16-OWJ200106 WCDMA Handover Principal (With Comment) ISSUE1.0

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OWJ200106 WCDMA OWJ200106 WCDMA Handover PrincipleHandover Principle

ISSUE 1.0ISSUE 1.0

HUAWEI TECHNOLOGIES CO., LTD. Page 2All rights reserved

Why mobile communication systems need handover?Why mobile communication systems need handover?

It is decided by the characters of mobile systemIt is decided by the characters of mobile system

The mobility of UEThe mobility of UE

The mobile system is composed by cells which The mobile system is composed by cells which the coverage ability is limitedthe coverage ability is limited

Providing the continuous service in mobile Providing the continuous service in mobile communication system is the basic element in communication system is the basic element in QoSQoS


Upon completion of this course, you will be able Upon completion of this course, you will be able

to learn:to learn:

The basic definitions of handoverThe basic definitions of handover

The algorithms of handover decision The algorithms of handover decision

The handover signalling flowThe handover signalling flow

The parameters of handoverThe parameters of handover


Chapter 1 Introduction of HandoverChapter 1 Introduction of Handover

Chapter 2 Measurement of HandoverChapter 2 Measurement of Handover

Chapter 3 The Basic HandoversChapter 3 The Basic Handovers


The Purpose of Handover

Providing the continuous service in mobile Providing the continuous service in mobile

communication system is the basic element in QoScommunication system is the basic element in QoS

The load balance: sharing the resource The load balance: sharing the resource

The hierarchy divided by speed and service: high The hierarchy divided by speed and service: high

efficiency of using resource efficiency of using resource


The Basic Concepts of Handover

Active SetActive Set Monitored SetMonitored Set Detected set Detected set Event reportingEvent reporting

Event reporting to Periodic reportingEvent reporting to Periodic reporting Periodic reportingPeriodic reporting Radio Link (RL)Radio Link (RL) Radio Link Set (RLS)Radio Link Set (RLS) Combination way:Combination way:

maximum ratio combinationmaximum ratio combination selection combinationselection combination

The soft handover gainThe soft handover gain CPICHCPICH Soft handover, softer handover, hard handoverSoft handover, softer handover, hard handover


The Categories of Handover

According to the signaling characters:According to the signaling characters:

Soft handover (softer handover)Soft handover (softer handover)

Hard handoverHard handover

According to the properties of source cell and target cellAccording to the properties of source cell and target cell

Intra-frequency handoverIntra-frequency handover

Inter-frequency handoverInter-frequency handover

Inter-system handover (UMTS <-> GSM)Inter-system handover (UMTS <-> GSM)

According to the purpose of handoverAccording to the purpose of handover

Based on CoverageBased on Coverage

Based on Load (Optional)Based on Load (Optional)

Based on mobility of UE (Optional)Based on mobility of UE (Optional)

Based on Service (Optional)Based on Service (Optional)


The Characters of Different Handovers

ItemItem Soft HandoverSoft Handover Hard HandoverHard Handover

The numbers of RL in The numbers of RL in

active set after active set after

handoverhandover

Several Several OneOne

Interruption during Interruption during

handoverhandover

NoNo YesYes

The frequencies of cellsThe frequencies of cells Only happened in Only happened in

Intra-frequency Intra-frequency

cellscells

Can be happened in Can be happened in Intra-Intra-

frequency cells or Inter-frequency cells or Inter-

frequency cellsfrequency cells

Comparison between soft handover and hard handover:Comparison between soft handover and hard handover:


The Characters of Different Handovers

Comparison between soft handover and softer handover:Comparison between soft handover and softer handover:

During softer handover, the uplink signaling are combined in NodeB by During softer handover, the uplink signaling are combined in NodeB by

maximum ratio combination, but during soft handover they are maximum ratio combination, but during soft handover they are

combined in RNC by selection combinationcombined in RNC by selection combination

Compare to later one, the maximum ratio combination can get more Compare to later one, the maximum ratio combination can get more

gain. So the performance of maximum ration combination is bettergain. So the performance of maximum ration combination is better

Since softer handover is completed in NodeB, it do not consume Since softer handover is completed in NodeB, it do not consume

transport resource of Iubtransport resource of Iub


RNC

NodeB 2NodeB 1

Soft Handover


RNC (WFMR)

NodeB

Softer Handover


Hard Handover

RNC

NodeB 2NodeB 1


Three Steps of Handover

Decision

Execute

Measurement







2.1 Measurement control and measurement report2.1 Measurement control and measurement report

2.2 The basic definitions of measurement2.2 The basic definitions of measurement

2.3 Measurement event2.3 Measurement event

2.4 Compressed mode2.4 Compressed mode


Measurement Control, normal case

UE UTRAN

MEASUREMENT CONTROL

Measurement Control


Measurement Control


UE UTRAN

MEASUREMENT CONTROL



UE UTRAN

MEASUREMENT REPORT

Measurement Report








The Basic Concepts of Measurement

The measurement quantities of HandoverThe measurement quantities of Handover

Soft handover and Intra-frequency hard handover : CPICH RSCP, CPICH Ec/N0, Soft handover and Intra-frequency hard handover : CPICH RSCP, CPICH Ec/N0, Path lossPath loss

Inter-frequencyInter-frequency ：： CPICH RSCP, CPICH Ec/N0CPICH RSCP, CPICH Ec/N0

Inter-systemInter-system ：： GSM Carrier RSSI, BSIC Identification, BSIC ReconfirmationGSM Carrier RSSI, BSIC Identification, BSIC Reconfirmation

The reporting methods of measurementThe reporting methods of measurement

Periodic reporting Periodic reporting

Event reportingEvent reporting

The events of reportingThe events of reporting

Intra-frequency eventsIntra-frequency events ：： 1A, 1B, 1C, 1D, 1F1A, 1B, 1C, 1D, 1F

Inter-frequency events Inter-frequency events ：： 2D, 2F, 2B, 2C2D, 2F, 2B, 2C

Inter-system events Inter-system events ：： 3A, 3C3A, 3C


Measurement Model

Layer 1filtering

Layer 3filtering

Evaluationof reporting

criteria

A DB C

C'

parameters parameters


Measurement Model


Reporting Criterion

Reporting CriterionReporting Criterion

Decision formula: for example, 1A event :Decision formula: for example, 1A event :

Path LossPath Loss

Other measurement (Ec/N0 or RSCP )Other measurement (Ec/N0 or RSCP ) ：：

),2/(10)1(1010 11

aBest

N

iiNew HRLogMWMLogWLogM

A

),2/(10)1(1010 11

aBest

N

iiNew HRLogMWMLogWLogM

A

New cell


Key Parameters

△ T △ T △ T

1A Event 1B Event Nottri ggered

Report i ngRange

Hyst

C

B

ACPI CHEc/ No








Intra-frequency Measurement Events

Intra-frequency measurement report events are identified with 1X :

1A : A primary pilot channel enters the reporting range. When the

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;

1F : The measurement value of a primary pilot channel become

lower than the absolute threshold


Inter-frequency Measurement Events

Inter-frequency measurement events are identified with 2X

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

2F : The estimated quality value of the used frequency is higher than a certain threshold


Inter-system Measurement Events

Inter-system measurement events are identified with 3X

3A : The estimated quality value of the used UTRAN frequen

cy is lower than a certain threshold, and that of the other syst

em is higher than a certain threshold;

3C : The estimated quality value of the other system is highe

r than a certain threshold ;








The Purpose of Compressed mode

Purpose：

Measure the inter-frequency cell or inter-system cell under F

DD mode

Categories :

Downlink compressed:

Uplink compressed


Compressed Mode Sketch Map

One frame(10 ms) Transmission gap available for

inter-frequency measurements


The realization Methods of Compressed mode

Realization Methods

SF/2

Higher layer scheduling







3.1 Soft Handover3.1 Soft Handover

3.2 Intra-frequency Hard Handover3.2 Intra-frequency Hard Handover

3.3 Inter-frequency Hard Handover3.3 Inter-frequency Hard Handover

3.4 Inter-system Hard Handover3.4 Inter-system Hard Handover


Brief Introduction of Soft Handover

Characters of Soft Handover

During handover, UE has several RLs with different cells----

active set.

The handover among different cells which are in same RLS

can be softer handover.

− Soft handover:

▪ Selection combination in uplink

▪ Maximum combination in downlink

− Softer handover

▪ Maximum combination in uplink and downlink


Brief Introduction of Soft Handover Advantages

Soft handover gain

Load balance

Decrease the possibility of call drop caused by ping-pong handover.

Disadvantages

More resource needed in downlink, especially for the code resource

of BE service.

Usually, the gain of downlink power is negative.

When the downlink power from different cells is not balanced, it will

bring side-effect.


Measurement of Soft Handover

The measurement of soft handover/softer handover

Measurement value： CPICH RSCP、 CPICH Ec/No、 Pathloss

Process of Measurement： Layer 1 filter, Layer 3 filter

Reporting way

− Periodic reporting

− Event reporting

▪ Event type： 1A、 1B、 1C、 1D、 1F

▪ UE measures the time difference between CFN and SFN

▪ Reporting rules: trigger condition, Relative threshold, Absolute threshold, Hysteresis, Time to trigger

− Event reporting to periodic reporting


The Decision Algorithm of Soft Handover

Soft /softer handover decision

1A : Radio Link Addition

1B : Radio Link Removal

1C : Combined Radio Link Addition

and Removal

1D : Change best cell


The Execution of Soft Handover

Soft handover execution

The update principal of measurement control

− Configure the neighbor cells and the parameters according to best cell

RLC mode

− AM mode is used for measurement control

− UM mode is used for measurement report

The compensation and restriction of soft handover

− From event reporting to periodic reporting


Soft Handover Flow (add RL)


Soft Handover Flow (del RL)


Key Parameters

Relative threshold

Time to trigger

Layer 3 filter coefficient

Absolute threshold of soft handover








The Characters of Intra-frequency Hard Handover Characters

UE only has one RL with one cell in the process of handover

Disconnect UE with the original cell, then hand it over to target cell

The working frequency of source cell and target cell are same

Advantages

Enhance the using efficiency of the OVSF code and hardware resource

Disadvantages

High call drop possibility because of the intra-frequency interference

Application scenarios

Without Iur interface between two RNCs or the Iur interface congestion (only happened in inter-RNC handover)

The different strategies can be used for different conditions, from the aspects of code resource, QoS and so on.


The Measurement, Decision and Execution of Intra-frequency Hard Handover

Measurement

Similar to soft handover Decision

1D event Execution

UE reports CFN-SFN information

− Synchronization hard handover

− Use the original DOFF value

− Continuous CFN

UE does not report CFN-SFN information

− The hard handover based on timing

− Re-configure DOFF

− Calculate CFN according to DOFF


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


Key Parameters

Handover decision threshold based on BE service bitrate

UE should do soft handover when the bitrate of BE

service is less than the threshold.

UE should do intra-frequency hard handover when the

bitrate of BE service is greater than the threshold.

The parameters about 1D event:

Time to trigger, hysteresis

The parameters should be set according to the QoS








The Brief Introduction of Inter-frequency Hard Handover

Characters

The working frequency is different after handover

The compressed mode needed if the UE only has one

receiver

Usually, the timing re-initiation hard handover is used

for hard handover


Disconnected coverage

Handover based on load

Hierarchy cells


Measurement Values and Events

The Inter-frequency hard handover measurement valu

es

Measurement values:

− CPICH RSCP、 CPICH Ec/No

Different handover purpose for different measurem

ent type:

− In the edge of carrier coverage: CPICH RSCP

− In the center of carrier coverage: CPICH Ec/No


Compressed Mode Initiation

Conditions for measurement initiated

2D event : The estimated quality value of the used

frequency is lower than a certain threshold

Conditions for Measurement stopping

2F event : The estimated quality value of the used

frequency is higher than a certain threshold


Cells Hierarchy Algorithm Based on UE Moving Speed

When UE is in one of the hierarchy cells, the moving speed

estimation algorithm is initiated

Handover events in a while decides whether the speed

of UE satisfies the current cell hierarchy condition

UE’s moving speed decided the result.


Decision Algorithm

The inter-frequency hard handover decision

The coverage triggers the handover

− 2B event：▪ the quality in the used frequency is lower than ab

solute threshold, but the quality in another non-used frequency is higher than another absolute threshold.

The UE moving speed triggers handover

− 2C event：▪ the quality in another frequency is higher than an

absolute threshold


Inter-frequency Hard Handover Signaling Flow

UE

1.RADIO LINK SETUP REQUEST

Target NODEB

Source NODEB SRNC

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) Parameters of Inter-frequency handover based on coverage:

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, trigger delay 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

Used frequency quality threshold for inter-frequency hard handover

The minimum access threshold for inter-frequency hard handover


Key Parameters (II)

Parameters of Inter-frequency handover based

on non-coverage

Inter-frequency measurement layer 3 filter

coefficient, trigger delay time and hysteresis

Threshold of Inter-frequency handover based

on non-coverage








The Brief Introduction of Inter-system Hard Handover


WCDMA FDD <－ >GSM

Characters

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 utilizing efficiency of old equipments(2G->3G)

Disadvantages

The flow is complicated, and it demands higher compatibility for equipments

Demands more complicated UE


Compressed Mode Initiated

The inter-system measurement (GSM measurement)

Measurement type:

− GSM Carrier RSSI

− BSIC Identification

− BSIC Reconfirmation

The process of measurement: layer 1 filter, layer 3 filter

Measurement reporting

− Event reporting

▪ 2D Event: initiate GSM measurement

▪ 2F Event: stop GSM measurement


Decision Algorithm

Inter-system handover based on coverage

Event reporting:

− 3A event: 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.

Periodic reporting:

− Evaluation: According to the periodic reported GSM RSSI

measurement value and the BSIC confirming state of target cell of

GSM system, and meanwhile the UE evaluates the GSM RSSI of

target cell is greater than the absolute threshold, then consider

the cell confirmed by BSIC.


Decision Algorithm

Inter-system handover based on non-coverage

Event reporting

3C event: The estimated quality value of the other

system is higher than a absolute threshold.


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

Inter-system Handover Flow


Key Parameters (I) Parameters of inter-system handover based on coverage

Inter-system measurement 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-system measurement values (2D, 2F)

− CPICH Ec/No

− CPICH RSCP

BSIC confirmed (Optional)

Inter-system handover caused by coverage parameters

− configure the GSM RSSI threshold of CS domain and PS domain separately

Using inter-system frequency quality handover threshold

Configure the trigger delay time, hysteresis for each event


Key Parameters (II)

Parameters of inter-system handover based on non-coverage

The decision threshold for inter-system handover: configure the

CS, PS separately

Trigger delay time

Configure BSIC with acknowledged and unacknowledged mode

Inter-frequency measurement layer 3 filter coefficient and

hysteresis

Penalty time

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16-OWJ200106 WCDMA Handover Principal (With Comment) ISSUE1.0