go na24 e1 1 gsm handover algorithm-34

7/28/2019 GO NA24 E1 1 GSM Handover Algorithm-34

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GSM Handover Algorithm

Zte university



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



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.

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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.

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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:

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4.How to choose the appropriate HO

algorithms on working site?

**This table is for reference only.Return



II Layer & HO priority

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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?



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



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



III Handover Flow

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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?



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

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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



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

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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



4. How to select target cells when BSC

decides to perform handover ？－2When inter-cell HO occurs,

Principle 1 must

be satisfied.

Return



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.

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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?



1. How to carry out penalty on inter-cell handover

failure？-1

General

procedure

of HO

failure

penalty

Next



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




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




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



V FAQ & Answers

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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?



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

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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



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.

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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.

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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

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go na24 e1 1 gsm handover algorithm-34

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