02 g-lii 300 handover-20081022-a-2.1
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HUAWEI TECHNOLOGIES CO., LTD. All rights reserved
www.huawei.com
Internal
Handover
ISSUE 2.0
HUAWEI TECHNOLOGIES CO., LTD. Page 2All rights reserved
Handover is key technology of Mobile
communication system and make
continued conversation possible.
Handover algorithm in Huawei product
is flexible and powerful
HUAWEI TECHNOLOGIES CO., LTD. Page 3All rights reserved
� 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
HUAWEI TECHNOLOGIES CO., LTD. Page 4All rights reserved
Chapter 1 Chapter 1 Introduction of HandoverIntroduction of Handover
Chapter 2 Chapter 2 HO Algorithm processHO Algorithm process
Chapter 3 Chapter 3 HO Data ConfigurationHO Data Configuration
Chapter 4 Chapter 4 HO Signaling processHO Signaling process
HUAWEI TECHNOLOGIES CO., LTD. Page 5All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 6All rights reserved
� Quick Handover
� Emergency
� TA handover
� Interference handover
� Quick level drop handover
� Bad quality handover
� Quick handover
� Enhanced dual-band network handover
� Load handover
� General handover
� Edge handover
� Fast-moving micro cell handover
� Inter-layer (better cell) handover
� PBGT handover
� AMR handover
� Better 3G cell handover
� TIGHT BCCH handover algorithm
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
HUAWEI TECHNOLOGIES CO., LTD. Page 8All rights reserved
Chapter 1 Chapter 1 Introduction of HandoverIntroduction of Handover
Chapter 2 Chapter 2 HO Algorithm processHO Algorithm process
Chapter 3 Chapter 3 HO Data ConfigurationHO Data Configuration
Chapter 4 Chapter 4 HO Signaling processHO Signaling process
HUAWEI TECHNOLOGIES CO., LTD. Page 9All rights reserved
Chapter 2 Chapter 2 HO Algorithm processHO Algorithm process
1.1 1.1 General HO processGeneral HO process
1.2 1.2 Measurement reportingMeasurement reporting
1.3 Measurement processing1.3 Measurement processing
1.4 1.4 HO judgmentHO judgment
HUAWEI TECHNOLOGIES CO., LTD. Page 10All rights reserved
General Process of HO Algorithm
MS entering
connection state
Measurement and
production of MRs
MR processing
Algorithms making
handover decision
Handover execution
MS entering new
connection state
HUAWEI TECHNOLOGIES CO., LTD. Page 11All rights reserved
Chapter 2 Chapter 2 HO Algorithm processHO Algorithm process
1.1 1.1 General HO processGeneral HO process
1.2 1.2 Measurement reportingMeasurement reporting
1.3 Measurement processing1.3 Measurement processing
1.4 1.4 HO judgmentHO judgment
HUAWEI TECHNOLOGIES CO., LTD. Page 12All rights reserved
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 downlink measurement report of
the serving cell
The uplink measurement
report of MSThe downlink measurement report
of the neighbor cell (BCCH)
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Measurement Report
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Period of measurement report
� The downlink MR is sent to BTS in SACCH uplink
�The interval is 480ms/per time when MS is on TCH
�The interval is 470ms/per time when MS is on SDCCH
12TCH 12TCH1SACCH 1 Idle
480ms4 TCH multi-frames
HUAWEI TECHNOLOGIES CO., LTD. Page 15All rights reserved
Chapter 2 Chapter 2 HO Algorithm processHO Algorithm process
1.1 1.1 General HO processGeneral HO process
1.2 1.2 Measurement reportingMeasurement reporting
1.3 Measurement processing1.3 Measurement processing
1.4 1.4 HO judgmentHO judgment
HUAWEI TECHNOLOGIES CO., LTD. Page 16All rights reserved
MR interpolation
�Every time BSC receives a measurement report, there will be an
update to the basic queuing 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.
HUAWEI TECHNOLOGIES CO., LTD. Page 17All rights reserved
How to interpolate MR?
MR MR MR MR MR
Measurement report No. n
Measurement report No. n+4
Continuous MR
flow
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Filter----Average several continuous MR.
Filtering
MRMR MRMR MR MR
Continuous MR flow
HUAWEI TECHNOLOGIES CO., LTD. Page 19All rights reserved
Chapter 2 Chapter 2 HO Algorithm processHO Algorithm process
1.1 1.1 General HO processGeneral HO process
1.2 1.2 Measurement reportingMeasurement reporting
1.3 Measurement processing1.3 Measurement processing
1.4 1.4 HO judgmentHO judgment
HUAWEI TECHNOLOGIES CO., LTD. Page 20All rights reserved
Handover judgment
� Penalty process
� Basic queuing
� 16bits queuing
� Handover judgment
HUAWEI TECHNOLOGIES CO., LTD. Page 21All rights reserved
Penalty Processing
1. An emergency handover caused by higher TA value succeeds;
2. An emergency handover caused by bad uplink quality succeeds;
3. An emergency handover caused by bad downlink quality succeeds;
4. Penalty after handover fails, including the handovers to 2G cells
and the handovers to 3G cells
5. Penalty on the microcell from which a fast-moving MS is handed
over to the macrocell;
6. A high-speed railway fast handover succeeds;
7. An overlaid-to-underlaid handover succeeds;
8. An overlaid-to-underlaid handover or underlaid-to-overlaid handover
fails;
The penalty scheme applies to the following situations:
HUAWEI TECHNOLOGIES CO., LTD. Page 22All rights reserved
BTS
TA HO
BSC
Cell A
Cell B
For example: TA HO succeeds
Punish the original serving cell when an emergency TA HO
occurs.
HUAWEI TECHNOLOGIES CO., LTD. Page 23All rights reserved
Procedure of Queuing
� Basic queuing and secondary queuing of cells are major parts of the HO
judgment. Queuing 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 queuing processes include:
�M criterion
�K criterion
�16-bit queuing
HUAWEI TECHNOLOGIES CO., LTD. Page 24All rights reserved
M criterion
� Only the cells with received signal level satisfy the following conditions can be put
into the candidate cell list, otherwise will be removed.
� Formula:
� Downlink receive level of the cell RXLEV (the level after filtration and penalty)
>= Min DL Power on HO Candidate Cell + Min Access Level Offset
� Uplink receive level of the cell RXLEV (the level after filtration and penalty)
>= Min DL Power on HO Candidate Cell + Min Access Level Offset
− For serving cell: Min Access Level Offset is always 0; For neighbor cells: Min
Access Level Offset is configured toward the neighbor cell
− The uplink level of neighbor cells can be estimated in BSC.
Formula: SS_UPn = MS_PWRn - Ln
Path loss: Ln = BSTXPWRn – SS_DOWNn = Transmit power of the BCCH TRX of
the neighbor cell – Downlink level in the neighbor cell after interpolation, filtration,
and level rectification
MS_PWRn is min(the maximum allowable power of MS, or the maximum allowable
transmission power of MS in this neighbor cell)
HUAWEI TECHNOLOGIES CO., LTD. Page 25All rights reserved
K criterion
� After the M criterion , the serving cell and candidate neighbor cells are queued in
descending order according to the receiving level only.
� The K value of the serving cell is 0.
� For a neighbor 2G cell, K = BCCH signal level of the neighbor cell after filtering – TCH
signal level of the serving cell after filtering – KIAS;
� 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.
141516 12345678910111213
HUAWEI TECHNOLOGIES CO., LTD. Page 26All rights reserved
16-bit queuing
DL RXLEV queuing1
DL RXLEV queuing2
Indicates the queuing result of seven cells (six neighbor cells + one serving cell)
based on RXLEV.
DL RXLEV queuing3
Set to 1 for a neighbor cell if RXLEV of the neighbor cell is lower than RXLEV of
the serving cell + Inter-cell HO Hysteresis.
Set to 0 for the serving cell.
Serving cell preferred4
HO Priority Hierarchy 15
HO Priority Hierarchy 26
HO Priority Hierarchy 37
HO Priority Hierarchy 48
HO Priority Hierarchy 59
Indicates the HCS (Hierarchical Cell Structure) priority. There are 64 levels in total
(4 layers with 16 levels on each layer).
HO Priority Hierarchy 610
Set to 1 if the current load of serving cell is higher than Load HO Threshold.
Set to 1 if the current load of neighbor cell is higher than Load Req. on Candidate Cell.
Current load of the cell higher
than load handover threshold
or not
11
Set to 1 in the case of not co-BSCCo-BSC or not12
Set to 1 in the case of not co-MSCCo-MSC or not13
Set to 1 for a neighbor cell if RXLEV is lower than Inter-layer HO Threshold +
Inter-layer HO Hysteresis.Set to 1 for the serving cell if RXLEV is lower than threshold - hysteresis.
DL RXLEV higher than Inter-
layer HO Threshold or not
14
ReservedRSVD15-16
HUAWEI TECHNOLOGIES CO., LTD. Page 27All rights reserved
GSM900
Cell
Micro Cell
Umbrella
Cell GSM 900
GSM1800 GSM1800GSM1800
GSM 900 GSM 900 GSM 900
GSM900GSM900
GSM1800GSM1800
GSM900 GSM900
GSM1800 GSM1800
GSM1800
Cell
Hierarchical cell structure
1
2
3
4
HUAWEI TECHNOLOGIES CO., LTD. Page 28All rights reserved
Handover judgment
� Each handover algorithm consists of two parts. One is to decide whether
the serving cell meets the triggering conditions, and the other is to select
the candidate cells.
� Key handover criterion
�Edge handover
�Hierarchical handover
�PBGT handover
HUAWEI TECHNOLOGIES CO., LTD. Page 29All rights reserved
Edge handover
� Measured value of signal strength on the uplink TCH after filtering < value of Edge
HO UL RX_LEV Threshold; Measured value of signal strength on the downlink TCH
after filtering < value of Edge HO DL RX_LEV Threshold
� According to the P/N criterion, if P reports out of the latest N MRs meet the previous
formulas, the uplink/downlink edge handover is triggered and the candidate cells are
selected.
� Remove the serving cell from the candidate cell list
� Remove the neighbor cell whose 16-bit sequence number is greater than the 16-
bit sequence number of the serving cell. If the sequence number is small, the
priority of the cell is high.
� Remove the neighbor cell whose BCCH receive level after filtering is less than
TCH receive level of serving cell after filtering + Inter-cell HO Hysteresis
� The neighbor cells should meet the P/N (Edge HO Valid Time (s)/Edge HO
Watch Time (s) ) criterion.
If Fringe HO Allowed is set to Yes, the edge handover is allowed.
HUAWEI TECHNOLOGIES CO., LTD. Page 30All rights reserved
Hierarchical handover
� The priority level of the neighbor cell is higher than the serving cell.
� The receive level of the BCCH in neighbor cell i after filtering meets the following
formula:
Where,
SSi_f indicates the receive level of the BCCH in the neighbor cell after filtering and penalty.
Tlayer indicates Inter-layer HO Threshold.
Hlayer indicates Inter-layer HO Hysteresis.
� The 16-bit sequence number of the neighbor cell is smaller than that of the serving
cell. If the sequence number is small, the priority of the cell is high.
� If all these conditions are met during the period specified by Layer HO Valid
Time(s) within the latest Layer HO Watch Time(s), that is, if the P/N criterion is
met, then the hierarchical handover is triggered.
If Level HO Allowed is set to Yes, the inter-layer handover is allowed. To enable the
handover between different priorities of cells at the same layer, you also need to set
this parameter to Yes.
_f layer layeriSS T H≥ +
HUAWEI TECHNOLOGIES CO., LTD. Page 31All rights reserved
PBGT handover
� The neighbor cell (not the serving cell) has the same hierarchy as the serving cell at
the same layer.
� For the neighbor cell, the following formula is met within the period specified by PBGT
Valid Time(s) out of the period specified by PBGT Watch Time(s).
− SS_DLs_f indicates the receive level of the downlink TCH in the serving cell after filtering.
− SS_DLi_f indicates the receive level of the BCCH in neighbor cell i after filtering and penalty.
− Poff_DLs_f indicates the offset of the transmit power of the BTS on the downlink after the filtering in the
serving cell to the maximum transmit power on the TCH. The step is 2 dB.
− Pms_i indicates the maximum transmit power of the MS in neighbor cell i. It is related to the frequency
band for neighbor cell i. Generally, GSM900/850, GSM1800, and GSM1900 correspond to different
transmit power.
− Pms_s indicates the maximum transmit power of the MS in the serving cell. It is related to the frequency
band for the serving cell. Generally, GSM900/850, GSM1800, and GSM1900 correspond to different
transmit power.
� The PBGT handover is triggered if the previous conditions are met and if the number
of candidate 2G cells is not zero. The candidate cells are the neighbor cells with the
smallest 16-bit sequence number.
( ) ( )_ _ _ __ _ 2i f s f s_f ms i ms s
SS DL SS DL Poff_DL P P Margin − + × − − >
HUAWEI TECHNOLOGIES CO., LTD. Page 32All rights reserved
Chapter 1 Chapter 1 Introduction of HandoverIntroduction of Handover
Chapter 2 Chapter 2 HO Algorithm processHO Algorithm process
Chapter 3 Chapter 3 HO Data ConfigurationHO Data Configuration
Chapter 4 Chapter 4 HO Signaling processHO Signaling process
HUAWEI TECHNOLOGIES CO., LTD. Page 33All rights reserved
Handover data configuration
� All data configurations are related to
handover.
HUAWEI TECHNOLOGIES CO., LTD. Page 34All rights reserved
HO data lookup process
� BA2 table defines BCCH frequencies of all neighbor cells. It is sent to MS by
system message 5, 5-bis and 5ter on SACCH channel.
� MS reports the serving cell and BCCH, BSIC and signal levels of 6 strongest
neighbor cells to BSS through MRs. This is done through SACCH uplink.
� After MR pre-process is done, BSC gets all neighbor cells’ Cell Index and
CGI which are derived from Adjacent cell Relation Property table, and Cell
Common Data table (or 2G External Cell Data table) through BCCH and
BSIC in the MR.
� BSC performs HO judgment process, such as basic queuing of cells
(completed in LAPD board). When BSC finds suitable target, It sends HO
request messages containing the target CGI to MPU of BSC.
� MPU sends a HO command message to the target module and step up the
‘inter-cell/ intra-cell HO request’ counter by one.
HUAWEI TECHNOLOGIES CO., LTD. Page 35All rights reserved
Chapter 1 Chapter 1 Introduction of HandoverIntroduction of Handover
Chapter 2 Chapter 2 HO Algorithm processHO Algorithm process
Chapter 3 Chapter 3 HO Data ConfigurationHO Data Configuration
Chapter 4 Chapter 4 HO Signaling processHO Signaling process
HUAWEI TECHNOLOGIES CO., LTD. Page 36All rights reserved
For example: 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
UA
HUAWEI TECHNOLOGIES CO., LTD. Page 37All rights reserved
Intra-BSC Handover Signaling process
� 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.
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