Handover&Powercontrol

7/28/2019 Handover&Powercontrol

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Handover

and

Power Control

ZXG10 System


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Hand-over

Hand-over is a process that transfers a MS that is in settingup or busy status to a new traffic channel. Generally, hand-

over will occur under the following two conditions:

1. A busy MS which is moving from a cell into another;

2. A MS is making a call at overlapping area of two cells,one of which is very busy in traffic. BSC notify MS to

measure signal intensity and channel quality of adjacent

cells. This call will be handed over to the cell which is not

busy in traffic. This kind of hand-over is occurred tobalance inter-cell traffics.


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Causes Resulting Hand-over

1Weak signal level

2Bad signal quality

3Severe interference, i.e., the channel a MS is

occupying is interfered suddenly and therefore isforced to use another channel of the same cell;

4The MS is far away from the BS;

5A more appropriate cell exists. This hand-

over is based on the whole system considerationaiming to reduce the overall system interference;


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Purpose of Hand-over

1Save the calls in progressbad quality)2Cell-boundary handing over to improve

ongoing calls (weak signal)

3intra-cell hand-over reducing interference

within a cell (severe interference)

(4) Compelled hand-over to balance traffic

distribution of inter-cells.


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Types of Hand-over1Intra-cell hand-over: hand-over occurs in the samecell. Controlled independently by the BSC the cell attached

to.

2Inter-cell hand-over of the same BSC: involving byMSC is not needed.

3Inter-BSC hand-over of same MSC: Before and afterhand-over, the two cells belong to different two BSCs which

are controlled by the same MSC. All the MSC and BSCs are

involved.

4Inter-MSCs hand-over: Before and after hand-over,the two cells belong to different two MSCs. All the relevant

MSCs and BSCs are involved.


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Hand-over inside BSC

BSC

BTS

BTS

M

S

M

S

In this case, BSC should set up a new link with new BTS and

assign a TCH in the new cell for MS.


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Hand-over between Different BSCsOld Link

New Link

MSC/VLR

BSC

BSC

M

S

M

S

1) The old BSC make a hand-over request to MSC which then

establish new link with new BSC and new BTS, and retain an idle

TCH in the new cell for MS.

2) MSC is responsible for releasing the old link.

3) After the call is completed, MS should originate location

updating because of the change of LAI.


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Inter-MSC Hand-over

1

5 Old Link

New Link

2 4

MSCA

MSCB

BSC

A

BSC

B

M

S

M

S

3

6

4

5

5

5

6

7

7

3

3


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Hand-over Procedures

1BSCA sends hand-over request to MSCA when deemed necessary

according to MSs measurement report.

2MSCA sends this request to MSCB which is responsible for setting

up links with BSCB and BTSB.

3MSCB sends back radio channel acknowledgement to MSCA.

4Communication links are established between MSCA and MSCBaccording to Hand-over Number(HON).

5MSCA send hand-over command to MS who then handed over to a

new TCH.

6BSCB send to MSCB, then to MSCA the command of hand-overcompletion.

7MSCA controls BSCA and BTSA to release the old TCH.


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Hand-over Classification

1Synchronous: MS use the same TA both in destinationand target cell. This usually applies to hand-over of same cellor different sectors within the same cell. This is the hand-over

with highest speed.

2Asynchronous: MS dont know the TA to be used in

target cell. When either of the two cells doesnt synchronizewith BSC, this mode should be used. The hand-over speed is

low.

3Pseudo-synchronous: MS is able to calculate out the

TA it should use in the target cell. When both cells havesynchronized with BSC, this mode may be used. The hand-

over speed is fast.


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Hand-over flow chart

DT1HO PERF

HO CMD

CH ACT

MEAS REP

RF CH REL ACK

RF CH REL

DIHO COM

EST IND

HO DET

CH ACT ACK

MS BTS1 BTS2 BSC MSC

MEAS RES

DRHO CMD

HO ACCESS

PHY INFO

SABM

UA

HO COM


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Queuing and Forced Disconnection

1Queuing: To increase the successful rate of hand-over,

when no radio resource is available, the applicant of hand-

over may be put into queuing and wait for release of radio

resources.2Forced disconnection: when in emergency and no radio

resource is available, some subscribers with lower priority

may be disconnected, or handed out forcibly to ensure that the

subscribers with higher priority could keep their callscontinuously.


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Base Station Pre-processing1 The base station receives the following

meas_rpt:

1Meas_rpts made by MS and reported from

SACCHDownlink RXLEV

Downlink RXQUAL(BER)

Other adjacent cells downlink RXLEVlessthan 6, designated by BA list)

Interference strip


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2Measurement report made by BTS

Uplink RXLEV

Uplink RXQUALTA


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Base Station Pre-processing2 Processing of BTS measurement data1RXLEV_XXXXDL or UL

For each connection, at least 32 sampling data

are retained and the average of RX level iscalculated out by BSS in each SACCH period.


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2Adjacent cells BCCH carrier receiving

level RXLEV_NCELL(n)

For each connection and each cell, the latest 32sampling data are stored by BSS to calculate out

the adjacent cells BCCH carrier receiving level.


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Base Station Pre-processing33Power BudgetPBGT

For each connection and each allowable cell, BSS

calculates PBGT as follows

PBGT(n) =(Min(MS_TXPWR_MAX,P)RXLEV_DL

PWR_C_D)(Min(MS_TXPWR_MAX(n),P)

RXLEV_NCELL(n))


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Where,

RXLEV_NCELL(n) and RXLEV_DL are got byabove definitions.

PWR_C_D is the difference of cell-allowed

downward maximum power with actual power

MS_TXPWR_MAX(current traffic channel)

MS_TXPWR_MAX(n) (adjacent cell n traffic channel)

P is the maximum transmission power of MS


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Base Station Pre-processing44TA

For each connection, BSS calculate the TA

using parameters Hreqt and Hreqave5Interference strip

BSS averages interference ( using INTAVE) on

idle time-slots and maps to five classes called

strips.


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Parameters in connection with

hand-over1UpLevThNPupward level threshold

2UpQualThNPupward quality threshold

3DwLevThNPdownward level threshold

4DwQualThNPdownward quality threshold5UpIntfThNPupward interference threshold

6DwIntfThNPdownward interference threshold

7MsDistThNPdistance thresholdsame unit with

TA)

8HoMarginnAdjacent cells hand-over margin


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Threshold Comparison (1)

1. Hand-over will occur if at least P out of N upward levels

are lower than UpLevTh.

2. Hand-over will occur if at least P out of N downward

levels are lower than DwLevTh.

3. Hand-over will occur if at least P out of N upward levels

are higher than UpQualTh.

4. Hand-over will occur if at least P out of N downward

levels are higher than DwQualTh.


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Threshold Comparison (2)

5. Hand-over will occur if the latest P out of N upward levels are

higher than UpIntfTh and condition 3 is met at the same time.

6. Hand-over will occur if the latest P out of N downward levels are

higher than DwIntfTh and condition 4 is met at the same time.

7. Hand-over will occur if the latest P out of N TAs are higher thanMsDistTh.

8. Hand-over will occur if PBGT of some adjacent cell is higher

than its corresponding HoMargin.


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Hand-over Algorithm

The hand-over algorithm BSC adopts is based

on the following equation:

RXLEV_NCELL(n) > RXLEV_MIN(n) + Max

(0, Pa) (1)

where: Pa = (MS_TXPWR_MAX(n)P)

PBGTn HO_MARGIN(n) > 0 (2)


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BSS selects from all adjacent cells that both

meets equation (1) and (2) and queue them

from large PBGT to small ones and serves as

candidate adjacent cells.


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Power Control

Purpose of Power Control

BTS Power Control Strategy


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Lower interference within a cell

Save power

Premises: Call quality or data

transmission quality be guaranteed

Purpose of Power Control


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Power Control Procedures

Save measured data

Average measured data

Power control decision

Send power control command

Measured data correction


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Relation of Level and Power Control

63

0

Upper limit

Lower limit

Fast power control zone


High

Low

Normal


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Relation of BER with Power Control

0

7

Upper limit

Lower limit



Low

High

Normal


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BTS Power Control Strategy

Keep current transmission power when received level is

normal.

Lower the transmission power when received level is high.

Increase the transmission power when received level is low.

Keep current transmission power when BER is normal.

Increase the transmission power when BER is high.

Lower the transmission power when BER is low.


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Corresponding Relation between RXQUAL

and BER

RXQUAL BER (%) Typical(%)0 BER


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MS Power Control Strategy

Normal LevelLEVECAUSE = 0

Low Level LEVELCAUSE = 1

High Level LEVECAUSE = 2

Normal BERQUALCAUSE = 0

Low BERQUALCAUSE = 1

High BERQUALCAUSE = 2

0 2 INCREASE

1 0 STAY1 1 STAY

1 2 INCREASE

2 0 DECREASE

2 1 DECREASE

2 2 INCREASE


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Range of Power Control1BTS Power Control

BTS has 6 classes of static power configured by network, each class has 15 levelsof dynamic power which can be configured by network.

2MS Power ControlGSM900 class A MS power capability 43dbm20WGSM900 class B MS power control 39dbm8WGSM900 class C MS power capability 37dbm

5W

GSM900 class D MS power capability 33dbm2WGSM900 class E MS power capability 29dbm0.8WGSM900 power control range of MS is 43dbm ~ 5dbm at least 2dbm one stepDCS1800 class A MS power control capability 30dbm1WDCS1800 class B MS power control capability 24dbm0.25WDCS1800 class C MS power control capability 36dbm4WDCS1800 class D MS power control range 36dbm ~ 0dbm2dbm one step

Date post:	03-Apr-2018
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