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Handover analysis
ObjectivesObjectives
How to configure the handover
parameters
How to do at handover
optimization
Upon completion of this course,you will be able to:
Course ContentsCourse Contents
Chapter 1Introduction
Chapter 2 handover principle
Chapter 3 SHO Optimization
Chapter4 Inter-RAT Optimization
IntroductionIntroduction
In WCDMA system, there are soft handover, Intra frequent
hard handover, Inter frequent hard handover, Inter system
handover. Handover is the most important part of mobile
manage. It plays very important role in RNO of WCDMA
system .
Chapter 2 Handover principle Chapter 2 Handover principle
2.1 Intra-frequency measurement2.1 Intra-frequency measurement
2.2 Hard handover measurement2.2 Hard handover measurement
2.3 Handover algorithms review
2.4 Handover parameters review
Intra-frequency measurementIntra-frequency measurementIntra-frequency measurementIntra-frequency measurement
Event 1A: A primary pilot channel enters the reporting range
When the measurement values satisfy the following formulas, the UE deems that a primary pilot channel has
entered the reporting range,the trig condition for Ec/Io:
MNew is the measurement result of the cell that has entered the reporting range
CIOnew is the cell individual offset which is configured for neighbor cells of servicing cell
Mi is the measurement result of the cells in the active set
NA is the number of cells in the current active set
MBest is the measurement result of the best cell in the current active set
W is the weight factor
R is the reporting range. With the signal strength as an example, R equals to the signal strength of the best cell
in the current active set minus a value
H1a is the hysteresis value of event 1A
)2/(log.10).1(.10.log10 11
abest
N
iinewnew HRMWMLogWCIOM
A
Intra-frequency measurementIntra-frequency measurementIntra-frequency measurementIntra-frequency measurement
Event 1B: A primary pilot channel leaves the reporting range
When the following formulas are satisfied, the UE deems that a primary pilot channel has left
the reporting range .trig condition for Ec/Io:
MOld is the measurement result of the cell that has left the reporting range
CIOold is the cell individual offset which is configured for neighbor cells of servicing cell
Mi is the measurement result of the cell in the active set
NA is the number of cells in the current active set
MBest is the measurement result of the best cell in the current active set
W is the weighted factor
R is the reporting range
H1b is the hysteresis value of event 1B
)2/(log.10).1(.10.log10 11
bbest
N
iioldold HRMWMLogWCIOM
A
Intra-frequency measurementIntra-frequency measurementIntra-frequency measurementIntra-frequency measurement
Event 1C: The primary pilot channel in a non active set is better than the primary pilot
channel in an active set
When the following formulas are satisfied, a non-active set cell replaces an old active set cell
and becomes an active set cell.trig condition for Ec/Io:
MNew is the measurement result Ec/Io of the cell not included in the active set.
CIONew is the individual cell offset for the cell becoming better than the cell in the active set if
an individual cell offset is stored for that cell. Otherwise it is equal to 0.
MInAS is the measurement result Ec/Io of the cell in the active set with the lowest
measurement result.
CIOInAS is the individual cell offset for the cell in the active set that is becoming worse than
the new cell
H1c is the hysteresis parameter for the event 1C, which is Hystfor1C.
2/.10.log10 1cInASInASnewnew HCIOLogMWInASCIOM
Intra-frequency measurementIntra-frequency measurementIntra-frequency measurementIntra-frequency measurement
Event 1D: The best cell changes
When the following formulas are satisfied, the best cell will be
changed .trig condition for Ec/Io:
MNotBest is the measurement result Ec/Io of a cell not stored in "best cell".
MBest is the measurement result Ec/Io of the cell stored in "best cell".
H1d is the hysteresis parameter for the event 1D, which is Hystfor1D
2/log.10log10 1DbestNotBest HMM
Chapter 2 Handover principle Chapter 2 Handover principle
2.1 Intra-frequency measurement2.1 Intra-frequency measurement
2.2 Hard handover measurement2.2 Hard handover measurement
2.3 Handover algorithms review
2.4 Handover parameters review
Hard handover measurementHard handover measurementHard handover measurementHard handover measurement
Event 2D: The estimated quality value of the used frequency is lower than a certain
threshold. Event 2D can be used to enable the compressed mode to perform inter-frequency
measurement.
Qcarrierj is the logarithmic form of the estimated quality value of frequency j
Mcarrier j is the estimated quality value of frequency j
Mi j is the measurement result of cell i with the frequency of j in the virtual active set
NA j is the number of cells with the frequency of j in the virtual active set
MBest j is the measurement result of the best cell with the frequency of j in the virtual
active set
Wj is the weight factor
H is the hysteresis value
,2/10)1(10101
HLogMWMLogWLogMQ jBestj
N
ijijjcarrierjcarrier
jA
Hard handover measurementHard handover measurementHard handover measurementHard handover measurement
Event 2F: The estimated quality value of the used frequency is higher than a certain
threshold. Event 2F can be used to disable the compressed mode to stop inter-frequency
measurement .
Qcarrierj is the logarithmic form of the estimated quality value of frequency j
Mcarrier j is the estimated quality value of frequency j
Mi j is the measurement result of cell i with the frequency of j in the virtual active set
NA j is the number of cells with the frequency of j in the virtual active set
MBest j is the measurement result of the best cell with the frequency of j in the virtual
active set
Wj is the weight factor
H is the hysteresis value
,2/10)1(10101
HLogMWMLogWLogMQ jBestj
N
ijijjcarrierjcarrier
jA
Chapter 2 Handover principle Chapter 2 Handover principle
2.1 Intra-frequency measurement2.1 Intra-frequency measurement
2.2 Hard handover measurement2.2 Hard handover measurement
2.3 Handover algorithms review
2.4 Handover parameters review
Handover Algorithms reviewHandover Algorithms review
Soft Handover Algorithms review
Inter-RAT Handover Algorithms review
Handover algorithms review: SHOHandover algorithms review: SHO
When event 1A report is received, if the active set is not full,
then links are sequenced and added in the order of good
quality to poor quality (CPICH Ec/No) (in case that multiple
cells report event 1A), until the active set is full; if the active
set is already full, no processing will be made.
When event 1B is received, if there are more than one links in
the active set, then the braches are sequenced and removed
in the order of poor quality to good quality (CPICH Ec/No) (in
case that multiple cells report event 1B), until only one link is
left; if there is only one in the active set, no processing will be
made.
Handover algorithms review: SHOHandover algorithms review: SHO
In case of event 1C, the UE will report the replacing and
replaced cells in the event trigger list. If the active set is not
full, then the triggered cell link will be added; if the active set is
already full at this moment and the replaced cell is not the
best cell in the active set, then this cell link will be removed.
In case of event 1D, if the triggered cell is an active set cell,
then it will be marked as the best cell and measurement
control is updated; if the triggered cell doe not belong to the
active set, then this cell link will be added (if the active set is
full, one of the non-best cell will be removed before this link is
added) and marked as the best cell, with measurement
control updated.
Handover algorithms review: Inter-RATHandover algorithms review: Inter-RAT
Inter-system handover is enabled only in cells located at the
verge of WCDMA FDD system coverage.
For inter-system handover, CPICH RSCP is used as the
physical measurement quantity and events 2D and 2F are
used to decide enabling or disabling the compressed mode.
For inter-system handover, three compressed mode style
sequences are used for concurrent measurement of GSM
RSSI, BASIC identification and BASIC reconfirm, and the
configuration of parameters is oriented to the cell type.
Handover algorithms review: Inter-RATHandover algorithms review: Inter-RAT
Periodic measurement reports are used for inter-system
handover, and the RNC decides whether to implement hard
handover according to the measurement reports.
Handover Evaluation, while the compressed mode is started
and this following formulas is satisfied, Inter-system handover
will be implemented. .
Mother_RAT + CIO Tother_RAT + H/2 Mother_RAT is the estimated quality value RSSI of inter-system frequency
Tother_RAT is the GSM RAT measurement init_threshold, the minimum
signal Rxlev requirement for GSM cell as a handover target cell.
CIO is Cell individual offset , the measurement signal Rxlev offset for GSM
cell
H is the hysteresis for GSM RSSI threshold.
Chapter 2 Handover principle Chapter 2 Handover principle
2.1 Intra-frequency measurement2.1 Intra-frequency measurement
2.2 Hard handover measurement2.2 Hard handover measurement
2.3 Handover algorithms review
2.4 Handover parameters review
Handover parameters review-SHOHandover parameters review-SHO
Report range (SHO relative threshold )
Intra-frequency measurement filter coefficient
Time to Trigger
Hysteresis
CIO (cell individual offset)
Handover parameters review-SHOHandover parameters review-SHO
Report range (SHO relative threshold )
The relative threshold parameters for soft handover include
IntraRelThdFor1A (relative threshold for event 1A) and
IntraRelThdFor1B (relative threshold for event 1B) .
The parameters determine the size of the soft handover area
and the soft handover subscriber proportion. If report range is
too larger, monitor cell adds to active set cell very easily, soft
handover area is too larger and the forward capacity will be
waste serious; if the 1A and 1B report range is too small,
monitor cell is difficult to join to active cell and SHO can’t
implement smoothly, and handover success rate may be low
Handover parameters review-SHOHandover parameters review-SHO
Intra-frequency measurement filter coefficient
The filter is configured at Layer 3 intra-frequency
measurement report. This parameter used to smooth the
influence of shadow fading and some fast fading burrs.
The bigger the filter coefficient is, the stronger the smoothing
capability of the burr will be, but the lower the signal tracing
capacity will be. If if this parameter is too small, unnecessary
soft handover and ping pong handover will influence the
system; if the filter is too bigger, soft handover can’t
implement in time and the call will always dropped in
handover area .
Handover parameters review-SHOHandover parameters review-SHO
Time to Trigger
The effect of the time-to-trigger is that the report is triggered
only after the conditions for the event have existed for the
specified time-to-trigger
Mobile stations moving at different speeds respond differently
to the time-to-trigger value. The call drop rate is more
sensitive to the time-to-trigger value when the mobile station
is in high-speed movement, while it is less sensitive when the
mobile station is in low-speed movement, and ping-pong
handover and mis-handover are suppressed to a certain
extent
Handover parameters review-SHOHandover parameters review-SHO
Hysteresis parameter related to SHO
To limit the amount of event-triggered reports.
The bigger the hysteresis is, the stronger the signal fluctuation
resistance capability will be, and the better the ping pong
effect will be suppressed; however, the response speed of the
handover algorithm on signal changes will be decreased.
Therefore, the radio environment (slow fading characteristics),
the actual handover distance and the user moving speed
should be fully considered for the setting of this parameter.
Handover parameters review-SHOHandover parameters review-SHO
CIO (Cell Individual Offset )
This offset mechanism provides the network with an efficient
tool to change the reporting of an individual primary CPICH .
The bigger this parameter is, the more easily soft handover
will occur, and the more UEs will be in the soft handover
state, but the more forward resources will be occupied; the
smaller this parameter is, the more difficultly soft handover will
occur, which will be likely to affect the receiving quality .
Handover parameters review-HHOHandover parameters review-HHO
compressed mode enable /disable threshold (2D/2F
Event threshold )
GSM RSSI threshold
filter coefficient
Time to Trigger
Hysteresis
CIO (cell individual offset)
Handover parameters review-HHOHandover parameters review-HHO
2D/2F Event threshold
UE will start compressed mode and measure GSM signal as
a handover target cell when the value of RSCP is below the
setting. UE will stop compressed mode l when the value of
WCDMA cell RSCP is higher than the setting.
if the compressed mode is expected to start as early as
possible, set the 2D event threshold to a relatively big value;
otherwise, set it to a relatively small value. To control the ping
pong effect of the compressed mode start/stop, increase
appropriately the difference between the thresholds for 2D
event and 2F .
Handover parameters review-HHOHandover parameters review-HHO
filter coefficient
The hysteresis for GSM RSSI threshold and the setting of
which can reduce the probability of mis-decision caused by
signal jitter .
Handover parameters review-HHOHandover parameters review-HHO
Time to Trigger
If the inter-RAT quality always satisfies the inter-RAT
handover decision condition within the time specified by this
parameter, the network will start the inter-RAT handover
process
In high-speed cells, as mobile stations usually move fast, they
pass through the handover area very quickly. In addition, as
the shadow fading variance in a high-speed cell is small and
signal jitter after filtered by mobile stations is relatively small,
this parameter can be set to 2000ms or lower for high-speed
cells.
Handover parameters review-HHOHandover parameters review-HHO
Hysteresis
The hysteresis for GSM RSSI threshold and the setting of
which can reduce the probability of mis-decision caused by
signal jitter.
Handover parameters review-HHOHandover parameters review-HHO
CIO
The measurement signal Rxlev offset for GSM cell .
The bigger this parameter is, the higher the handover priority
of the GSM cells will be .
Course ContentsCourse Contents
Chapter 1Introduction
Chapter 2 handover principle
Chapter 3 SHO Optimization
Chapter4 Inter-RAT Optimization
Soft Handover OptimizationSoft Handover Optimization
SHO Optimization Target
Drive Routes
Optimization Solution
Optimization Analysis approach
Soft Handover OptimizationSoft Handover Optimization
SHO Optimization Target
In the early phase of the network, from KPI target, soft
handover success rate for event 1A&1B&1C should be larger
than 95%, and the call drop rate should be smaller than 5%.
Soft Handover OptimizationSoft Handover Optimization
Drive Routes
In the early phase of the network, because KPI result don’t
change in evidence prior and post optimization, GPS drive
test is very important .It is essential to use identical drive
routes prior and post any optimization changes in order to
accurately quantify the impact of such changes.
Soft Handover OptimizationSoft Handover Optimization
Optimization Solution
Many handover problems can be resolved through adjusting
the soft handover parameters, such as:
1A & 1B report range
time to trigger
intra-frequceny measurement filter coefficient
CIO
hysteresis
Soft Handover Optimization: Optimization Analysis approach
Soft Handover Optimization: Optimization Analysis approach
Small handover area
The active set quality decreases quickly but the good quality
monitor cell can’t add to active set in time.
This issue may be RNP problem but sometime this can’t be
resolved at RF optimization stage and also could be due to
soft handover configuration problem .
Enlarge 1A &1B&CIO report range to make the UE monitor
cell easily add to active set;
Short 1A time to trig to make the measurement report in time,
also can optimize the intra-frequency measurement
coefficient;
Soft Handover OptimizationSoft Handover Optimization
CIO Handover optimization example
After setting 3dB CIO of 506 and 505 cell, we can see
that the drop calls between 505 and 506 decreased.
(Left picture is before optimization)
Soft Handover Optimization: Optimization Analysis approach
Soft Handover Optimization: Optimization Analysis approach
Ping-Pong handover
The active set cell change frequently between the same cells.
This issue may be RF problem, and also cell soft handover
configuration problem.
Cells with many Ping-Pong handover may be causing call
dropped and poorer cell capacity.
This can enlarge intra-frequency measurement coefficient and
time to trigger.
Soft Handover OptimizationSoft Handover Optimization
Ping-Pong handover example
The ping-pong handover of 505 cell and 506 cell
can be seen.
Course ContentsCourse Contents
Chapter 1Introduction
Chapter 2 handover principle
Chapter 3 SHO Optimization
Chapter4 Inter-RAT Optimization
Inter-RAT OptimizationInter-RAT Optimization
Presently, the main purpose of inter-RAT handover is to
extend the signal coverage range, so that the UEs at the
verge of WCDMA coverage can implement handover to the
GSM system without communication interruption.
The configuration GSM neighbor list of WCDMA cells is very
important and always make wrong. At the same time, the
parameters optimization is very important.
The optimization solution is parameters configuration such as:
2D & 2F Event threshold, GSM RSSI threshold, Inter-RAT
handover trigger time, intra-frequceny measurement filter
coefficient, CIO and Hysteresis.