go na24 e1 1 gsm handover algorithm-34
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7/28/2019 GO NA24 E1 1 GSM Handover Algorithm-34
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GSM Handover Algorithm
Zte university
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Return
1. Why should we perform HO?
2. What are the features of ZTE system HO algorithms?
3. What HO algorithms are provided in ZTE systems?
4. How to choose the appropriate HO algorithms on
working site?
I Basic concept of ZTE system handover
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1. Why should we perform HO?
For the service area of one site is limited, the telecom network systems
must fulfill the service relay to meet the mobility requirement of subscribers. This kind of relay is referred to as signal handover-a unique
feature of mobile communications.
Functions of HO consist of the
following five: Retrieval HO-to retrieve the on-going calls;
Marginal HO (Homargin BPGT)-to improve the quality of
on-going calls;
Intra-cell HO-to reduce interference in the cell;
Forced HO-to balance the traffic dispersion in the cells;
Directed-retry HO-to improve call establishment rate.
Return
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2.What are the features of ZTE system HO
algorithms?
Dynamic priority
Static priority Traffic volume Power budget
ZTE system adopts cell ordering strategy of dynamicpriority.
Dynamic priority
comprehensively
considers the
static priority of
cells, trafficvolume and
power budget.
Return
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3.What HO algorithms are provided in ZTE systems?
1. CO-BCCH
2. UL Interference HO
3. DL Interference HO
4. UL Quality HO5. DL Quality HO
6. UL Level HO
7. DL Level HO
8. TA HO
9. UL Fast-Fading HO10. PBGT HO
11. Macro-micro latency HO
12. Traffic HO
13. Directed-shift HO
ZTE systems provide various kinds of HO algorithms
to suit different application scenarios:
Return
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4.How to choose the appropriate HO
algorithms on working site?
**This table is for reference only.Return
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II Layer & HO priority
Return
1. How to control traffic distribution in dense traffic areas?
2. How does layer affect HO priority?
3. What’s the function of layer timer Tmicro?
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1.How to control traffic distribution in dense traffic
areas?
Layer1
Layer2
Layer2
Layer2
Layer3 Layer3 Layer3 Layer3 Layer3 Layer3 Laye r3 Layer3 Layer3
Layer2 Layer2
Cells on different layers in ZTE BSS system are logically divided (which
is the concept of relative layer). With hierarchical cell structure (HCS)
adopted, we can control traffic distribution and congestion more
efficiently, in the meantime, make redundancy backup of network
capacity
To realize
control of
traffic
distribution
It affects the selection
of target cell and cell
priority. Return
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2.How does layer affect HO priority?-2
Layer priority has obvious influence on the selection of target cells.
Return
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3. What’s the function of layer timer Tmicro?
If HO is triggered before Tmicro expires, the priority of target cell selection will be
affected. Refer to Handover Priority Table for detailed priority sequence of layers.
If HO is triggered after Tmicro expires, select layer priority according to normal sequence.
Tmicro works in handovers, except intra-cell HO, CO-BCCH HO, traffic HO, directed-shift
HO and fast-fading HO.
Function of Tmicro
Range of Tmicro
Tmicro Timelength
Defaultvalue
50 5s
80(8s) …. ….
200 20sReturn
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III Handover Flow
Return
1. What’s the basic handover flow?
2. What is handover preprocess?
3. How does BSC process measurement report?
4. How to select target cells when BSC decides to perform
handover?
5. How to select target cells when more than one candidate
cells are available?
6. How to avoid repeated handover failure to one cell with
ZTE handover algorithms?
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1. What’s the basic HO flow?
Process
of MR
Decision
of HO
start
Selection
of target
cell
Orderin
g of
target
cells
Start of
HO
Basic HO Flow
Return
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3. How does BSC process MR?-1
BSC conducts averaging process of MR (preprocess report), with sliding
window mechanism.
Process the MR reported by BTS according to the values of window size and
weight (which are based on the level, quality and distance) and the valueof
ZeroAllowed.
The process result will be applied in P/N process. If the number of values
meeting handover judgment threshold is P out of a certain number of values N,
the handover is decided to take place.
Next
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3. How does BSC process MR?-2
MR1/PR1
Average_MR1MR2/PR2
Average_MR2MR3/PR3
Average_MR3
MR4/PR4
Average_MR4
N/P
judgment
MR5/PR5
MR6/PR6
MR7/PR7
Suppose the window value is 4,and N is 4
Return
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4. How to select target cells when BSC decides to perform
handover? -1
When intra-cell HO occurs,
select TRX according to TRX priority;
select the timeslot with lowest interference band;
Select a timeslot randomly, and prefer to select a timeslot on
different TRX when more than one TRX are available in the cell.
When BSC decides to perform HO, it selects target cell according to
specific HO cause.
Next
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4. How to select target cells when BSC
decides to perform handover ?-2When inter-cell HO occurs,
Principle 1 must
be satisfied.
Return
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5. How to select target cells when more than one
candidate cells are available?
①Order the target cells on
different layers according
to the priority of layers.
②For candidate cells on
the same layer, first order
them according to their
dynamic priority, then
order them according to
their power budget.
Layer priority of
candidate cells
Static
priorityResource
percentage
Power budget
margin
Dynamic priority
When more than one target cell are available, BSC will sort them
in order.
Return
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IV Handover Failure Penalty
Return
1. How to carry out penalty on inter-cell handover
failure?
2. How to carry out penalty on intra-cell handover
failure?
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1. How to carry out penalty on inter-cell handover
failure?-1
General
procedure
of HO
failure
penalty
Next
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1. How to carry out penalty on inter-cell
handover failure?-2HO judgment
/implementation
HO failure?
Start HoFailPenalTime
PenalCount<3
Compare the
cell’s priority
and the
acceptable
priority
The punished cell
has highest priority?
PenalCount=Pen
alCount+1
Y
Y
Y
End HO flow N
RxLev(n)=RxLev(n)-
PenaltyLevOffset;
PenaltyCount=Penalt
yCount+1
N
N
HoFailPenalTime expires?
Screen the target cell
Relieve target cell
of penalty
Y
N
Flow of inter-cell
HO penalty algorithm
Return
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2. How to carry out penalty on intra-cell handover
failure?-1
When an MS continuously makes intra-cell HO, it means intra-cell HO no
longer contributes to reducing interference. In this case, BSC will forbid
the MS to make intra-cell HO during the penalty period.
Procedure of HO failure penalty:
① Judge if intra-cell HO happens frequently through the
number of intra-cell HO started in a cell within a certain
period of time. If it frequent intra-cell HO exists, carry out the
next step.
② Temporarily close intra-cell HO, only allow inter-cell HO
within the penalty period.
Theory of intra-cell HO penalty
Next
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2. How to carry out penalty on intra-cell handover
failure?-2
TMaxIHo expires?
HO judgment
Start intra-cell HO?
Start HoFailPenalTime
IHoCount=0
Y
Y
Other HO flow N
IHoCount=IHoCount+1;
TMaxIHo=0
IHoCount=MaxIHo?
Stop intra-cell HO
IHoCount=MaxIHo?
Y
N
Y
N
If conditions of other
HO are satisfied?
Y
N
N
Flow of intra-cell
HO penalty algorithm
Return
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V FAQ & Answers
Return
1. What are the common types of HO?
2. What HO measurements does ZTE system possess?
3. What data should be configured in MSC for inter-
MSC HO?
4. What is external cell/internal cell?
5. What impact does HO have over speech quality?
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1. What are the common types of HO?
According to starting condition:
Power budget HO
Retrieval level HO
Retrieval quality HO
Long-distance HO
Traffic HO
According to TA:
Synchronous HO
Asynchronous HO
According to related network unit :
Intra-cell HO
Inter-cell HO
Intra-BSC HO
Inter-BSC HO
Inter-MSC HO
According to systems related :
Intra-system HO
HO between GSM and UMTS
HO between GSM and TD-
SCDMA
Return
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2. What HO measurements does ZTE system
possess?
Measurement of HO causesTo measure the number and proportion of handovers caused by
different reasons, so as to reflect the cell’s radio conditions.
Basic measurement of HO
To measure the number of HO attempts, HO success, HO failure and
the number of different causes, so as to reflect the cell’s HO successrate.
Measurement of HO in adjacent cells
To measure the number of incoming /outgoing HO attempts, HO
success and HO causes, so as to reflect certain inter-cell HO success
rate.
Measurement of sub-cell statistics
To measure HO between sub-cells, so as to reflect if the traffic
distribution in sub-cells is reasonable. Return
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3. What data should be configured in MSC for inter-
MSC HO?
For inter-MSC HO, The following data should be configured in MSC:
The LAI information of target MSC, so that the serving MSC can recognize target
cell;
The MSCid of adjacent MSC, so that the serving MSC can recognize target MSC;
Correct route address, so that the serving MSC can correctly pass messages to
target MSC.
Problems resulted from wrong configuration in MSC: inter-MSC HO failure;
no reception of HO command at Um interface and Abis interface; HO
required reject message is received at A interface and E interface, or no
response from target MSC is received.
Return
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4. What is external cell/internal cell?
BTS
Cell A
Internal cell
Cell B
BSC ABSC B
External cell
Cell C
For ZTE BSS system , cells under the serving BSC are internalones.
All adjacent cells outside the serving BSC are external ones.
Return
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5.What impact does HO have over speech quality?-
2
Because PESQ (one of MOS algorithms) considers influence of HO on
speech quality, too many handovers will affect MOS.
Test result shows that when there are 13 times of HO within 100s of
speech, MOS value drops by 7.99% (0.215) compared with that in the
same period without HO; when there are 10 ro 6 times of HO within
100s, MOS drops by 4.69% (0.13); when there are only 3 times of HO in 100s,
MOS remains almost unchanged.
Influence of HO frequency on speech quality
Handover is necessary, but frequent handover will seriously
affect subscribers’ satisfaction degree about speech.
Conclusion
Return
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