UMTS Handover description
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Transcript of UMTS Handover description
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WCDMA Handover Principal and Analysis
ISSUE 1.0
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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 element
in 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 1 Chapter 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 RL in active set after handover
Several One
Interruption during handover
No Yes
The frequencies of cells
Only possible in Intra-frequency cells
Occurs in Intra-frequency cells or Inter-frequency cells
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 and
the 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 2 Handover 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 Measurement Measurement Control and Measurement ReportReport
Measurement Control :
UE UTRAN
MEASUREMENT CONTROL
Measurement Control, normal case
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Measurement Control and Measurement Measurement 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
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Measurement ModelMeasurement Model
Layer 1filtering
Layer 3filtering Evaluation
of reportingcriteria
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, TimHysteresis, Time to Triggere to Trigger
),2/(10)1(1010 11
aBest
N
iiNew HRLogMWMLogWLogM
A
),2/(10)1(1010 11
aBest
N
iiNew HRLogMWMLogWLogM
A
Mnew : measurement result of cell entering reporting rangeMi : measurement result of cells in active setNA : number of cells in active setMbest : measurement result of best cell in active setW : weight factorR : Reporting rangeH1a : 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
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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 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
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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 event
s
Section 4 Inter-frequency and
inter-system measurement events
Section 5 UE Internal Measurement
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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 higher than 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 lower than 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 2 Chapter 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 smalle
r 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-frequency measurement? 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 application scenarios.
SummarySummary
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Chapter 1 Introduction to Handover
Chapter 2 Handover Measurement
Chapter 3Chapter 3 Basic 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
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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 is softer handover.
Soft handover Combination:– Selection combination in uplink– Maximum combination in downlink
Softer handover Combination:– Maximum combination in uplink and downlink
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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 can decrease
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.
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Measurement of Soft Handover Measurement 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
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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
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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
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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 acco
rding to best cell
RLC mode UM mode is used for measurement control AM mode is used for measurement reporting
The compensation and restriction of soft handover From event reporting to periodic reporting
– Parameters : Periodic reporting time interval Number for reporting ti
mes
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Soft Handover Flow (Add RL)Soft Handover Flow (Add RL)
The execution of soft handover (Add RL)
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Soft Handover Flow (Del RL)Soft Handover Flow (Del RL)
The execution of soft handover (Del RL)
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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-pong
handover 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 pin
g-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 2 Intra-frequency Hard Handover
Section 3 Inter-frequency Hard Handover
Section 4 Inter-system Hard Handover
Section 5 Compressed Mode
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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.
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Measurement, Decision and Execution of Intra-Measurement, Decision and Execution of Intra-frequency Hard Handoverfrequency Hard Handover
Measurement Similar to soft handover
Decision 1D event
Execution
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Intra-frequency Hard Handover FlowIntra-frequency Hard Handover Flow
Intra-frequency hard handover flow
UE
1.RADIO LINK SETUP REQUEST
Target NODEB
Source NODEB SRNC
2. RADIO LINK SETUP RESPONSE
3.ALCAP establish
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 release
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Key ParametersKey Parameters
Handover decision threshold based on BE rate
UE should do soft handover when the rate of BE service is less than the threshold.
UE should do intra-frequency hard handover when the rate of BE service 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 3 Inter-frequency Hard Handover
Section 4 Inter-system Hard Handover
Section 5 Compressed Mode
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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 scenarios Application scenarios Disconnected coverage Handover based on load
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Inter-frequency Hard Handover Measurement Inter-frequency Hard Handover Measurement Values and EventsValues and 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
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Measurement Values and Events of Inter-frequency Measurement Values and Events of Inter-frequency Hard Handover Hard 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
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Compressed Mode ICompressed Mode Initiatnitiation in Inter-frequency ion in Inter-frequency 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.
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Inter-frequency Hard Handover Decision AlgorithmInter-frequency Hard Handover Decision Algorithm
The inter-frequency hard handover decision
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
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Execution of Inter-frequency Hard HandoverExecution of Inter-frequency Hard Handover
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 information UE 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
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Inter-frequency Hard Handover FlowInter-frequency Hard Handover Flow
Signaling flow
UEUE
1.RADIO LINK SETUP REQUEST
Target Target NodeBNodeB
SourceSourceNodeBNodeB 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
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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 RS
CP 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 4 Inter-system Hard Handover
Section 5 Compressed Mode
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Introduction of Inter-system Hard HandoverIntroduction of Inter-system Hard Handover
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 measurem
ent
Advantages For coverage, it can solve the problems from one system to anoth
er system For capacity, it can enhance the utilization efficiency of old equip
ments(2G->3G)
Disadvantages The flow is complicated, and it demands higher compatibility for e
quipments Demands more complicated UE
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Measurement for Inter-systemMeasurement for Inter-system :: Compressed MoCompressed Mode Initiatedde 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
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Inter-system Hard Handover Decision AlgorithmInter-system Hard Handover Decision Algorithm
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:– Evaluation : According to periodic report GSM RSSI measure
ment 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.
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Inter-system Handover FlowInter-system Handover Flow
The execution of inter-system handover
1. Relocation Required 2. Prepare
Handover 3. Handover
Request
4. Handover Request Ack
12. Iu Release Command
13. Iu Release Complete 14. Send End
Signal Response
5. Prepare Handover Response
6. Relocation Command
7. DCCH : Handover from UTRAN Command
8. Handover
Detect
9. Handover Complete
10. Handover Complete
11. Send End
Signal Request
UE Node B SRNC CN MSC BSC
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Key Parameters (I)Key Parameters (I)
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 for PS domain and CS domain, the different 2D and 2F parameters are configured
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 domain separately
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
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Purpose of Compressed modePurpose of Compressed mode
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 has t
o 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.
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Compressed Mode Sketch MapCompressed Mode Sketch Map
One frame(10 ms) Transmission gap available for
inter-frequency measurements
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Realization Methods of Compressed modeRealization Methods of Compressed mode
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 scheduling Higher layer permit only some transport format to be used in CM, to generate
gap. Appropriate for variable-rate service. Complicated method
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QuestionsQuestions
What are the differences between soft handover and softer handover?
What is compressed mode? Draw out the hard handover signaling flow.
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SummarySummary
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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