gsm p&o a en handover algorithmsv1[1].4 training material 201011 50
TRANSCRIPT
GSM Handover Algorithms ----Special Subject Training
V1.4
Suitable for staff with junior P&O skill certificates (lower than certificate III) Issued by GSM Network Planning & Optimization Dept.
Version introductionVersionV1.0 V1.4
Date
Writer
AssessorZheng Hao
Amendment recordNone Explanation of MR is added.
2007-07-25 Chen Chun
2009-03-12 Fei Aiping Chang Haijie
Training goalsGet to know theories and classification of GSM handover; Get to know the various kinds of ZTE handover algorithms.
Contents
Overview of handover Flow of handovers Basic handover algorithms Advanced handover algorithms Inter-system handovers
Aims of handoversNeighbour cell C Freq. C
Serving cell BTS Neighbour cell B Freq. B
To ensure normal phone calls
Neighbour cell A Freq. A
To improve call quality
GSM handover belongs to system hard handover.
Aims of handoversRetrieval handoverto
retrieve the on-going calls;
Marginal handoverto improve the on-going call;
Forced handoverto balance traffic dispersion in different cells;
handoverto reduce interference in the cell;
Intra-cell
Directed retryto
improve the call establishment rate.
Handover featuresVarious algorithms Various algorithms can function simultaneously; Controlled by switches; System makes handover decision automatically.
Ordering of target cells
Static priority; Resource available(%); Budget power value.
Automatic traffic balance
Directed retry; Traffic load handover started by MSC; Priority adjustment by traffic load; Force directed-shift handover;
Unique penalty mechanism
Fast-fading handover algorithm
Application scenes for handovers IAlgorithms
scenesTraffic load handove r started by MSC Co-BCCH handover Path loss& TAbased concen tric handov er CIbased conce ntric hando ver Forc ed traffic -shift hand over
UL/DL interfer ence handov er
UL/DL quality handov er
UL/DL level handov er
Long MS-BS distanc e hando ver
UL fastfading hando ver
Macr omicro hand over
PB GT han dov er
Scenes
urban Dense urban suburb
The table is for reference only!
Application scenes for handovers II network typesAlgorithmsUL/DL interfe rence hando ver UL/DL quality hando ver UL/DL level hando ver Long MSBS distan ce hando ver UL fastfadin g hand over Mac romicr o han dov er PBGT hando ver Traffic load hando ver starte d by MSC Co-BCCH handover Path loss& TAbased conce ntric hando ver CIbased conce ntric hando ver Force d trafficshift hando ver
Scenes Dual-band network Doublelayer network CO-BCCH Longdistance coverage
The table is for reference only!
Contents
Overview of handover Flow of handover Basic handover algorithms Advanced handover algorithms Inter-system handover
Overall handover flow
Overall handover flow
Decision of handover start
Selection of target cells
Ordering of target cells
Start of handover
What is MR?
UL MR 1. DL DTX performance 2. UL receive level/quality 3. BS Power 4. MS power level 5. TA 6. DL dynamic power control
DL MR 1. UL DTX performance 2. DL receive level/quality 3. Adjacent cell level 4. UL dynamic power control
MR cycle
MR is sent to BTS in SACCH UL direction;
When MS is in SDCCH, MR cycle is 470ms/time; When MS is in TCH, MR cycle is 480ms/time.
480ms
26 multimultiframes of 4 TCHs
12TCH
1SACCH
12TCH
1
Process of MRFeatures
Number of MR shall reach the average size of window;
Consider DTX weight;
The max number of missing MR is ZeroAllowed;
When power control is on, power compensation shall be made to handover decision threshold.
Measurement report is the original data base for handover decision. ZXG10 process adopts roll average method with various weights, which can ensure smooth handover.
The max number of missing MR - ZeroAllowed
Suppose ZeroAllowed=1MR1/PR1 MR1 MR2/PR2 MR2 MR3/PR3 MR3 MR4/PR4 MR4 MR5/PR5 MR5 MR6/PR6 MR6 MR7/PR7 MR7 Average_MR1 =(MR1+0+MR3+MR4)/(4-1) = Average_MR2 =(0+MR3+MR4+0)/4 =
missing
Handover preprocess at BTS
Suppose HOPreprocess is open and the value is 2.MR1 Preprocess Result1 MR2 BSC MR3 Preprocess Result2 MR4
If HOPreprocess=0, how to upload MR?
Process of MR at BSC
Suppose window value=4, N=4MR1/PR1 MR2/PR2 MR3/PR3 MR4/PR4 Average_MR3 MR5/PR5 MR6/PR6 MR7/PR7 Average_MR4
Average_MR1 Average_MR2 N/P decision
Selection of target cells
Macrocell normal TRX Macrocell special TRX Other TRX in microcellAvRxLevNCell(n) > RXLEV_MIN(n) + MAX(0,(MS_TXPWR_MAX(n)- P(n)))condition 1 must be satisfied
Intra-cell handover
Handover types Inter-cell handover
1
2 3
PBGT(n ) > HO_MARGIN(n) AvRxLevNCell(n) > avRxLevDL + HO_MARGIN_LEVEL(n) AvRxLevNCell(n) > avRxLevDL + HO_MARGIN_QUAL(n)
4
Settings of cell layer & priority
Functions of cell layer structure:
More reasonable control of traffic dispersion; Control of traffic congestion; Backup of network capacity redundancy.
Serial1 2 3 4 5 6 7 8 9
Handover causesCO-BCCH UL interference DL interference UL quality DL quality UL level DL level Long distance UL fast fading
Handover types PriorityIntra-cell Intra-cell Intra-cell Inter-cell Inter-cell Inter-cell Inter-cellAlgorithms Inter-cell
After Tmicro overtimes
Before Tmicro overtimes
Invalid Invalid Invalid Same layer- upper layer -lower layer Same layer- upper layer -lower layer Same layer- upper layer -lower layer Same layer- upper layer -lower layer Same layer- upper layer -lower layer First search for related cells Upper layer same layer lower layer
Invalid Invalid Invalid Upper layer same layer -lower layer Upper layer same layer -lower layer Upper layer same layer -lower layer Upper layer same layer -lower layer Upper layer same layer -lower layer Invalid
are related to their layers
Inter-cell
Serial10
Handover causesPBGT
Handover typesInter-cell
Priority
After Tmicro overtimes
Before Tmicro overtimes
According to PbgtHoLayer: Same layer- upper layer lower layer Handover to lower layer According to TrafficHoLayrCtl TrafficHoFreqCtl Invalid
No cells on same layer and lower layer selected
11 12
Macro-micro time hyteresis Traffic
Inter-cell Inter-cell
No handover Invalid
13
Forced directed shift
Inter-cell
Invalid
Parameter-NcellLayer(NcellLayer) is a mathematical array. Each element determines the layer relation between the serving cell and its adjacent cells. The number of cells in an array rests on NcellNum.
NcellNum value 0 1 2 3 Other values N, undefined SAME, the serving cell and its adjacent cells are on the same layer UPPER, adjacent cells are on the serving cells up layer LOWER, adjacent cells are on the serving cells low layer Reserved Meaning
Layer parameter-TmicroTmicro is started when the MS accesses into new channel; The layer selection priority of target cells will be affected, if handover is started within the time set on Tmicro. Default: 80(8s).
Tmicro 50 51 200 5s 5.1s 20s Time duration
Ordering of target cellsLayer priority of candidate cells
Static priority
Resource available(%) Dynamic priority
Power budget margin
Handover decision/ execution
Penalty strategy of inter-cell handover failure
N Handover failure? Y Start HoFailPenalTime Y Y PenalCount=HoUlQualThs AvRxQualDL>=HoDlQualThs
Selection of target cells:1 2 AvRxLevNCell(n) > RXLEV_MIN(n) + MAX(0,(MS_TXPWR_MAX(n)- P(n))) AvRxLevNCell(n) > AvRxLevDL + HO_MARGIN_QUAL(n)
That is: 1. Adjacent cells level must be larger than the minimum receive level set for it; 2. Adjacent cells level shall be larger than the sum of quality handover threshold and the serving cells DL level.
UL/DL level handoverDecision of handover start:AvRxLevelUL= RXLEV_MIN(n) + MAX(0,(MS_TXPWR_MAX(n)- P(n))) AvRxLevNCell(n) > AvRxLevDL + HO_MARGIN_LEVEL(n)
That is: 1. Adjacent cells level must be larger than the minimum receive level set for it; 2. Adjacent cells level shall be larger than the sum of level handover threshold and the serving cells DL level.
Long BS-MS distance handoverDecision of handover start:AvDistance>DistanceThreshold(TA)Radio environment quality is not regarded as decision standard.
Selection of target cells:1
AvRxLevNCell(n) > RXLEV_MIN(n) + MAX(0,(MS_TXPWR_MAX(n)- P(n)))
The only condition is that the adjacent cells level is larger than the minimum receive level set for it.
Application range:This kind of handover is usually used in networks with long distance coverage.
PBGT handoverThis handover happens mostly in urban area; It isnt for saving handover, but for better call quality.
Decision of handover start:Make handover decision to each adjacent cell in rotation; when an adjacent cells PBGT value is higher than 0, handover condition is satisfied.
Selection of target cells:1 2 AvRxLevNCell(n) > RXLEV_MIN(n) + MAX(0,(MS_TXPWR_MAX(n)- P(n))) PBGT(n ) > HO_MARGIN(n) That is: 1 Adjacent cells level shall be larger than the minimum receive level set for it; 2 Its power budget value shall be larger than the PBGT handover threshold set for adjacent cell.
Directed retry-decision of handover startMS applies for TCH
Yes Assignment success
Usable TCH available? No
Successful force disconnetion, force handover and ordering
successful
Force disconnetion, force handover and ordering attempt unsuccessful
Directed retry
Yes
Directed retry switch open or not No TCH occupancy failure
Directed retry handover
It happens in the process of calling access; It dynamically adjusts call traffic between cells; It can lower call loss rate; Selection of target cells must fulfill condition 1.Get to know the flow of internal & external directed retry How to control 2/3G handover priority?
Its suggested that ordering process be opened first, since its effect is better than that of directed retry.
Penalty on directed retry failureN (N>3, failure) No candidate cells found Start the dedicated timer After timer expires Order candidat e cells Y Handover
BSC internal cells Candidate cells have no radio resources
2nd candida te cell N
Y Handover
BSC external cells
Complete
N (N>3, or T3107 expires, give up directed retry)
Failure due to radio link problem
Delete the attempt cells
2nd candida te cell
Y Handover
Contents
Overview of handover Flow of handover Basic handover algorithms Advanced handover algorithms Inter-system handover
UL fast fading handover
This is a kind of algorithm for saving handover due to UL level decrease; It is flexibly used in dense urban areas, like micro-cells, highways, corners and slopes, where in-time outgoing handovers are needed; Selection of target cell shall fulfill condition 1; Given condition 1 is fulfilled, handover to relevant cells is preferred.
MR1/PR1 MR2/PR2 MR3/PR3 MR4/PR4
P unavailable
Directly report MR to BTS
Number of consecutive handover decisions (N)
Macro-micro handover
Handover trigger conditions: measured values of adjacent cells signal strength is higher than threshold, and this reaches certain consecutive times.AvRxLevUL(n)>= MacroMicroHoThs
Selection of target cell: Condition 1 is fulfilled; Layer relation with neighbor cell Lower.Serving cell: macrocell Target cell: microcell Microcell T=-80dBm N=6
NcellLayer
is
MacrocellMicrocell
Traffic handover
When the serving cell suffers from congestion, for MS which has established a call, BSC will hand it over to an adjacent cell which can fulfill traffic handover conditions.Adjust call traffic in different cells to reach traffic balance.
Decision of handover start:TCHBusyPercent>TrafficThsExcluding congested TCHs; Regardless dynamic HR and dynamic PDTCH.
Selection of target cell:Condition 1 PBGT(n) > TrafficLevThs
MSC-started traffic load handover
Its started by MSC; Select at most NumOfMS calls; Handover from high loaded cells to low loaded ones.Inter-BSC load adjustment; No data configuration needed at radio side.
Note: Precondition for this handover algorithm: MSC starts the function, and BSC supports load report. Currently, no manufacturer makes this function open. ?????
Forced directed-shift handover
The last means to adjust traffic;
Mainly used in CO-BCCH cells;
FeaturesApplicable scenes:900M 1800M cell of the same direction;
Target cell must be forced firected shift handover cell.
Forced directed-shift handover strategyDecision of handover start:PathLoss(n)