owj103103 wcdma power control issue1.0 ppt

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ISSUEISSUE

OWJ103103 WCDMA Power Control

OWJ103103 WCDMA Power OWJ103103 WCDMA Power ControlControl

1.01.0

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


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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

power 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.


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Power Control – Link QualityPower Control – Link Quality

! 1, SIR : Signal to Interference Ratio

! 2, BLER X% # SIR Y

SIR

BLERX%

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

power 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

BC


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.


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!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 “fast-near” effect in uplink

# To overcome effects of fast fading and slow fading in radio interface


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! 1.1 What is power control?

! 1.2 Why power control is

needed?

!! 1.3 How many types of 1.3 How many types of

power control are there?power control are there?


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Power Control TypesPower Control Types

!There are four types of power control strategies:

# Open loop power control

# Close loop power control

# Inner loop power control (ILPC)

# Outer loop power control (OLPC)! Note: Close loop power control includes inner and outer

power control.


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Power Control TypesPower Control Types

!Different power control types are applied on different channels.

XPICH

XAICH

XPRACH

XSCCPCH

XPCCPCH

XXXDPCCH

XXDPDCH

No power control

Outer loopInner loopOpen loop Physical channel


23

QuestionsQuestions

! Should all UEs in a cell transmit power at its maximum value?


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AnswersAnswers

! No

# Waste UE power

# Cause extra interference to other UEs

# UE close to site will block the cell


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Discussion


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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


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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


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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


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!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

4 5


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!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.

•BLER

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.


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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

data 1

2

3

Modify SIRtar

4


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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 SuburbUrban

Dense urban

For exampleonly

X%

Y1 Y2 Y3


39

QuestionsQuestions

! How many “TPC cmd” can be sent out in 1 frame?

! 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


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!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


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! 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 “Preamble 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 “Preamble Retrans Max * PRACH Power Ramp Step”


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! Power control sequence for PRACH (continuous)# “Power offset Pp-m ” is a power deviation of the last

preamble 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 IPLC and OPLC to adjust its power;

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

comparison 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


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!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


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! 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.


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! 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


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! UL DPCH OLPC parameters (important)# “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.


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! UL DPCH ILPC parameters (important)# “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

✁ D P C C H = ✁ T P C % T P C _ c m d

DPCCHPP kk ∆+= −1

DPCCH

DPDCH

c

d

PP=

ββ

dβcβ


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 the 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

SIRtargetUser 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.

# “ ”: downlink cell orthogonal factor.

# Ptotal: Cell total DL power.

( )

×−

⋅⋅

= total

CPICH

c

CPICHb P

IE

PW

RI

EP α

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 += −

1−kp


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

DPDCHTFCI

NTFCI bitsPilot

Npilot bitsData1

Ndata1 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.


62





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 the system work well?

# GSM system can work without PC, but WCDMA even can’t work without it.


65

owj103103 wcdma power control issue1.0 ppt

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