14 Handover Issue2.0.ppt

8/10/2019 14 Handover Issue2.0.ppt

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Internal

Handover

ISSUE 2.0




Handover is key technology of Mobile

communication system and make

continued conversation possible.

Handover algorithm in Huawei product

is flexible and powerful




Upon completion this course, you will be

able to:

Understand the type of handover.

Master handover judgment flow

Configure handover data

Master handover signaling flow




Chapter 1 Introduction of Handover

Chapter 2 HO Algorithm process

Chapter 3 HO Data Configuration

Chapter 4 HO Signaling process




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




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

Classification by Reason


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Classification by Synchronization

Synchronous handover: source

and target cell belong the same

BTS

Asynchronous handover: source and

target cell belong the different BTS





1.1 General HO process

1.2 Measurement report preprocessing

1.3 Penalty processing

1.4 Basic ranking and Secondary ranking

1.5 Condition of handover




General process of HO Algorithm

M.R. preprocessing

Penaltyprocessing

Basic ranking

Secondaryranking

HO judgment

TA emergency HO

BQ emergency HO

RSD emergencyHO

Interf. emergency HO

Load Sharing HO

Edge HO

Layer HO

PBGT HO

Processingprogram

OM forced HO

Directed retry

Overlaid/underlaid HO

Fast moving MS HO

1

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.

Serving cell Neighbour cell

The downlinkmeasurement report

of the serving cell

The uplink measurement

report of MSThe downlink measurement reportof the neighbour cell (BCCH)



HUAWEI TECHNOLOGIES CO., LTD. All rights reserved Page 15

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.




MRMR

MR MR MR

Measurementreport No. n

Measurement rNo. n+4

ContinuousMR

flow

How to interpolate MR?




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 emergency HO

( base on BQ and TA ) is performed.

Penalty on other high priority layer cells after a fast moving HO

is performed.

A new HO attempt is prohibited within the penalty time after an

overlaid/underlaid HO fails.




BTS

HO failure

BSC

Cell A

Cell B

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.




BTS

BQ& TA HO

BSC

Cell A

Cell B

Penalty on the Source Cell

Punish the original serving cell when an emergency HO

( due to BQ and TA) occurs.




Back? No way!

Umbrella

Micro cell

penalty on Non-umbrella Layer

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.




Underlaid

Overlaid Do not

attemptagain after a

failed HO!

Penalty on Overlaid/underlaid Cell

A new Overlaid/underlaid HO is prohibited within a penalty time

after an Overlaid/Underlaid HO failure.




Procedure of 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




M rule Only the cells with received signal level satisfy the following conditions

can be put into the candidate cell list.

For serving cell

RX_LEV (o) >MSRXMIN(o) + MAX(0,Pa(o))

For Neighbor cell

RX_LEV (n) > MSRXMIN(n)+ MAX(0,Pa(n))+ OFFSET

Pa(0) : MS_TXPWR_MAX(0) – P

Pa(n) : MS_TXPWR_MAX(n) – P

MS_TXPWR_MAX( ) : The appointed MS transmitting power by theBSS.

P : Max_Power_of_MS

Max_Power_of_MS : MS maximum transmitting power




K rule Criterion

After the M rule , the serving cell and candidate neighbor cells are

ranked in descending order according to the receiving level only

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 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1




The 4th bit: determined by HO hysteresis

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 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1




The 5th—10th bit: determined by Layer

The 5th-10th bits: bit value is decided according to their position inHuawei 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 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1




GSM900

Cell

Micro Cell

Umbrella

CellGSM 900

GSM1800 GSM1800GSM1800

GSM 900 GSM 900 GSM 900

GSM900GSM900

GSM1800GSM1800

GSM900 GSM900

GSM1800 GSM1800

GSM1800

Cell

Hierarchical cell structure




The 11th bit: determined by load

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 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1




The 12th/13th bit: determined by co-BSC/MSC

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 lowerthan 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 sameconcept as the 12th bit.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1




The 14th bit: determined by Layer HO

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 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1




The 14th bit: determined by Layer HO

Neighbor cell criterionReceive 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 = 25 ( -85 dBm )

note

The layer HO threshold and hierarchical hysteresis correspond to thevalue of that individual cell‘s value.

Usual situation : When the neighbor cells are of the same layer, each ofthe neighbor cell‘s layer HO threshold value will be the same. Same

concept goes for the layer HO hysteresis. This can maintain the entirehierarchical layers of the cell.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1




The 15th bit: determined by Cell Type

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 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1




Types of HO

Emergency HO

TA HO

BQ HO

interference HORx_Level_Drop HO

Load HO

Normal HO

Edge HO, layer cell HO and PBGT HO

Fast moving HO

Overlaid/underlaid HO




TA&Bad Quality 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 ofHO)

Select the first cell in the neighbor cell list i.e. lowest 16bits

value.




Rx_Level_Drop 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.




Interference HO

Interference HO (DL&UL) :

When the receiving level > receiving threshold level. But

Receiving quality < threshold of quality interference.


The target cell is in the cell list.




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 cellLoad of target cell < Load HO threshold

BTS

BSC




Edge 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.


The target cell should be ranked in front of the serving cell.




Layer 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.




PBGT HO

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.




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 themicro cell. Note :In this case, the micro cell is only used

under urgency conditions( Poor TA and BQ ).




Overlaid/Underlaid Cell

Assume, 6TRX in one cell, one CDU and one SCU are adopted

Where can we configure BCCH CH? CDU or SCU?

SCU

CDU

Antenna

Antenna

TRX

TRX

TRX

TRX

TRX

TRX




Overlaid/Underlaid Cell

Purpose

Maximize coverage area

Reduce interference and improve frequency reuse density

Construct method

Different combiner loss

Decrease the power of TRX

By HO parameter, it is called IUO

Classify

Normal Underlaid/Overlaid

IUO: Enhance Underlaid/Overlaid




How to Allocate SDCCH/TCH?

SDCCH

SDCCH are always allocated in Underlaid

Layer is allocated according the transmission delay of

access burst

TCH

The receiving level

TA

They are included in MR of SDCCH CH on uplink reportedby BTS




Factor of Handover between Under/Overlaid

Normal Underlaid/Overlaid

Receiving level

Time Advance

Quality

Enhanced Underlaid/Overlaid

Receiving level

Time Advance

Quality

Traffic Load of Underlaid




underlaid

overlaid

:

Division of underlaid and overlaid is decided by MS

downlink receive level ,TA value and quality.

Normal Overlaid/Underlaid HO

The quality boundary is elided in this figure




Normal Overlaid/Underlaid HO

Criterion for HO from overlaid to underlaid:

TA value => TA threshold + TA hysteresis OR

RX_LEV <= RX_LEV threshold－RX_LEV hysteresis OR

Qua. =>Qua. threshold

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 AND

Qua. =<Qua. threshold

Satisfying P/N rule




Enhance Overlaid/Underlaid HO

Criterion for HO from overlaid to underlaid:

TA value => TA threshold + TA hysteresis OR

RX_LEV <= O to U level OR

Qua. =>Qua. threshold

Satisfying P/N rule

Criterion for HO from underlaid to overlaid:

TA value =< TA threshold － TA hysteresis AND

RX_LEV >= U to O level AND

Qua. =<Qua. Threshold

If the box ―U to O HO traffic threshold‖ is checked, just in the condition

that underlaid load is more than this threshold, U to O handover based

on previous conditions can be triggered

Satisfying P/N rule




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




Parameter

name Meaning Valuerange

Recommend

value

Co BSC/MSC

Adj.

It means whether the 12 and 13 bits acts in the 16bit order.―Yes‖ means handover in the same BSC/MSC is preferred.

―No‖ means that the 12 and 13 bits are shielded and set to‖0.

Yes,No

Yes

Penalty

allowed

It determines whether to punish the target cell of handoverfailure, or the original served cell of handover upon too big TAor bad quality. The penalty measures can apply to cells in or

out of the same BSC

Yes,No

Yes

Load HO

allowed

It determines whether to perform the handover to share trafficload. Load sharing can lower the channel assignment failure

ratio caused by cell congestion, so as to make evenerallocation of the service in respective cells, and lower the cell

congestion rate , and improve network performance. It on lyapplies 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 thealgorithm. It is only recommended in special a reas (such as a

highway), to lower CPU load. This algorithm should only beused in suitable conditions, and usually it is not applied

Yes,No

No

Handover Control Table




Parameter

name

Meaning

Value rangeRecommended

value

RX _L evel 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 y (this parameter acts

when intra BSC handover occurs

Yes, No Yes





Parameter

nameMeaning

Value

range

Recommended

value

MR.

reprocessing

―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





Parameter

nameMeaning

Value range

Recommended

value

TransferOriginal 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 rep ort 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





Parameter

name Meaning

Value

range

Recommen

ded

value

Sent Freq. of

Preprocessed

MR.

It indicates the time interval at which a measurement report

is preprocessed at B TS side and sent to BSC the

Preprocessed measurement report. This parameter acts

only when ―Measurement t report preprocessing‖ 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 nee ding P/N judgment such as edge

handover, layer handover, PBGT handover and

overlaid/underlaid handover

Twice per

second,

Once

persecond

According to

Concrete

conditions





Parameter

name

MeaningValue

range

Recommended

value

Layer of the

cell

Huawei hierarchical network structure is divided into 4 layers. 16 The

priorities can be set for each layer, which provides enough room

of network planning for the operator to adapt to various complex

network environment. Normally, Macro layer is the major 900 layers

layer, Micro layer is the major 1800 layer, Pico is the 900 and

1800 micro cell layer. The smaller layer value, the higher

priority.

1 ~4M900 : layer 3

M1800:Laye 2r

Cell priority

Each layer may have 16 priorities, used to control the handover

priority between cells at the same layer. Usually priorities of priorities

cells at the same layer are set the same. For cells at the same

layer, the smaller the priority value, the higher the priority

1~16 1

Layer HO

Thrsh.

It affects the value of the 14th bit in the 16bit ranking , and it is

also the level requirement on the target cell for interference

handover and load handover. Then such levelshould be higher than layer handover threshold + layer

handover hysteresis. The layer handover threshold should be

set >= Edge handover threshold + Inter cell handover

hysteresis.

0 ~ 63 25

Layer HO

hysteresisWorks together with the Layer handover threshold. 0 ~ 63dB 3

Cell Description Table




Parameter

nameMeaning

Value

range

Recommended

value

Penalty on

MS Fasting

moving HO

It is valid when the fast moving handover algorithm is

enabled . It is the signal level penalty value on the other

neighbor cells when MS moves fast and is handed over

To umbrella cell. The parameter is only valid within the

penalty time.

0~ 63dB 30

Penalty

Time on MS

Fasting

moving HO

It means that within this time, the penalty on the other

neighbor cells will be exerted after MS is handed over

to umbrella cell by fast moving HO.

0 ~ 255

seconds40

Min DL level

0n

Candidate

cell

This is the min signal level requirement for the cell itself

to be a candidate cell low configuration may easily

cause call drops, while too high a configuration might

turn handover too hard to occur.

0 ~ 63 15

Cell Description Table




Parametername Meaning Value range

Recommendedvalue

Min accesslevel offset

This offset is based on ―Min downlink level of handovercandidate cell‖. Different offsets can be defined for different

adjacent cells, and to enter the candidate cell list, thecorresponding adjacent cell receiving signal level must behigher than the sum of ―Min. downlink level of handover

candidate cell‖ and ― Min. Access level offset‖.

0 ~ 63dB 0

PBGT HOthrsh

It means that PBGT handover is performed when thedifference between the target cell downlink path loss and the

corresponding toserving cell downlink path loss is bigger than PBGT handoverthreshold. When PBGT handover is enabled, and ―Inter cell

handover hysteresis‖ > ―PBGT handover threshold (corresponding dB value)‖, ―Intercell handover hysteresis‖takes place of ―PBGT handover threshold‖ to act. . PBGT

handover threshold also needs to be adjusted according tohandover performance statistics result

0~127corresponding

--64~63dB

It is around 68 in thedensely populated

downtown, andaround 72 on the

outskirts.

Inter cellHO

hysteresis

Handover hysteresis between an adjacent cell and the servingcell. It is set to reduce ―Ping pang‖ HO. The hysteresis value

also needs to be adjusted according to the handoverperformance statistics result and live network. Flexible

configuration of the value can effectively lead handover andtraffic between two adjacent cells.

0 ~ 63db

It is around 4 in thedensely populated

downtown, andaround 8 on the

outskirts.

Adjacent Cell Relation Table




Parameter

name Meaning Value range

Recommended

value

Penalty level

after HO fail

The signal level value in dB, to punish the target cell

which has caused a HO failure due to problems such

as congestion , to prevent MS from a handover

attempt to that cell again. This value is only valid

within the penalty time for handover failure.

0 ~ 63 dB30

Penalty time

after HO fail

Penalty time on the corresponding target cell after seconds

handover failure0 ~ 60second 10

Penalty level

after BQ HO

fail

The signal level penalty value for the original serving

cell, to avoid ―Ping- pang‖ handover after emergency

handover upon bad quality. It is only valid within the

penalty time for BQ HO.

0 ~ 63d B 63

Penalty time

after BQ HO

fail

Penalty time for the original serving cell after BQ HO. seconds 0 ~ 60second 10

Penalty Table




Parameter

name Meaning

Value

range

Recomm

ended

value

Eenalty

level after

TA HO fail

The signal strength penalty value for the original serving cell,

to avoid ―Ping - pang‖ handover after TA emergency

handover. It is only valid within the penalty time for ta

handover

0 ~ 63d B 63

Penalty time

after TA HO

fail

Penalty time for the original serving cell after TA emergency

Seconds handover

0 ~

60second10

Penalty time

after IUO

HO fail

After an overlaid/underlaid handover failure (big circle hands Seconds over to

small circle or vice versa), within certain time (this Parameter configuration

value) overlaid/underlaid handover is forbidden for the same call

0 ~

16second10

Penalty Table




Emergency Handover Table

Parameter


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




Parameter

nameMeaning Value range

Recommended

value

UL

Qual.

Thrsh

for interf.

HO

Uplink receiving quality threshold in the serving cell for interference

handover. When frequency hopping or DTX is to enbaled , RQ

becomes worse (normal phenomenon), this

value should be set to 60. The adjustment should also base

on the current network quality and handover statistics. When

triggering interference handover. If the serving cell is in the

first position and intra cell handover is permitted, perform

intra cell handover . Otherwise select the second candidate

cell to perform inter cell handover.

corresponding

to BQ levels of

0~7

50, interference

quality threshold

must be better

than

the emergency

quality threshold

DL Qual.

Thrsh. For

interf HO

Downlink receiving quality threshold in the serving cell for

interference handover.

0~70,

corresponding

to BQ levels of

0~7

50





Parameter

r name Meaning

Value

range

Recommended

value

UL

RX_LEV

Thrsh. For

interf.HO

Min uplink receiving power threshold from the serving cell

required for interf. HO, when interference handover is

triggered if the uplink quality is worse than quality thresholdand at this time the uplink signal level is higher than the signal

threshold. When triggering interference handover, If the

serving cell is in the first position in the cell list, and intra cell

handover permitted , then start intra cell HO. Otherwise select

the second cell to perform intercell HO.

0 ~ 6 3 25

DL

RX_LEV

Thrsh. For

interf HO.

Min downlink receiving power threshold from the serving cell

required for interf. HO.0 ~ 63 30





Parametername.

Meaning Valuerange

Recommen

ded

value

Filter

Parameters

A1~A8

Used for configuration of filter for rapid signal

drop judgment, and together with filter parameter

B, they are 9 parameters for a filter. The

corresponding formula is (in the program, A1~A8

is configuration value minus 10 and B is the

negative configuration value):

C1(nt)=A1×C(nt)+A2×C(nt-t)+A3×C(nt－ 2t)+

+A8×C(nt-7t)

Where, C (nt) is the receiving signal level in the

uplink measurement report of the serving cell

sent at the time of nt. If C1 ( nt ) < B, and C (nt) is

below the edge handover threshold, then the

signal level is considered to be of rapid drop.

0 ~ 20 10

Filter

parameter B

Used for configuration of filter for rapid signal

drop judgment. Please refer to the explanation

for A1~A8 of filter.

0 ~255 0





Parameter


Recommended

value

System flux

Thrsh. For

load HO

The pre condition for load HO is that the system flow (signaling

flow) is lower the threshold. This value can not be set too high

because load handover upon max threshold may cause serious

effect to the system.

0, 8~11 system

flow levels, to

corresponding

0, 70, 80, 90and 95.

10

Load HO

Thrsh

Load handover is triggered when the serving cell load is

than the threshold, TCH seized in the cell has reaching the

corresponding percentage.

0~7 cell load

levels,

Corresponding

to 0 , 50 , 60 , 70 ,

75, 80 , 85 , 90

5

Load Req.

on

candidate

cell

The Load threshold for the target cells that can accept MS from

serving cell in load HO, i.e. when the TCH under Idle mode in

the neigh bor cell is lower than the corresponding percentage

the cell refuses to accept MS from serving cell handed over due

to the load reason

0~7,

Corresponding

to 0 , 50 , 60 , 70 ,

75, 80 , 85 , 90

2

Load Handover Table




Load Handover Table

Parameter


Recomme

ndedvalue

Load HO

bandwidth

This configuration is related to the edge handover

threshold. Load handover is only allowed when the MS

receiving level from the serving cell is within the range of

margin handover threshold, margin handover threshold +

load handover bandwidth

0~ 63db 25

Load HO

step

period

When a cell is up to conditions for load handover, all calls

within the serving cell will send handover request at the

same time, this will cause abrupt increase on processor

load, and under certain conditions this will cause the

target cell congestion and result in call drops. Thereby,

step by step load handover algorithm is used to control

handover. The cycle is the time needed for handovers of

each step.

1~60 seconds 10

Load HO

step

level

The whole load HO bandwidth will be divided into several Sub-bands by

this parameter.1~ 63db 5




Normal Handover Table

Parameter

name Meaning

Value

rangeRecommended value

Edge HO UL

RX_LEVThrsh.

During the statistics time, if the time in which the uplink

receiving level is lower than the value is longer than

certain time called continuous time, edge handover

will be performed. If PBGT handover is enabled,

Corresponding edge handover threshold will be set

lower

0 ~ 63

25 (without PBGT

handover, downtown),

15 (single station on

outskirts), 15 (with

PBGT handover,

downtown)

Edge HO DL

RX_LEV

Thrsh.

Downlink consideration for edge HO 63

30 (without PBGT

handover, downtown),

20 (single station on

outskirts), 20 (with

PBGT handover,

downtown)





Parameter


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

timeSee the above. 1 ~16 seconds 4





Parameter


Recommended

value

Layer HO

watch timestatistics time for Layer HO judgment 1 ~ 16 seconds 5

Layer HO

valid timeContinuous time for Layer HO judgment 1 ~ 16 seconds 4

PBGT watch

timeStatistics 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





Parameter


Recommended

value

MS

Fast -moving

watch cells

The cell sum P for judge whether MS is fast moving.

The value, if too large, may cause abrupt increase of

system flow, while too small value may cause

inaccurate judgment for fast moving MS.

1~ 10 3

MS

Fast –moving

valid cells

The cell sum N by which MS actually quickly passes. If

within P cells that MS continuously past, the number of

cells by which the MS is judged to pass quickly is equal

to or more than N, then the MS will be judged as a fast

moving MS.

1~ 10 2

MS

Fast –moving

Time Thrsh.

The time threshold (2r/v) determined by the cell radius

(r) and moving speed (v). If the time in which MS seconds

passes the cell is smaller than the threshold, then MS

is judged to quickly pass the cell.

1~ 225 15




Common Concentric Data

Parameter


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-

optimumlevel 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





Parameter

name Meaning

Value

range

Recommended

value

Pref. subcellin 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 whichlayer is preferred to provide service for the MS.

overlaid ,

underlaid ,none

None





Parameter

name Meaning Value range Recommended value

RX_QUALThrsh.

In case of Qual. Is worse than this value, MS handoverfrom overlay to underlay

0--70 60

UO HO watchtime

P/N judgment statistics time for U/O HO judgment. 0 ~ 16 seconds 5

UO HO validtime

P/N judgment continuous time for U/O HO judgment. 0 ~ 16 seconds 4

TA thrsh. OfAssignment

Pref.

TA is more than this value, TCH in underlay will beallocated

0--63According concrete

condition

TA Thrsh. OfImme-Assign

Pref.

TA is more than this value, SDCCH in underlay will beallocated

0--63According concrete

condition

TA Prfe. OfImme-Assign

AllowedTA attend allocation of SDCCH or not Yes, No

According concretecondition





Parameter


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

UO HO watch

timeP/N judgment statistics time for U/O HO judgment. 0 ~ 16 seconds 5

UO HO valid

timeP/N judgment continuous time for U/O HO judgment. 0 ~ 16 seconds 4




Normal Concentric Data

Parameter


RX_LEV

Thrsh

Rx level hysteresis, Receiving Quality Thrsh.,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

UO signalintensity

difference

Transmitting Power at antenna difference between

underlaid and overlaid may cause MS receiving

signal intensity difference in underlaid and overlaid .

The parameter usually 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




Enhance IUO Data

Parametername

Meaning Value range Recommendedvalue

Enhance IUO

AllowedEnable function of Enhance IUO or not Yes, No

Set according to

actual conditions

UtoO Traffic

HO AllowedEnable traffic to be one condition of HO or not Yes, No

Set according to

actual conditions

OtoU HO

Received

Level Thrsh.

In case of receiving level in overlay is less than this

value, HO occurs from overlay to underlay0--63 25

UtoO HO

Received

Level Thrsh.

In case of receiving level in underlay is more than this

value, and traffic in underlay is more than Traffic Thrsh.

Of Underlay, HO occurs from underlay to overlay0 — 63 35




Concentric Cell Handover Table

Parameter name Meaning Value range

Recomm

ended

value

Traffic Thrsh. Of

Underlay

If the traffic in underlay is over this value, MS will

handover from under to overlay0—100% 80

Underlay HO Step

Period

If there are some handover requests from under to

overlay at the same time, system will handover the call

with level firstly. This value determine period per step

1—255s 5

Underlay HO Step

Level

It is the step that handover band decreases, used to

control the grade by grade handover band from underlay

to overlay with ―underlay HO step level‖

1—63dB 5

Penalty Time of

UtoO HO

To prevent ping-pong handover, the call can‘t be handed

over back within penalty time when a call is handed over

from underlay to overlay

0—255s 10




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 levelsof 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.




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 themodule 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.





1.1 Intra BSC Handover

1.2 Intra MSC Handover

1.3 Inter MSC Handover




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 SABM

Establish_IND

PHY INFO

Handover Complete

Handover_Performed





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.




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)





Measurement Points of Intra BSC Handover

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




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 Release

Clear Complete

Attempted outgoing interBSC inter cell handovers

Attempted incoming interBSC inter cel l handovers

Successful incoming inter BSC handovers

Successful outgoing interBSC inter cell handovers

Intra-MSC HO Signaling process





1.1 Intra BSC Handover

1.2 Intra MSC Handover

1.3 Inter MSC Handover




MSC-BMSC-A VLR-BBSC-A BSC-B

HO-REQUIREDMAP_Prepare_HO

MAP_Prepare_HO_ACK

MAP_Allocate_HO_NUM

MAP_Send_HO_Repor t

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

IAI

ACM

Signaling process between MSC




MSC-BMSC-A VLR-BBSC-A BSC-B

HO-REQUIREDMAP_Prepare_HO

MAP_Prepare_HO_ACK

MAP_Allocate_HO_NUM

MAP_Send_HO_Repor t

MAP_Send_HO_Report_ACK

MS

HO-REQUEST

HO-REQUEST-ACK

HO-Command

MS

HO-AccessMAP_Process_Access_Signalling

HO-Complete

MAP_Send_End_SignalClear-Command

Clear-Complete

MAP_Send_End_Signal_ACK

Some intermediate steps are omitted

IAI

ACM

Signaling process between MSC




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 cell.

− The target cell has no channel available.

− VLR-B has no HO number available.

− HO error or unsuitable data.




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




Highway

MSC-AMSC-C

MSC-B MSC-C

Inter MSC HO—Subsequent HO process

Subsequent HO




Inter MSC HO Signaling process

Statistics counter —same as Intra MSC HO, Statistics is

handled by BSC

HO formula-- same as Intra MSC HO




Major differences

There is no ―HO request‖ information for intra-BSC HO, and all of the HO are analyzedand processed in BSC. Once the target cell as required is found in the BSC, ―Channel

activation‖ information is sent to it directly.

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.

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 allocateHO 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.




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 .




Summary

In this course, we have learned:

Classify of handover

Judgment and Ranking step

Handover Data Configuration

Handover signaling Flow

Summary



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14 Handover Issue2.0.ppt

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