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OBJECTIVES
To understand the procedures of GSMHandover
To understand the procedures of PowerControl
To identify parameters needed forHandover and Power Control Operation
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HAND-OVER ANDPOWER CONTROL
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HAND-OVER
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PURPOSES 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 interferencewithin a cell (severe interference)
4. Compelled hand-over to balance traffic
distribution of inter-cells.
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NETWORK OVERVIEW
MSC BSC
BTSMS
BSC Evaluation and Decisionof HO
MSC: routes the call to the otherMSC during Inter-MSC HO
BTS preprocessmeasurements UL and DL
MS measures:
Signal Strength DL own celland neighboring cells, QualityDL
Signal Strength ofNeignboring Cells
BTS measures:
Signal Strength UL, QualityUL , TA
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1. Intra-cell hand-over: hand-over occurs in the samecell. Controlled independently by the BSC the cellattached to.
2. Inter-cell hand-over of the same BSC: involving byMSC is not needed.
3. Inter-BSC hand-over of same MSC: Before and afterhand-over, the two cells belong to different two BSCswhich are controlled by the same MSC. All the MSCand BSCs are involved.
4. Inter-MSCs hand-over: Before and after hand-over,the two cells belong to different two MSCs. All therelevant MSCs and BSCs are involved.
TYPES OF HANDOVER
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In this case, BSC should set up a new link with new BTS andassign a TCH in the new cell for MS.
HAND-OVER INSIDE BSCBSC
H/O
BTS OLD BTS NEW
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HAND-OVER BETWEEN DIFFERENTBSCs
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HANDOVER FLOWCHARTInter-BSC Handover
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
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INTER-MSC HANDOVER
OLD LINK
NEW LINK
BSC OLD
H/OBSC NEW
MSC OLD MSC NEW
BTS OLD BTS NEW5
5
5
1
5
5
7
2
3
446
3
5
7
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INTER-MSC HANDOVERPROCEDURE (1)
1 BSCA sends hand-over request to MSCA whendeemed necessary according to MSs measurementreport.
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 toMSCA.4 Communication links are established between MSCAand MSCB according to Hand-over Number(HON).
5 MSCA send hand-over command to MS who thenhanded over to a new TCH.
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INTER-MSC HANDOVERPROCEDURES (2)
6 BSCB send to MSCB, then to MSCA the commandof hand-over completion.
7 MSCA controls BSCA and BTSA to release the oldTCH.
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HANDOVER FLOWCHARTInter-MSC Handover
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HANDOVER CLASSIFICATION
1. Synchronous
2. Asynchronous
3. Pseudo-synchronous
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QUEUING AND FORCEDDISCONNECTION
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 radioresources.
Forced disconnection - when in emergency andno radio resource is available, some subscribers withlower priority may be disconnected, or handed out forcibly
to ensure that the subscribers with higher priority couldkeep their calls continuously.
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BASE STATION PRE-PROCESSING
1. RXLEV_XX XX DL or UL For each connection, at least 32 sampling data areretained and the average of RX level is calculated out by
BSS in each SACCH period.
2. Adjacent cells BCCH carrier receiving levelRXLEV_NCELL(n)
For each connection and each cell, the latest 32 samplingdata are stored by BSS to calculate out the adjacent cellsBCCH carrier receiving level.
PROCESSING OF BTS MEASURED DATA
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BASE STATION PRE-PROCESSING
3. POWER BUDGET (PBGT)
For each connection and each allowable cell,
BSS calculates PBGT as follows
PROCESSING OF BTS MEASURED DATA
PBGT(n)=RxLevDL(n)-[RxLevDL(s)+BSTxPwrMax(s)-BSCurrentTxPwr(s)]
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BASE STATION PRE-PROCESSING
4. Timing AdvanceFor each connection, BSS calculate the TA usingparameters Hreqt and Hreqave
5. Interference bandBSS averages interference on idle time-slots and
maps to five classes called strips.
PROCESSING OF BTS MEASURED DATA
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PARAMTERS IN CONNECTION WITHHAND-OVER
PARAMETER FUNCTION
UpLevTh N P upward level thresholdUpQualTh N P upward quality threshold
DwLevTh N P downward level thresholdDwQualTh N P downward quality thresholdUpIntfTh N P upward interference thresholdDwIntfTh N P downward interference thresholdMsDistTh N P distance threshold same unit with TA)HoMargin n Adjacent cells hand-over margin
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THRESHOLD COMPARISON
1. Hand-over will occur if at least P out of N upward levels arelower than UpLevTh.
2. Hand-over will occur if at least P out of N downward levelsare lower than DwLevTh.
3. Hand-over will occur if at least P out of N upward levels arehigher than UpQualTh.
4. Hand-over will occur if at least P out of N downward levelsare higher than DwQualTh.
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THRESHOLD COMPARISON
5. Hand-over will occur if the latest P out of N upward levelsare higher than UpIntfTh and condition 3 is met at the sametime.
6. Hand-over will occur if the latest P out of N downward levelsare higher than DwIntfTh and condition 4 is met at thesame time.
7. Hand-over will occur if the latest P out of N TAs are higherthan MsDistTh.
8. Hand-over will occur if PBGT of some adjacent cell is higher
than its corresponding HoMargin.
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HANDOVER ALGORITHM
The hand-over algorithm BSC adopts is based on the
following equation:
1) RXLEV_NCELL(n) > RXLEV_MIN(n) + Max (0, Pa)
where: Pa = (MS_TXPWR_MAX(n) P)
2) PBGT (n) - HO_MARGIN(n) > 0
BSS selects from all adjacent cells that both meets equation(1) and (2) and queue them from large PBGT to smallones and serves as candidate adjacent cells.
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POWER CONTROL
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POWER CONTROL PROCEDURES
MEASURED DATA
AVERAGE MEASURED DATA
POWER CONTROL DECISION
SEND POWER CONTROL
COMMAND
MEASURED DATA
CORRECTION
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RELATION OF LEVEL WITH POWERCONTROL
63
0
Upper limit
Lower limit
Fast power controlzone
Fast power control zone
High
Low
Normal
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RELATION OF BER WITH POWERCONTROL
0
7
Upper limit
Lowerlimit
Fast power controlzone
Fast power control zone
Low
High
Normal
C di R l i b
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Corresponding Relation betweenRXQUAL and BER
RXQUAL BER (%) Typical(%)0 BER
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BTS POWER CONTROLSTRATEGY
Keep current transmission power when received levelis normal.
Lower the transmission power when received level ishigh.
Increase the transmission power when received levelis 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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MS POWER CONTROL STRATEGY
Normal Level LEVELCAUSE = 0
Low Level LEVELCAUSE = 1High Level LEVELCAUSE = 2
Normal BER QUALCAUSE = 0
Low BER QUALCAUSE = 1High BER QUALCAUSE = 2
LEVELCAUSE QUALCAUSE OUTPUT0 2 INCREASE1 0 STAY1 1 STAY1 2 INCREASE2 0 DECREASE2 1 DECREASE2 2 INCREASE
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RANGE OF POWER CONTROL 1 B T S Po w e r Co n t r o l
BTS has 6 classes of static power configured by network, each classhas 15 levels of dynamic power which can be configured bynetwork.
2 M S Po w e r Co n t r o l
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 stepDCS1800 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 power control range 36dbm ~ 0dbm 2dbm one step
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