Power Control

POWER CONTROL

HUAWEI RNP/RNO

WCDMA

June 12, 20083rd Floor. SSS Bldg., Ayala Ave.

Makati City

ERIC BABIA HUWEI RNP/RNO

POWER CONTROL

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Why do we need Power Control?

To maintain the quality of a connection using as

little radio resources as possible.

To allow access to as many users as possible while

keeping the interference caused by these users at a

minimum.

The task of power control is to keep the

transmission powers used for a connection, both by

the UE and the BTS, at a minimum


POWER CONTROL

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The Basic Idea

Too Weak!

Louder Plz!

Still Weak!

!

Louder Plz!!

Good!

PTX

PTX

PTX


POWER CONTROL

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POWER CONTROL LOOPs in WCDMA

UE RNC

INNER-LOOPPOWER CONTROL

OUTER-LOOPPOWER CONTROL

WCDMA BTS

OPEN LOOP POWER CONTROL(INITIAL ACCESS - UPLINK)

OPEN LOOP POWER CONTROL(INITIAL ACCESS - DOWNLINK)


POWER CONTROL

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Uplink transmission character Self-interference

Capacity is limited by interference

Near-far effect

Fading

Uplink power control Ensure uplink quality with minimum transmission power

Decrease interference to other UE, and increase capacity

Solve the near-far effect

Save UE transmission power

Purpose of uplink power control


POWER CONTROL

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NEAR-FAR PROBLEM in WCDMA

UE2

UE3

UE1

D1

D3

D2

D1 > D2 > D3

PRX1 = PRX2 = PRX3

PTX1 > PTX2 > PTX3

PTX1

PTX2

PTX3

PRX1PRX3

PRX2


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NEAR-FAR PROBLEM in WCDMA UEs move around in the cell and find themselves at

varying distances from the BTS at different points in time.

The further away from the BTS a UE is, the more power it

has to use; thus, the power has to be adjusted

continuously.

BTS receives equally strong signals from all UEs at all

times despite the continuously varying distances.

The signals from all transmitting UE must always be

equally strong at the receiving end.


POWER CONTROL

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Downlink transmission character Interference among different subscribers since the

orthogonality is influenced by transmission environment

Interference from other adjacent cells

Downlink capacity is limited by NodeB transmission power

Fading

Downlink power control Ensure Downlink quality with minimum transmission power

Decrease interference to other cells, and increase capacity

Save NodeB transmission power

Purpose of downlink power control


POWER CONTROL

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The Relationship between Tx Power and Rx Power

0 200 400 600 800-20

-15

-10

-5

0

5

10

15

20

Time (ms)

Rel

ati

ve

po

wer

(d

B)

Channel Transmitted power

Received power


POWER CONTROL

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Power Control Classification Power control classification

open loop power control

closed loop power control

Uplink inner-loop power control

Downlink inner-loop power control

Uplink outer-loop power control

Downlink outer-loop power control


POWER CONTROL

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Power control methods adopted for various physical channels

Power control methods adopted for various physical channels

“Y" – can be applied, "–" – not applied

Physi calchannel

Open l ooppowercontrol

I nner l ooppowercontrol

Outer l ooppowerControl

No power control process,power i s speci fi ed byupper l ayers.

DPDCH － Y Y －DPCCH Y Y Y －PCCPCH －－－ YSCCPCH －－－ YPRACH Y －－－AI CH －－－ YPI CH －－－ Y


POWER CONTROL

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OPEN LOOP POWER CONTROL

UE RNC

WCDMA BTS

OPEN LOOP POWER CONTROL(INITIAL ACCESS - UPLINK)

OPEN LOOP POWER CONTROL(INITIAL ACCESS - DOWNLINK)


POWER CONTROL

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Open loop Power Control Overview Purpose

UE estimates the power loss of signals on the

propagation path by measuring the downlink channel

signals, then calculates the transmission power of the

uplink channel

Principle

Path loss of the uplink channel is related to path loss of

the downlink channel


POWER CONTROL

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Open loop Power Control Overview Disadvantage

This power control method is rather rough

Application scenarios

In a cell, signal fading caused by fast fading is usually

more serious than that caused by propagation loss

open loop power control is applied only at the

beginning of connection setup, generally in setting the

initial power value


POWER CONTROL

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Open loop Power Control of PRACH

AICH accessslots RX at UE

PRACH accessslots TX at UE

One access slot

p-a

p-mp-p

Pre-amble

Pre-amble

Message part

Acq.Ind.


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Open loop Power Control of PRACH

The initial value of PRACH power is set through open loop

power control

Preamble_Initial_Power

= PCPICH DL TX power - CPICH_RSCP + UL interference

+ Constant Value


POWER CONTROL

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Open loop power control of PRACH

NO. Parameter Parameter meaning

1 Power Offset Pp-m The power offset of the last access preamble and message control part. This value plus the access preamble power is the power of the control part

2 Constant Value This parameter is the correction constant used for the UE to estimate the initial transmission power of PRACH according to the open loop power

3 PRACH Power Ramp Step This parameter is the ramp step of the preamble power when the UE has not received the capture indication from NodeB

4 Preamble Retrans Max This parameter is the permitted maximum preamble repeat times of the UE within a preamble ramp cycle

Power Ramp Step

Pp-m

10ms/20ms

Preable_Initial_power


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Open loop power control of PRACHOpen loop power control of PRACH

UE Node BServing RNS

Serving RNC

1. CCCH : RRC Connection Request

open loop power control of PRACH

5. Downlink Synchronization

DCH - FP

Allocate RNTISelect L1 and L2parameters

RRC RRC

NBAP NBAP3. Radio Link Setup Response

NBAP NBAP2. Radio Link Setup Request

RRC RRC7. CCCH : RRC Connection Set up

Start RX description

Start TX description

4. ALCAP Iub Data Transport Bearer Setup

RRCRRC9. DCCH : RRC Connection Setup Complete

6. Uplink Synchronization

NBAP NBAP

8. Radio Link Restore Indication

DCH - FP

DCH - FP

DCH - FP

Application scenariosApplication scenarios


POWER CONTROL

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Open loop power control of DL DPCCH

The DL DPCCH open loop power control can be calculated by the following formula:

P=(Ec/Io)Req-CPICH_Ec/Io + CPICH_Power

Parameters explanation (Ec/Io)req is the required Ec/Io, which should ensure

that UE can receive the message from the dedicated channel correctly

CPICH_Ec/Io is measured by UE, then it is sent to UTRAN by RACH

CPICH_Power is the transmission power of CPICH


POWER CONTROL

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Open loop power control of DL DPCCHOpen loop power control of DL DPCCH


Serving RNC



DCH - FP


RRC RRC









NBAP NBAP


DCH - FP

DCH - FP

DCH - FP


open loop power control of DPCCH


POWER CONTROL

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Serving RNC

DCH - FP

Allocate RNTISelect L1 and L2 parameters

RRC RRC

NBAP NBAP

3. Radio Link Setup Response

NBAP NBAP

2. Radio Link Setup Request

RRC RRC

7. CCCH : RRC Connection Set up




RRC RRC

9. DCCH : RRC Connection Setup Complete


NBAP NBAP


DCH - FP

DCH - FP

DCH - FP


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Open loop power control of UL DPCCH The UL DPCCH open loop power control can be

calculated by the following formula:

DPCCH_Initial_Power

= DPCCH_Power_Offset - CPICH_RSCP


POWER CONTROL

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Serving RNC



DCH - FP


RRC RRC









NBAP NBAP


DCH - FP

DCH - FP

DCH - FP




POWER CONTROL

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CLOSED LOOP POWER CONTROL

UE RNC

INNER-LOOPPOWER CONTROL

OUTER-LOOPPOWER CONTROL

WCDMA BTS


POWER CONTROL

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Closed loop power control overview The characteristics of open loop power control

The results from open loop power control are not accurate enough

open loop power control can only decide the initial power

The advantages of closed loop power control Guarantee the QoS Decrease the interference Increase the system capacity


POWER CONTROL

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BLERtar

Closed loop power control overview

TPC=0 Power

TPC=1 Power

Ensure the QoS with minimum

power

Outer loop

SIRtar TPC

Inner loop

BLERmea<BLERtar→SIRtar

BLERmea>BLERtar→SIRtar

Until BLERmea=BLERtar

SIRmea>SIRtar→TPC=0

SIRmea<SIRtar→ TPC=1

Until SIRmea=SIRtar


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INNER LOOP POWER CONTROL


POWER CONTROL

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Uplink-inner loop power control

NodeB

UEset SIRtar

1500Hz1500Hz

Transmit TPC

Inner loop

TPC Decision(0 ， 1)

TPC_CMD（ -1, 0, 1 ）

Adjust DPCCH Tx△ DPCCH= tpc×TPC_cmd△

PCA1 PCA2

Adjust DPDCH Tx(βc,βd)

Compare SIRmeas with SIRtar

SIRmea>SIRtar→TPC=0SIRmea<SIRtar→ TPC=1

NodeB compares the measured SIR to the preset target SIR

TPC DECISION

Adjust POWER


POWER CONTROL

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UE gets one TPC in each time slot

If TPC=0, TPC_cmd= -1

If TPC=1, TPC_cmd= 1

This control is done in each time slot

Power control frequency is 1500HZ

TPC_CMD

TPC

Uplink inner-loop PCA1 without soft handover

0 1 1 0 1 1 0 1 1 1

-1 1 1 -1 1 1 -1 1 1 1


POWER CONTROL

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Each time slot, combine TPC from different RLS ， then get Wi

Get TPC_cmd based on

TPC_cmd = γ (W1, W2, … WN)

Uplink inner-loop PCA1 with soft handover

CELL1 CELL2

CELL4CELL3

RL11 RL12

RLS1

RLS2 RLS3

RLS1-TPC (W1)

RLS2-TPC (W2)

TPC_CMD

0110110110

1010101101

RLS3-TPC (W3) 1101100100

0000100100

If TPC(Wi) is all ‘1’ for each RLS, TPC_CMD = 1

Otherwise,

TPC_CMD = 0


POWER CONTROL

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10ms/frame

Group 2Group 1 Group 3

TPC

Transmission power will be controlled in each 5 time slots

The frequency is 300HZ

Uplink inner-loop PCA2 Without soft handover

0TS0

0TS1

0TS3

0TS4

1TS5

1TS8

1TS7

1TS6

0TS12

1TS11

1TS9

1TS10

0TS2

1TS14

1TS13

0 0 0 0 -1 00 0 0 1 0 00 0 -1

TPC_CMD


POWER CONTROL

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Combine TPC from same RLS in each time slot

Calculate TPC_cmd

TPC_CMD=1

TPC_CMD=-1

Otherwise TPC_CMD=0

Calculate TPC_tempi for each RLSIf 5 TPC are all 1, TPC_tempi=1

If 5 TPC are all 0, TPC_tempi=-1Otherwise, TPC_tempi =0

5.0_1

1

N

iitempTPC

N

5.0_1

1

N

iitempTPC

N

CELL1 CELL2

CELL4CELL3

RL11 RL12

RLS1

RLS2 RLS3

Uplink inner-loop PCA2 With soft handover


POWER CONTROL

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Comparison between PCA1 and PCA2 The control frequency

TPC1, the power control frequency is 1500Hz

TPC2, the power control frequency is 300Hz


POWER CONTROL

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Downlink Inner loop power control

NodeB

Set SIRtar

Measure SIR and compare

it with SIRtar

1500Hz

Adjust Tx power

with 0.5, 1, 1 or 2dB

Transmit TPC in each TS

L3

EXECUTE TPC_CMD


POWER CONTROL

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Downlink inner loop power control

When UE is not in soft handover

The TPC which is generated by UE is transmitted in TPC domain of

UL channel

When UE is in soft handover, two power control modes can be

used, which is decided by DPC_mode:

DPC_MODE ＝ 0 ， UE will transmit TPC in every slot

DPC_MODE ＝ 1 ， UE will transmit the same TPC in every three time

slot

When the downlink channel is in out of synchronization, UE will

transmit TPC 1 because UE can not measure the downlink SIR

How to generate TPCHow to generate TPC


POWER CONTROL

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The transmission power can not be higher than

Maximum_DL_Power, and not less than

Minimum_DL_Power neither.

Downlink power adjustment:

Pk Pk 1PTPCkPbalk

Where

P(k-1) is power of previous

PTPC(k) is the adjustment

Pbal(k) is correction value


How to adjust powerHow to adjust power


POWER CONTROL

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Where

PTPC(k) is the adjustment value

TPCest(k) is uplink TPC value

△TPC is downlink power adjustment step(0.5, 1,

1.5 or 2dB)

PTPC(k)

Without “Limited Power Raise Used”


How to adjust powerHow to adjust power

0)(TPCifΔ

1)(TPCifΔ)(P

estTPC

estTPCTPC k

kk


POWER CONTROL

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Where

PTPC(k)

With “Limited Power Raise Used”


0)(TPC if

e_LimitPower_Rais)( and 1)(TPC if

e_LimitPower_Rais)( and 1)(TPC if

0)(

est

est

est

k

kk

kk

kP TPCsum

TPCsum

TPC

TPC

TPC

PTPC(k) is the adjustment value

TPCest(k) is uplink TPC value

△TPC is downlink power adjustment step(0.5, 1, 1.5 or 2dB)

Power_Raise_Limit: the limited value for Power ramping in a timer

DL_power_averaging_window_size ： timer for power ramping (TS)

1

1____

)()(k

SizeWindowAveragingPowerDLkiTPCsum iPk


POWER CONTROL

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Downlink Power Balance

Downlink power balance process

SRNC can monitor every single

NodeB’s transmission. If SRNC found

the power offset in soft handover is

excessive, it will initiate the DPB

process

The initiation and stop of DPB

The power offset of two RLs is greater

than the DPB initial threshold, the

DPB process is initiated

The power offset of two RLs is less

than the DPB stop threshold, the DPB

process is stopped


POWER CONTROL

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OUTER LOOP POWER CONTROL


POWER CONTROL

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Outer loop power control

The character of outer loop power control

The QoS which NAS provides to CN is BLER, not SIR

The relationship between inner loop power control and outer

loop power control

SIRtar should be satisfied with the requirement of decoding

correctly. But different multi-path radio environments request

different SIR

Therefore, the outer loop power control can adjust the SIR to get

a stable BLER in the changeable radio environment


POWER CONTROL

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Uplink outer loop power control

Transmit TPC

Measure and compare SIR

Inner-loop

Set SIRtar

Out loop

Measure received data and compare BLER in the TrCH

Set BLERtar

10-100Hz


POWER CONTROL

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NodeB

set SIRtar

Transmit TPC

Measure and compare SIR

Measure and compare BLER

Outer loop

Inner loop L1

L3

10-100Hz1500Hz

Downlink outer loop power control


POWER CONTROL

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Outer loop power controlSIR target adjustment SIR target adjustment stepstep

etBLERt

etBLERtBLERmeastepSIRAdjustSoefficientSIRAdjustcSIRtar

arg

arg**

Where

SirAdjustStep: Outer loop power control adjustment

step

SirAdjustFactor: Coefficient for outer loop power

control

BLERest: Estimated BLER

BLERtar: Target BLER

Thank you

Power Control

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