39034739-handover-training
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Huawei Confidential
OMF010002 HandoverOMF010002 Handover
2
Summary of Handover
HO Algorithm process
HO Data Configuration
HO Signaling process
Course Contents
3
Summary of HO—Purposes of HO
• 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
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• Classification of HO: Emergency HO
• Timing Advance (TA) Emergency HO• Bad quality (BQ) Emergency HO • Rx_Level_Drop Emergency HO• Interference Emergency HO
load HO Normal HO
• Edge HO• Layer HO• Power Budget (PBGT) HO
Speed-sensitive HO (Fast moving MS HO) Concentric Cell HO
Summary of HO—Classification of HO
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Summary of Handover (HO)
HO Algorithm process
HO Data Configuration
HO Signaling process
Course Contents
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• General HO process
• Measurement report preprocessing
• Penalty processing
• Basic ranking and Secondary ranking
• HO judgment
HO Algorithm process
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General process of HO Algorithm
M.R.preprocessing
Penalty processing
Basic ranking
Secondary ranking
HO judgement
TA emergency HO
BQ emergency HO
RSD emergency HO
Interf. emergency HO
Load Sharing HO
Edge HO
Layer HO
PBGT HO
Processing program
OM forced HO
Directed retry
Overlaid/underlaid HO
Fast moving MS HO
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1
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HO Algorithm process
• General HO process
• Measurement report preprocessing
• Penalty processing
• Basic ranking and secondary ranking
• HO judgment
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Measurement Report Preprocessing
• Measurement Report (MR): 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 Neighbour cell
The downlink measurement report of the neighbour cell (BCCH)
The downlink measurement report of the serving cell
The uplink measurement report of MS
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Measurement Report Preprocess
• MR interpolation Every time BSC receives a measurement report,
there will be an update to the basic rank of the cells.
BTS may fail to receive the measurement report from MS. Before the rank-update, BSC needs to recover the lost measurement reports according to Filter Table. If the lost MR amount is within the allowed range, then recovers the lost MR according to the algorithm.
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How to interpolate MR?
MR MR MR MR MR
Measurement report No. n
Measurement report No. n+4
Continuous MR flow
Measurement Report Preprocess
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• General HO process
• Measurement report preprocessing
• Penalty processing
• Basic ranking and secondary ranking
• HO judgment
HO Algorithm process
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Penalty Processing
• There are altogether four types of penalty process (second step of HO algorithm process )
Penalty on the target cell when a HO fails. Penalty on the original serving cell when an emergen
cy HO ( base on BQ and TA ) is performed. Penalty on other high priority layer cells after a fast m
oving HO is performed. A new HO attempt is prohibited within the penalty ti
me after an overlaid/underlaid HO fails.
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BTS
HO failure
BSC
Cell A
Cell B
Penalty Processing
• Penalty on the target cell: Punish the target cell when a HO fails. This is to avoid
the MS to select this cell again in next HO judgment.
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BTS
BQ& TA HO
BSC
Cell A
Cell B
Penalty Processing
• Penalty on the serving cell: Punish the original serving cell when an emergency HO
( due to BQ and TA) occurs.
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Back? No way!Back? No way!
Umbrella
Micro cell
Penalty Processing
• Giving penalty on the other three layers after MS handovers to Umbrella cell by fast-moving-HO. This is to keep MS staying in the umbrella cell and avoid frequent HO.
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Underlaid
Overlaid Do not attempt
again after a
failed HO!
Penalty Processing
• A new Overlaid/underlaid HO is prohibited within a penalty time after an Overlaid/Underlaid HO failure.
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HO Algorithm process
• General HO process• Measurement report preprocessing• Penalty processing• Basic ranking and secondary ranking • HO judgment
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Basic Ranking and Secondary Ranking
• Basic ranking and secondary ranking of cells are major parts of the HO judgment. Ranking is made through 16bits-algorithm. The serving cell and the neighbor cells will be listed in a cell list according to their 16bits value. The ranking processes include:
M rule
K rule
16bits ranking
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M rule:
Only the cells with received signal level satisfy the following conditions can be put into t
he candidate cell list.
For serving cell: RX_LEV (o) >MSRXMIN(o) + MAX(0,Pa(o))
i.e : RX_LEV(o) – MSRXMIN(o)-MAX(0,Pa(o)) > 0 ……….. ( 1 )
For Neighbor cell: RX_LEV (n) > MSRXMIN(n)+ MAX(0,Pa(n))+ OFFSET
i.e : Having the same formula as above
Pa(0) : MS_TXPWR_MAX(0) – P
Pa(n) : MS_TXPWR_MAX(n) – P
MS_TXPWR_MAX( ) : The appointed MS transmitting power by the BSS.
P : Max_Power_of_MS
Max_Power_of_MS : MS maximum transmitting power
Basic ranking and Secondary ranking
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• K rule Criterion: After the M rule , the serving cell and candidate neighb
or cells are ranked in descending order according to the receiving level only.
Basic Ranking and Secondary Ranking
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• The 16bits rule Both the serving cell and the neighbor cells have
their own 16bits value. The smaller the value is, the higher the priority and position the cell is in the cell list.
The 1st-3rd bits: bit value is decided 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.
16 9101112131415 12345678
Basic Ranking and Secondary Ranking
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The 4th bit: bit value is determined by inter-cell HO ( of the same layer ) hysteresis.
• The 4th bit of the serving cell is always 0,
• The receiving signal level of the neighbor cell >= The receiving level of the serving cell + Inter-cell HO ( of the same layer ) hysteresis, bit 4th is set to 0.
• The receiving level of the neighbor cell < The receiving level of the serving cell + Inter-cell HO ( of the same layer ) hysteresis, bit 4th is set to 1.
– 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.
16 9101112131415 12345678
Basic ranking and Secondary ranking
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The 5th-10th bits: bit value is decided according to their position in Huawei hierarchical network structure.
• When the signal level of the neighbor cells or the serving cell is lower than the layer HO threshold and hysteresis, this function is turned off and all bits are set to 0.
• That is to say only when the above criterions are met, then this function take effect.
• 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.
16 9101112131415 12345678
Basic ranking and Secondary ranking
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GSM900 Cell
Micro Cell
Umbrella Cell GSM 900
GSM1800 GSM1800GSM1800
GSM 900 GSM 900 GSM 900
GSM900GSM900
GSM1800GSM1800
GSM900 GSM900
GSM1800 GSM1800
GSM1800 Cell
• Hierarchical cell structure
Basic ranking and Secondary ranking
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The 11th bit: bit value is decided by cell-load-sharing criterion.
• Serving cell: if Cell Load>= Start threshold of load HO, bit 11th is set to 1, otherwise is set to 0.
• Neighbor cell: if Cell Load>=Receive threshold of load HO, bit 11th is set to 1, otherwise is set to 0.
• Refer to Load HO Table for the load HO threshold and load req. on candidate cell.
– Clue : When the cell load is higher than the threshold, then the bit 11th is set to 1.This is done in order to put the cell in a lower part of the cell list.
16 9101112131415 12345678
Basic Ranking and Secondary Ranking
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12th bit: bit value is decided by co-BSC criterion.
• Serving cell: is always set to 0.
• Neighbor cell: if co-BSC with the serving cell, 12th bit is set to 0, otherwise is set to 1.
• When the signal level from the neighbor cell or the serving cell is lower than layer HO threshold and hysteresis. This function is turned off and the value is set to 0.
• If the parameter – “Co-BSC/MSC Adj.” in the HO control table is set to “No”, then this function is turned off and the value is 0.
13th bit : Bit value is decided by Co-MSC parameter, having the same concept as the 12th bit.
16 9101112131415 12345678
Basic Ranking and Secondary Ranking
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The 14th bit: Layer HO threshold adjustment bit• Serving cell criterion:
– Receive level >= layer HO threshold – layer HO hysteresis, bit 14th is set to 0. At the same time, bit 13th, 12th and 10th—5th bits are set to 0.
– If the above criterion is not met, then bit 14th is set to 1.
– Example : 20-5 = 15 ( -95 dBm )
16 9101112131415 12345678
Basic Ranking and Secondary Ranking
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Basic Ranking and Secondary Ranking
• Neighbor cell criterion: – Receive level >=layer HO threshold + layer HO hyste
resis, bit 14th is set to 0. At the same time, bit 13th, 12th and 10th—5th bits are set to 0
– If the above criterion is not met, then bit 14th is set to 1.
– Example : 20+5 = 25 ( -85 dBm )• note :
– The layer HO threshold and hierarchical hysteresis correspond to the value of that individual cell’s value.
– Usual situation : When the neighbor cells are of the same layer, each of the neighbor cell’s layer HO threshold value will be the same. Same concept goes for the layer HO hysteresis. This can maintain the entire hierarchical layers of the cell.
16 9101112131415 12345678
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The 15th bit: Bit value is decided by cell type
• Serving cell or Neighbor cells:
• When cell type is extension cell 1.
• When cell type is normal cell 0.
The 16th bit: Reserved bit
16 9101112131415 12345678
Basic Ranking and Secondary Ranking
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• General HO process• Measurement report preprocessing• Penalty processing• Basic ranking and secondary ranking • HO judgment
HO Algorithm process
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HO Algorithm
Initializing
M rule
K rule
16bits rule
Emergency HO judgment
Load-HO judgment
Normal HO judgment
Fast moving HO judgmentLayer HO judgment
PBGT HO judgment
Send HO command
Send HO command
Send HO command
Overlaid/underlaid HO judgment
Edge HO judgment
Forced HO Direct re-tryO&M reason
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Types of HO
• Types of HO : Emergency HO
• TA & BQ HO, interference HO, Rx_Level_Drop HO Load HO Normal HO
• Edge HO, layer cell HO and PBGT HO Fast moving HO Overlaid/underlaid HO
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Emergency HO
• TA HO criterion : TA of the serving cell > TA Thrsh.
• BQ HO criterion : The average value of the uplink quality of the
serving cell >
UL Qual. Thrsh.
The average value of the downlink quality of the serving cell > DL Qual. Thrsh.
• Requirements on the target cell (same as the above two types of HO):
Select the first cell in the neighbor cell list i.e. lowest 16bits value.
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Emergency HO
• Rx_Level_Drop HO: Due to downlink signal level drop Triggered upon detecting rapid level drop during MS
busy mode.
• Requirements for the target cell: The target cell is the first cell in the neighbor cell list.
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Emergency HO
• Interference HO (DL&UL) : When the receiving level > receiving threshold
level. But Receiving quality < threshold of quality interference.
• Requirements for the target cell: The target cell is in the cell list.
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Cell Load HO
• Cell Load HO Criterions : System load of BSC < Permissible load of HO
threshold
Load of serving cell > Load HO threshold
• Requirements for the target cell Load of target cell < Load HO threshold
BTS
BSC
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Normal HO
• Edge HO Criterion: In N seconds, when there are P seconds that neighbor
cell’s DL or MS’s UL signal level is lower than the Edge HO threshold. Then the criterion is met and Edge HO occurs. This method utilizes the P/N rule.
• Requirements for the target cell: The target cell should be ranked in front of the serving
cell.
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Normal HO
• Layer HO criterions: Serving cell :
• No requirement.
Target cell :
• Layer of the target cell is lower than the serving cell.
• Receive level of the target cell > layer cell threshold + layer cell hysteresis.
• Target cell should be ranked in front of the serving cell. The priority of target cell should be higher than the serving cell’s.
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• PBGT HO Criterions : Target cell’s path loss is smaller than the serving
cell’s path loss by the PBGT threshold value.
Satisfying the P/N rule.
Target cell should be ranked in front of the serving cell.
• Note : PBGT HO can only occur between same-priority
cell. If the system permits PBGT HO for the cell, PBGT HO can occur in either inter-BSC or inter-MSC.
PBGT HO
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Fast-Moving HO
• When the serving cell is micro cell : When the MS has traveled through P numbers of
cell, and there are Q (=<P) numbers of cell that the MS has traveled in high speed, the criteria is satisfied. MS will be handed over to umbrella cell.
• When the serving cell is umbrella cell : When the MS is traveling high speed in umbrella
cell, a greater penalty can be given to the micro cell for a duration of time (penalty time). In this way, the MS will not use the micro cell. Note :In this case, the micro cell is only used under urgency conditions( Poor TA and BQ ).
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underlaid
overlaid
• Overlaid/underlaid : Division of underlaid and overlaid is decided by MS downlin
k receive level and TA value.
Overlaid/Underlaid HOOverlaid/Underlaid HO
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• Criterion for HO from overlaid to underlaid: TA value => TA threshold + TA hysteresis Or RX_LEV <= RX_LEV threshold - RX_LEV hysteresis Satisfying P/N rule
• Criterion for HO from underlaid to overlaid: TA value =< TA threshold - TA hysteresis and RX_LEV =< RX_LEV threshold + RX_LEV hysteresis Satisfying P/N rule
Overlaid/Underlaid HOOverlaid/Underlaid HO
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QuestionQuestion
• Can you list the function of each bit in 16bit ranking?
• What is the period of measurement report?
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Summary of Handover (HO)
HO Algorithm process
HO Data Configuration
HO Signaling process
Course Contents
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Major HO Parameters Configuration
• Major HO parameter configuration 1.[Handover Control Table]
2.[Cell Description Table]
3.[Adjacent Cell Relation Table]
4.[Penalty Table]
5.[Emergency Handover Table]
6.[Load Handover Table]
7.[Normal Handover Table]
8.[Fast-Moving Handover Table]
9.[Concentric Cell Handover Table]
• HO data lookup process
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Major HO Parameters Configuration
[Handover Control Table] -1Parameter
name Meaning Value range Recommen
ded value Co-BSC/MSC Adj.
It means whether the 12th and 13th bits acts in the 16bit order. “Yes” means handover in the same BSC/MSC is preferred. “No” means that the 12th and 13th bits are shielded and set to “0”.
Yes, No Yes
Penalty allowed
It determines whether to punish the target cell of handover failure, or the original served cell of handover upon too big TA or bad quality. The penalty measures can apply to cells in or out of the same BSC.
Yes, No No
Load HO allowed
It determines whether to perform the handover to share traffic load. Load sharing can lower the channel assignment failure ratio caused by cell congestion, so as to make evener allocation of the service in respective cells, and lower the cell congestion rate, and improve network performance. It only applies in the same BSC or cells at the same level.
Yes, No No
MS Fast moving HO allowed
It determines whether to handle the fast moving MS with the algorithm. It is only recommended in special areas (such as a highway), to lower CPU load. This algorithm should only be used in suitable conditions, and usually it is not applied.
Yes, No No
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Major HO Parameters Configuration
[Handover Control Table] -2Parameter name Meaning Value range Recommended
value RX_Level_Drop HO allowed
It means whether RX_Level_Drop emergency handover algorithm is allowed, handover the MS which receiving signal level is dropping quickly in advance to avoid potential call drop. This algorithm should be applied in suitable conditions, and usually it is not used. To apply the handover algorithm, BSC must have original measurement report.
Yes, No No
PBGT HO allowed
It means whether PBGT handover algorithm is allowed. PBGT handover algorithm currently is processed on LAPD board. To avoid Ping-pang handover, PBGT handover is only performed between cells at the same layer and with the same priority, and meanwhile it is only triggered on TCH.
Yes, No Yes
MS power prediction after HO
It means after a handover whether MS is to use proper predicted transmitting power to access the new channel. This can reduce system interference and improve service quality (this parameter acts when intra BSC handover occurs).
Yes, No Yes
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Major HO Parameters Configuration
Parameter name
Meaning Value range Recommended value
MR. Preprocessing
“Yes” means perform measurement report preprocessing on BTS; “No” means preprocessing on BSC, then the two parameters of “Send original measurement report” and “Send BS/MS power level” do not act. “Yes” means decreasing of Abis interface signaling and BSC load, and improving of network response time performance. The switch determines where to perform power control. When it is set to “Yes”, power control is performed at BTS side. When it is set to “No”, power control is performed at BSC side. When setting this parameter, first be clear whether BTS supports the power control algorithm to set or not.
Yes, No Yes
[Handover control table] -3
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Major HO Parameters Configuration
Parameter name
Meaning Value range Recommended value
Transfer original MR.
It means whether to send the original measurement report to BSC after measurement report preprocessing on BTS. When it is set to “Yes”, BTS sends not only processed measurement report but also original measurement report to BSC.
Yes, No No
Transfer BS/MS power class
It means whether to send BS/MS power level from BTS to BSC. This function is used to view the effect of power control on BTS. Meanwhile, when preprocessing is available, if BS/MS power level is not reported, the uplink and downlink balance measurements will be affected, and handover types such as PBGT handover and overlaid/underlaid handover needing power compensation will be abnormal.
Yes, No Yes
[Handover control table] -4
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Parameter name
Meaning Value range Recommended value
Sent Freq. of preprocessed MR.
It indicates the time interval at which a measurement report is preprocessed at BTS side and sent to BSC the Preprocessed measurement report. This parameter acts only when “Measurement report pre-processing” is enabled. For 15:1 link configuration, the report frequency should be as low as once per second due to limited link resource. At this time, for handover needing P/N judgment such as edge handover, layer handover, PBGT handover and overlaid/underlaid handover,
Twice per second, Once per second
According to concrete conditions
[Handover control table] -5
Major HO Parameters Configuration
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Major HO Parameters Configuration
[Cell Description Table] -1
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Major HO Parameters Configuration
[Cell Description Table] -2
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Major HO Parameters Configuration
[Adjacent Cell Relation Table] -1
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[Adjacent Cell Relation Table] -2
Major HO Parameters Configuration
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[Penalty Table] -1
Major HO Parameters Configuration
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[Penalty Table] -2
Major HO Parameters Configuration
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[Emergency Handover Table] -1
Parameter name
Meaning Value range Recommended value
TA Thrsh.
When TA≥this value, emergency handover is triggered
0~63 bit period
63
DL QUAL. Thrsh
The downlink receiving quality threshold for BQ emergency handover. When frequency hopping or DTX is enabled, RQ becomes worse (normal phenomenon), this value should be set to 70. The adjustment should also base on the current network quality and handover statistics. When triggering emergency handover, the first to select is the inter-cell handover, the intra-cell handover is only triggered when there is no candidate cell and the intra-cell handover is allowed in the serving cell.
0~70, corresponding to BQ levels of 0~7
60
UL QUAL. Thrsh.
The uplink receiving quality threshold for BQ emergency HO.
corresponding to BQ levels of 0~7
60
Major HO Parameters Configuration
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[Emergency Handover Table] -2
Major HO Parameters Configuration
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[Emergency Handover Table] -3
Major HO Parameters Configuration
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[Emergency Handover Table] -4
Major HO Parameters Configuration
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[Load Handover Table] -1
Major HO Parameters Configuration
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[Load Handover Table] -2
Major HO Parameters Configuration
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[Normal Handover Table] -1Parameter
nameMeaning Value range Recommended value
Edge HO UL RX_LEV Thrsh.
During the statistics time, if the time in which the uplinkreceiving level is lower than the value is longer thancertain time called continuous time, edge handoverwill be performed. If PBGT handover is enabled,Corresponding edge handover threshold will be setlower.
0~63 25 (without PBGThandover, downtown),15 (single station onoutskirts), 15 (withPBGT handover,downtown)
Edge HO DLRX_LEV Thrsh.
Downlink consideration for edge HO. 63 30 (without PBGThandover, downtown),20 (single station onoutskirts), 20 (withPBGT handover,downtown)
Major HO Parameters Configuration
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[Normal Handover Table] -2Parameter
name Meaning Value range Recommended
value Edge HO watch time
It means that within the time statistics, if the time in which the signal level is lower than threshold is higher than the continuous time, then margin HO is to be triggered.
1~16 seconds 5
Edge valid time
See the above. 1~16 seconds 4
Major HO Parameters Configuration
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[Normal Handover Table] -3
Parameter name
Meaning Value range Recommended value
PBGT watch time
Statistics time for PBGT HO signal level judgment. 1~16 seconds 5
PBGT valid time
Continuous time for PBGT HO signal level judgment. 1~16 seconds 4
Major HO Parameters Configuration
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[Normal Handover Table] -4Parameter
name Meaning Value range Recommended
value Layer HO watch time
Statistics time for Layer HO judgment 1~16 seconds 5
Layer HO valid time
Continuous time for Layer HO judgment. 1~16 seconds 4
Major HO Parameters Configuration
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[Fast-Moving Handover Table]
Major HO Parameters Configuration
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[Concentric Cell Handover Table] -1Paramete
r nameMeaning Value range Recommended
value
UO signal intensity difference
BTS transmitting Power difference between underlaid and overlaid may cause MS receiving signal intensity difference in underlaid and overlaid . The parameter uaually indicates the antenna EIRP difference in dB between underlaid cell and overlaid cell. According to field measurement, multi-point measurement is necessary if the underlaid and overlaid use different antenna.
0~63db Set according to actual conditions
Major HO Parameters Configuration
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[Concentric Cell Handover Table] -2Paramete
r nameMeaning Value range Recommende
d value
RX_LEV Thrsh
Rx level hysteresis, TA threshold and TA hysteresis jointly define underlaid area and overlaid area. It must be bigger than edge handover threshold, and the recommended value is: edge handover threshold + signal intensity difference between underlaid and overlaid .
0~63 25
RX_LEV hysteresis
Works with Rx threshold. 0~63 5
TA Thrsh.
It must be bigger than TA emergency handover threshold.
0~63 bit period, with 1 bit period corresponding to 0.55km
TA hysteresis
Works with TA threshold. 0~63 bit period
Major HO Parameters Configuration
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[Concentric Cell Handover Table] -3Parameter name Meaning Value
range Recommended
value UO HO watch time P/N judgment statistics time for U/O HO judgment. 0~16
seconds 5
UO HO valid time P/N judgment continuous time for U/O HO judgment. 0~16 seconds
4
Major HO Parameters Configuration
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[Concentric Cell Handover Table] -4Parameter
nameMeaning Value range Recommended
value
Assign optimum layer
In Overlaid/Underlaid, the following selection are available for TCH assignment: (1) The system judges according to the measurement report on SDCCH and assign to the best sub-cell. (2) Select the overlaid first for TCH assignment. (3) Select the underlaid first for TCH assignment. (4) Do not give extra priority.
System optimization, overlaid , underlaid , no preferential
System optimization
Assign-optimum level Thrsh.
If system optimization is selected, estimate (interpolate, filter) current SDCCH level value through uplink measurement value in the former SDCCH measurement report, and compare with “ Assign-optimum Level threshold”, so as to assign overlaid or underlaid channel.If SDCCH is in the overlaid : edge handover threshold + signal intensity difference between underlaid and overlaid + uplink and downlink balance allowance + SDCCH and TCH difference allowance. If SDCCH is in the underlaid : edge handover threshold + uplink and downlink balance allowance + SDCCH and TCH difference allowance.
0~63
Major HO Parameters Configuration
76
[Concentric Cell Handover Table] -5
Parameter name
Meaning Value range
Recommended value
Pref. subcell in HO of intra-BSC
When the cell is configured into a Overlaid/Underlaid, there are two processing methods for incoming handover request in BSC: (1) No special processing for channel assignment. (2) Add BCCH signal level value of the target cell in inter-cell handover request message to BSC to make BSC allocate optimum channel for MS from underlaid or overlaid .
Yes, No Yes
Incoming-to-BSC HO optimum layer
If there is a incoming BSC HO, and the target cell is a Overlaid/Underlaid, then, this parameter will show which layer is preferred to provide service for the MS.
overlaid , underlaid , none
None
Major HO Parameters Configuration
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HO Parameters Configuration
• HO data lookup process BA2 table defines BCCH frequencies of all
neighbor cells. It is sent to MS by system message 5, system message 5-bis and system message 5ter on SACCH channel.
MS reports the serving cell and BCCH, BSIC and signal levels of 6 strongest neighbor cells to BSS. This is done through SACCH.
MR pre-process is done in BTS. Module number, cell number and CGI of all neighbor cells are derived from Adjacent cell Relation Table, and Cell Description Table (or External Cell Description Table) through BCCH and BSIC in the MR.
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• HO data lookup process BSC performs HO judgment process, such as
basic rank of cells (completed in LAPD board). When BSC finds suitable target, It sends HO request messages containing the target CGI to MPU of BSC. According to CGI, MPU derive the module number of the cell from Cell Module Information Table.
MPU sends a HO command message to the target module and step up the ‘inter-cell/ intra-cell HO request’ counter by one.
Summary of BSC HO
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Summary of Handover (HO)
HO Algorithm process
HO Data Configuration
HO Signaling process
Course Contents
80
HO Signaling process
• Intra BSC Handover
• Intra MSC Handover
• Inter MSC Handover
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Intra-BSC Handover Signaling process
MS MSBTS1 BTS2BSC MSC
Measurement Report from MS
Channel_Active
Channel_Active ACK
HANDOVER COMMAND
Handover Access
Handover_DetectPHY INFO
First SABMEstablish_IND
PHY INFO
Handover Complete
Handover_Performed
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Intra-BSC Handover Signaling process
• Attention In asynchronous HO, if MS could not reach the
new TCH channel after the target cell has sent PHY INFO up to max times, the target cell reports CONN FAIL IND to BSC with the reason: HO access failure.
After the above message is received, BSC release the assigned TCH channel in the target cell .
Max resend times of physical information*Radio link connection timer > Time interval between EST IND and HO DETECT (120~180ms). This is to make sure that the physical information reach MS.
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MS BTS BTSBSC MSCMeasurement Report
Measurement Report
Channel_Activate
Channel_Activate ACK
Handover Command (Old FACCH)
Handover Access (New FACCH)
Handover Complete (New FACCH)
RF Channel ReleaseHandover Performed
T09++T12++
T10++T13++
Attempted outgoing internal inter cell handovers
Attempted incoming internal inter cell handovers
Successful incoming internal inter cell handovers
Successful outgoing internal inter cell handovers
(Original) (Target)
Intra-BSC Handover Signaling process
Intra-BSC Handover Signaling process
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• Handover formula definition Internal inter cell radio handover success rate
=(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Incoming internal inter cell handovers + Outgoing internal inter cell handovers )
Internal inter cell handover success rate
=(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Attempted incoming internal inter cell handovers + Attempted outgoing internal inter cell handovers)
• Internal inter cell radio handover success rate >= Internal inter cell handover success rate
Measurement Points of Intra BSC Handover
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HO Signaling process
• Intra BSC Handover
• Intra MSC Handover
• Inter MSC Handover
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MS BTS BTSBSC1 BSC2MSC(original) (Target)
Measurement Report
Measurement ReportHandover Required
Handover Request
Channel_Active
Channel_Active_ACKHandover_Request_ACK
Handover Command
Handover Access
Handover Detect
Handover Complete
Handover Complete
Clear Command (HO Successful)
RF Channel ReleaseClear Complete
Attempted outgoing interBSC inter cell handovers
Attempted incoming interBSC inter cell handovers
Successful incoming inter BSC handovers
Successful outgoing interBSC inter cell handovers
Signaling intra MSC
Intra-MSC HO Signaling process
Intra-MSC HO Signaling process
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HO Signaling process
• Intra BSC Handover• Intra MSC Handover• Inter MSC Handover
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Signaling process between MSC
MSC-BMSC-A VLR-BBSC-A BSC-B
HO-REQUIRED MAP_Prepare_HO
MAP_Prepare_HO_ACK
MAP_Allocate_HO_NUM
MAP_Send_HO_Report
MAP_Send_HO_Report_ACK
MS
HO-REQUEST
HO-REQUEST-ACK
HO-Command
MS
HO-AccessMAP_Process_Access_Signalling
HO-CompleteMAP_Send_End_Signal
Clear-Command
Clear-Complete
MAP_Send_End_Signal_ACK
Some intermediate steps are omitted
IAIACM
Measurement Points of Inter-BSC Handover
90
Signaling process between MSC
MSC-BMSC-A VLR-BBSC-A BSC-B
HO-REQUIRED MAP_Prepare_HO
MAP_Prepare_HO_ACK
MAP_Allocate_HO_NUM
MAP_Send_HO_Report
MAP_Send_HO_Report_ACK
MS
HO-REQUEST
HO-REQUEST-ACK
HO-Command
MS
HO-AccessMAP_Process_Access_Signalling
HO-CompleteMAP_Send_End_Signal
Clear-Command
Clear-Complete
MAP_Send_End_Signal_ACK
Some intermediate steps are omitted
IAIACM
Measurement Points of Inter-BSC Handover
91
Inter-MSC HO Signaling process
• Signaling process – Abnormal conditions The following conditions will cause HO failure
• MSC-B fails to identify the target cell.• MSC-B does not allow HO to the indicated target ce
ll.• The target cell has no channel available.• VLR-B has no HO number available.• HO error or unsuitable data.
92
Roaming
E
MS
MSCa MSCbMSCb'
VLRbVLRb'
BSS2
BSS2'
Radio transmission signal measurementHO REQUIRED (target cell table)
Perform subsequent HO(MAP) (target cell ID, serving cell ID, MSC number)
Perform HO(target cell ID, serving cell ID, channel type)
HO REQUEST (PCM&Channel type)
HO REQUEST ACKNOWLmargin (including New TCH number and HO number)
Allocate HO number
Send HO report(HON)Radio channel ack. (MAP) (includes New TCH number and HON)
IAI
ACM
Subsequent HO ack.
HO COMMAND HO DETECT
HO COMPLETESend end signal (MAP)
ANS
End signal (MAP)Release HO report Release HON
CLEAR COMMAND
CLEAR COMPLETERelease (TUP)
Cut physical connection between MSCa and MSCb
End signal (MAP)
Release (TUP/ISUP)Release HO report Release HON
Cut physical connection between MSCAa and MSCb'
~~ ~~
MS
Inter MSC HO—Subsequent HO process
93
Highway
MSC-AMSC-C
MSC-B MSC-C
Inter MSC HO—Subsequent HO process
• Subsequent HO
94
Inter MSC HO Signaling process
• Statistics counter—same as Intra MSC HO, Statistics is handled by BSC
• HO formula-- same as Intra MSC HO
95
Basic process of HO Signaling process
1. There is no “HO request” information for intra-BSC HO, and all of the HO are analyzed and processed in BSC. Once the target cell as required is found in the BSC, “Channel activation” information is sent to it directly.
2. When the target cell is not in the same BSC, BSC reports CGI numbers of the serving cell and target cell, and HO cause to MSC through “Ho-Required”. When MSC finds the LAC of the target cell is in the MSC, it sends “Ho-Request” to the BSC of the target cell, and the target BSC activates the target cell channel to complete the following procedure.
3. When MSC finds that the target cell LAC does not belong to the MSC, it will query its “LAI and GCI Table” (including LAC and router address of the adjacent MSC), and send “Prepare-HO” message to the target MSC-B according to the router address. The message includes CGI of the target cell and indication whether or not to allocate HO number, etc. According to the message, the target MSC-B sends “HO-Request” message to the target BSC-B after demanding HO number (unless it is not required in the indication) from VLR-B, and sends “Prepare-HO acknowledgement” to serving MSC after received “HO-Request acknowledgement”, to execute the next procedure.
96
Intra-BSC HO and Inter-BSC HO
• Major differences: Inter BSC HO transfers “HO-REQ” message through
MSC, with CGI of the serving cell and target cell carried in the message.
Intra BSC HO does not have any CGI in any messages, it is handled inside BSC.
Intra BSC HO only sends “HO-Performed” to MSC upon completion of HO, and MSC is not involved before that time.
In inter BSC HO, MSC is involved since the HO request .
97
Question
• What is the content of PHY INFO? When will the system send this message to MS?
• Why Internal inter cell radio handover success rate >= Internal inter cell handover success rate?
Thank You
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