Hysteresis-BQ HO Margin", the Inter-
cell HO Hysteresis will act instead of the BQ HO Margin. When "Inter-cell
HO Hysteresis-BQ HO Margin" is assigned with a value smaller than 64, MS
can hand over to a lower level neighboring cell. 69 for popular urban areas,
72 for suburbs.
Remarks: If the data is updated from M900/M1800 BSC to HUAWEI
BSC6000,the default value of this parameter is 5.Then it's necessary tomodify the value of this parameter to 69,otherwise the BQ HO algorithm will
be invalid.
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GSM Handover Algorithm N-81
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General HO Process
MS Goes into New
Dedicated Mode
MS Goes into
Dedicated Mode
Measure and MeasurementResult Report
1
MR. Preprocessing2
Handover Judgment3
Handover Implementation4
TA HO
Interference HO
Rx_Level_Drop HO
Bad Quality HO
Load HO
Edge HO
Layer HO
PBGT HO
AMR HO
No DL MR HO
Concentric Cell HO
MS Fast Moving HO
Enhanced Dual Band HO
Penalty Processing
Ranking Processing
OM Forced HO
Direct Retry
Emergency HO
Normal HO
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GSM Handover Algorithm N-82
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Enhanced Dual Band HO
Enhanced dual band cell is two different band cells which locate a
common site, and have the same azimuth.
Purpose
During the procedure of channel assignment and handover,
900M cell and 1800M cell can share their resource.
Assign the channel with low load in UL to MS preferentially.
Make MS handover from the high load cell to the low load cell.
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GSM Handover Algorithm N-83
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Channel Assignment of Enhanced Dual Band HO
RX_LEV_OL>= [Incoming OL Subcell HO level Threshold(dB)] and
RX_LEV_UL RX_LEV (n) >[Distance Between Boundaries of UL and OL Subcells(dB)]Attention:
RX_LEV (n): RX_LEV of the strongest neighboring cell which has the same frequency band and layerwith underlaid subcell, but locates in a different BTS. If there is no such a cell, this value is -110dBmIf [ATCBHoSwitch] is [Close], the second condition is turn off.
A:
Beginfrom UL
[Assignment Optimization
of UL Subcell Allowed
or not] ?
Cell load of UL >[UL Subcell General
Overload Threshold(%)]?
Yes
A
Yes
No
Any idle TCH
Available in OL?
Assign TCH
in OL
YesNo
Yes
Assign TCH in UL
or direct retry identification
or queuing
No
No
TCH assignment (SDCCH channel in UL)
TCH assignment (SDCCH channel in underlaid)
IfAssignment Optimization of UL Subcell Allowed or not is set to NO, assign
TCH in underlaid as the normal assignment procedure
IfAssignment Optimization of UL Subcell Allowed or not is set to YES, assign
TCH in overlaid when the following conditions are met
Cell load of underlaid > UL Subcell General Overload Threshold
RX_LEV_OL >= Incoming OL Subcell HO level Threshold
RX_LEV_ULRX_LEV (n) > Distance Between Boundaries of UL and OL
SubcellsDistance Hysteresis Between Boundaries of UL and OL Subcell(dB)
RX_LEV (n): RX_LEV of the strongest neighboring cell which has the
same frequency band and layer with underlaid subcell, but locates in a
different BTS. If there is no such a cell, this value is -110dBm
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GSM Handover Algorithm N-84
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Data Configuration of Channel
Assignment
[ATCBHoSwitch]
Value Range: Close, Open
Default Value: Open
Description: The switch of the ATCB handover algorithm.
[Assignment Optimization of UL Subcell Allowered Or Not]
Value Range: Yes, No
Default Value: Yes
Description: This parameter indicates whether the access request originated in the underlaid subcell is
preferably assigned between overlaid subcell cell and underlaid subcell cell according to the Out Cell
Low Load Thred.
[UL Subcell General OverLoad Threshold(%)]
Value Range: 0~100
Unit: %
Default Value: 80
Description: If the ratio of underlaid subcell channel occupancy is greater than the value of this
parameter, some calls in the underlaid subcell are handed over to the overlaid subcell. Moreover, calls
originated in the underlaid subcell are preferably assigned to the channel in overlaid subcell.
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GSM Handover Algorithm N-85
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Data Configuration of Channel
Assignment
[Distance Between boundaries of UL And OL Subcells(dB)]
Value Range:0~63
Unit: dB
Default Value: 10
Description: This parameter indicates the distance between the overlaid subcell and
underlaid subcell. The value of this parameter is comparative. The greater the value is, the
longer the distance is. The enhanced dual-band network handover algorithm refers to the
boundary between underlaid subcell and overlaid subcell based on the comparative value of
signal strength of serving cell and neighboring cell. Suppose the signal strength of serving
cell is SS(s), and neighboring cell SS(n). If SS(s) is equal to SS(n), the cell is in the underlaid
subcell boundary. If the value of SS(s) - SS(n) is larger than the value of Distance Between
boundaries of UL And OL Subcells(dB), the cell is in the overlaid subcell.
[Incming OL Subcell HO Level Threshold(dB)]
Value Range: 0~63
Unit: dB
Default Value: 30
Description: This parameter indicates the lowest threshold of overlaid subcell level of the
handover from underlaid subcell to overlaid subcell. When the MS receive level is higher
than the value of this parameter, the BSC allows the handover of overlaid subcell cell.
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GSM Handover Algorithm N-86
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Begin
from OL
[Assignment Optimization
of OL Subcell Allowed or
not ] No ?
Cell load of UL= UL Subcell Lower Load
Threshold
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GSM Handover Algorithm N-87
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Data Configuration of Channel
Assignm