04_u-lii 302 principles of handover in wcdma-20080917-a-1.0_level 2

8/12/2019 04_U-LII 302 Principles of Handover in WCDMA-20080917-A-1.0_level 2

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HUAWEI TECHNOLOGIES CO., LTD.

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www.huawei.com

Huawei Confidential

WCDMA HandoverPrinciple



HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 1

Why mobile systems need handover?

Mobile systems are composed by cellswhich the coverage is limited.

The mobility of the UE.

Providing the continuous service - thebasic element in QoS.




TS25.331 Flow of Handover andRelated Parameters

TS25.133 Measurement Process

TS25.215 Definitions of MeasurementIndexes




After studying this course, you will:

Understand basic concepts abouthandover

Understand the flow of soft handover

Master basic parameters about softhandover

Master soft handover decision algorithms




Chapter 1 Overview of Handover

Chapter 2 Handover MeasurementChapter 3 Soft Handover

Chapter 4 Hard Handover





1.1 Purposes of Handover

1.2 Modes and Status of the UE

1.3 Methods and Types ofHandover

1.4 Comparison between SoftHandover and Hard Handover




Purposes of Handover

Providing the continuous service in mobile system is the basicelement in QoS

Providing continuous communication service is the main purposeof handover.

The load balance: sharing the resourceThe hierarchy divided by speed and service: high efficiency ofusing resource







1.3 Methods and Types ofHandover





CELL_DCH CELL_FACH

CELL_PCHURA_PCH

IDLEDEAD R RC c o n n e c t io n

UE Modes and Status




CELL_DCH CELL_FACH

CELL_PCHURA_PCH

IDLE

DEAD

- Searching a PLMN- Find a cell to camps on

- Monitering the paging channel- Cell reselecting

- Dedicated channel - Common channel,low speed service

- Triggered by theCN

- Reducing activities, DRX, saving power and resource

R RC c o n n e c t io n

These statuses are only appliedin the UTRAN and UE. Theyare transparent to the CN.

UE Modes and Status (Status migration)

SMSVP/Voice/PS

Low speed PS

Cell Update No trafficAfter several CellUpdates

URA Update







1.3 Methods and Types of Handover

1.4 Comparison between Soft

Handover and Hard Handover




Handover Methods

Changing cells in the status of CELL_DCHHandover

Direct retry

Changing residing cells in the statuses of IDLE, CELL_FACH,CELL_PCH, and URA_PCH

Cell reselection (forward handover)




Handover Types in CELL_DCH

Classify bySystem Change

Classify bySignaling Flow

Classify byFrequency

ChangeDescription

Intra- system

Soft handover

Intra-frequency

Low-rate services (such as AMR

Hard handover

High-rate services (such asPS384K)

Without the Iur interface

Inter-frequency

For the purpose of coverage orload balancing (e.g. handoverbetween carriers with differentload, handover to the carrier thatsupports the HSDPA service.

WCDMA-to-GSM handover)

Inter-system(Inter-RAT)







1.3 Methods and Types of Handover





Features Comparison between Soft Handoverand Hard Handover

Item Soft Handover (Softer Handover) Hard HandoverNumber of radio links in

the activate set Several One

Interruption duringhandover No Yes

Frequencies in the cellsbefore and after

handoverIntra-frequency

Intra-frequency

Inter-frequency orInter-RAT

Handover gainMaximum-ratio combining or selectivecombining which can reduce the impact offading and transmission power of the UE.

None

Disadvantage

Occupies more resources.

Problems occur when the power of softhandover cells is unbalanced.

Call drop ratio isrelatively higher

In a word, some resources are wasted to obtain optimal system performance in soft handover.




Soft Handover – (Connection before Disconnection)

RNCNodeB1 NodeB2




Softer Handover – (A Special Case of Soft Handover)

RNCNode B

Cell A Cell B




Hard Handover- (Disconnection before Connection)

RNCNodeB1 NodeB2




Questions

What are the differences between softhandover, softer handover, and hardhandover?

Why intra-frequency handover is notalways soft handover?

How does handover gain arise? Howmuch are various handover gains?




Summary

This chapter describes the purposes ofhandover, working modes of the UE andcommon handover types in the WCDMAsystem, compares soft handover and hardhandover and describes respectiveadvantages and disadvantages.

In addition, this chapter describes a briefflow of each type of handover.





Chapter 2 Handover Measurement

Chapter 3 Soft Handover





2.1 Basic Concepts aboutHandover

2.2 Three Steps of Handover

2.3 Measurement Control

2.4 Measurement Report




Basic Concepts about Handover

Active set

monitor set

Detection set

Event report

Event to periodic report

Periodic report

Radio link (RL)

Radio link set (RLS)

Maximum-ratio combining

Selective combining

Soft handover gain

Pilot channel (CPICH)





2.1 Basic Concepts about Handover







Three Steps of Handover

Decision

Execution

Measurement

The following figure shows handoverprocedure (measurement quality setto PCPICH Ec/No)

UE measures the CPICH Ec/Noof its serving cell(s) andneighbor cells. And sends themeasurement report to RNC.

Are handover criteria meet?

Perform a handoverand update relativeparameters

Measure

Decision

Execution

Y

N





2.1 Basic Concepts about Handover







Measurement Control

Measurement control is used to notify the UE of the object to bemeasured, neighbor cell list, report method, and event parameters.

When measurement conditions are changed, the RNC notifies theUE of new conditions.

Measurement Control, normal case

UE UTRAN

Measurement Control




Measurement ControlMeasurement Control

The RNC sends a

measurement control message

according to the best cell in the

active set.

− Measurement identity

− Measurement command

− Measurement type

− Measurement object

− Criteria of measurement report

− Measurement report mode




Measurement Objects

Measurement objects

Intra-frequency measurement

− CPICH RSCP, CPICH Ec/Io, or Pathloss (normally Ec/Io)

Inter-frequency measurement

− CPICH RSCP, CPICH Ec/Io

Inter-RAT measurement

− GSM Carrier RSSI, BSIC Identification, and BSIC Reconfirmation




Measurement Model

Measurement time of layer 1 is 200 ms. The vendorcan decide the filtering method.

Filtering parameters of layer 3 can be configured.Measurement results are reported when the reportingcriteria are met.

Layer 1filtering

Layer 3filtering Evaluation

of reportingcriteria

A DB C

C'

parameters parameters




Measurement Model - Layer 3 Filtering

Filtering of measurement results by the UE is calculated according to

the following formula:

Fn (1- α)F n-1 +αM n

Fn: new measurement result after filtering

Fn-1 : the last measurement result after filtering

Mn: the latest measurement result from the physical layer of the UE

α 0.5 k/2 , K is the parameter in filter coefficient in the measurementcontrol message (default=3 ). If it is set to 0 , layer 3 filtering isunavailable.





2.1 Basic Concepts aboutHandover

2.2 Three Steps in Handover






Measurement Report

When the measurement reporting criteria are met, the UEreports the results to the RNC as an event.

Measurement Report

UE UTRAN

Measurement Report




Measurement Report Methods

Event reportThe measurement report is sent when the reporting criteria are met.

Periodic report (event to periodic report)

If the RNC does not respond after several events are reported, theUE switches to periodic report.

The interval between report and total report times are controlledthrough parameters.




Intra-frequency Measurement Events

Intra-frequency measurement events are identified

through 1X. They include:1A: A primary pilot channel enters the reporting range. Means a monitoredcell is good enough that the UE can add it into active set .

1B A primary pilot channel leaves the reporting range. Means a cell in the

active set is not good enough according to the best cell .1C: Substitution event. A primary pilot channel in an monitor set is better thanthat in the active set.

1D: Event of changing the best serving cell.

1F: Event that measurement results of the cells in the active set are lowerthan the absolute threshold.




Inter-frequency Measurement Events

Inter-frequency measurement events are identified by 2X.

2B event: The quality of the serving cell is lower than an absolutethreshold value and the quality of another inter-frequency neighbor cell ishigher than another threshold value.

2C event: The quality of the inter-frequency neighbor cell is higher thanan absolute threshold value.

2D event: The quality of the serving cell is lower than a certain absolutethreshold value. It is used to start the compress mode.

2F event: The quality of the serving cell is higher than a certain absolutethreshold value. It is used to stop the compress mode.




Inter-RAT Measurement Events

Inter-RAT Measurement events are identified through 3X.

3A event: The quality of the currently used frequency is lower than anabsolute threshold value, but the quality in a GSM cell is higher thananother absolute threshold value.

3C event: The quality in a GSM cell is higher than an absolute threshold

value.2D event: The quality of the currently used frequency is lower than acertain absolute threshold value. It is used to start the compressed mode.

2F event: The quality of the currently used frequency is higher than acertain absolute threshold value. It is used to stop the compressed mode.




Some Event Report Control Parameters

Relative threshold (reporting range)

Unidirectional difference between two measurement results, for example,relative threshold value between 1A event and 1B event

Absolute threshold (threshold)

Measurement results reach an absolute value, for example, absolute

threshold values of 1E event and 1F eventHysteresis

Bi-directional difference between two measurement results

Time to trigger

Time that lasts until the previous threshold value is met

Weight factor (W)

Control calculation of comparative benchmark values




Event Report Decision

Deciding according to the judgment inequation

Example: decision inequation of 1A event

If W = 0, for RSCP and Ec/Io,

10LogM(New)≥10LogM(Best) - (R1a-H1a/2)

M: measurement results

R: relative threshold values

H: hysteresis

W: weight factor. It is zero generally .

),2/(10)1(1010 11

a Best

N

ii New H R LogM W M Log W LogM

A

2. Other measurement variables (e.g. RSCP, Ec/Io)

),2/(10)1(1010 11

a Best

N

ii New H R LogM W M Log W LogM

A

1. Path loss




Event Report Decision- Example of 1A Event Measurement Report

Measurement results in the primary cell

1A event occurs




Event Report Decision (Continued)

Trigger criteria of 1B event:

)2/(10)1(1010 111

bb Best

N

iinew H R LogM W M Log W LogM

A

,2/11 f f New H T M Trigger criteria of 1F event:

,2/1d Best NotBest H M M Trigger criteria of 1D event:

,2/1c InAS New H M M Trigger criteria of 1C event:

E R D i i




Event Report Decision- Example of 1B Event Measurement Report

1B event is reported

Delete the cell in which the interference code is 23

Event Report




Event Report

Event Report




Event Report

E ent Report




Event Report




Questions

In which cases does the RNC triggermeasurement control?

Is the start time of intra-frequency,inter-frequency, and Inter-RATmeasurement the same?

When is an event reported?How to report an event?

What events does intra-frequencymeasurement contain?

What events does inter-frequencymeasurement contain?




Summary

This chapter describes concepts related tohandover, explains measurement control, which

covers measurement objects, event report.





3.1 Flow of Soft Handover

3.2 Common Parameters and IntraFrequency Neighbor Cell

Fl f S ft H d Addi R di Li k




Flow of Soft Handover - Adding Radio Link

(Reporting 1A event )

( Add new radio link )




Flow of Soft Handover - Adding Radio Link




Flow of Soft Handover - Deleting Radio Link

(Reporting 1B event )

(Del old radio link )




Chapter 3 Flow of Soft Handover

3.1 Flow of Soft Handover

3.2 Common Parameters and IntraFrequency Neighbor Cell

Setting Common Parameters of Soft Handover




Setting Common Parameters of Soft HandoverRelative threshold

1A and 1B event have their individual values.

The value of 1B should be larger than that of 1A, to avoid ping-ponghandover. ( 1A < 1B )

− Default setting: 1A: 3 dB; 1B: 6 dB

Hysteresis

Configure it for each event separately.Usually the threshold values of 1A event and 1B event are 0 dB and thoseof 1C, 1D, 1F are 4 dB.

This value affects the soft handover area of the UE.

MML command for adding cell-class intra-frequency handoverparameters: ADD CELL INTRA FREQ HOMML Command for setting RNC-class intra-frequency handoverparameters: SET INTRA FREQ HO

C P f S f H d (C i d)




Common Parameters of Soft Handover (Continued)

Time to trigger

Configured it for each event separately.

The value of 1B should be larger than that of 1A, to avoid ping-ponghandover. ( 1A < 1B )

− Default setting: 1A: 320 ms; 1B: 640 ms; 1C, 1D: 640 ms

Lay 3 filtering coefficient

It is shared by all types of intra-frequency measurement.

This parameter is sensitive to the delay of event triggering and ping-pong handover.

It is usually set to 3.




Intra Frequency Neighbor Cell

The Handover can only happened among the neighbor cells

MML: Add Intra Freq NCell:

Configure neighbor cells with the same frequency

The maxim number of IntraFreqNCell for each cell is 31




Questions

Draw the signaling flow chart of softhandover.

What is the impact of parameters in softhandover on system performance?

What parameters can affectperformance of soft handover besidesthe parameters described in thischapter?




Summary

This chapter describes the signalingflow and common parameters of softhandover in WCDMA.

O h H d




Other Handovers

The WCDMA system supports many handover technologies.

Besides soft (softer) handover described previously, there areintra-frequency hard handover, inter-frequency hard handover,and Inter-RAT handover.

If the system supports HSDPA, the WCDMA system alsosupports handover between carrier frequency of HSDPA andordinary carrier frequency to balance load and to utilize networkresources efficiently.

Refer to supplementary contents for description of intra-frequency hard handover, inter-frequency hard handover, andInter-RAT handover. This part is provided for self-study.

C S




CourseSummary

Course Summary

This course describers the principles,

algorithm, related parameters andgeneral flow of soft handover in theWCDMA system.



Thank youwww.huawei.com





4.1 Intra-frequency Hard Handover

4.2 Inter-frequency Hard Handover

4.3 Inter-RAT Hard Handover

Intra-frequency Hard Handover




Intra-frequency Hard Handover- Measurement and Event

Measurement

It is similar to that in soft handover

Related events

1D event

Intra frequency Hard Handover




Intra-frequency Hard Handover- Handover Flow

TARGET NODEB SOARCE NODEB

3. ALCAP ESTABLISHMENT

9. ALCAP RELEASE

Intra-frequency Hard Handover




q y- Common Parameters

BeBitrateThd: BE service handover rate decision threshold.

If the maximum rate of transmission channel of the BE service is not morethan this threshold, the system performs soft handover for the users usingthis service.

If the maximum rate of transmission channel of the BE service is greaterthan this threshold, the system performs intra-frequency hard handover for

the users using this service.MML: SET HOCOMM

Parameters related to the 1D event

Time to trigger (640ms), hysteresis (4dB)

The parameters should be appropriate so the system can not only trackchanges of the signal to perform handover, but also avoid ping-ponghandover.








Inter frequency Hard Handover Overview




Inter-frequency Hard Handover Overview

Features

The frequency is different after handover.

For the UE with only one transceiver, the compressed mode should bestarted to assist measurement.

Advantages

The handover success rate is higher than that of intra-frequency hardhandover.

The load on carrier frequencies are balanced.

Inter-frequency Hard Handover Overview




Inter frequency Hard Handover Overview(Continued)

DisadvantagesThe compressed mode causes extra radio resource

Application scenarios

Uncontinuous coverage of carrier

Load caused handover

Hierarchical cell

Inter-frequency Hard Handover




Inter frequency Hard Handover- Measurement and Event

Measurement in inter-frequency hard handoverMeasurement variables:

− CPICH RSCP, CPICH Ec/N0

Different measurement types are used for different handover purposes:

− Edge of carrier coverage area: CPICH RSCP

− Center of carrier coverage area: CPICH Ec/No





- Measurement and Event (Continued)

Measurement Report Methods

Event report− 2D event: The quality of current frequency is lower than a certain absolute

threshold value. It is used to start the compressed mode.

− 2F event: The quality of current frequency is higher than a certain absolutethreshold value. It is used to stop the compressed mode.

− 2B event: The quality of current frequency is lower than the absolutethreshold value, and the quality of the neighbor frequency is higher thananother absolute threshold value. It is used in coverage handover trigger.

− 2C event: The quality of the neighbor frequency is higher than a certain

absolute threshold value. It is used in load handover trigger.

Periodic report





- Starting and Stopping of the Compression ModeStarting conditions of measurement

2D event: If the quality of the currently frequency is lower than a certainabsolute threshold value, the compressed mode is started.

Use the velocity estimation algorithm to decide starting of inter-frequencyhandover measurement.

Stopping conditions of measurement2F event

After the best cell is changed, the new best cell does not have any inter-frequency neighbor cell.

The timer of inter-frequency measurement expires.

The speed estimate status of the UE changes, and related inter-frequencyhandover measurement is disabled according to the hierarchical cell algorithm

In hard handover, if the coverage reason is triggered, handover is stoppedsimultaneously.

Inter frequency Hard Handover Flow




Inter-frequency Hard Handover Flow

Signaling flow

9. ALCAP RELEASE

3. ALCAP ESTABLISHMENT

SOARCE NODEBTARGET NODEB





- Common ParametersInter-frequency coverage handover parameters:

Methods for report inter-frequency measurement: periodic or eventInter-frequency measurement variables: CPICH Ec/No or CPICH RSCP.

Inter-frequency measurement layer 3 filtering coefficient, time to trigger,and hysteresis

Starting and stopping threshold values of inter-frequency measurement:Configure it respectively for CPICH Ec/No, CPICH RSCP, and configure2D, 2F event for CS and PS.

Inter-frequency coverage handover threshold value: quality threshold valueof the target cell

Quality threshold value of used frequency in inter-frequency hard handoverLowest access threshold value in inter-frequency handover

Inter-frequency Hard Handover - Questions




q yWhy the compressed mode threshold for the CS and PS areconfigured different?

The Eb/No required by these two services are different, so theRSCPs are also different.

If the UE uses the CS service and PS service at the same time,the 2D and 2F parameters of which service are used to decidestarting the compressed mode?

If the parameters of any service meet the threshold, thecompressed mode is started.

Is the compressed mode started immediately after the UE sendsthe 2D parameter?

The compressed mode is started after the RNC reconfigure the RB.




Inter-RAT Hard Handover

Overview

Measurement and Event

Handover Decision Algorithm

Handover Flow

Common Parameters

Inter-RAT Hard Handover - Overview




CategoryWCDMA FDD < >GSMWCDMA FDD < >WCDMA TDDWCDMA FDD < >CDMA2000

FeaturesThe radio access technology (RAT) adopted in the system after handoveris different.

Need compressed mode to assist measurement. Advantages

Coverage: Solve the problem of transition between different systems.Capacity: Improve the utilization of old equipments to the greatest extent(2G->3G)

DisadvantagesThe flow is complicated, and the requirement for compatibility ofequipment is high.The UE is complicated.





- Measurement and Event

Measurement in Inter-RAT hard handover (GSM measurement)Measurement types:

− GSM Carrier RSSI

− BSIC Identification

− BSIC Reconfirmation

Measurement processing: layer-1 filtering, layer-3 filtering





- Measurement and Event (Continued)

Measurement Report− Event report

▪ 2D event: starting GSM measurement

▪ 2F event: stopping GSM measurement

▪ 3A event: The quality of WCDMA is lower than an absolute threshold butquality of a GSM neighbor cell is higher than another absolute threshold.

▪ 3C event: The quality of a GSM neighbor cell is higher than an absolutethreshold.

Inter-RAT Hard Handover - Decision Algorithm




Inter RAT Hard Handover Decision Algorithm

Decision of Inter-RAT handover

Inter-RAT handover based on coverage

− Event

▪ 3A event: The quality of the currently used frequency is lowerthan an absolute threshold value, but quality of a GSM cell is

higher than another absolute threshold value.

− Periodic

▪ Evaluation: Confirm the status according to the GSM RSSImeasurement value and the BSIC of the target cell in GSM andevaluate the cell of which the GSM RSSI exceeds the absolutethreshold value. If both conditions are met, consider the cell ofwhich the BSIC is confirmed.





- Decision Algorithm (Continued)

Inter-RAT handover based on non-coverage

− Event

▪ The 3C event means that the quality of the GSM cell is

higher than an absolute threshold value .

Inter-RAT Handover Flow




1. RelocationRequired 2. Prepare

Handover 3. HandoverRequest

4. HandoverRequest 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. Send

End

UE Node B SRNC CN MSC BSC

Inter-RAT Handover - Common Parameters




Inter-RAT coverage handover parameters

Starting and stopping thresholds of Inter-RAT measurement: They

determine the thresholds of the 2D event and 2F event. Configure CPICHEc/No, CPICH RSCP for the CS service and PS service respectively.

Measurement variables for the 2D event and 2F event in Inter-RAThandover: Select CPICH Ec/No or PICH RSCP.

BSIC selection confirmation switch

Inter-RAT coverage handover threshold: GSM RSSI threshold in Inter-RATcoverage handover. Configure it for the CS service and PS servicerespectively.

Quality threshold of used frequency in Inter-RAT handover

Configure time to trigger and hysteresis for each event respectivelyPenalty duration

f



Summary - 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 handover

− Inter-frequency handover

− Inter- RAT handover (UMTS ↔ GSM/GPRS)

According to the purpose of handover:

− Based on Coverage

− Based on Noncoverage

04_u-lii 302 principles of handover in wcdma-20080917-a-1.0_level 2

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