7. wcdma handover principal
TRANSCRIPT
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Huawei Confidential. All Rights Reserved
WCDMA Handover Principal and
Analysis
ISSUE 1.0
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2Internal Use
Why mobile systems need
handover?
UE mobility
The mobile system is composed of
cells which the coverage ability is
limited.
Provide continuous service in
mobile system is the basic elementin QoS.
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ObjectiveObjective
Upon completion this course, you will
be able to understand:
The basic definitions of Handover
The algorithms of handover
decision
The handover flow
The parameters of handover
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Chapter 1Chapter 1 Introduction to HandoverIntroduction to Handover
Chapter 2 Handover Measurement
Chapter 3 Basic Handovers
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The Purpose of HandoverThe Purpose of Handover
Providing the continuous service in mobile system is the basic
element in QoS.
The load balance: sharing the resource
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The Basic Concepts of HandoverThe Basic Concepts of Handover
Active Set Monitored Set Detected set Event reporting
Event reporting to Periodic reporting Periodic reporting Radio Link (RL)
Radio Link Set (RLS) Combination way:
maximum ratio combination selection combination
The soft handover gain
CPICH Soft handover, softer handover, hard handover
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Types of HandoverTypes of Handover
According to the signaling characters: Soft handover (softer handover)
Hard handover
According to the properties of source cell and target cell Intra-frequency handover
Inter-frequency handover
Inter-mode handover (FDD TDD)
Inter-system handover (UMTS GSM/CDMA2000)
According to the purpose of handover Based on Coverage
Based on Load (Optional) Based on mobility of UE (Optional)
Based on Service (Optional)
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The Characters of Different HandoversThe Characters of Different Handovers
ItemItem Soft HandoverSoft Handover Hard HandoverHard Handover
The numbers of RLin active set afterhandover
Several One
Interruption duringhandover No Yes
The frequencies ofcells
Only possible inIntra-frequencycells
Occurs in Intra-frequencycells or Inter-frequencycells
Comparison between soft handover and hard handover:
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The Characters of Different HandoversThe Characters of Different Handovers
During softer handover, the uplink signaling are
combined in NodeB by maximum ratio combination, but
during soft handover they are combined in RNC by
selection combination.
Compare to later one, the maximum ratio combination
give more gain. So the performance of maximum ratio
combination is better.
Since softer handover is completed in NodeB, it does not
consume a lot of transport resource of Iub.
Comparison between soft handover and softer handover:
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RNC
NodeB 2NodeB 1
Soft HandoverSoft Handover
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RNC
NodeB
Softer HandoverSofter Handover
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Hard HandoverHard Handover
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Three Steps of HandoverThree Steps of Handover
Decision
Execute
Measurement
Measurement Measurement control
Measurement execution andthe result processing
The measurement report Mainly accomplished by UE
Decision Based on Measurement The application and distribution
of resource Mainly accomplished by RRM
in RNC
Execution The process of signaling Support the failure drawback
Measurement control refresh
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QuestionsQuestions
The differences among Soft handover,softer handover and hard handover
Typical application scenarios
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SummarySummary
This chapter focus on the purpose of handovers and the
categories of handover in WCDMA.
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Chapter 1 Introduction to Handover
Chapter 2Chapter 2Handover MeasurementHandover Measurement
Chapter 3 Basic Handovers
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Chapter 2 Handover MeasurementChapter 2 Handover Measurement
Section 1 Measurement control and
measurement report
Section 2 Basic definitions of measurement
Section 3 Intra-frequency measurement event
Section 4 Inter-frequency and
inter-system measurement event
Section 5 UE internal measurement
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Measurement Control and MeasurementMeasurement Control and Measurement
ReportReport
Measurement Control
UE UTRAN
MEASUREMENT CONTROL
Measurement Control, normal case
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Measurement Control and MeasurementMeasurement Control and Measurement
ReportReport
Measurement report
UE UTRAN
MEASUREMENT REPORT
Measurement report, normal case
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Chapter 2 Measurement of HandoverChapter 2 Measurement of Handover
Section 1 Measurement control and
measurement report
Section 2 Basic concepts of measurement
Section 3 Intra-frequency measurement event
Section 4 Inter-frequency and
inter-system measurement event
Section 5 UE Internal Measurement
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Basic Concepts of MeasurementBasic Concepts of Measurement
Measurement values of Handover
Intra-frequency and inter-frequency:
CPICH RSCP, CPICH Ec/No, Path loss
Inter-frequency
CPICH RSCP, CPICH Ec/No
Inter-system
GSM Carrier RSSI, BSIC Identification, BSIC Reconfirmation
Reporting methods of measurement Periodic reporting
Event reporting
The events of reporting Intra-frequency events 1A,1B,1C,1D,1E,1F
Inter-frequency events 2D,2F,2B,2C
Inter-system events 3A,3C
Others 6G,6F
M t M d lM t M d l
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Measurement ModelMeasurement Model
Layerfiltering
Layerfiltering Evaluation
of reportin
criteria
A DB C
C'
parameters parameters
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Reporting CriteriaReporting Criteria
Reporting Criteria
Decision formula: For example, 1A event :
1.Path Loss
2.Other measurement
Relative thresholdRelative threshold, Absolute threshold, Hysteresis,Hysteresis,
Time to TriggerTime to Trigger
),/()(
aBest
N
i
iNew HRLogMWMLogWLogMA
++
=
),/()(
aBest
N
i
iNew HRLogMWMLogWLogMA
+
=
Mnew : measurement result of cell entering reporting range
Mi : measurement result of cells in active set
NA : number of cells in active set
Mbest : measurement result of best cell in active set
W : weight factor
R : Reporting range
H1a : hysteresis value of 1A event
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Key ParametersKey Parameters
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Chapter 2 Measurement of HandoverChapter 2 Measurement of Handover
Section 1 Measurement control and
measurement report
Section 2 Basic definitions of measurement
Section 3 Intra-frequency measurement events
Section 4 Inter-frequency and
inter-system measurement events
Section 5 UE Internal Measurement
I f M E
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Intra-frequency Measurement EventsIntra-frequency Measurement Events
Intra-frequency measurement events are identified with 1x :
1A : A primary pilot channel enters the reporting range.If active set of UE is full, UE stops reporting 1A
event;
1B : A primary pilot channel leaves the reporting range;
1C : The primary pilot channel in a non active set is betterthan the primary pilot channel in an active set;
1D : The best cell changes;
1E : The measurement value of a primary pilot channel exceeds
the absolute threshold 1F : The measurement value of a primary pilot channel is lower
than the absolute threshold
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27Internal Use
Chapter 2 Measurement of HandoverChapter 2 Measurement of Handover
Section 1 Measurement control and
measurement report
Section 2 Basic definitions of measurement
Section 3 Intra-frequency measurement
events
Section 4 Inter-frequency and
inter-system measurement events
Section 5 UE Internal Measurement
I f M EI t f M t E t
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Inter-frequency Measurement EventsInter-frequency Measurement Events
Inter-frequency measurement events are identified with 2x:
2A : The best frequency changes
2B : The quality of the current cell frequency is lower than a
certain threshold, but that of the non-used frequency is
higher than a certain threshold
2C : The estimated quality of the non-used frequency is higherthan a certain threshold
2D : The estimated quality of the used frequency is lower than a
certain threshold
2E : The estimated quality of the non-used frequency is lower
than a certain threshold
2F : The estimated quality of the used frequency is higher than
a certain threshold
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Inter-system Measurement EventsInter-system Measurement Events
Inter-system measurement events are identified with 3x:
3A: The estimated quality value of the used UTRAN
frequency is lower than a certain threshold, and that of the
other system is higher than a certain threshold;
3B: The estimated quality value of the other system is lowerthan a certain threshold;
3C: The estimated quality value of the other system is higher
than a certain threshold;
3D: The best cell in the other system changes
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Chapter 2Chapter 2 Measurement of HandoverMeasurement of Handover
Section 1 Measurement control and
measurement report
Section 2 The basic definitions of measurement
Section 3 Intra-frequency measurement events
Section 4 Inter-frequency and
inter-system measurement events
Section 5 UE Internal Measurement
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UE Internal MeasurementUE Internal Measurement
UE Internal measurement events are identified with 6x :
6G : The time difference between downlink receiving
and uplink transmission of the UE is smaller than
an absolute threshold;
6F : The time difference between downlink receiving
and uplink transmission of the UE is bigger than
an absolute threshold;
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QuestionsQuestions
How many events are there in intra-frequencymeasurement? What are they?
How many events are there in UE internal measurement?
How many events are there in inter-frequency
measurement? What are they?
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SummarySummary
This chapter covers intra-frequency measurement, inter-
frequency measurement, inter-system measurement and UE
internal measurement from their definitions and applicationscenarios.
SummarySummary
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Chapter 1 Introduction to Handover
Chapter 2 Handover Measurement
Chapter 3Chapter 3Basic HandoversBasic Handovers
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Chapter 3 Basic HandoversChapter 3 Basic Handovers
Section 1 Soft Handover
Section 2 Intra-frequency Hard Handover
Section 3 Inter-frequency Hard Handover
Section 4 Inter-system Hard Handover
Section 5 Compressed Mode
f S fI t d ti f S ft H d
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Introduction of Soft HandoverIntroduction of Soft Handover
Soft Handover Features
UE has several RLs with different cells----active set.
The handover among different cells which are in same RLS issofter handover.
Soft handover Combination: Selection combination in uplink Maximum combination in downlink
Softer handover Combination: Maximum combination in uplink and downlink
I t d ti f S ft H dI t d ti f S ft H d
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Introduction of Soft HandoverIntroduction of Soft Handover
AdvantagesAdvantages
Soft handover gain: Multi-Cell gain: Multiple unrelated radio links can reduces the
required fading margin. Macro Diversity Combining gain: Gain for the link demodulation of
the soft handover:
Load balance:
Different cells receive the signal from a UE in uplink, which candecrease the transmission power of UE. Similarly, UE receive signal from different cells, which also can
decrease the required transmission power of base station. Decrease the possibility of call drop caused by ping-pong handover.
DisadvantagesDisadvantages More resource needed in downlink, especially for the code resource of
BE service.
M t f S ft H dM t f S ft H d
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Measurement of Soft HandoverMeasurement of Soft Handover
The measurement of soft/softer handover
Measurement value CPICH RSCP, CPICH Ec/No, Pathloss Process of Measurement Layer 1 filter, Layer 2 filter
Reporting way
Periodic reporting
Event reporting
Event type 1A, 1B, 1C, 1D, 1F
Reporting rules: Trigger condition, Relative threshold (or
Absolute threshold), Hysteresis, Time_to_Trigger
Event reporting to periodic reporting
The Events of Soft Handover MeasurementThe Events of Soft Handover Measurement
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The Events of Soft Handover MeasurementThe Events of Soft Handover Measurement
Soft/softer handover measurement events
Intra-frequency events reporting:1A :A primary pilot channel enters the reporting range.
If active set of UE is full, UE stops reporting 1A event;
1B : A primary pilot channel leaves the reporting range;
1C : The primary pilot channel in a non active set is better
than the primary pilot channel in an active set;
1D: The best cell changes;
1E : The measurement value of a primary pilot channel
exceeds the absolute threshold
1F : The measurement value of a primary pilot channel is
lower than the absolute threshold
Decision Algorithm of Soft HandoverDecision Algorithm of Soft Handover
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Decision Algorithm of Soft HandoverDecision Algorithm of Soft Handover
Soft/softer handover decision
1A : Add RL into active set
1B : Delete RL from active set
1C : Replace cell
1D : Change best cell
E ti f S ft H dE ti f S ft H d
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Execution of Soft HandoverExecution of Soft Handover
Soft handover execution
The principal of measurement control
Configure the neighbor cells and the parameters
according to best cell
RLC mode
UM mode is used for measurement controlAM mode is used for measurement reporting
The compensation and restriction of soft handover
From event reporting to periodic reporting
Parameters Periodic reporting time intervalNumber for reporting times
S ft H d Fl (Add RL)Soft Handover Flow (Add RL)
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Soft Handover Flow (Add RL)Soft Handover Flow (Add RL)
The execution of soft handover (Add RL)
Soft Handover Flow (Del RL)Soft Handover Flow (Del RL)
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Soft Handover Flow (Del RL)Soft Handover Flow (Del RL)
The execution of soft handover (Del RL)
Key Parameters To OptimizeKey Parameters To Optimize
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Key Parameters To OptimizeKey Parameters To Optimize
Relative thresholdRelative threshold Set 1A, 1B value separately
1A < 1B which makes deleting RL is more difficult, and it can avoid ping-ponghandover
Usually 1A:Usually 1A:3dB;3dB; 1B: 6dB
Time to triggerTime to trigger Each event can be set separately Usually, 1B>1A which makes deleting RL is more difficult, and it can avoid
ping-pong handover Usually, 1A: 320ms, 1B: 640ms
Layer 3 filter coefficientLayer 3 filter coefficient Only one value for all intra-frequency measurement Sensitive to the delay of event trigger and ping-pong handover Usually 3
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Chapter 3 The Basic HandoversChapter 3 The Basic Handovers
Section 1 Soft Handover
Section 2Intra-frequency Hard Handover
Section 3 Inter-frequency Hard Handover
Section 4 Inter-system Hard Handover
Section 5 Compressed Mode
Characteristic of Intra frequency Hard HandoverCharacteristic of Intra frequency Hard Handover
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Characteristic of Intra-frequency Hard HandoverCharacteristic of Intra-frequency Hard Handover
Characteristic UE has one RL with one cell in the process of handover Disconnect UE from the original cell, then hand it over to target cell The working frequency of source cell and target cell are same
Advantages Enhance the efficiency of the OVSF code and hardware resource
Disadvantages High call drop possibility because of the intra-frequency interference
Application scenarios
No Iur interface between two RNCs or the Iur interface congested (only
happened in inter-RNC handover).
Handover of BE services that exceeds threshold rate.
Measurement, Decision and Execution of Intra-Measurement, Decision and Execution of Intra-
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Measurement, Decision and Execution of IntraMeasurement, Decision and Execution of Intra
frequency Hard Handoverfrequency Hard Handover
Measurement Similar to soft handover
Decision
1D event
Execution
Intra-frequency Hard Handover FlowIntra-frequency Hard Handover Flow
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Intra frequency Hard Handover FlowIntra frequency Hard Handover Flow
Intra-frequency hard handover flow
UE.RADIO LINK SETUP REQUEST
Target
NODEB
Source
NODEBSRNC
. RADIO LINK SETUP RESPONSE
.ALCAP establish
. PHYSICAL CHANNEL RECONFIGURATION
. RADIO LINK
FAILURE INDICATION
. PHYSICAL CHANNEL RECONFIGURATION COMPLETE
. RADIO LINK
DELETION REQUEST
. RADIO LINK
DELETION RESPONSE
.ALCAP release
Key ParametersKey Parameters
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Key ParametersKey Parameters
Handover decision threshold based on BE rate
UE should do soft handoverwhen the rate of BE service is less thanthe threshold.
UE should do intra-frequency hard handoverwhen the rate of BEservice is greater than the threshold.
The parameters about 1D event:
Time to trigger Hysteresis
The parameters should be set accord with the Qos
MML Command:MML Command: SET HOCOMMSET HOCOMM
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Chapter 3 The Basic HandoversChapter 3 The Basic Handovers
Section 1 Soft Handover
Section 2 Intra-frequency Hard Handover
Section 3Inter-frequency Hard Handover
Section 4 Inter-system Hard Handover
Section 5 Compressed Mode
Introduction of Inter-frequency Hard HandoverIntroduction of Inter-frequency Hard Handover
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Introduction of Inter frequency Hard HandoverIntroduction of Inter frequency Hard Handover
CharacteristicCharacteristic
The working frequency is different after handover
The compressed mode needed if the UE only has one receiver
AdvantagesAdvantages
Compare to intra-frequency hard handover, the success possibility is
higher
To balance the load among cells of different frequencies DisadvantagesDisadvantages
Compressed mode results in extra radio resource occupied
The timing re-initiation hard handover increase the time of handover
and the risk of call drop
Application scenariosApplication scenarios
Disconnected coverage
Handover based on load
Inter-frequency Hard Handover Measurement ValuesInter-frequency Hard Handover Measurement Values
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and Eventsand Events
Inter-frequency hard handover measurement values
Measurement values:
CPICH RSCP, CPICH Ec/No
Different handover purpose for different measurement type:
At the edge of carrier coverage: CPICH RSCP
At the center of carrier coverage: CPICH Ec/No
Measurement Values and Events of Inter-frequencyMeasurement Values and Events of Inter-frequency
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q yq y
Hard HandoverHard Handover
Measurement reporting Periodic reporting Event reporting
2A: The best frequency changes;
2B: The estimated quality value of the used frequency is lower than a certain
threshold, and that of the non-used frequency is higher than a certain
threshold;
2C: The estimated quality value of the non-used frequency is higher than a
certain threshold;
2D: The estimated quality value of the used frequency is lower than a certain
threshold
2E:The estimated quality value of the non-used frequency is lower than a
certain threshold
2F:The estimated quality value of the used frequency is higher than a certain
threshold
Compressed Mode Initiation in Inter-frequencyCompressed Mode Initiation in Inter-frequency
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p q yp q y
Hard HandoverHard Handover
Conditions to initiate Compressed Mode (CM) measurement
2D event2D event Used to enable the compressed mode to perform inter-
frequency measurement.
Conditions to stop measurement
2F event2F event Used to stop compressed mode. When used frequency quality
exceeds the threshold.
Inter-frequency Hard Handover Decision AlgorithmInter-frequency Hard Handover Decision Algorithm
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Inter-frequency Hard Handover Decision AlgorithmInter frequency Hard Handover Decision Algorithm
The inter-frequency hard handoverdecision
Coverage trigger handoverCoverage trigger handover
2B event2B event
the quality of current serving cell is lower than absolute
threshold, but the quality in other cell is higher than
another absolute threshold. Both cells are of different frequency
Load triggers handoverLoad triggers handover
2C event2C event
the quality of another frequency is higher than an
absolute threshold
Execution of Inter-frequency Hard HandoverExecution of Inter-frequency Hard Handover
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q yq y
Execution of Inter-frequency hard handover
UE report the timing information
UE with two receivers does not need compressed mode.
Synchronization hard handover
Using the original DOFF
UE does not report timing informationUE with a single receiver has to initiate compressed mode
If the NodeB of target cell is different from the cells in active set :
Timing re-initiation hard handover
Re-configure DOFF
If the NodeB of target cell is the same which the cells in active set:
Calculate the target cell timing relationship
Synchronization hard handover
Using the original DOFF
Inter-frequency Hard Handover FlowInter-frequency Hard Handover Flow
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q yq y
Signaling flow
UEUE
1.RADIO LINK SETUP REQUEST
TargetTarget
NodeBNodeB
SourceSource
NodeBNodeB SRNCSRNC
2. RADIO LINK SETUP RESPONSE
3.ALCAP established
4. PHYSICAL CHANNEL RECONFIGURATION
5. RADIO LINK
FAILURE INDICATION
6. PHYSICAL CHANNEL RECONFIGURATION COMPLETE
7. RADIO LINK
DELETION REQUEST
8. RADIO LINK
DELETION RESPONSE
9.ALCAP released
Key Parameters (I)Key Parameters (I)
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Key Parameters (I)Key Parameters (I)
Inter-frequency coverage handover parameters:
Inter-frequency measurement reporting:
periodic reporting or event reporting
Inter-frequency measurement values:
CPICH Ec/No or CPICH RSCP
Inter-frequency measurement layer 3 filter coefficient, delay trigger time
and hysteresis
Inter-frequency initiated and stopped threshold:
Considering the different demands of CPICH Ec/No and CPICH
RSCP for PS domain and CS domain, the different 2D and 2F
parameters are configured.
Inter-frequency handover based on coverage:
the quality threshold of target cell
Using frequency quality threshold in inter-frequency hard handover
The minimum access threshold for inter-frequency handover
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Chapter 3 The Basic HandoversChapter 3 The Basic Handovers
Section 1 Soft Handover
Section 2 Intra-frequency Hard Handover
Section 3 Inter-frequency Hard Handover
Section 4Inter-system Hard Handover
Section 5 Compressed Mode
Introduction of Inter-system Hard HandoverIntroduction of Inter-system Hard Handover
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yy
Application scenarios WCDMA FDD GSM
WCDMA FDD WCDMA TDD WCDMA FDD CDMA2000
Characteristic Different radio access technology is used after handover Usually, compressed mode should be used to help the
measurement
Advantages For coverage, it can solve the problems from one system to
another system For capacity, it can enhance the utilization efficiency of old
equipments(2G->3G)
Disadvantages The flow is complicated, and it demands higher compatibility for
equipments Demands more complicated UE
Measurement for Inter-systemMeasurement for Inter-system CompressedCompressed
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yy pp
Mode InitiatedMode Initiated
The inter-system measurement (GSM measurement)
Measurement type:GSM Carrier RSSI
BSIC Identification
BSIC Reconfirmation
Measurement reporting
Event reporting
2D Event: initiate GSM measurement
2F Event: stop GSM measurement
Inter-system Hard Handover Decision AlgorithmInter-system Hard Handover Decision Algorithm
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y g
The inter-system hard handover decision
Inter-system handover due to coverage issue
Event reporting:
3A event3A event
The estimated quality value of UTRAN frequency is lower than
a certain threshold, and that of the other system is higher than
a certain threshold
Periodic reporting:
EvaluationAccording to periodic report GSM RSSI
measurement value and the BSIC confirming state of target cell
of GSM system, and UE evaluates GSM RSSI of target cell is
greater than the absolute threshold, then consider the cell. Inter-system handover not because of coverage issue
Event reporting
3C event3C event:
The estimated quality value of the other system is higher than
an absolute threshold.
Inter-system Handover FlowInter-system Handover Flow
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y
The execution of inter-system handover
. RelocationRequired . Prepare
Handover. Handover Request
. Handover Request Ack
. Iu ReleaseCommand
. Iu ReleaseComplete . Send End
Signal Response
. PrepareHandover. Relocation
Command.DCCH : Handover
from UTRAN Command. Handover
Detect
. Handover Complete
. Handover Complete
. SendEnd
UE Node B SRNC CN MSC BSC
Key Parameters (I)Key Parameters (I)
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y ( )y ( )
Parameters for Inter-system handover
Inter-system measurement initiated and stopped thresholdInter-system measurement initiated and stopped threshold:
Considering different demands of CPICH Ec/No and CPICH RSCP forPS domain and CS domain, the different 2D and 2F parameters areconfigured
Inter-system measurement values (2D, 2F)Inter-system measurement values (2D, 2F)
CPICH Ec/No
CPICH RSCP
Configure the GSM RSSI threshold of CS domain and PS domainseparately
Using inter-system frequency quality handover threshold
Trigger time delay, Hysteresis for each event
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Chapter 3 The Basic HandoversChapter 3 The Basic Handovers
Section 1 Soft Handover
Section 2 Intra-frequency Hard Handover
Section 3 Inter-frequency Hard Handover
Section 4 Inter-system Hard Handover
Section 5 Compressed Mode
Purpose of Compressed modePurpose of Compressed mode
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p pp p
Purpose Measure the inter-frequency cell or inter-system cell under FDD
mode
Cause:
Since one receiver only can work in one frequency, the UE hasto stop working in current frequency if it is going to measure the
signal from another frequency cell. To ensure the downlink
service unaffected, the remained data should be sent in the
limited time.
Compressed Mode Sketch MapCompressed Mode Sketch Map
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One f rame( ms) Transmission gap available for
in ter-frequenc y m easurements
Realization Methods of Compressed modeRealization Methods of Compressed mode
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CM MethodsCM Methods
Reduce SF by halfReduce SF by half
This double the data rate. But since amount of data not changed, it halves the
time in which it is sent, open up a gap.
Advantage: easy to handle for RNC
Disadvantage: occupied the resource of NodeB, decrease the utilizing efficiency
of OVSF
PuncturingPuncturing
Decrease the coding redundancy
Advantage: easy to handle for RNC;
Disadvantage: limited to the property of channel coding; decreased the coding
gain
Higher layer schedulingHigher layer schedulingHigher layer permit only some transport format to be used in CM, to generate
gap. Appropriate for variable-rate service.
Complicated method
QuestionsQuestions
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What are the differences between soft handover and softer
handover?
What is compressed mode?
Draw out the hard handover signaling flow.
SummarySummary
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y
This chapter focus on the basic handovers in WCDMA: soft
handover, softer handover, intra-frequency hard handover, inter-frequency hard handover and inter-system hard handover. It also
introduced the application scenarios for these different handovers
Meanwhile, compressed mode is introduced in this chapter
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