7.handover&power control

中兴通讯学院 www.univ.zte.com.cnwww.univ.zte.com.cn

Handover

and

Power Control


Hand-over

Hand-over is a process that transfers a MS that is in setting up 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 to balance inter-cell traffics.


Causes Resulting Hand-over

（ 1 ） Weak signal level ；（ 2 ） Bad signal quality ；（ 3 ） Severe interference, i.e., the channel a MS is occupying is interfered suddenly and therefore is forced to use another channel of the same cell;（ 4 ） The MS is far away from the BS;（ 5 ） A more appropriate cell exists. This hand-over is based on the whole system consideration aiming to reduce the overall system interference;


Purpose of Hand-over

（ 1 ） Save the calls in progress （ bad quality)

（ 2 ） Cell-boundary handing over to improve ongoing calls (weak signal)

（ 3 ） Intra-cell hand-over reducing interference within a cell (severe interference)

(4) Compelled hand-over to balance traffic distribution of inter-cells.


Types of Hand-over

（ 1 ） Intra-cell hand-over: hand-over occurs in the same cell. Controlled independently by the BSC the cell attached to.

（ 2 ） Inter-cell hand-over of the same BSC: involving by MSC is not needed.

（ 3 ） Inter-BSC hand-over of same MSC: Before and after hand-over, the two cells belong to different two BSCs which are controlled by the same MSC. All the MSC and BSCs are involved.

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

2023年4月12日星期三

深圳市中兴通讯股份有限公司 6 中兴通讯学院 www.univ.zte.com.cnwww.univ.zte.com.cn

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.


Hand-over between Different BSCs

Old 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.


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

3

5

6

77

3

3


Hand-over Procedures 1 ） BSCA sends hand-over request to MSCA when deemed

necessary according to MS’s measurement report.

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

setting up links with BSCB and BTSB.

3 ） MSCB sends back radio channel acknowledgement to MSCA.

4 ） Communication links are established between MSCA and

MSCB according to Hand-over Number(HON).

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

to a new TCH.

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

over completion.

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


Hand-over Classification

（ 1 ） Synchronous: MS use the same TA both in destination and target cell. This usually applies to hand-over of same cell or different sectors within the same cell. This is the hand-over with highest speed.

（ 2 ） Asynchronous: MS don’t know the TA to be used in target cell. When either of the two cells doesn’t synchronize with BSC, this mode should be used. The hand-over speed is low.

（ 3 ） Pseudo-synchronous: MS is able to calculate out the TA it should use in the target cell. When both cells have synchronized with BSC, this mode may be used. The hand-over speed is fast.


Hand-over flow chart

DT1：HO PERF

HO CMD

CH ACT

MEAS REP

RF CH REL ACK

RF CH REL

DI：HO COM

EST IND

HO DET

CH ACT ACK

MS BTS1 BTS2 BSC MSC

MEAS RES

DR：HO CMD

HO ACCESS

PHY INFO

SABM

UA

HO COM


Queuing and Forced Disconnection

1 ） Queuing: 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.

2 ） Forced 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 calls continuously.


Base Station Pre-processing （ 1 ）

• The base station receives the following meas_rpt:

（ 1 ） Meas_rpts made by MS and reported from SACCH

－ Downlink RXLEV

－ Downlink RXQUAL(BER)

－ Other adjacent cells’ downlink RXLEV

（ less than 6, designated by BA list)

－ Interference strip


（ 2 ） Measurement report made by BTS

－ Uplink RXLEV

－ Uplink RXQUAL

－ TA



• Processing of BTS measurement data

（ 1 ） RXLEV_XX （ XX ＝ DL or UL ）For each connection, at least 32 sampling data are retained and the average of RX level is calculated out by BSS in each SACCH period.


（ 2 ） Adjacent cells‘ BCCH carrier receiving level RXLEV_NCELL(n) ）

For each connection and each cell, the latest 32 sampling data are stored by BSS to calculate out the adjacent cells’ BCCH carrier receiving level.



（ 3 ） Power Budget （ PBGT ）

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))


Where,

RXLEV_NCELL(n) and RXLEV_DL are got by above 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



（ 4 ） TA

For each connection, BSS calculate the TA using parameters Hreqt and Hreqave

（ 5 ） Interference strip

BSS averages interference ( using INTAVE) on idle time-slots and maps to five classes called strips.


Parameters in connection with hand-over

（ 1 ） UpLevTh ， N ， P ）： upward level threshold ；（ 2 ） UpQualTh ， N ， P ）： upward quality threshold ；（ 3 ） DwLevTh ， N ， P ）： downward level threshold ；（ 4 ） DwQualTh ， N ， P ）： downward quality threshold；（ 5 ） UpIntfTh ， N ， P ）： upward interference threshold；（ 6 ） DwIntfTh ， N ， P ）： downward interference threshold（ 7 ） MsDistTh ， N ， P ）： distance threshold （ same unit with TA)（ 8 ） HoMargin （ n ）： Adjacent cells’ hand-over margin


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.


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 than MsDistTh.

8. Hand-over will occur if PBGT of some adjacent cell is higher than its corresponding HoMargin.


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)

• PBGT （ n ) － HO_MARGIN(n) > 0 (2)


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.


• Purpose of Power Control

• BTS Power Control Strategy

Power Control


• Lower interference within a cell

• Save power

• Premises: Call quality or data transmission quality be guaranteed

Purpose of Power Control


Power Control Procedures

Save measured data

Average measured data

Power control decision

Send power control command

Measured data correction


Relation of Level and Power Control

63

0

Upper limit

Lower limit

Fast power control zone


High

Low

Normal


Relation of BER with Power Control

0

7

Upper limit

Lower limit



Low

High

Normal


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.


Corresponding Relation between

RXQUAL and BER

RXQUAL BER (%) Typical(%)

0 BER<0.2 0.14

1 0.2<BER<0.4 0.28

2 0.4<BER<0.8 0.57

3 0.8<BER<1.6 1.13

4 1.6<BER<3.2 2.26

5 3.2<BER<6.4 4.53

6 6.4<BER<12.8 9.05

7 12.8<BER 18.10


MS Power Control Strategy

Normal Level ： LEVECAUSE = 0Low Level ： LEVELCAUSE = 1High Level ： LEVECAUSE = 2

Normal BER ： QUALCAUSE = 0Low BER ： QUALCAUSE = 1High BER ： QUALCAUSE = 2

0 2 INCREASE

1 0 STAY

1 1 STAY

1 2 INCREASE

2 0 DECREASE

2 1 DECREASE

2 2 INCREASE


Range of Power Control

1 ， BTS Power Control BTS has 6 classes of static power configured by network, each class has 15 levels

of dynamic power which can be configured by network.

2 ， MS Power Control GSM900 class A MS power capability 43dbm （ 20W ）GSM900 class B MS power control 39dbm （ 8W ）GSM900 class C MS power capability 37dbm （ 5W ）GSM900 class D MS power capability 33dbm （ 2W ）GSM900 class E MS power capability 29dbm （ 0.8W ）GSM900 power control range of MS is 43dbm ~ 5dbm ， at least 2dbm one step DCS1800 class A MS power control capability 30dbm （ 1W ） DCS1800 class B MS power control capability 24dbm （ 0.25W ） DCS1800 class C MS power control capability 36dbm （ 4W ） DCS1800 class D MS power control range 36dbm ~ 0dbm ， 2dbm one step

7.handover&power control

Engineering