OG 201 Handover Issue2.0 Caiwei.ppt

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Internal
Handover
ISSUE 2.0

HUAWEI TECHNOLOGIES CO., LTD. All rights reserved Page 2
Handover is key technology of Mobile
communication system and make
continued conversation possible.
Handover algorithm in Huawei product
is flexible and powerful

 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

Chapter 1 Introduction of Handover
Chapter 2 HO Algorithm process
Chapter 3 HO Data Configuration
Chapter 4 HO Signaling process

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

 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

Classification by Synchronization
 Synchronous handover: source
and target cell belong the same
BTS
 Asynchronous handover: source and
target cell belong the different BTS

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

General process of HO Algorithm
M.R.
preprocessing
Penalty
processing
Basic ranking
Secondary
ranking
HO judgment
TA emergency HO
BQ emergency HO
RSD emergency
HO
Interf. emergency HO
Load Sharing HO
Edge HO
Layer HO
PBGT HO
Processing
program
OM forced HO
Directed retry
Overlaid/underlaid HO
Fast moving MS
HO
1
1

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 MS
The downlink measurement report
of the neighbour cell (BCCH)

MR interpolation
Every time BSC receives a measurement report, there will
be an update to the basic rank 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.

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How to interpolate MR?

Penalty Processing
 There are altogether four types of penalty process (second step of
HO algorithm process )
 Penalty on the target cell when a HO fails.
 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 the penalty time after an
overlaid/underlaid HO fails.

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.

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.

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 MS staying in
the umbrella cell and avoid frequent HO.

Underlaid
Overlaid Do not
attempt
again after a
failed HO!
Penalty on Overlaid/underlaid Cell
 A new Overlaid/underlaid HO is prohibited within a penalty time
after an Overlaid/Underlaid HO failure.

Procedure of Ranking
 Basic ranking and secondary ranking of cells are major parts of
the HO judgment. Ranking 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 ranking processes include:
M rule
K rule
16bits ranking

M rule
 Only the cells with received signal level satisfy the following conditions
can be put into the candidate cell list.
 For serving cell
 RX_LEV (o) >MSRXMIN(o) + MAX(0,Pa(o))
 For Neighbor cell
 RX_LEV (n) > MSRXMIN(n)+ MAX(0,Pa(n))+ OFFSET
Pa(0) : MS_TXPWR_MAX(0) – P
Pa(n) : MS_TXPWR_MAX(n) – P
MS_TXPWR_MAX( ) : The appointed MS transmitting power by the
BSS.
P : Max_Power_of_MS
Max_Power_of_MS : MS maximum transmitting power

K rule Criterion
 After the M rule , the serving cell and candidate neighbor cells are
ranked in descending order according to the receiving level only
 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.
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

The 4th bit: determined by HO hysteresis
 The 4th bit: bit value is determined by inter-cell HO ( of the same layer )
hysteresis.
 The 4th bit of the serving cell is always 0,
 The receiving signal level of the neighbor cell >= The receiving level of the
serving cell + Inter-cell HO ( of the same layer ) hysteresis, bit 4th is set to 0.
 The receiving level of the neighbor cell < The receiving level of the serving
cell + Inter-cell HO ( of the same layer ) hysteresis, bit 4th is set to 1.
Note: In PBGT HO, whichever the greater of the inter-cell ( of the same
layer ) hysteresis and PBGT threshold, that value will be used in the
PBGT HO.
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

The 5th—10th bit: determined by Layer
 The 5th-10th bits: bit value is decided according to their position in
Huawei hierarchical network structure.
 When the signal level of the neighbor cells or the serving cell is lower
than the layer HO threshold and hysteresis, this function is turned off
and all bits are set to 0.
 That is to say only when the above criterions are met, then this
function take effect.
 Huawei cell layers can be divided into 4 layers and each layer can be
further divided into 16 different priorities. So there are 64 different
priorities in Huawei hierarchical cell structure.
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

GSM900
Cell
Micro Cell
Umbrella
Cell GSM 900
GSM1800 GSM1800
GSM1800
GSM 900 GSM 900 GSM 900
GSM900
GSM900
GSM1800
GSM1800
GSM900 GSM900
GSM1800 GSM1800
GSM1800
Cell
Hierarchical cell structure

The 11th bit: determined by load
 The 11th bit: bit value is decided by cell-load-sharing criterion.
 Serving cell: if Cell Load>= Start threshold of load HO, bit 11th is set to 1,
otherwise is set to 0.
 Neighbor cell: if Cell Load>=Receive threshold of load HO, bit 11th is set to 1,
 Refer to Load HO Table for the load HO threshold and load req. on
candidate cell.
Clue : When the cell load is higher than the threshold, then the bit 11th is
set to 1.This is done in order to put the cell in a lower part of the cell list.
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

The 12th/13th bit: determined by co-BSC/MSC
 12th bit: bit value is decided by co-BSC criterion.
Serving cell: is always set to 0.
Neighbor cell: if co-BSC with the serving cell, 12th bit is set to 0,
When the signal level from the neighbor cell or the serving cell is lower
than layer HO threshold and hysteresis. This function is turned off and
the value is set to 0.
If the parameter – “Co-BSC/MSC Adj.” in the HO control table is set to
“No”, then this function is turned off and the value is 0.
 13th bit : Bit value is decided by Co-MSC parameter, having the same
concept as the 12th bit.
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

The 14th bit: determined by Layer HO
 The 14th bit: Layer HO threshold adjustment bit
 Serving cell criterion
Receive level >= layer HO threshold – layer HO hysteresis, bit 14th
is set to 0. At the same time, bit 13th, 12th and 10th—5th bits are
set to 0.
If the above criterion is not met, then bit 14th is set to 1.
Example : 20-5 = 15 ( -95 dBm )
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

The 14th bit: determined by Layer HO
 Neighbor cell criterion
Receive level >=layer HO threshold + layer HO hysteresis, bit 14th is set
to 0. At the same time, bit 13th, 12th and 10th—5th bits are set to 0
If the above criterion is not met, then bit 14th is set to 1.
Example : 20+5 = 25 ( -85 dBm )
 note
The layer HO threshold and hierarchical hysteresis correspond to the
value of that individual cell’s value.
Usual situation : When the neighbor cells are of the same layer, each of
the neighbor cell’s layer HO threshold value will be the same. Same
concept goes for the layer HO hysteresis. This can maintain the entire
hierarchical layers of the cell.
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

The 15th bit: determined by Cell Type
 The 15th bit: Bit value is decided by cell type
− Serving cell or Neighbor cells:
− When cell type is extension cell 1.
− When cell type is normal cell 0.
 The 16th bit: Reserved bit
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Types of HO
 Emergency HO
TA HO
BQ HO
interference HO
Rx_Level_Drop HO
 Load HO
 Normal HO
Edge HO, layer cell HO and PBGT HO
 Fast moving HO
 Overlaid/underlaid HO

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 (same as the above two types of
HO)
Select the first cell in the neighbor cell list i.e. lowest 16bits
value.

Rx_Level_Drop HO
 Rx_Level_Drop HO
Due to downlink signal level drop
Triggered upon detecting rapid level drop during MS busy
mode.
 Requirements for the target cell:
The target cell is the first cell in the neighbor cell list.

Interference HO
 Interference HO (DL&UL) :
When the receiving level > receiving threshold level. But
Receiving quality < threshold of quality interference.
The target cell is in the cell list.

Cell Load HO
 Cell Load HO Criterions :
System load of BSC < Permissible load of HO threshold
Load of serving cell > Load HO threshold
 Requirements for the target cell
Load of target cell < Load HO threshold
BTS
BSC

Edge HO
 Edge HO Criterion:
In N seconds, when there are P seconds that neighbor
cell’s DL or MS’s UL signal level is lower than the Edge HO
threshold. Then the criterion is met and Edge HO occurs.
This method utilizes the P/N rule.
The target cell should be ranked in front of the serving cell.

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 cell’s.

PBGT HO
 PBGT HO Criterions :
Target cell’s path loss is smaller than the serving cell’s path
loss by the PBGT threshold value.
Satisfying the P/N rule.
Target cell should be ranked in front of the serving cell.
 Note :
PBGT HO can only occur between same-priority cell. If the
system permits PBGT HO for the cell, PBGT HO can occur
in either inter-BSC or inter-MSC.

Fast-Moving HO
 When the serving cell is micro cell :
When the MS has traveled through P numbers of cell, and
there are Q (=<P) numbers of cell that the MS has traveled
in high speed, the criteria is satisfied. MS will be handed
over to umbrella cell.
 When the serving cell is umbrella cell :
When the MS is traveling high speed in umbrella cell, a
greater penalty can be given to the micro cell for a duration
of time (penalty time). In this way, the MS will not use the
micro cell. Note :In this case, the micro cell is only used
under urgency conditions( Poor TA and BQ ).

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

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
Normal Underlaid/Overlaid
IUO: Enhance Underlaid/Overlaid

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

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

underlaid
overlaid
:
Division of underlaid and overlaid is decided by MS
downlink receive level ,TA value and quality.
Normal Overlaid/Underlaid HO
The quality boundary is elided in this figure

Normal Overlaid/Underlaid HO
 Criterion for HO from overlaid to underlaid:
TA value => TA threshold + TA hysteresis OR
 RX_LEV <= RX_LEV threshold －RX_LEV hysteresis OR
 Qua. =>Qua. threshold
Satisfying P/N rule
 Criterion for HO from underlaid to overlaid:
TA value =< TA threshold － TA hysteresis AND
 RX_LEV >=RX_LEV threshold + RX_LEV hysteresis AND
 Qua. =<Qua. threshold

Enhance Overlaid/Underlaid HO
 Criterion for HO from overlaid to underlaid:
TA value => TA threshold + TA hysteresis OR
 RX_LEV <= O to U level OR
 Qua. =>Qua. threshold
 Criterion for HO from underlaid to overlaid:
TA value =< TA threshold － TA hysteresis AND
 RX_LEV >= U to O level AND
 Qua. =<Qua. Threshold
If the box “U to O HO traffic threshold” is checked, just in the condition
that underlaid load is more than this threshold, U to O handover based
on previous conditions can be triggered

Major HO Parameters Configuration
 Major HO parameter configuration
1.[Handover Control Table]
2.[Cell Description Table]
3.[Adjacent Cell Relation Table]
4.[Penalty Table]
5.[Emergency Handover Table]
6.[Load Handover Table]
7.[Normal Handover Table]
8.[Fast-Moving Handover Table]
9.[Concentric Cell Handover Table

Parameter
name
Meaning
Value
range
Recommend
value
Co BSC/MSC
Adj.
It means whether the 12 and 13 bits acts in the 16bit order.
“Yes” means handover in the same BSC/MSC is preferred.
“No” means that the 12 and 13 bits are shielded and set to”0.
Yes,
No
Yes
Penalty
allowed
It determines whether to punish the target cell of handover
failure, or the original served cell of handover upon too big TA
or bad quality. The penalty measures can apply to cells in or
out of the same BSC
Yes,
No
Yes
Load HO
allowed
It determines whether to perform the handover to share traffic
load. Load sharing can lower the channel assignment failure
ratio caused by cell congestion, so as to make evener
allocation of the service in respective cells, and lower the cell
congestion rate , and improve network performance. It on ly
applies in the same BSC or cells at the same level
Yes,
No
No
MS Fast
moving HO
allowed
It determines whether to handle the fast moving MS with the
algorithm. It is only recommended in special a reas (such as a
highway), to lower CPU load. This algorithm should only be
used in suitable conditions, and usually it is not applied
Yes,
No
No
Handover Control Table

Parameter
name
Meaning
Value range
Recommended
value
RX _L evel Drop
HO allowed
It means whether RX _ Level Drop emergency
handover algorithm is allowed, handover the MS
which receiving signal level is dropping quickly in
advance to avoid potential call drop. This algorithm
should be applied in suitable conditions, and usually it
is not used. To apply the handover algorithm, BSC
must have original measurement report.
Yes, No No
PBGT HO
allowed
It means whether PBGT handover algorithm is
allowed. PBGT handover algorithm currently is
processed on LAPD board. To avoid Ping -pang
handover, PBGT handover is only performed between
cells at the same layer and with the same priority, and
meanwhile it is only triggered on TCH.
Yes, No Yes
MS power
prediction after
HO
It means after a handover whether MS is to use
proper predicted transmitting power to access the
new channel. This can reduce system interference
and improve service quality y (this parameter acts
when intra BSC handover occurs
Yes, No Yes

Parameter
name
Meaning
Value
range
Recommended
value
MR.
reprocessing
“Yes” means perform measurement report
preprocessing on BTS “No” means preprocessing on
BSC, then the two parameters of “Send original
measurement report” and “Send BS/MS power level”
do not act. “Yes” means decreasing of Abis interface
signaling and BSC load, and improving of network
response time performance. The switch determines
where to perform power control. When it is set to
“Yes”, power control is performed at BTS side. When
it is set to “No”, power control is performed at BSC
side. When setting this parameter, first be clear
whether BTS supports the power control algorithm to
set or not.
Yes, No Yes

Parameter
name
Meaning
Value range
Recommended
value
Transfer
Original MR.
It means whether to send the original measurement
report to BSC after measurement report preprocessing
on BTS. When it is set to “Yes”, BTS sends not only
processed measurement rep ort but also original
measurement report to BSC.
Yes, No No
Transfer
BS/MS power
class
It means whether to send BS/MS power level from BTS
to BSC. This function is used to view the effect of power
control on BTS. Meanwhile, when preprocessing is
available , if BS/MS power level is not reported, the uplink
and downlink balance measurements will be affected,
and handover types such as PBGT handover and
overlaid/underlaid handover needing power
compensation will be abnormal.
Yes, No Yes

Parameter
name Meaning
Value
range
Recommen
ded
value
Sent Freq. of
Preprocessed
MR.
It indicates the time interval at which a measurement report
is preprocessed at B TS side and sent to BSC the
Preprocessed measurement report. This parameter acts
only when “Measurement t report preprocessing” is enabled
For 15:1 link configuration, the report frequency should be
as low as once per second due to limited link resource. At
this time, for handover nee ding P/N judgment such as edge
handover, layer handover, PBGT handover and
overlaid/underlaid handover
Twice per
second,
Once
per
second
According to
Concrete
conditions

Parameter
name
Meaning
Value
range
Recommended
value
Layer of the
cell
Huawei hierarchical network structure is divided into 4 layers. 16 The
priorities can be set for each layer, which provides enough room
of network planning for the operator to adapt to various complex
network environment. Normally, Macro layer is the major 900 layers
layer, Micro layer is the major 1800 layer, Pico is the 900 and
1800 micro cell layer. The smaller layer value, the higher
priority.
1 ~4
M900 : layer 3
M1800:Laye 2r
Cell priority
Each layer may have 16 priorities, used to control the handover
priority between cells at the same layer. Usually priorities of priorities
cells at the same layer are set the same. For cells at the same
layer, the smaller the priority value, the higher the priority
1~16 1
Layer HO
Thrsh.
It affects the value of the 14th bit in the 16bit ranking , and it is
also the level requirement on the target cell for interference
handover and load handover. Then such level
should be higher than layer handover threshold + layer
handover hysteresis. The layer handover threshold should be
set >= Edge handover threshold + Inter cell handover
hysteresis.
0 ~ 63 25
Layer HO
hysteresis
Works together with the Layer handover threshold. 0 ~ 63dB 3
Cell Description Table

Parameter
name
Meaning
Value
range
Recommended
value
Penalty on
MS Fasting
moving HO
It is valid when the fast moving handover algorithm is
enabled . It is the signal level penalty value on the other
neighbor cells when MS moves fast and is handed over
To umbrella cell. The parameter is only valid within the
penalty time.
0~ 63dB 30
Penalty
Time on MS
Fasting
moving HO
It means that within this time, the penalty on the other
neighbor cells will be exerted after MS is handed over
to umbrella cell by fast moving HO.
0 ~ 255
seconds
40
Min DL level
0n
Candidate
cell
This is the min signal level requirement for the cell itself
to be a candidate cell low configuration may easily
cause call drops, while too high a configuration might
turn handover too hard to occur.
0 ~ 63 15
Cell Description Table

Parameter
name Meaning Value range Recommended
value
Min access
level offset
This offset is based on “Min downlink level of handover
candidate cell”. Different offsets can be defined for different
adjacent cells, and to enter the candidate cell list, the
corresponding adjacent cell receiving signal level must be
higher than the sum of “Min. downlink level of handover
candidate cell” and “ Min. Access level offset”.
0 ~ 63dB 0
PBGT HO
thrsh
It means that PBGT handover is performed when the
difference between the target cell downlink path loss and the
corresponding to
serving cell downlink path loss is bigger than PBGT handover
threshold. When PBGT handover is enabled, and “Inter cell
handover hysteresis” > “PBGT handover threshold
(corresponding dB value)”, “Intercell handover hysteresis”
takes place of “PBGT handover threshold” to act. . PBGT
handover threshold also needs to be adjusted according to
handover performance statistics result
0~127
corresponding
--64~63dB
It is around 68 in the
densely populated
downtown, and
around 72 on the
outskirts.
Inter cell
HO
hysteresis
Handover hysteresis between an adjacent cell and the serving
cell. It is set to reduce “Ping pang” HO. The hysteresis value
also needs to be adjusted according to the handover
performance statistics result and live network. Flexible
configuration of the value can effectively lead handover and
traffic between two adjacent cells.
0 ~ 63db
It is around 4 in the
densely populated
downtown, and
around 8 on the
outskirts.
Adjacent Cell Relation Table

Parameter
name
Meaning Value range
Recommended
value
Penalty level
after HO fail
The signal level value in dB, to punish the target cell
which has caused a HO failure due to problems such
as congestion , to prevent MS from a handover
attempt to that cell again. This value is only valid
within the penalty time for handover failure.
0 ~ 63 dB
30
Penalty time
after HO fail
Penalty time on the corresponding target cell after seconds
handover failure
0 ~ 60second 10
Penalty level
after BQ HO
fail
The signal level penalty value for the original serving
cell, to avoid “Ping- pang” handover after emergency
handover upon bad quality. It is only valid within the
penalty time for BQ HO.
0 ~ 63d B 63
Penalty time
after BQ HO
fail
Penalty time for the original serving cell after BQ HO. seconds 0 ~ 60second 10
Penalty Table

Parameter
name
Meaning
Value
range
Recomm
ended
value
Eenalty
level after
TA HO fail
The signal strength penalty value for the original serving cell,
to avoid “Ping - pang” handover after TA emergency
handover. It is only valid within the penalty time for ta
handover
0 ~ 63d B 63
Penalty time
after TA HO
fail
Penalty time for the original serving cell after TA emergency
Seconds handover
0 ~
60second
10
Penalty time
after IUO
HO fail
After an overlaid/underlaid handover failure (big circle hands Seconds over to
small circle or vice versa), within certain time (this Parameter configuration
value) overlaid/underlaid handover is forbidden for the same call
0 ~
16second
10
Penalty Table

Emergency Handover Table
Parameter
name
Meaning Value range
Recommended
value
TA Thrsh. When TA≥this value, emergency handover is triggered 0~63 bit period 63
DL QUAL.
Thrsh
The downlink receiving quality threshold for BQ emergency
handover. When frequency hopping or DTX is enabled, RQ
becomes worse (normal phenomenon), this value should be
set to 70. The adjustment should also base on the current
network quality and handover statistics. When triggering
emergency handover, the first to select is the inter-cell
handover, the intra-cell handover is only triggered when there
is no candidate cell and the intra-cell handover is allowed in
the serving cell.
0~70,
corresponding
to BQ levels of
0~7
60
UL QUAL.
Thrsh.
The uplink receiving quality threshold for BQ emergency HO.
corresponding
to BQ levels of
0~7
60

Parameter
name
Meaning Value range
Recommended
value
UL
Qual.
Thrsh
for interf.
HO
Uplink receiving quality threshold in the serving cell for interference
handover. When frequency hopping or DTX is to enbaled , RQ
becomes worse (normal phenomenon), this
value should be set to 60. The adjustment should also base
on the current network quality and handover statistics. When
triggering interference handover. If the serving cell is in the
first position and intra cell handover is permitted, perform
intra cell handover . Otherwise select the second candidate
cell to perform inter cell handover.
corresponding
to BQ levels of
0~7
50, interference
quality threshold
must be better
than
the emergency
quality threshold
DL Qual.
Thrsh. For
interf HO
Downlink receiving quality threshold in the serving cell for
interference handover.
0~70,
corresponding
to BQ levels of
0~7
50

Parameter
r name
Meaning
Value
range
Recommended
value
UL
RX_LEV
Thrsh. For
interf.HO
Min uplink receiving power threshold from the serving cell
required for interf. HO, when interference handover is
triggered if the uplink quality is worse than quality threshold
and at this time the uplink signal level is higher than the signal
threshold. When triggering interference handover, If the
serving cell is in the first position in the cell list, and intra cell
handover permitted , then start intra cell HO. Otherwise select
the second cell to perform intercell HO.
0 ~ 6 3 25
DL
RX_LEV
Thrsh. For
interf HO.
Min downlink receiving power threshold from the serving cell
required for interf. HO.
0 ~ 63 30

Parameter
name.
Meaning
Value
range
Recommen
ded
value
Filter
Parameters
A1~A8
Used for configuration of filter for rapid signal
drop judgment, and together with filter parameter
B, they are 9 parameters for a filter. The
corresponding formula is (in the program, A1~A8
is configuration value minus 10 and B is the
negative configuration value):
C1(nt)=A1×C(nt)+A2×C(nt-t)+A3×C(nt － 2t)+
+A8×C(nt-7t)
Where, C (nt) is the receiving signal level in the
uplink measurement report of the serving cell
sent at the time of nt. If C1 ( nt ) < B, and C (nt) is
below the edge handover threshold, then the
signal level is considered to be of rapid drop.
0 ~ 20 10
Filter
parameter B
Used for configuration of filter for rapid signal
drop judgment. Please refer to the explanation
for A1~A8 of filter.
0 ~255 0

Parameter
name
Meaning Value range
Recommended
value
System flux
Thrsh. For
load HO
The pre condition for load HO is that the system flow (signaling
flow) is lower the threshold. This value can not be set too high
because load handover upon max threshold may cause serious
effect to the system.
0, 8~11 system
flow levels, to
corresponding
0, 70, 80, 90
and 95.
10
Load HO
Thrsh
Load handover is triggered when the serving cell load is
than the threshold, TCH seized in the cell has reaching the
corresponding percentage.
0~7 cell load
levels,
Corresponding
to 0 , 50 , 60 , 70 ,
75, 80 , 85 , 90
5
Load Req.
on
candidate
cell
The Load threshold for the target cells that can accept MS from
serving cell in load HO, i.e. when the TCH under Idle mode in
the neigh bor cell is lower than the corresponding percentage
the cell refuses to accept MS from serving cell handed over due
to the load reason
0~7,
Corresponding
to 0 , 50 , 60 , 70 ,
75, 80 , 85 , 90
2
Load Handover Table

Load Handover Table
Parameter
name
Meaning Value range
Recomme
nded
value
Load HO
bandwidth
This configuration is related to the edge handover
threshold. Load handover is only allowed when the MS
receiving level from the serving cell is within the range of
margin handover threshold, margin handover threshold +
load handover bandwidth
0~ 63db 25
Load HO
step
period
When a cell is up to conditions for load handover, all calls
within the serving cell will send handover request at the
same time, this will cause abrupt increase on processor
load, and under certain conditions this will cause the
target cell congestion and result in call drops. Thereby,
step by step load handover algorithm is used to control
handover. The cycle is the time needed for handovers of
each step.
1~60 seconds 10
Load HO
step
level
The whole load HO bandwidth will be divided into several Sub-bands by
this parameter.
1~ 63db 5

Normal Handover Table
Parameter
name
Meaning
Value
range
Recommended value
Edge HO UL
RX_LEV
Thrsh.
During the statistics time, if the time in which the uplink
receiving level is lower than the value is longer than
certain time called continuous time, edge handover
will be performed. If PBGT handover is enabled,
Corresponding edge handover threshold will be set
lower
0 ~ 63
25 (without PBGT
handover, downtown),
15 (single station on
outskirts), 15 (with
PBGT handover,
downtown)
Edge HO DL
RX_LEV
Thrsh.
Downlink consideration for edge HO 63
30 (without PBGT
handover, downtown),
20 (single station on
outskirts), 20 (with
PBGT handover,
downtown)

Parameter
name
Meaning Value range
Recommended
value
Edge HO
watch time
It means that within the time statistics, if the
time in which the signal level is lower than
threshold is higher than the continuous time,
then margin HO is to be triggered
1 ~16 seconds 5
Edge valid
time
See the above. 1 ~16 seconds 4

Parameter
name
Meaning Value range
Recommended
value
Layer HO
watch time
statistics time for Layer HO judgment 1 ~ 16 seconds 5
Layer HO
valid time
Continuous time for Layer HO judgment 1 ~ 16 seconds 4
PBGT watch
time
Statistics time for PBGT HO signal level judgment. 1 ~ 16 seconds 5
PBGT valid
time
Continuous time for PBGT HO signal level judgment. 1 ~ 16 seconds
4

Parameter
name
Meaning Value range
Recommended
value
MS
Fast -moving
watch cells
The cell sum P for judge whether MS is fast moving.
The value, if too large, may cause abrupt increase of
system flow, while too small value may cause
inaccurate judgment for fast moving MS.
1~ 10 3
MS
Fast –moving
valid cells
The cell sum N by which MS actually quickly passes. If
within P cells that MS continuously past, the number of
cells by which the MS is judged to pass quickly is equal
to or more than N, then the MS will be judged as a fast
moving MS.
1~ 10 2
MS
Fast –moving
Time Thrsh.
The time threshold (2r/v) determined by the cell radius
(r) and moving speed (v). If the time in which MS seconds
passes the cell is smaller than the threshold, then MS
is judged to quickly pass the cell.
1~ 225 15

Common Concentric Data
Parameter
name
Meaning Value range
Recommended
value
Assign
optimum
layer
In Overlaid/Underlaid, the following selection are available
for TCH assignment: (1) The system judges according to
the measurement report on SDCCH and assign to the
best sub-cell. (2) Select the overlaid first for TCH
assignment. (3) Select the underlaid first for TCH
assignment. (4) Do not give extra priority.
System
optimization,
overlaid ,
underlaid , no
preferential
System optimization
Assign-
optimum
level Thrsh.
If system optimization is selected, estimate (interpolate,
filter) current SDCCH level value through uplink
measurement value in the former SDCCH measurement
report, and compare with “ Assign-optimum Level
threshold”, so as to assign overlaid or underlaid channel.
If SDCCH is in the overlaid : edge handover threshold +
signal intensity difference between underlaid and overlaid
+ uplink and downlink balance allowance + SDCCH and
TCH difference allowance. If SDCCH is in the underlaid :
edge handover threshold + uplink and downlink balance
allowance + SDCCH and TCH difference allowance.
0~63

Parameter
name
Meaning
Value
range
Recommended
value
Pref. subcell
in HO of
intra-BSC
When the cell is configured into a Overlaid/Underlaid, there
are two processing methods for incoming handover request
in BSC: (1) No special processing for channel assignment.
(2) Add BCCH signal level value of the target cell in inter-
cell handover request message to BSC to make BSC
allocate optimum channel for MS from underlaid or overlaid
Yes, No Yes
Incoming-to-
BSC HO
optimum
layer
If there is a incoming BSC HO, and the target cell is a
Overlaid/Underlaid, then, this parameter will show which
layer is preferred to provide service for the MS.
overlaid ,
underlaid ,
none
None

Parameter
name Meaning Value range Recommended value
RX_QUAL
Thrsh.
In case of Qual. Is worse than this value, MS handover
from overlay to underlay 0--70 60
UO HO watch
time P/N judgment statistics time for U/O HO judgment. 0 ~ 16 seconds 5
UO HO valid
time P/N judgment continuous time for U/O HO judgment. 0 ~ 16 seconds 4
TA thrsh. Of
Assignment
Pref.
TA is more than this value, TCH in underlay will be
allocated 0--63 According concrete
condition
TA Thrsh. Of
Imme-Assign
Pref.
TA is more than this value, SDCCH in underlay will be
allocated 0--63
According concrete
condition
TA Prfe. Of
Imme-Assign
Allowed
TA attend allocation of SDCCH or not Yes, No
According concrete
condition

Parameter
name
Meaning Value range Recommended value
TA Thrsh.
It must be bigger than TA emergency handover
threshold.
0~63 bit period,
with 1 bit period
corresponding to
0.55km
TA hysteresis Works with TA threshold. 0~63 bit period
UO HO watch
time
P/N judgment statistics time for U/O HO judgment. 0 ~ 16 seconds 5
UO HO valid
time
P/N judgment continuous time for U/O HO judgment. 0 ~ 16 seconds 4

Normal Concentric Data
Parameter
name
Meaning Value range Recommended value
RX_LEV
Thrsh
Rx level hysteresis, Receiving Quality Thrsh.,TA
threshold and TA hysteresis jointly define underlaid
area and overlaid area. It must be bigger than
edge handover threshold, and the recommended
value is: edge handover threshold + signal intensity
difference between underlaid and overlaid .
0~63 25
RX_LEV
hysteresis
Works with Rx threshold. 0~63 5
UO signal
intensity
difference
Transmitting Power at antenna difference between
underlaid and overlaid may cause MS receiving
signal intensity difference in underlaid and overlaid .
The parameter usually indicates the antenna EIRP
difference in dB between underlaid cell and overlaid
cell. According to field measurement, multi-point
measurement is necessary if the underlaid and
overlaid use different antenna.
0~63dB
Set according to actual
conditions

Enhance IUO Data
Parameter
name
Meaning Value range
Recommended
value
Enhance IUO
Allowed
Enable function of Enhance IUO or not Yes, No
Set according to
actual conditions
UtoO Traffic
HO Allowed
Enable traffic to be one condition of HO or not Yes, No
Set according to
actual conditions
OtoU HO
Received
Level Thrsh.
In case of receiving level in overlay is less than this
value, HO occurs from overlay to underlay
0--63 25
UtoO HO
Received
Level Thrsh.
In case of receiving level in underlay is more than this
value, and traffic in underlay is more than Traffic Thrsh.
Of Underlay, HO occurs from underlay to overlay
0—63 35

Concentric Cell Handover Table
Parameter name Meaning Value range
Recomm
ended
value
Traffic Thrsh. Of
Underlay
If the traffic in underlay is over this value, MS will
handover from under to overlay
0—100% 80
Underlay HO Step
Period
If there are some handover requests from under to
overlay at the same time, system will handover the call
with level firstly. This value determine period per step
1—255s 5
Underlay HO Step
Level
It is the step that handover band decreases, used to
control the grade by grade handover band from underlay
to overlay with “underlay HO step level”
1—63dB 5
Penalty Time of
UtoO HO
To prevent ping-pong handover, the call can’t be handed
over back within penalty time when a call is handed over
from underlay to overlay
0—255s 10

HO data lookup process
 BA2 table defines BCCH frequencies of all neighbor cells. It is
sent to MS by system message 5, system message 5-bis and
system message 5ter on SACCH channel.
 MS reports the serving cell and BCCH, BSIC and signal levels
of 6 strongest neighbor cells to BSS. This is done through
SACCH.
 MR pre-process is done in BTS. Module number, cell number
and CGI of all neighbor cells are derived from Adjacent cell
Relation Table, and Cell Description Table (or External Cell
Description Table) through BCCH and BSIC in the MR.

HO data lookup process
 BSC performs HO judgment process, such as basic rank of
cells (completed in LAPD board). When BSC finds suitable
target, It sends HO request messages containing the target
CGI to MPU of BSC. According to CGI, MPU derive the module
number of the cell from Cell Module Information Table.
 MPU sends a HO command message to the target module and
step up the ‘inter-cell/ intra-cell HO request’ counter by one.

1.1 Intra BSC Handover
1.2 Intra MSC Handover
1.3 Inter MSC Handover

Intra-BSC Handover Signaling process
MS MS
BTS1 BTS2
BSC MSC
Measurement Report from MS
Channel_Active
Channel_Active ACK
HANDOVER COMMAND
Handover Access
Handover_Detect
PHY INFO
First SABM
Establish_IND
PHY INFO
Handover Complete
Handover_Performed

 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.

MS BTS BTS
BSC MSC
Measurement Report
Measurement Report
Channel_Activate
Channel_Activate ACK
Handover Command (Old FACCH)
Handover Access (New FACCH)
Handover Complete (New FACCH)
RF Channel Release
Handover 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)

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
inter cell handovers )
Internal inter cell handover success rate
 =(Successful incoming internal inter cell handovers +
Successful outgoing internal inter cell handovers) /
(Attempted incoming internal inter cell handovers +
Attempted outgoing internal inter cell handovers)
 Internal inter cell radio handover success rate >= Internal inter
cell handover success rate

MS BTS BTS
BSC1 BSC2
MSC
(original) (Target)
Measurement Report
Measurement Report
Handover Required
Handover Request
Channel_Active
Channel_Active_ACK
Handover_Request_ACK
Handover Command
Handover Access
Handover Detect
Handover Complete
Handover Complete
Clear Command (HO Successful)
RF Channel Release
Clear Complete
Attempted outgoing interBSC inter cell handovers
Attempted incoming interBSC inter cell handovers
Successful incoming inter BSC handovers
Successful outgoing interBSC inter cell handovers
Intra-MSC HO Signaling process

MSC-B
MSC-A VLR-B
BSC-A BSC-B
HO-REQUIRED MAP_Prepare_HO
MAP_Prepare_HO_ACK
MAP_Allocate_HO_NUM
MAP_Send_HO_Repor
t
MAP_Send_HO_Report_ACK
MS
HO-REQUEST
HO-REQUEST-ACK
HO-Command
MS
HO-Access
MAP_Process_Access_Signalling
HO-Complete
MAP_Send_End_Signal
Clear-Command
Clear-Complete
MAP_Send_End_Signal_ACK
Some intermediate steps are omitted
IAI
ACM
Signaling process between MSC

MSC-B
MSC-A VLR-B
BSC-A BSC-B
HO-REQUIRED
MAP_Prepare_HO
MAP_Prepare_HO_ACK
MAP_Allocate_HO_NUM
MAP_Send_HO_Repor
t
MAP_Send_HO_Report_ACK
MS
HO-REQUEST
HO-REQUEST-ACK
HO-Command
MS
HO-Access
MAP_Process_Access_Signalling
HO-Complete
MAP_Send_End_Signal
Clear-Command
Clear-Complete
MAP_Send_End_Signal_ACK
Some intermediate steps are omitted
IAI
ACM
Signaling process between MSC

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.

Roaming
E
MS
MSCa MSCb
MSCb'
VLRb
VLRb'
BSS2
BSS2'
Radio transmission signal measurement
HO 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 COMPLETE
Release (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 HO—Subsequent HO process

Highway
MSC-A
MSC-C
MSC-B MSC-C
Inter MSC HO—Subsequent HO process
 Subsequent HO

Inter MSC HO Signaling process
 Statistics counter—same as Intra MSC HO, Statistics is
handled by BSC
 HO formula-- same as Intra MSC HO

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
the LAC of the target cell is in the MSC, it sends “Ho-Request” to the BSC of the target
cell, and the target BSC activates the target cell channel to complete the following
procedure.
 When MSC finds that the target cell LAC does not belong to the MSC, it will query its
“LAI and GCI Table” (including LAC and router address of the adjacent MSC), and
send “Prepare-HO” message to the target MSC-B according to the router address.
The message includes CGI of the target cell and indication whether or not to allocate
HO number, etc. According to the message, the target MSC-B sends “HO-Request”
message to the target BSC-B after demanding HO number (unless it is not required in
the indication) from VLR-B, and sends “Prepare-HO acknowledgement” to serving
MSC after received “HO-Request acknowledgement”, to execute the next procedure.

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.
 In inter BSC HO, MSC is involved since the HO request .

Summary
In this course, we have learned:
 Classify of handover
 Judgment and Ranking step
 Handover Data Configuration
 Handover signaling Flow
Summary

OG 201 Handover Issue2.0 Caiwei.ppt

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