3 omf810002 gsm handover algorithm issue2.0

OMF010002 Handover ISSUE2.1GSM Handover Algorithm
Foreword
Handover is a key technology of mobile communication system and make continued conversation possible.
Handover algorithm in Huawei product is flexible and powerful.
Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Objectives
Upon completion of this course, you will be able to:
Outline the types of handover
Master handover judgment flow
Explain HO data configuration
Contents
Contents
Purposes of HO
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.
Classification by Reason
Timing Advance (TA) HO
Classification by Synchronization
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 4
Case 5
Synchronous handover: source and target cell belong the same BTS
Asynchronous handover: source and target cell belong the different BTS
Classification by Equipment and Channel
SDCCH → TCH
(Direct Retry)
SDCCH → SDCCH
Inter – Cell HO
Intra – BSC HO
Intra – MSC HO
Inter – MSC HO
Contents
Contents
2.3 Measurement Report Preprocessing
General HO Process
MS Goes into Dedicated Mode
Measure and Measurement Result Report
1
General HO Process
Measure and Measurement Result Report
1
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.
The downlink measurement report
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 is used. 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.
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.
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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
12TCH
1SACCH
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.
The SACCH measurement report period varies with the channel occupied by MS in dedicated mode.
When associated with SDCCH, SACCH measurement period is 470ms, this is because there is an entire SACCH message block in 2 SDCCH 51-multiframes.
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 one SACCH burst in each 26-multiframe, therefore only four 26-multiframe can constitute a complete measurement report.
General HO Process
Measurement Report Preprocessing
1
2
MR Preprocessing
MR Preprocessing
Filtering
MR preprocessing consists of two steps: interpolation and filtering.
MR Interpolation
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.
MR Filtering
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.
Data Configuration of MR Preprocessing
[MR Preprocessing]
Description: This parameter indicates whether the BTS pre-processes the MR.
This parameter determines the location where power control is performed. If this parameter is 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]
Default Value: No
Description: This parameter indicates whether the original MR is transferred to the BSC after 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 is greater than 2.
[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.
[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 this threshold 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. When this 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 response is 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.
[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.
General HO Process
1
Penalty Processing
Intra-cell HO
HO Fails
Punish on other high priority layer cells
AMR HO
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
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
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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Data Configuration of Penalty for Handover Failure
[Penalty Level after HO Fail]
Value Range: 0~63
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.
Data Configuration of Penalty for Handover Failure
[RscPenaltyTimer]
Default Value: 5
Description: This parameter indicates the length of the penalty timer for handover failure between adjacent cells due to cell congestion.
[UmPenaltyTimer]
Default Value: 10
Description: This parameter indicates the length of the penalty timer for handover failure between adjacent cells due to failed air interface connection.
[CfgPenaltyTimer]
Default Value: 255
Description: This parameter indicates the length of the penalty timer for handover failure between adjacent cells due to incorrect data configuration.
Penalty for Emergency Handover
BSC
Punish the original cell when an emergency HO ( due to BQ and TA) 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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Data Configuration of Penalty for Emergency Handover
[Penalty Level after BQ HO]
Value Range: 0~63
Default Value: 63
Description: This parameter indicates the penalty level given to the original serving cell where emergency handover is 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 the original 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
Default Value: 15
Description: This parameter indicates the penalty time given to the original serving cell where emergency handover is 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.
Data Configuration of Penalty for Emergency Handover
[Penalty Level after TA HO]
Value Range: 0~63
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.
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.
Back? No way!
Micro cell
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.
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
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.
Penalty for Concentric Cell
A new concentric cell HO is prohibited within a penalty time after a concentric cell HO failure.
Underlaid
Overlaid
Do not attempt again during penalty time after one failed HO(O->U)!
Do not attempt again after N failed HO(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.
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.
Penalty for Enhanced Concentric Cell
A new UO HO is prohibited within a penalty time after a OU HO is performed successfully.
Underlaid
Overlaid
This penalty is valid only for Enhanced Concentric Cell.
Data Configuration of Penalty for Enhanced Concentric Cell
[Penalty Time of UtoO HO(s)]
Value Range: 0~255
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.
Penalty for Intra-cell HO
A new intra-cell HO is prohibited if it occurs too frequently.
3
7
12
32
Forbidden time after Max. times: 20s
Interval for consecutive HO Jud: 6s
1st.
Because of the co-channel interference and other interference, the voice quality of a MS on certain frequency may lower than the handover threshold, now, the voice quality can be satisfied if the MS hands over to another frequency in the same cell. On the other side, the signaling flow of this kind of intra-cell handover is less and handover successful ratio is higher.
But under some specific condition (for example: several frequency are all interfered in a cell), then continual intra-cell handover may occurred. So it is necessary to control the frequency of intra-cell handover.
Data…

3 omf810002 gsm handover algorithm issue2.0

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