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Handover
Issue
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Upon completion this course, you will beable to:
Understand the type of handover. Master handover judgment flow
Configure handover data
Master handover signaling flow
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Chapter 1 Introduction of Handover
Chapter 2 HO Algorithm process
Chapter 3 HO Data Configuration
Chapter 4 HO Signaling process
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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
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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
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Chapter 1 Introduction of Handover
Chapter 2 HO Algorithm process
Chapter 3 HO Data Configuration
Chapter 4 HO Signaling process
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Chapter 2 HO Algorithm process
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
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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 MSHO
1
1
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Chapter 2 HO Algorithm process
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
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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)
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MRMR
MR MRMR
Measurementreport No. n
Measurement rNo. n+4
ContinuousMR
flow
How to interpolate MR?
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Chapter 2 HO Algorithm process
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
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Penalty processing There are altogether four types of
penalty process (second step of HO
algorithm process )
Penalty on the target cell when a HOfails.
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
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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.
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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.
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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 MSstaying in the umbrella cell and avoid
frequent HO.
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Underlaid
Overlaid Do not
attemptagain after a
failed HO!
Penalty on overlaid/underlaid
cellA new Overlaid/underlaid HO is prohibited
within a penalty time after an
Overlaid/Underlaid HO failure.
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Chapter 2 HO Algorithm process
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
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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
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Chapter 2 HO Algorithm process
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
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Types of HO
Emergency HO
TA HOBQ HO
interference HO
Rx_Level_Drop HO Load HO
Normal HO
Edge HO, layer cell HO and PBGT
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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
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Rx_level_drop HO
Rx_Level_Drop HO
Due to downlink signal level drop
Triggered upon detecting rapid level dropduring MS busy mode.
Requirements for the target cell:
The target cell is the first cell in the neighborcell list.
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Interference HO
Interference HO (DL&UL) :
When the receiving level > receiving
threshold level. But Receiving quality Load HO threshold
Requirements for the target cell
Load of target cell < Load HO thresholdBTS
BSC
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Edge HO Edge HO Criterion:
In N seconds, when there are P seconds that
neighbor cells DL or MSs UL signal level is
lower than the Edge HO threshold. Then thecriterion is met and Edge HO occurs. This
method utilizes the P/N rule.
Requirements for the target cell:The target cell should be ranked in front of the
serving cell.
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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 cells.
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Pbgt ho
PBGT HO Criterions :
Target cells path loss is smaller than the
serving cells path loss by the PBGT threshold
value.
Satisfying the P/N rule.
Target cell should be ranked in front of theserving cell.
Note :
PBGT HO can only occur between same-
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Fast-moving HO
When the serving cell is micro cell :
When the MS has traveled through P
numbers of cell, and there are Q (=
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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
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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
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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 reported by BTS
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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
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underlaid
overlaid
:
Division of underlaid and overlaid is decidedby MS downlink receive level ,TA value and
quality.
Normal overlaid/underlaid HO
The quality boundary is elided in this figure
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Chapter 1 Introduction of Handover
Chapter 2 HO Algorithm process
Chapter 3 HO Data Configuration
Chapter 4 HO Signaling process
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Chapter 4 HO Signaling process
1.1 Intra BSC Handover
1.2 Intra MSC Handover
1.3 Inter MSC Handover
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Intra-bsc handover signaling
processMS MSBTS1 BTS2BSC MSCMeasurement Report from MS
Channel_Active
Channel_Active ACK
HANDOVER COMMANDHandover Access
Handover_DetectPHY INFO
First SABM
Establish_IND
PHY INFO
Handover Complete
Handover_Performed
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Intra-bsc handover signaling process
Attention
In asynchronous HO, if MS could not reach
the new TCH channel after the target cell hassent 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, BSCrelease the assigned TCH channel in the
target cell .
Max resend times of physical
information*Radio link connection timer >
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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)
Intra-bsc handover signaling process
Measurement points of intra BSC
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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 intercell handovers )
Internal inter cell handover success
rate
=(Successful incoming internal inter
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Chapter 4 HO Signaling process
1.1 Intra BSC Handover
1.2 Intra MSC Handover
1.3 Inter MSC Handover
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Chapter 4 HO Signaling process
1.1 Intra BSC Handover
1.2 Intra MSC Handover
1.3 Inter MSC Handover
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MSC-BMSC-A VLR-BBSC-A BSC-B
HO-REQUIREDMAP_Prepare_HO
MAP_Prepare_HO_ACK
MAP_Allocate_HO_NUM
MAP_Send_HO_Report
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
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MSC-BMSC-A VLR-BBSC-A BSC-B
HO-REQUIREDMAP_Prepare_HO
MAP_Prepare_HO_ACK
MAP_Allocate_HO_NUM
MAP_Send_HO_Report
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
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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.
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Roaming
EMS
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 COMPLETE
Send 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 hosubsequent HO process
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Highway
MSC-AMSC-C
MSC-B MSC-C
Inter MSC hosubsequent HO process
Subsequent HO
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Inter MSC HO signaling process
Statistics countersame as Intra MSC HO,
Statistics is handled by BSC
HO formula-- same as Intra MSC HO
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Major differences
There is no HO request information for
intra-BSC HO, and all of the HO are
analyzed and 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
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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.
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Summary
In this course, we have
learned:
Classify of handover
Judgment and Ranking
step
Handover Data
Configuration
Handover signaling Flow
Summary