3 WCDMA Handover

WCDMA Handover Principle and Relevant Parameterswww.huawei.com

Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved.

Foreword

Why mobile systems need handover?It is decided by the characters of mobile system:

The mobility of UE The mobile system is composed by cells which the coverage ability is limited.

Providing the continuous service in mobile system is the basic element in QoS.


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Objectives

Upon completion of this course, you will be able to:Know the basic definitions of Handover The algorithms of handover decision The handover flow The parameters of handover


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Contents1. Introduction of Handover 2. Measurement of Handover 3. The Basic Handovers


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Page4

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 Set Monitored Set Detected set Radio Link (RL) Radio Link Set (RLS)

maximum ratio combination selection combination The soft handover gain CPICH


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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 handover Inter-frequency handover Inter-RAT handover (UMTS GSM/GPRS)

According to the purpose of handover:

Based on Coverage Based on Noncoverage


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The Characters of Different Handover

Comparison between soft handover and hard handover:

ItemThe number of RLs in active set after handover Interruption during handover The frequencies of cells

Soft HandoverSeveral One

Hard Handover

No

Yes

Only happened between Intrafrequency cells

Can be happened in Intrafrequency cells or Inter-frequency cells


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The Characters of Different Handover

Comparison between soft handover and softer handover :

ItemUL combination

Soft HandoverSignal combined in RNC by selective combination

Softer HandoverSignal combined in NodeB by maximum ratio combination

DL combination

Signal combined in UE by maximum ratio combination

Signal combined in UE by maximum ratio combination


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Soft HandoverRNC

NodeB 1

NodeB 2

Cell A

Cell B


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Softer HandoverRNC

NodeB

Cell A Cell B


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Hard HandoverRNC

NodeB 1

NodeB 2

Cell A

Cell B


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Three Steps of HandoverThe following figure shows handover procedure (measurement quality set to PCPICH Ec/No)Measure the CPICH Ec/N0 of the serving cell and its neighboring cells as well as the relative time difference between the cells

Measurement phase

Measurement

Decision

No Are handover criteria satisfied? Decision phase

Execution

Yes

Perform a handover and update relative parameters

Execution phase


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Contents2. Measurement of Handover2.1 Measurement Control and Measurement Report 2.2 Measurement Phase


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Measurement Control

UE

UTRAN

MEASUREMENT CONTROL

Measurement Control, normal case


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Measurement Report

UE

UTRAN

MEASUREMENT REPORT

Measurement Control, normal case


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Contents2. Measurement of Handover2.1 Measurement Control and Measurement Report 2.2 Measurement Phase


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Measurement Modelparameters parameters

A

Layer 1 filtering

B

Layer 3 filtering

C C'

Evaluation of reporting criteria

D

A is measurement value at the physical layer B is the measurement value after layer 1 filtering at physical layer. The value goes from the physical layer to high layer C is measurement after processing in the layer3 filter C is another measurement value D is measurement report information sent on the radio interface or Iub interface


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Measurement Quantity

Ec/No

CPICH signal quality

RSCP

CPICH signal level

RSSI

GSM cell signal level


Page20

Measurement Quantity Configuration

IntraFreqMeasQuantityParameter name: Intra-frequency measure quantity The default value of this parameter is Ec/No

InterFreqMeasQuantityParameter name: Inter-frequency measure quantity The default value of this parameter is Both

MeasQuantityOf3AParameter name: 3A Measure Quantity The default value of this parameter is RSCP


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Layer 3 filteringFn ! (1 a) Fn 1 a M nWhere:

Fn is the new measurement value after filtering. Fn-1 is the last measurement value after filtering. Mn is the latest measurement value from the physical layer. a = 1/2(k/2) (k is set to Intra-freq meas L3 filter coeff)


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Layer 3 filtering coefficient

FilterCoefParameter name: Intra-frequency measurement filter coefficient The default value of this parameter is D3

InterFreqFilterCoefParameter name: Inter-frequency measure filter coefficient The default value of this parameter is D3

InterRATFilterCoefParameter name: Inter-RAT filter coefficient The default value of this parameter is D3


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Measurement Report Mode

Periodic Report Event Trigger Report Event to Periodic Report


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Page25

Contents3. The Basic Handovers3.1 Soft Handover 3.2 Intra-frequency Hard Handover 3.3 Inter-frequency Hard Handover 3.4 Inter-RAT Hard Handover 3.5 Blind Handover


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Page27

Brief Introduction of Soft Handover

Characters of Soft Handover

During handover, UE has several RLs with different cells The handover among different cells which are in same RLS can be softer handover

Signals from each RL will be combined in UL and DL.


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Brief Introduction of Soft Handover

Advantages

Soft handover gain Decrease the possibility of call drop

Disadvantages

More resource needed in downlink it may cause side-effect


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Measurement of Soft Handover

Measurement quantity

CPICH RSCP CPICH Ec/No

Reporting mode

Periodic reporting Event trigger reporting Event trigger reporting to Periodic reporting

Event type

1A,1B,1C,1D


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Soft Handover Measurement EventsEvent 1A Description The PCPICH quality of the cells in the monitored set enters the reporting range . This indicates that the quality of a cell is close to the quality of the best cell . A relative high combined gain can be achieved when the cell is added to the active set 1B The PCPICH quality of the cells in the active set leaves the reporting range. This indicates that quality of a cell is much worse than the quality of the best cell. The cell should not stay in the active set 1C A non-active PCPICH becomes better than an active PCPICH. This indicates that the quality of a cell is close to the quality of the best cell. In addition ,the number of cells in the active set has reached the maximum value. The cell replaces the worst cell in the active set ; thus achieving a higher combined gain 1D Event of the change of the best cell


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The Trigger Algorithm of 1A Event

Event 1A is triggered on the basis of the following formula

10 LogM New CIONew

NA u W 10 Log M i (1 W ) 10 LogM Best ( R1a H 1a / 2), i !1

10 LogM New CIONew

NA W 10 Log M i (1 W ) 10 LogM Best ( R1a H1a / 2), i !1


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Example of 1A Event

A: signal curve of the best cell in the active set B: signal curve of a cell in the monitoring set C: The 1A curve


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Key parameters of 1A Event

INTRARELTHDFOR1ACSParameter name: CS service 1A event relative threshold The default value of this parameter is 6 ( 3dB )

INTRARELTHDFOR1APSParameter name: PS service 1A event relative threshold The default value of this parameter is 6 ( 3dB )


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Key parameters of 1A Event

HYSTFOR1AParameter name: 1A event hysteresis The default value of this parameter is 0( 0dB )

TRIGTIME1AParameter name: 1A event trigger delay time The default value of this parameter is D320 ( 320ms )


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The Trigger Algorithm of 1B Event

Event 1B is triggered on the basis of the following formula

10 LogM Old CIOOld

NA e W 10 Log M i (1 W ) 10 LogM Best ( R1b H 1b / 2), i !1


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Example of 1B Event

A: signal curve of the best cell in the active set B: signal curve of a cell in the monitoring set C: The 1B curve


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Key parameters of 1B Event

INTRARELTHDFOR1BCSParameter name: CS service 1B event relative threshold The default value of this parameter is 12 ( 6dB )

INTRARELTHDFOR1BPSParameter name: PS service 1B event relative threshold The default value of this parameter is 12 ( 6dB )


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HYSTFOR1BParameter name: 1B event hysteresis The default value of this parameter is 0( 0dB )

TRIGTIME1BParameter name: 1B event trigger delay time The default value of this parameter is D640 ( 640ms )


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The Trigger Algorithm of 1C Event

Event 1C is triggered on the basis of the following formula

10 LogM New CIONew u 10 LogM InAS CIOInAS H1c / 2,


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Example of 1C Event

A: signal curve of the best cell in the active set B: signal curve of a cell in the active set C: signal curve of the worst cell in the active set D: signal curve of a cell in the monitoring set E: The 1C curve Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved. Page41

Key parameters of 1C Event

HYSTFOR1CParameter name: 1C event hysteresis The default value of this parameter is 8( 4dB )

TRIGTIME1CParameter name: 1C event trigger delay time The default value of this parameter is D640 ( 640ms )


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The Trigger Algorithm of 1D Event

Event 1D is triggered on the basis of the following formula

10 LogM Notbest u 10 LogM Best H1d / 2,


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Example of 1D Event

A: signal curve of the best cell in the active set B: signal curve of a cell in the active set or monitoring set C: Th1D curve


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Key parameters of 1D Event

HYSTFOR1DParameter name: 1D event hysteresis The default value of this parameter is 8( 4dB )

TRIGTIME1DParameter name: 1D event trigger delay time The default value of this parameter is D640 ( 640ms )


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Other key parameters for SHO

WeightParameter name: Weighted factor The default value of this parameter is 0

SHOQualminParameter name: Min quality THD for SHO The default value of this parameter is -24(-24 dB)

CELLINDIVIDALOFFSETParameter name: Cell offset The default value of this parameter is 0 ( 0dB )


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Brief Introduction of Intra-Frequency Hard Handover

Characters of Intra-Frequency Hard Handover

During handover, UE has only one RL with one cell Switch off the RL with the original cell, then setup the RL with target cell

The frequency of source cell and target cell are same


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Brief Introduction of Intra-Frequency Handover

Advantages

Enhance the usage efficiency of the OVSF code and hardware

Disadvantages

High call drop possibility because of the intra-frequency interference


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Key parameters of Intra-frequency Hard handover

BEBITRATETHDParameter name: BE service handover rate threshold The default value of this parameter is 384k

The Parameters about 1D EventTime to trigger Hysteresis


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Page51

Brief Introduction of Inter-Frequency Handover

Characters of Inter-frequency Hard Handover

The frequency of original cell and source cell are different There is only one RL for the UE The compressed mode is needed


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Compressed Mode

Purpose

Measure the inter-frequency cell or Inter-RAT cell under FDD mode

Categories

Downlink compressed mode Uplink compressed mode

Realization Methods

SF/2 Higher layer scheduling


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Measurement of Inter-frequency Handover

Measurement quantity

CPICH RSCP CPICH Ec/No

Reporting mode

Periodic reporting Event trigger reporting Event trigger reporting to Periodic reporting

Event type

2B,2C,2D,2F


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Inter-frequency Handover Measurement EventsEvent 2D Description When the current signal quality is lower than the preset threshold , the UTRAN enables the compressed mode and starts inter-frequency measurement 2F When the current signal quality is higher than the preset threshold, the UTRAN disables the compressed mode and stops inter-frequency measurement 2B When the current signal is lower than the preset threshold and the signal quality of an inter-frequency neighbouring cell is higher than the preset threshold , the UTRAN trigger an inter-frequency handover based on coverage 2C The estimated quality of a inter-frequency neighbor cell is higher than the preset thresholdCopyright 2006 Huawei Technologies Co., Ltd. All rights reserved. Page55

The Trigger Algorithm of 2D EventEvent 2D is triggered on the basis of the following formula

QUsed e TUsed 2 d H 2 d / 2


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Key parameters of of 2D Event

InterFreqCSThd2DEcN0Parameter name: Inter-freq CS measure start Ec/No THD The default value of this parameter is -14 dB

InterFreqPSThd2DEcN0Parameter name: Inter-freq PS measure start Ec/No THD The default value of this parameter is -14 dB


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Key parameters of of 2D Event

InterFreqCSThd2DRSCPParameter name: Inter-freq CS measure start RSCP THD The default value of this parameter is -95 dBm

InterFreqPSThd2DRSCPParameter name: Inter-freq PS measure start RSCP THD The default value of this parameter is -95 dBm


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Key parameters of 2D Event

HYSTFOR2DParameter name: 2D event hysteresis The default value of this parameter is 4( 2dB )

TRIGTIME2DParameter name: 2D event trigger delay time The default value of this parameter is D320 ( 320ms )


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The Trigger Algorithm of 2F Event

Event 2F is triggered on the basis of the following formula

QUsed u TUsed 2 f H 2 f / 2


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Key parameters of 2F Event

InterFreqCSThd2FEcN0Parameter name: Inter-freq CS measure stop Ec/No THD The default value of this parameter is -12 dB

InterFreqPSThd2FEcN0Parameter name: Inter-freq PS measure stop Ec/No THD The default value of this parameter is -12 dB


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InterFreqCSThd2FRSCPParameter name: Inter-freq CS measure stop RSCP THD The default value of this parameter is -92 dBm

InterFreqPSThd2FRSCPParameter name: Inter-freq PS measure stop RSCP THD The default value of this parameter is -92 dBm


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HYSTFOR2FParameter name: 2F event hysteresis The default value of this parameter is 4( 2dB )

TRIGTIME2FParameter name: 2F event trigger delay time The default value of this parameter is D1280 ( 1280ms )


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The Trigger Algorithm of 2B EventEvent 2B is triggered on the basis of the following formula

QNon used u TNon used 2b H 2b / 2

, and

QUsed e TUsed 2b H 2b / 2


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InterFreqCovHOCSThdEcN0Parameter name: Inter-freq CS target frequency trigger Ec/No THD The default value of this parameter is -12 dB

InterFreqCovHOPSThdEcN0Parameter name: Inter-freq PS target frequency trigger Ec/No THD The default value of this parameter is -12 dB


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InterFreqCovHOCSThdRSCPParameter name: Inter-freq CS target frequency trigger RSCP THD The default value of this parameter is -92 dBm

InterFreqCovHOPSThdRSCPParameter name: Inter-freq PS target frequency trigger RSCP THD The default value of this parameter is -92 dBm


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IFHOUsedFreqCSThdEcN0Parameter name: Inter-freq CS Used frequency trigger Ec/No THD The default value of this parameter is -12dB

IFHOUsedFreqPSThdEcN0Parameter name: Inter-freq PS Used frequency trigger Ec/No THD The default value of this parameter is -12 dB


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IFHOUsedFreqCSThdRSCPParameter name: Inter-freq CS Used frequency trigger RSCP THD The default value of this parameter is -92dBm

IFHOUsedFreqPSThdRSCPParameter name: Inter-freq PS Used frequency trigger RSCP THD The default value of this parameter is -92 dBm


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HYSTFOR2BParameter name: 2B event hysteresis The default value of this parameter is 4( 2dB )

TRIGTIME2BParameter name: 2B event trigger delay time The default value of this parameter is D0 ( 0ms )


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The Trigger Algorithm of 2C EventEvent 2C is triggered on the basis of the following formula

QNon used u TNon used 2c H 2c / 2


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Key parameters of 2C Event

InterFreqNCovHOThdEcN0Parameter name: Inter-freq CS target frequency trigger Ec/No THD The default value of this parameter is -16 dB

Hystfor2CParameter name: 2C hysteresis The default value of this parameter is 6 (3dB)

TrigTime2CParameter name: 2C event trigger delay time The default value of this parameter is D640 (640ms)


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Page72

Brief Introduction of Inter-RAT Handover

Characters of Inter-RAT HandoverBased on handover directions, inter-RAT handover is of two types:

UMTS->GSM handover UMTS->GSM coverage-based handover UMTS->GSM load-based handover UMTS->GSM service-based handover

GSM->UMTS handover


Page73

Brief Introduction of Inter-RAT Handover

AdvantagesFor 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)

DisadvantagesThe flow is complicated, and it demands higher compatibility for equipments Demands more complicated UE


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Measurement of Inter-RAT Handover

Measurement quantityCPICH_Ec/N0 CPICH_RSCP BOTH

Reporting modePERIODICAL_REPORTING EVENT_TRIGGER

Event type2D, 2F 3A, 3C


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Inter-RAT Handover Measurement EventsEvent 2D Description When the signal quality of the currently used frequency is lower than the preset threshold, the RNC enables the compressed mode and starts inter-RAT measurement. 2F When the signal quality of the currently used frequency is higher than the preset threshold, the RNC disables the compressed mode and stops inter-RAT measurement. 3A When the signal quality of the currently used UMTS frequency is lower than the preset threshold while the signal quality of any other system is higher than the preset threshold, the RNC triggers UMTS->GSM handover based on coverage. 3C When the signal quality of any other system is higher than the preset threshold, the RNC triggers UMTS->GSM handover based on load or service.


Page76

The Trigger Algorithm of 2D Event

Event 2D is triggered on the basis of the following formula:

Q Used e TUsed2d - H 2d / 2


Page77

Key Parameters of 2D Event

INTERRATCSTHD2DECNOParameter name: Inter-RAT CS measure start Ec/No THD The default value of this parameter is -14 ( -14 dB )

INTERRATPSTHD2DECNOParameter name: Inter-RAT PS measure start Ec/No THD The default value of this parameter is -15 ( -15 dB )


Page78


INTERRATCSTHD2DRSCPParameter name: Inter-RAT CS measure start RSCP THD The default value of this parameter is -100 ( -100 dBm )

INTERRATPSTHD2DRSCPParameter name: Inter-RAT PS measure start RSCP THD The default value of this parameter is -110 (-110 dBm )


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HYSTFOR2DParameter name: 2D hysteresis The default value of this parameter is 4 ( 2 dB )

TRIGTIME2DParameter name: 2D event trigger delay time The default value of this parameter is D320 (320 ms )


Page80


Event 2F is triggered on the basis of the following formula:

Q Used u TUsed2f H 2f / 2


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Key Parameters of 2F Event

INTERRATCSTHD2FECNOParameter name: Inter-RAT CS measure stop Ec/No THD The default value of this parameter is -12 ( -12 dB )

INTERRATPSTHD2FECNOParameter name: Inter-RAT PS measure stop Ec/No THD The default value of this parameter is -13 ( -13 dB )


Page82


INTERRATCSTHD2FRSCPParameter name: Inter-RAT CS measure stop RSCP THD The default value of this parameter is -97 ( -97 dBm )

INTERRATPSTHD2FRSCPParameter name: Inter-RAT PS measure stop RSCP THD The default value of this parameter is -107 (-107 dBm )


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HYSTFOR2FParameter name: 2F hysteresis The default value of this parameter is 4 ( 2 dB )

TRIGTIME2FParameter name: 2F event trigger delay time The default value of this parameter is D1280 (1280 ms )


Page84

The Trigger Algorithm of 3A Event

Event 3A is triggered on the basis of the following formula:

Q Used e TUsed3a H 3a / 2M OtherRat CIOOtherRat u TOtherRat H 3a / 2


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Key Parameters of 3A Event

IRHOUSEDFREQCSTHDECNOParameter name: Inter-RAT CS Used frequency trigger Ec/No THD The default value of this parameter is -12 ( -12 dB )

IRHOUSEDFREQPSTHDECNOParameter name: Inter-RAT PS Used frequency trigger Ec/No THD The default value of this parameter is -13 ( -13 dB )


Page86


IRHOUSEDFREQCSTHDRSCPParameter name: Inter-RAT CS Used frequency trigger RSCP THD The default value of this parameter is -97 ( -97 dBm )

IRHOUSEDFREQPSTHDRSCPParameter name: Inter-RAT PS Used frequency trigger RSCP THD The default value of this parameter is -107 (-107 dBm )


Page87


INTERRATCOVHOCSTHDParameter name: Inter-RAT CS handover decision THD The default value of this parameter is 16 ( -95 dBm )

INTERRATCOVHOPSTHDParameter name: Inter-RAT PS handover decision THD The default value of this parameter is 16 ( -95 dBm )


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HYSTFOR3AParameter name: 3A hysteresis The default value of this parameter is 4 ( 2 dB )

TRIGTIME3AParameter name: 3A event trigger delay time The default value of this parameter is D0 ( 0 ms )


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CELLINDIVIDALOFFSETParameter name: Cell individual offset The default value of this parameter is 0 ( 0 dB )


Page90

The Trigger Algorithm of 3C Event

Event 3C is triggered on the basis of the following formula:

M OtherRat CIOOtherRat u TOtherRat H 3c / 2


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Key Parameters of 3C Event

INTERRATNCOVHOCSTHDParameter name: Inter-RAT CS handover decision THD The default value of this parameter is 21 ( -90 dBm )

INTERRATNCOVHOPSTHDParameter name: Inter-RAT PS handover decision THD The default value of this parameter is 21 (-90 dBm )


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HYSTFOR3CParameter name: 3C hysteresis The default value of this parameter is 0 ( 0 dB )

TRIGTIME3CParameter name: 3C event trigger delay time The default value of this parameter is D640 ( 650 ms )


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PENALTYTIMEFORINTERRATHOParameter name: Inter-RAT handover failure penalty timer length The default value of this parameter is 30 ( 30 s )

INTERRATHOATTEMPTSParameter name: Inter-RAT handover max attempt times The default value of this parameter is 16


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INTERRATMEASTIMEParameter name: Inter-RAT measure timer length [s] The default value of this parameter is 60 ( 60 s )


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Page96

Blind Handover Measurement

Blind handover means UE can directly handover to the neighboring cell without measuring it.


Page97


10 LogM Old e T1 f H 1 f / 2

Where:MOld is the measurement value of the cell signal that becomes worse T1f is the absolute threshold of event 1F. H1f is the hysteresis value of event 1F.


Page98

The Trigger Algorithm of 1F EventMeasurement Quantity

Cell 11F Trigger Delay Time Absolute Threshold T1f Hysteresis H1f /2

TimeReporting event 1F


Page99

Key Parameters of Event 1F

INTRAABLTHDFOR1FECNOParameter name: 1F event absolute EcNo threshold The recommended value is -24 dB

INTRAABLTHDFOR1FRSCPParameter name: 1F event absolute RSCP threshold The recommended value is -115 dBm


Page100

Key Parameters of Event 1F

HYSTFOR1FParameter name: 1F hysteresis The recommended value is 8, namely 4 dB

TRIGTIME1FParameter name: 1F event trigger delay time The recommended value is D640, namely 640 ms


Page101

Blind Handover Decision

After receiving event 1F of best cell from UE, the RNC would check if blind handover neighbor is configured for the cell.

If multiple blind handover neighbors are configured, the RNC would perform blind handover to the target cell with the highest priority


Page102

Key Parameters of Blind Handover

BLINDHOFLAGParameter name: Blind handover flag The default value is FALSE

BLINDHOPRIOParameter name: Blind handover Priority The value is set according to actual situation.


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3 WCDMA Handover