7. WCDMA Handover Principal

8/3/2019 7. WCDMA Handover Principal

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Huawei Confidential. All Rights Reserved

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 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


measurement report

Section 2 Basic concepts of measurement

Section 3 Intra-frequency measurement event


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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measurement report


Section 3 Intra-frequency measurement events


inter-system measurement events


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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measurement report


Section 3 Intra-frequency measurement

events




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


measurement report

Section 2 The basic definitions of measurement

Section 3 Intra-frequency measurement events





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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 2Intra-frequency Hard Handover




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



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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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Section 3Inter-frequency Hard Handover



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


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


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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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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Section 4Inter-system Hard Handover


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



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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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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

7. WCDMA Handover Principal

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