Owj103103 Wcdma Power Control Issue1.1

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ISSUEISSUE

OWJ103103 WCDMA Power OWJ103103 WCDMA Power ControlControl

OWJ103103 WCDMA Power OWJ103103 WCDMA Power ControlControl

1.11.1

Confidential Information of Huawei. No Spreading without Permission.

Security Level: Internal

2

ReviewReview

Here, we want to talk about power control

principle applied in WCDMA system.

For better comprehension and application, some

important parameters are also covered here.

At the end of every chapter, we raise some

questions to review the content.



3

ObjectivesObjectives

Know how many types of power control

methods in WCDMA

Understand how power control works

Do some optimization to power control

parameters

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



4

Course ContentsCourse Contents

Concepts for WCDMA Power Control

Power Control Principle

Power Control Process &Parameters

Discussion



5

Concepts for WCDMA Power ControlConcepts for WCDMA Power Control

1.1 What is power control?1.1 What is power control?

1.2 Why power control is

needed?

1.3 How many types of po

wer control ?



6

The Basic IdeaThe Basic Idea

This is the basic idea of power control:

Too Weak!

Louder Pls!

Still Weak!

!

Louder Pls!!

Good!



7

What is Power ControlWhat is Power Control

Power control is:

Measure the path loss

Adjust the transmission power of transmitter

To guarantee the link quality of receiver.



8

Power Control – Link QualityPower Control – Link Quality

How to measure the link quality?

SIR

BER or BLER BER: Bit Error Ratio, e.g. 10e-3, 10e-6

BLER: Block Error Ratio, e.g. 1%, 5%

BER or BLER is relating to SIR in certain

environment.



9

Power Control – Link QualityPower Control – Link Quality

1, SIR : Signal to Interference Ratio

2, BLER≤X% SIR≥Y

SIR

BLER

X%

Y



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1.1 What is power control?

1.2 Why power control is 1.2 Why power control is

needed?needed?

1.3 How many types of po

wer control are there?



11

Self-interference SystemSelf-interference System

WCDMA cocktail party

What can you hear?..•If you can only speak Chinese ？•If you speak Chinese, but other person speaks Russian loudly?



12

频率

时间

码字CDMA


Many users communicate at the same carrier.

Users at the same frequency interfere with each other

A

B

C



13


Power control is especially important.

Minimize the interference

How to serve as many users as we can in a

cell?



14

Received

power

f

Far and Near EffectFar and Near Effect

What is far and near effect?

All UEs transmit at their maximum power

The farther the UE is from NodeB, the weaker its signal is at

the receiver.

Difference for received signals at NodeB varies from 30 to

70dB.



15


Far and near effect affects network

performance hardly

Weak signals can’t be decoded

Network capacity decreases

Even one UE close to site can block the whole cell

Other UE can’t connect network because of

lack of enough power

What can we do?



16


Power control in uplink can guarantee signal strength

balance at the receiver.

Received power for every UE is just enough.

Received

power

f

Received power

f



17

Fast FadingFast Fading

What is fast fading?

Received signal is composed of multi-path signals

Signal varies with peaks and troughs

Troughs appear quickly within several centimetres.



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Fast FadingFast Fading

Fast fading makes received signal quality get bad.

Bits met with troughs maybe can’t be decoded.

BER or BLER will get higher.

Fast power control can conquer this problem.

Frequency for fast power control is faster than that of

signal trough.



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Effect of Power ControlEffect of Power Control

Summary:

To adjust transmitting power to a suitable level

To guarantee the service quality of receiver

To minimize the interference at UU interface

To overcome the “far-near” effect in uplink

To overcome effects of fast fading and slow fading

in radio interface



20


1.1 What is power control?

1.2 Why power control is

needed?

1.3 How many types of po1.3 How many types of po

wer control are there?wer control are there?



21

Power Control TypesPower Control Types

Types of power control:

Open loop power control

Close loop power control

Inner loop power control (ILPC)

Outer loop power control (OLPC)



22

Power Control TypesPower Control Types

Different power control types are applied on dif

ferent channels.

Physical channel

Open loop Inner loop Outer loop No power control

DPDCH X X

DPCCH X X X

PCCPCH X

SCCPCH X

PRACH X

AICH X

PICH X



23

QuestionsQuestions

Should all UEs in a cell transmit power at its

maximum value?



24

AnswersAnswers

No

Waste UE power

Cause extra interference to other UEs

UE close to site will block the cell



25





Discussion



26

Power Control PrinciplePower Control Principle

1.1 Open loop power 1.1 Open loop power

controlcontrol

1.2 Inner loop power

control

1.3 Outer loop power

control



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Open Loop Power Control Open Loop Power Control

What is open loop power control?

Estimate own transmit power through measuring the

received signal

No feedback from the opposite side

Only be used to set the initial power for its Inaccuracy.



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Open Loop Power Control Open Loop Power Control

For Example

Open loop power control on uplink PRACH

Transmission on PRACH after adjustment

Measure downlink signal strength- CPICH RSCP

Estimate uplink transmission power



29

Open Loop Power Control -WhyOpen Loop Power Control -Why

Speed up SIR convergence

With less transmitting power at initial time

Less interference

time

power

time

power

Without open loop power control

With open loop power control

SIR target



30

Power Control PrinciplePower Control Principle

1.1 Open loop power

control

1.2 Inner loop power 1.2 Inner loop power

controlcontrol

1.3 Outer loop power

control



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Inner Loop Power Control Inner Loop Power Control

What is inner loop power control? Based on the comparison between received SIR and the target

SIR

The receiver command the transmitter to increase or decrease

the transmitting power

Have a feedback loop between receiver and transmitter

Purpose is to maintain a certain signal-to-interference ratio of

transmission signal



32


For example

Inner loop power control on UL DPCCH

Inner loop

UE

NodeB

Send TPC command

Measure received signal SIR and

compare with SIR target

RNC set SIRtar

Frequency:1500Hz/s

Change UL transmission power

1

2

3

45



33


But ? Even if the mean signal-to-interference ratio is above a

certain threshold, the communication quality (BER or FER or

BLER) is not likely fulfilled because of environment changes.

•BLE

R

SIR

BLER

For different environments



34

How Power Control WorksHow Power Control Works

1.1 Open loop power

control

1.2 Inner loop power

control

1.3 Outer loop power 1.3 Outer loop power

controlcontrol



35

Outer Loop Power ControlOuter Loop Power Control

What is outer loop power control?

Based on the comparison between measured BLER and

the target BLER

To set the target SIR for the ILPC.



36

Outer Loop Power ControlOuter Loop Power Control

For example

Outer loop power control on uplink DCCCH

NodeB

Set SIRtar

Outer loop

RNC

Measures received data BLER and compares it with BLER tar

Set BLERtar

10-100Hz

Received data with BLER stable

data1

2

3

Modify SIRtar

4



37

Outer Loop Power Control － WhyOuter Loop Power Control － Why

The Mapping between BLER and SIR is not fixed.

When propagation environment changed, the

mapping will be changed.

SIR

BLER

The token for service Qos



38

Outer Loop Power Control － WhyOuter Loop Power Control － Why

As channel condition changing, the required SIR (target) is

changing slowly.

Outer loop power control is needed.

SIR

BLER Suburb

Urban

Dense urban

For example

only

X%

Y1 Y2 Y3



39

QuestionsQuestions

How many “TPC cmd” can be sent out in 1 fra

me?

What is change during OLPC?



40

AnswersAnswers

TPC command is transmitted every timeslot,

so there are 15 TPC commands in a frame.

SIR target



41





Discussion



42

Power Control Process &ParametersPower Control Process &Parameters

1.1 Power control on PRACH1.1 Power control on PRACH

1.2 Power control on UL

DPCH

1.3 Power control on DL

DPCH



43

Power Control on PRACHPower Control on PRACH

Power control sequence for PRACH

12timeslots

Power Ramp step

Pp-m

10ms/20ms(15/30timeslots)

Preable_Initial_power

Message part



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Only open loop power control is applied on PRACH

Initial power for PRACH is calculate by UE

according the formula below:

Preamble_Initial_Power = Primary CPICH DL TX

power - CPICH_RSCP + UL interference + Constant

Value



45


Primary CPICH DL TX power

CPICH channel transmit power, broadcast in SIB5.

UL interference

Measured by NodeB and broadcast in SIB7.

Constant Value

Set by user, and broadcast in SIB5 and SIB6.

CPICH_RSCP

Measured by UE



46


Power control sequence for PRACH

UE will retransmit preambles if it doesn’t get the access

indicator from NodeB.

The max retransmission times is set by parameter “Prea

mble Retrans Max”

For every preamble, UE increases it’s transmit power by

“PRACH Power Ramp Step”

So, the maximum power for PRACH preamble may be “Pr

eamble Retrans Max * PRACH Power Ramp Step”



47

Power control sequence for PRACH (continuous)

“Power offset Pp-m ” is a power deviation of the last pr

eamble to message.




48

Power Control Algorithms and ParametersPower Control Algorithms and Parameters

1.1 Power control on PRACH

1.2 Power control on UL 1.2 Power control on UL

DPCHDPCH

1.3 Power control on DL

DPCH



49

Power Control on UL DPCHPower Control on UL DPCH

UL DPCH power control

After DPCCH channel gets its initial power by open loop, it will

use ILPC and OLPC to adjust its power;

In UL ILPC, NodeB controls UE’s TX power, based on the compa

rison of received SIR and SIRtarget;

In UL OLPC, RNC updates the SIRtarget in NodeB, according to

the measured BLER and the required BLER(target);

UL ILPC is between UE and NodeB;

UL OLPC is done in RNC



50


Figure for UL DPCH PC

NodeB

Iub Interface

UE RNC

Uu interface

Signal

TPC cmd

SIRtarget

User data

UL ILPC UL OLPC

UL DCH power control

Initial power

UL open Loop



51


Open loop power control is applied to estimate

the DPCCH initial power

DPCCH_Initial_power = DPCCH_Power_offset - CPICH_RSCP

“CPICH_RSCP” is measured by UE

“DPCCH_Power_offset” is calculated by RNC and sent to UE in

“RRC connection setup” message.



52


UL DPCH power control (ILPC and OLPC)

UENodeB

Send TPC

Measures received signal SIR and compares it with SIR tar

Inner loop

Set SIRtar

Outer loop

RNC

Measures received data BLER and compares it with BLER tar

Set BLERtar

10-100Hz

Received data with BLER stable

1500Hz



53


UL DPCH OLPC parameters

“BLER target”: Service-varied, if BLER measured closes to

BLER target, service quality is acceptable. It is set by user.

“SirAdjustPeriod ”: In every period, RNC will change SIR

target once. Set by user.

“SirAdjustStep ”: RNC change SIR target by this step. Set by

user.



54


UL DPCH ILPC parameters “TPC step size”: UE uses this to calculate the adjusted power

as follow:

and the transmit power for UL DPCCH in current timeslot is

UL DPDCH power is decided by the formula below,

are set by RNC

DPCCH TPC TPC_cmd

DPCCHPP kk 1

DPCCH

DPDCH

c

d

P

P

dc



55

Power Control Algorithms and ParametersPower Control Algorithms and Parameters

1.1 Power control on PRACH

1.2 Power control on UL

DPCH

1.3 Power control on DL 1.3 Power control on DL

DPCHDPCH



56

Power Control on DL DPCHPower Control on DL DPCH

DL PC is used to control the DL power and quality;

Open loop power control is used for initial power estimation.

In DL ILPC, the UE controls the NodeB tx power, based on the

comparison of received SIR and target SIR.

DL ILPC is between UE and NodeB

In DL OLPC, UE update the SIRtarget for DL-ILPC, based on t

he comparison of received BLER and the required BLER.

DL OLPC is in UE internal implemented.



57

Power Control on DL DPCHPower Control on DL DPCH

Figure for DL DPCH PC

NodeB

UE

SIRtarget

User data

Uu

TPC cmd

SignalDL OLPC

DL ILPC

DL PC



58

Open Loop Power Control on DL DPCHOpen Loop Power Control on DL DPCH

Open loop power control is also used on DL DPCH.

(Eb/Io)*(R/W) SIR required.

Eb/Io: Determined by bearer service and environments

Pcpich: Primary CPICH transmit power.

(Ec/Io)cpich: measurement value reported by the UE.

“α”: downlink cell orthogonal factor.

Ptotal: Cell total DL power.

total

CPICH

c

CPICHb P

IEP

WR

IEP

0

0



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is the previous timeslot transmission power.

But, downlink power is not allowed to rise without limitation

“Power_Raise_Limit” is used to limit power rise in a period of “DL_power_averaging_window ”

ILPC on DL DPCHILPC on DL DPCH

NodeB adjusts it DL power according to the

formula:

)(1 kppp TCPkk

1kp



60


Frame structure for downlink DPCH

One radio frame, Tf = 10 ms

TPC NTPC bits

Slot #0 Slot #1 Slot #i Slot #14

Tslot = 2560 chips, 10*2k bits (k=0..7)

Data2Ndata2 bits

DPDCH

TFCI NTFCI bits

Pilot Npilot bits

Data1Ndata1 bits

DPDCH DPCCH DPCCH



61


How to calculate the transmission power for

DL DPCCH? PO1 ： power offset of TFCI part relative to DPDCH

PO2 ： power offset of TPC part relative to DPDCH

PO3 ： power offset of PILOT part relative to DPDCH

These parameters are sent to NodeB from RNC when RL is

setup.



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Discussion



63

DiscussionDiscussion

In soft handover status, if different cells get

different TPC command because of wrong

decoding, what should happen?

Link power drift

Interference increases



64

DiscussionDiscussion

If there is no power control in WCDMA, can th

e system work well?

GSM system can work without PC, but

WCDMA even can’t work without it.



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Owj103103 Wcdma Power Control Issue1.1