07 WCDMA Handover Principal ISSUE1.0

8/13/2019 07 WCDMA Handover Principal ISSUE1.0

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HUAWEI TECHNOLOGIES CO., LTD. All rights reserved

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OWJ200106 WCDMA

Handover PrincipalISSUE 1.0


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HUAWEI TECHNOLOGIES CO., LTD. All rights reserved Page 1

Why mobile systems need handover?

It is decided by the characters ofmobile system:

The mobility of UE

The mobile system is composedby cells which the coverage abilityis limited.

Providing the continuous servicein mobile system is the basicelement in QoS.


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Upon completion of this course, you willbe able to:

The basic definitions of Handover

The algorithms of handover decision

The handover flow

The parameters of handover


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Chapter 1 Introduction of Handover

Chapter 2 Measurement of Handover

Chapter 3 The Basic Handovers


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The Purpose of Handover

Providing the continuous service in mobile system is

the basic element in QoS.

The load balance: sharing the resource

The hierarchy divided by speed and service: high

efficiency of using resource


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The Basic Concepts of Handover

Active SetMonitored SetDetected setEvent reporting

Event reporting to Periodic reporting

Periodic reportingRadio Link (RL)Radio Link Set (RLS)Combination way:

maximum ratio combination

selection combinationThe soft handover gainCPICHSoft handover, softer handover, hard handover


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The Categories 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 handoverInter-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 Handovers

Compari son between sof t handover and hard handover:

Item Soft Handover Hard Handover

The numbers of RL inactive set after handover

Several One

Interruption duringhandover

No Yes

The frequencies of cells Only happened in

Intra-frequency cells

Can be happened in Intra-

frequency cells or Inter-frequency cells


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The Characters of Different Handovers

Comparison between soft handover and softer handover:

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 ration combination

can get more gain. So the performance of maximum

ration combination is better.

Since softer handover is completed in NodeB, it do not

consume transport resource of Iub.


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RNC

NodeB 2NodeB 1

Soft Handover


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RNC (WFMR)

NodeB

Softer Handover


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Hard Handover

RNC

NodeB 2NodeB 1


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Three Steps of Handover

MeasurementMeasurement controlMeasurement execution and the resultprocessingThe measurement reportMainly accomplished by UE

DecisionBased on MeasurementThe application and distribution of resourceMainly accomplished by RRM in RNC

ExecutionThe process of signaling

Support the failure drawbackMeasurement control refresh

Decision

Execute

Measurement


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Questions

The differences among Soft handover, softer handover

and hard handover

Typical application scenarios


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Summary

This chapter focus on the purpose ofhandovers and the categories ofhandover in WCDMA.

Summary


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2.1 Measurement control and measurement report

2.2 The basic definitions of measurement

2.3 Intra-frequency measurement event

2.4 Inter-frequency and inter-system measurement event

2.5 UE internal measurement

2.6 Compressed mode


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Measurement Control and Measurement Report

M easur ement Control

Measurement Control, normal case

UE UTRAN

MEASUREMENT CONTROL


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Measurement Control and Measurement Report

M easur ement report

Measurement Control, normal case

UE UTRAN

MEASUREMENT REPORT


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2.6 Compressed mode


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The Basic Concepts of Measurement

The measurement values of HandoverIntra-frequency and inter-frequency: CPICH RSCP CPICH Ec/N0 Path loss

Inter-frequency CPICH RSCP CPICH Ec/N0

Inter-system GSM Carrier RSSI BSIC Identification BSIC Reconfirmation

The reporting methods of measurement

Periodic reporting

Event reporting

The events of reporting

Intra-frequency events 1A,1B,1C,1D,1F

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

Inter-system events 3A,3C

Others 6G,6F


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Measurement Model

Layer 1filtering

Layer 3filtering Evaluationof reporting

criteria

A DB C

C'

parameters parameters


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Reporting Criterion

Reporting CriterionDecision formula: for example, 1A event :

1.Path Loss

2.Other measurement

Relative threshold, Absolute threshold, Hysteresis, Time to

trigger

),2/(10)1(1010 11

a Best

N

ii New H R LogM W M Log W LogM

A

),2/(10)1(1010 11

a Best

N

ii New H R LogM W M Log W LogM

A


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Key Parameters


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2.6 Compressed mode


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Intra-frequency Measurement Events

All intra-frequency measurement report events are identified with 1X :

1A A primary pilot channel enters the reporting range. When theactive 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 theprimary pilot channel in an active set;

1D The best cell changes;

1E The measurement value of a primary pilot channel exceeds theabsolute threshold

1F, The measurement value of a primary pilot channel is lower thanthe absolute threshold


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2.6 Compressed mode


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Inter-frequency Measurement Events

Inter-frequency measurement events are identified with 2X2A: The best frequency changes;

2B: The estimated quality value of the used frequency is lower thana certain threshold, and that of the non-used frequency is higherthan a certain threshold;

2C: The estimated quality value of the non-used frequency is higherthan a certain threshold;

2DThe estimated quality value of the used frequency is lower than acertain threshold

2E:The estimated quality value of the non-used frequency is lowerthan a certain threshold

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


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Inter-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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UE Internal Measurement

UE Internal measurement events are identified with 6X

6G: The time difference between downlink receiving

and uplink transmission of the UE is shorter than anabsolute threshold;

6F: The time difference between downlink receiving

and uplink transmission of the UE is bigger than an

absolute threshold;


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The Purpose of Compressed mode

Purpose Measure the inter-frequency cell or inter-system cell under FDD mode

Cause:

Downlink compressed:

Since one receiver only can work in one frequency, the UE has to stopworking 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.

Uplink compressed

UE should stop the uplink transmission when the uplink working frequency

is very close to the measured frequency, for example GSM 1800/1900 is

very close to the UMTS FDD uplink working frequency.


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Compressed Mode Sketch Map

Compr essed mode sketch map

One frame (10 ms) Transmission gap available for

inter-frequency measurements


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The realization Methods of Compressed modeRealization Methods

SF/2

Should use the replace scrambling code

Advantage: easy to handle for RNC

Disadvantage: occupied the resource of NodeB, decrease the utilizingefficiency of OVSF, influenced the coverage and increased interferencecaused by the replace scrambling code.

rate matching/puncturing

Decrease the coding redundancy

Advantage: easy to handle for RNC; the SF 4 can be used; no influence toutilizing efficiency of OVSF

Disadvantage: limited to the property of channel coding; decreased the codinggain

higher layer scheduling

MAC can restrict TFCS to change the downlink data rate.

Advantage: the interference is lower

Disadvantage: complicated for higher layer, only fit for non-timing data service.


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Questions

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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Summary

This chapter covers intra-frequency

measurement, inter-frequencymeasurement, inter-system measurement

and UE internal measurement from their

definitions and application scenarios.

Summary


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Chapter 1 Introduction of Handover




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3.1 Soft Handover3. 2 Intra-frequency Hard Handover

3.3 Inter-frequency Hard Handover

3.4 Inter-system Hard Handover


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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


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Brief Introduction of Soft Handover Advantages

Soft handover gain:

Multi-Cell gain: Multiple irrelated soft handover branches low the requiredmargin for fading

Macro Diversity Combining gain: Gain for the link demodulation of the softhandover:

Load balance: Different cells receive the signals from UE in uplink, which candecrease the transmission power of UE. And UE receive signal from differentcells, which also can decrease the transmission power of base station.

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.


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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 2 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


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The Decision 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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Soft Handover Flow (add RL)The execution of soft handover (add RL )


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Soft Handover Flow (del RL)The execution of soft handover (del RL)


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The Characters of Intra-frequency Hard HandoverCharacters

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 jam (onlyhappened in inter-RNC handover)

The different strategies can be used for different conditions, such ascode resource condition, the QoS condition and so no.


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

MeasurementSimilar 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


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Intra-frequency Hard Handover FlowI ntr a-fr equency hard handover f low

UE

1.RADIO LINK SETUP REQUEST

TargetNODEB

SourceNODEB SRNC

2. RADIO LI NK SETUP RESPONSE

3.ALCAP establish

4. PHYSICAL CHANNEL RECONFIGURATION

5. RADIO LINKFAILURE INDICATION

6. PHYSICAL CHANNEL RECONFIGURATION COMPLETE

7. RADIO LINKDELETION REQUEST

8. RADIO LINKDELETION RESPONSE

9.ALCAP release


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The Brief Introduction of Inter-frequency Hard HandoverCharacters

The working frequency is different after handoverThe compressed mode needed if the UE only has one receiver

Usually, the timing re-initiation hard handover is used for hardhandover

Advantages

Compare to intra-frequency hard handover, the success possibility is

higherThe load balance among cells with different frequencies

Can realize the reasonable configuration for hierarchy cells

Disadvantages

Compressed mode results in extra radio resource occupied

The timing re-initiation hard handover increase the time of handoverand the risk of call drop

Application scenarios

Disconnected coverage

Handover based on load

Hierarchy cells


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The Inter-frequency Hard Handover MeasurementValues and Events

The Inter-frequency hard handover measurement

values

Measurement values:

CPICH RSCP CPICH Ec/Io

Different handover purpose for different

measurement type:

In the edge of carrier coverage: CPICH RSCP

In the center of carrier coverage: CPICH Ec/No


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Compressed Mode Initiation in Inter-frequency HardHandover

Conditions for measurement initiated

2D event can be used to enable the compressed mode to performinter-frequency measurement.

Enable inter-frequency measurement by moving speed estimation

algorithmConditions for Measurement stopping

2F event

After the best cell is changed, the cell does not contain inter-frequencyneighbor cells.

Inter-frequency measurement timer expired

Because the moving speed of UE is changed, the inter-frequencyhandover measurement is stopped by cell hierarchy algorithm.


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Cells Hierarchy Algorithm Based on UE Moving Speed

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

Handover events in a while decides whether the speed of UEsatisfies the current cell hierarchy condition

UE is remained in the current cell if the speed is medium. If the speed is very high, it will be handed over to higher

hierarchy cell. And if not, hand it over to lower hierarchy cell.

UEs moving speed decided the result.

If the hierarchy is configured by different frequencies, the inter-

frequency blind handover or inter-frequency measurementhandover can be initiated.

If the hierarchy is configured by one frequency, the intra-frequency handover can be initiated.


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Inter-frequency Hard Handover Decision Algorithm

The inter-frequency hard handover decisionThe coverage triggers the handover

2B event

the quality in the used frequency is lower than

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

The load triggers handover

2C event

the quality in another frequency is higher than anabsolute threshold


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Inter-frequency Hard Handover FlowSignaling f low

UE

1.RADIO LINK SETUP REQUEST

TargetNODEB

SourceNODEB SRNC

2. RADIO LINK SETUP RESPONSE

3.ALCAP established

4. PHYSICAL CHANNEL RECONFIGURATION

5. RADIO LINKFAILURE INDICATION

6. PHYSICAL CHANNEL RECONFIGURATION COMPLETE

7. RADIO LINKDELETION REQUEST

8. RADIO LINKDELETION RESPONSE

9.ALCAP released


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Key Parameters (I)Inter-frequency coverage handover parameters:

Inter-frequency measurement reporting: periodic reporting or eventreporting

Inter-frequency measurement values: CPICH Ec/No or CPICH RSCP

Inter-frequency measurement layer 3 filter coefficient, delay trigger

time and hysteresisInter-frequency initiated and stopped threshold: Considering thedifferent demands of CPICH Ec/No and CPICH RSCP for PS domainand CS domain, the different 2D and 2F parameters are configured.

Inter-frequency handover based on coverage: the quality threshold oftarget cell

Using frequency quality threshold in inter-frequency hard handover

The minimum access threshold for inter-frequency handover


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Key Parameters (II)

Inter-frequency handover parameters caused by

non-coverage ability

Inter-frequency measurement layer 3 filtercoefficient, delay trigger time and hysteresis

Inter-frequency handover based on non-

coverage ability


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The Brief Introduction of Inter-system Hard Handover

Application scenariosWCDMA FDD < >GSM

WCDMA FDD < >WCDMA TDD

WCDMA FDD < >CDMA2000

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


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The Measurement for Inter-system Compressed Mode Initiated

The inter-system measurement (GSM measurement)

Measurement type:

GSM Carrier RSSI

BSIC Identification

BSIC ReconfirmationThe process of measurement: layer 1 filter, layer 3 filter

Measurement reporting

Event reporting

2D Event: initiate GSM measurement 2F Event: stop GSM measurement


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The Inter-system Hard Handover Decision Algorithm

The inter-system hard handover decision

Inter-system handover caused by non-coverage

Event reporting

3C event: The estimated quality value of the other

system is higher than a absolute threshold.


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1. RelocationRequired 2. Prepare

Handover 3. HandoverRequest

4. Handover

Request Ack

12. Iu ReleaseCommand

13. Iu ReleaseComplete 14. Send End

Signal Response

5. PrepareHandover6. Relocation

Command7. DCCH : Handover

from UTRAN Command

8. HandoverDetect

9. Handover Complete

10. HandoverComplete11. SendEnd

UE Node B SRNC CN MSC BSC

Inter-system Handover FlowThe execution of inter-system handover


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Key Parameters (I)Inter-system handover caused by coverage parameters

Inter-system measurement initiated and stopped threshold:Considering the different demands of CPICH Ec/No and CPICHRSCP for PS domain and CS domain, the different 2D and 2Fparameters 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 PSdomain separately

Using inter-system frequency quality handover threshold

Configure the delay trigger time, hysteresis for each event


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Key parameters (II)

Inter-system handover caused by non-coverage parameters

The period of inter-system measurement report

The decision threshold for inter-system handover: configure the

CS, PS, signaling separately

Time delay trigger : configure BSIC with acknowledged and

unacknowledged mode

Inter-frequency measurement layer 3 filter coefficient and

hysteresis

Penalty time


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Questions

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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Summary

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. Italso introduced the application scenarios for

these different handovers

Meanwhile, compressed mode is introduced in

this chapter

Summary


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07 WCDMA Handover Principal ISSUE1.0

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