4 wcdma key technologies 42

WCDMA Key Technologies

ZTE University

TD&W&PCS BSS Course Team

Course Objectives

At the end of this course, you will be able to:

Master key technologies of WCDMA

Master characteristic of WCDMA system

capacity

Power Control

Handover

Rake receiver

Call Admission Control & traffic control

Capacity of WCDMA system

Content

Why Power Control?

All CDMA users occupy the same frequency at the same time! Frequency and time are not used as discriminators.

CDMA operates by using CODES to discriminate between users.

CDMA interference comes mainly from nearby users

Each user is a small voice in a roaring crowd -- but with a uniquely recoverable code.

Transmit power on all users must be tightly controlled so their signals

reach the base station at the same signal level and at the absolute

minimum power level necessary to ensure acceptable service quality.

Power Control

Overpowered by strong signalsBlock the whole cell

Power

f

Near-Far Effect

Power Control

Power control

Power

f

Power

f

Nearby terminals have higher probability of success

Power control tech reduce the interference among each UEs and increase system capacity

Power Control

Power Control

Overcome Near-Far effect and fading compensationReducing multi-address interference, ensuing network capacity

Prolonging the working time of cell

DL power control

Cell transmitting power

Transmitting power control bit

UE signal

Power control order

UL power control

Power Control

Three methods of power control

Open loop:

measure received signal level and adjust transmitting power

Inner-loop (closed loop):

Frequency:1500HZ

Measured SIR> Target SIR, lower transmitting power

Measured SIR< Target SIR, increase transmitting power

Outer-loop (closed loop):

Measure BLER, adjust target SIR

Power Control

Power control

UE

RNC

Node B

Open loop power control（ no feedback）

Closed loop power control（ feedback）

UE Node B

RNCOuter-loop

Inner-loop

Power Control

Open loop power control

If received signal is stronger,then UE can speak softer

NodeB

NodeB

1

2

1

2

problem ：Unbalanced for UL/DL signal, not accurate, only used in initial

stage

Open loop

If received signal is weaker,then UE can speak louder

Power Control

Closed loop power control

Inner-loop power control is fastInner-loop ： according to SIR estimation,Node-B control UE transmission power.conducted every 0.66ms (1500Hz )

Outer-loop： according to BLER measurement estimation RNC control and adjust SIR target

Node B

...

”Power down”

Power up command

”Power ...”SIR estimation

SIR estimationRNCSIR target ”Power up”

TPC:1500HzBLER tar SIR tar

Power down command

Power Control

Closed loop power control

Inner Loop Power control UL/DL (fast)

UE or Node-B will use:

Signaling channel, TPC,

Continuously @ rate 1500 times/s,

To relatively changes (up or down) the power to reach the

SIR target.

Outer loop Power control (Slow)

If the BLER measured is below/above the target,

UE/RNC increase/reduce SIR target.

Use the new target for the Inner loop PC.

Power Control

The Effect of Power Control

The purpose of DL power control:

Saving power resource of NodeB, reducing interference to other N

odeB.

The purpose of UL power control:

Overcoming Near-Far effect, save power of UE

WCDMA system capacity

depend on power control

Power Control

Power Control

Handover

Rake receiver



Content

Handover

Handover refers to the process in which when a UE

moves from one Node B to another during calling.

Purpose:

Keep service continuity.

In the WCDMA system, handover is divided into soft

handover and hard handover.

Handover

Type of handover

Intra-RNC, inter-Node B Inter-RNC

Soft handover ：

Same Node B, Inter- sector

Softer handover ：

Intra-frequency handover Inter-frequency handover Inter-system (3G&2G) Inter-mode (FDD&TDD)

Hard handover ：

WCDMA system support

multi handover technology

Handover

Hand-over

Hard Handover

Soft Handover

Handover

Soft/Softer Hand-over

A

B

C

A

B

C

A

B

C

A

B

C

A

B

C

A

B

C

Handover

Soft/Softer Handover

The soft/softer handover allows to swap from one cell to

another without call interruption or without deleting all old radio

links (by opposition to hard HO).

It also allows the UE to be connected to more than one cell

simultaneously and take benefit from macro-diversity.

Soft Handover Softer Handover

CN CN

Iur

The two Node Bs may belong to the

same RNC

The two Node Bs may belong to the Same RNC


SRNC DRNC

CN

Node B

SRNC

CN


Node B

CN

Handover

Hard Handover

The hard handover procedure is used in case of

service quality degradation or for traffic

distribution management.

During the hard handover procedure, all the old

radio links with the UE are abandoned before

new ones are established.

Hard handover may occur in the following

main cases :

When the UE is handed over another UTRAN

carrier, or another technology mode.

When soft handover is not permitted (if O&M

constraint)

Hard Handover

Node B

SRNCRNC or BSC

CN

Node B or BTS

Handover

Basic concepts

Active Set:

The set of cells connected with UE;

User information is transmitted from these cells.

Monitor Set:

The set of cells not within the active set but being

monitored by a UE according to the adjacent node list

allocated by UTRAN.

Detect Set:

The set of cells in neither the active set nor the monitor set.

Handover

Soft handover process

Measurement The RNC sends a measurement control message to UE. UE should perform measurement as required and report the measurement

result. Generally, the measured quantity is the common pilot’s Ec/No.

Decision The RNC stores data of different cells according to the measurement result

s. The RNC makes preliminary decision according to the event decision meth

od.

e.g. When the event is reported and the target cell is acceptable, send an activ

e set update command to add/delete the cell into/from the active set.

Execution The RNC sends an active set update command to UE and UE starts hando

ver.

Handover

Soft handover event

Event Description

1AQuality of target cell improves, entering a report range of relatively activating set quality

1BQuality of target cell decreases, depart from a report range of relatively activating set quality

1CThe quality of a non-activated set cell is better than that of a certain activated set cell

1D Best cell generates change

1EQuality of target cell improves, better than an absolute threshold

1FQuality of target cell decreases, worse than an absolute threshold

Handover

Example of soft handover

UE Target Node B Source Node B RNC

RRC: Measurement Report(Event 1a) (From Source Node B to RNC)

NBAP: Radio Link Setup Request

NBAP: Radio Link Setup Response

Executing handoverjudgement andadding a radio linkin Target Node B

Start to receive

Distributing transmission resources on Iub interface

Start to send

RRC: Active Set Update(E1a) (From Source Node B to UE)

RRC: Active Set Update Complete (From Source & Target Node B to RNC

simutaneously)

UE connects to Source Node B and Target Node B simutaneously

Power Control

Handover

Rake receiver



Content

RAKE Receiving

d1 d2

t t t

d3

transmitti

ng

Receivin

gRake

combinationnoise

Rake receiver

Multi-finger receiver

receivertransmitter

coding decodingDirect signal

Reflect signal

Dispersive time < 1 chip length

Multi-finger receiver can’t supply multi-finger diversity

decodingDirect signal

Reflect signaltransmitter receiver

Dispersive time > 1 chip length

Multi-finger receiver can supply multi-finger diversity,improve signal gain

coding

Rake receiver

RAKE Receiving

RAKE overcome multi-finger interference， improve receive capability

receiverreceiver

Single receiving

Single receiving

Single receiving

searcher calculatecalculate

combining

tt

s(t) s(t)

signal

Rake receiver

Multi-finger receiver

Maximal ratio combining(MRC)

at each time delay phase shifting by adding

Finger 1

Finger 2

Finger 3

Rake receiver

Power Control

Handover

Rake receiver



Content

Call Admission Control

When user initiates a call, RRM decides weather access

or deny this call according to the resource situation.

When accessing, network allocate resource (such as

OVSF, Scramble code)


Traffic control

When traffic surpass system

threshold, traffic control begin.

To accept as many as possible

services while keep the stability of

the system.


Example for load control

Breath effect of cellBreath effect of cell

With the increase of activated terminals,

interference increase

the increase of high speed service,the

increase of interference

The shrink of cell coverage area

Coverage blind spot occurs

Drop of call will happen at the edge of cell Coverage and

capacity are relative


Power Control

Handover

Rake receiver



Content

System capacity and QoS can be interconverted

Different combination of service has different capacity

Different service has

different capacity

Soft Capacity


Capacity of WCDMA System

=

=

=

Under the circumstance of single services::


Capacity of WCDMA System

…...

Under the circumstance of mixture of services：

X Y Z+ +


Coverage and Capacity

WCDMA performance is determined by such factors as： Number of users Transmission rate Mobile rate Wireless environment

indoors Outdoors

The sizes of cell depend on such factors as: Local radio conditions (local interference) Traffic in neighbouring cells (distanced interference)

Cell Radius decrease according to the Increase of user number


Coverage/capacity vs Data Rate

Higher rate needs higher power

High data rate transmission is only available nearby the

station

>12.2 kbps

>64 kbps

>384 kbps

>144 kbps

Coverage decrease

Subscriber num increase


DL transmission diversity (Tx Div) high power amplifier(TEU 50 W)

DL transmission diversity (Tx Div) high power amplifier(TEU 50 W)

UL tower mounted amplifier (TMA)4RxDivMUDOTSR

UL tower mounted amplifier (TMA)4RxDivMUDOTSR

DL/UL:Add carrier six sectors Smart antenna

DL/UL:Add carrier six sectors Smart antenna

Add basestation

“last choice”

Add basestation

“last choice”

Coverage and Capacity

In order to overcome cell breath caused by increased

traffic and different requirement for capacity and coverage

in different environment ,such solution supplied:


Exercise

what is the near-far effect

what is the purpose of Power Control .

Power control is diveided into ( ) ( ) ( )

pls describe WCDMA Hand Over Technology category.

soft handover events include( ) ( ) ( ) ( )( ) ( )

What is the cell breath effect.

4 wcdma key technologies 42

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