WCDMA Power Control Algorithm and Parameters

WCDMA Power Control Algorithm and Parameters www.huawei.com

Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.

Foreword 

Power control types: 

Open loop power control



Closed loop power control 

Inner loop power control



Outer loop power control

Foreword 

Power control types: 

Open loop power control



Closed loop power control 

Inner loop power control



Outer loop power control

References 

3GPP TS 25.211 

Physical Channels and Mapping of Transport Channels onto Physical Channels (FDD)



3GPP TS 25.214 



3GPP TS 25.331 



Physical Layer Procedures (FDD)

RRC Protocol Specification

3GPP TS 25.433 

UTRAN Iub Interface NodeB Application Part (NBAP) Signaling

Objectives 

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

Describe the purpose and function of power control



Perform parameters modification of open loop power control



Perform parameters modification of inner loop power control



Perform parameters modification of outer loop power control

Contents 1. Power Control Overview 2. Open Loop Power Control 3. Closed Loop Power Control

Purpose of Uplink Power Control Uplink transmission character 

Self-interference system



Uplink capacity is limited by interference level



Near-far effect



Fading

Uplink power control function 

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 Downlink Power Control Downlink transmission character 

Interference among different

Downlink power control function 

subscribers 

Interference from other adjacent

minimum transmission power 

cells 

Downlink capacity is limited by NodeB transmission power



Fading

Ensure downlink quality with Decrease interference to other

cells, and increase capacity 

Save NodeB transmission power

Effect of Power Control 20 Channel Fading

15

Transmitting power Receiving power

10

) B d ( r 5 e w o p 0 e v i t -5 a l e R -10 -15 -20 0

200

400

Time (ms)

600

800

Power Control Classification

Open Loop Power Control …



Uplink/Downlink open

loop power control

Closed Loop Power Control …



Uplink/Downlink inner

loop power control 

Uplink/Downlink outer

loop power control

Power Control for Physical Channels 

Power control methods are adopted for these physical channels: 

“√" : can be applied; “ ×“: can not be applied

Closed Loop Power Control

Open Loop Power Control

Inner Loop Power Control

Outer Loop Power Control

SCH

×

×

×

PCCPCH

×

×

×

SCCPCH

×

×

×

×

×

Physical Channel DPDCH DPCCH

PRACH AICH

×

×

×

PICH

×

×

×

Common Physical Channel Power Parameters 



MaxTxPower 

Parameter name: Max transmit power of cell [0.1dBm]



Recommended value: 430, namely 43dBm

PCPICHPower 

Parameter name: PCPICH transmit power [0.1dBm]




Common Physical Channel Power Parameters (Cont.) 



PSCHPower and SSCHPower 

Parameter name: PSCH / SSCH transmit power [0.1dB]



Recommended value: -50, namely -5dB

BCHPower 

Parameter name: BCH transmit power [0.1dB]







MaxFachPower 

Parameter name: Max transmit power of FACH [0.1dB]



Recommended value: 10, namely 1dB

PCHPower 

Parameter name: PCH transmit power [0.1dB]







AICHPowerOffset 

Parameter name: AICH power offset




PICHPowerOffset 

Parameter name: PICH power offset





Contents 2. Open Loop Power Control 2.1 Open Loop Power Control Overview 2.2 PRACH Open Loop Power Control 2.3 Downlink Dedicated Channel Open Loop Power Control 2.4 Uplink Dedicated Channel Open Loop Power Control

Open Loop Power Control Overview Purpose

Principle

•Calculate the initial

•Estimates the

•Open loop power

transmission power

downlink signal

control is applied only

of uplink/downlink

power loss on

at the beginning of

channels

propagation path

connection setup to set

•Path loss of the

the initial power value

uplink channel is related to the downlink channel

Application


PRACH Open Loop Power Control NodeB

UE

SRNC

1. CCCH : RRC Connection Request

RRC

Open loop power control of PRACH

RRC Allocate RNTI Select L1 and L2 parameters

NBAP

2. Radio Link Setup Request NBAP

Start RX description 3. Radio Link Setup Response NBAP

NBAP 4. ALCAP Iub Data Transport Bearer Setup DCH - FP DCH - FP

5. Downlink Synchronization 6. Uplink Synchronization

DCH - FP DCH - FP

Start TX description RRC

7. CCCH : RRC Connection Setup

RRC

8. Radio Link Restore Indication NBAP

RRC

9. DCCH : RRC Connection Setup Complete

NBAP RRC

PRACH Open Loop Power Control 

Power ramping for preamble retransmission: Power R amp Step Power Offset P p-m Preamblen

Preamble_Initial _P ower

Preamble1

Preamble2

Preamble3

Message 10ms or 20ms

……

PRACH p-p

Timing offset

p-m

AI

AICH p-a

PRACH Open Loop Power Control 

When UE needs to set up a RRC connection, the initial power of uplink PRACH preamble can be calculated according to the following formula:

Preamble_Initial_Power = PCPICHPower - CPICH_RSCP + UL interference + Constantvalue

PRACH Open Loop Power Control Parameters 

Constantvalue 

Parameter name: Constant value for calculating initial TX power




PRACH Open Loop Power Control Parameters (Cont.) 

AICHTxTiming 

Parameter name: AICH transmission timing



Content: 

When AICHTXTIMING AICHTXTIMING = 0, p-p,mi n =



p-a =

7680 chips,

p-m =

15360 chips

AICHTXTIMING = 1, When AICHTXTIMING p-p,mi n =



15360 chips,

20480 chips,

p-a =

Recommended value: 1

12800 chips,

p-m =

20480 chips




PowerRampStep 

Parameter name: Power increase step




PreambleRetransMax 

Parameter name: Max preamble retransmission







Mmax 

Parameter name: Max preamble loop




NB01min / NB01max 

Parameter name: Random back-off lower / upper limit



Recommended value: 0 for both NB01min / NB01max


PowerOffsetPpm 

Parameter name: Power offset



Recommended value:

Message Data Part

PowerOffsetPpm

GainFactorBetaC

GainFactorBetaD

Signaling

-3

13

15

Service

-2

10

15


Parameters diagrammatic presentation Power Ramp Step

Message Power Offset

Message Initial Power

Preamble Ramping Cycle Preamble Ramping Procedure


The transmit power on the PRACH cannot be greater than the maximum allowed uplink transmit power:



MaxAllowedUlTxPower 

Parameter name: Max allowed UE UL TX power





DL DPCH Open Loop Power Control NodeB

UE

SRNC


RRC


NBAP



NBAP 4. ALCAP Iub Data Transport Bearer Setup

DL DPCH open loop power control

DCH - FP DCH - FP


DCH - FP DCH - FP

Start TX description RRC

7. CCCH : RRC Connection Setup

RRC

8. Radio Link Restore Indication NBAP

RRC

9. DCCH : RRC Connection Setup Complete

NBAP RRC

DL DPDCH Open Loop Power Control 

When a dedicated channel is set up, the initial power of downlink DPDCH can be calculated according to the following formula:

 P CPICH  Eb P init   ( ) DL     P Total  W No  ( Ec / No) CPICH  R

DL DPCCH Open Loop Power Control 1 timeslot Downlink Transmit Power

PO2

Data1 DPDCH

PO1

TPC

TFCI

DPCCH

PO3

Data2

Pilot

DPDCH

DPCCH

Downlink Power Control Restriction 

The power of downlink dedicated channel is limited by an upper and lower limit for each radio link



RlMaxDlPwr/RlMinDlPwr 

Parameter name: RL Max/Min DL TX power



Recommended value is shown in the next page

Downlink Power Restriction Parameters 

Recommended configurations for typical services: Service

RL Max Downlink Transmit Power (dB)

RL Min Downlink Transmit Power (dB)

Downlink SF

CS Domain 12.2 kbps AMR

-3

-18

128

28 kbps

-2

-17

64

32 kbps

-2

-17

64

56 kbps

0

-15

32

64 kbps

0

-15

32

PS Domain 8 kbps

-8

-23

128

32 kbps

-4

-19

64

64 kbps

-2

-17

32

144 kbps

0

-15

16

256 kbps

2

-13

8

384 kbps

4

-11

8


UL DPCH Open Loop Power Control NodeB

UE

SRNC


RRC


NBAP



NBAP 4. ALCAP Iub Data Transport Bearer Setup DCH - FP DCH - FP


DCH - FP DCH - FP

Start TX description 7. CCCH : RRC Connection Setup

RRC

UL DPCH open loop power control RRC

RRC

8. Radio Link Restore Indication NBAP 9. DCCH : RRC Connection Setup Complete

NBAP RRC

UL DPCCH Open Loop Power Control 

The initial power of the uplink DPCCH can be calculated according to the following formula: DPCCH_Initial_Power = DPCCH_Power_Offset - CPICH_RSCP



Where: 

DPCCH_Power_Offset is provided by the RNC to the UE via RRC signaling



CPICH_RSCP is the received signal code power of the PCPICH

UL DPCCH Open Loop Power Control Parameter 

DefaultConstantValue 

Parameter name: Constant value configured by default




Uplink Power Control Restriction 

There are four parameters which correspond to the maximum allowed transmit power of four classes of services: 

MaxUlTxPowerforConv



MaxUlTxPowerforStr



MaxUlTxPowerforInt



MaxUlTxPowerforBac 

Parameter name: Max UL TX power of conversational/streaming/interactive/background service





Contents 3. Closed Loop Power Control 3.1 Closed Loop Power Control Overview 3.2 Uplink Inner Loop Power Control 3.3 Downlink Inner Loop Power Control 3.4 Outer Loop Power Control

Closed Loop Power Control Overview 

Why closed loop power control is needed? 



Open loop power control is not accurate enough, it can only estimate the initial transmission power Closed loop power control can guarantee the QoS with minimum power. By decreasing the interference, the system capacity will be increased Outer Loop

S IR mea>SIR tar → TP C=0

B L E R mea>BLER tar →SIR tar B L E R tar B L E R mea
Inner Loop

S IR tar S IR mea S IR tar → TP C=1 Until S IR mea=SIR tar

TPC TPC=1 TPC=0

Power Power


Uplink Inner Loop Power Control 

NodeB compares the measured SIR to the target SIR, then derives TPC and sends the TPC Decision to UE TPC Decision Compare S IR mea with S IR tar

S IR mea S IR tar S IR mea S IR tar

( 0, 1 )

TP C = 0 → TP C = 1

Single RL / Soft HO PCA1 / PCA2

Generate TPC_cmd

Inner Loop

( -1, 0, 1 )

Set SIRtar

NodeB

Transmit TPC

UE

Adjust DPCCH Tx DPCCH = TP C TPC_cmd

Adjust DPDCH Tx

(

c ,

d )

Uplink Inner Loop PCA1 with Single Radio Link 

For single radio link and PCA1, UE derives one TPC_cmd in each time slot as follows: TPC

……

0

1

1

0

1

1

0

1

1

0

……

TPC_cmd

……

-1

1

1

-1

1

1

-1

1

1

-1

……

This control is performed in each time slot, so the power control frequency is 1500Hz

Uplink Inner Loop PCA2 with Single Radio Link 

For single radio link and PCA2, UE derives one TPC_cmd in each 5-slot group as follows: 10ms radio frame

TPC

Group 2

Group 1

Group 3

TS0

TS1

TS2

TS3

TS4

TS5

TS6

TS7

TS8

TS9

TS10

TS11

TS12

TS13

TS14

0

0

0

0

0

1

1

1

1

1

1

1

0

1

1

0

0

0

0

-1

0

0

0

0

1

0

0

0

0

0

……

……

TPC_cmd

This control is performed in each 5-slot group, so the power control frequency is 300Hz

……

……

Uplink Inner Loop Power Control with Soft Handover 

When UE enters soft handover state, on the NodeB side, there are two phases :





Uplink synchronization phase



Multi-radio link phase

On UE side, UE will receive different TPCs from different RLS in one time slot. Therefore, the UE should combine all the TPCs to get a unique TPC_CMD

Uplink Inner Loop PCA1 with Soft Handover CELL1

For each slot, combine TP C from the same RLS, then get W i

CELL2

RL1-1

RL1-2 RLS1

Get TPC_cmd based on

RLS3

RLS2

TP C _cmd = (W 1 , W 2, … W N ) CELL4

CELL3

RLS1-TPC (W1)

……

0

1

1

0

1

1

0

1

1

0

……

RLS2-TPC (W2)

……

1

0

1

1

0

1

0

1

0

1

……

RLS3-TPC (W3)

……

0

0

1

0

0

1

1

0

1

1

……

TPC_cmd

……

-1 -1

1

-1 -1

1

-1 -1 -1 -1

……

Uplink Inner Loop PCA2 with Soft Handover Combine TPC from same RLS in each time slot CELL1

CELL2

RL1-1 RLS1

Calculate TPC_temp i for each RLSi

RLS2

Calculate TPC_cmd 

If any TP C_tempi = -1, TP C_cmd = -1



1 N TPC _ tempi  0.5 , TP C_cmd = 1 If N i 1



Otherwise, TPC_cmd = 0



RL1-2

CELL3

RLS3

CELL4

Uplink Inner Loop PCA2 with Soft Handover (Cont.) 10ms/frame Group 1

Group 2

Group 3

TPC TS0

TS1

TS2

TS3

TS4

TS5

TS6

TS7

TS8

TS9

TS10

TS11

TS12

TS13

TS14

RLS1

0

0

1

0

0

0

0

0

0

0

0

1

0

0

1

RLS2

1

1

1

1

1

0

0

0

0

0

1

1

0

0

1

RLS3

1

1

1

1

1

0

0

0

0

0

1

1

1

1

1

TS0

TS1

TS2

TS3

TS4

TS5

TS6

TS7

TS8

TS9

TS10

TS11

TS12

TS13

TS14

RLS1

0

0

0

0

0

0

0

0

0

-1

0

0

0

0

0

RLS2

0

0

0

0

1

0

0

0

0

-1

0

0

0

0

0

RLS3

0

0

0

0

1

0

0

0

0

-1

0

0

0

0

1

TS0

TS1

TS2

TS3

TS4

TS5

TS6

TS7

TS8

TS9

TS10

TS11

TS12

TS13

TS14

0

0

0

0

1

0

0

0

0

-1

0

0

0

0

0

……

……

TPC_tempi ……

……

TPC_cmd ……

……

Uplink Inner Loop Power Control Parameters 



PwrCtrlAlg 

Parameter name: Power control algorithm selection



Recommended value: ALGORITHM1

UlTpcStepSize 

Parameter name: UL closed loop power control step size





Downlink Inner Loop Power Control 

UE L1 compares the measured SIR to the target SIR, then derives TPC and sends the TPC Decision to NodeB Derive TP C es t (k )

L3 set S IR tar

(0, 1) DPC_MODE

Inner Loop

Generate P TP C ( k)

L1 compare S IR mea with

S IR tar Calculate P(k)

NodeB

Derive and transmit TPC based on

DPC_MODE

Adjust DPCH Tx Power

UE

Downlink Inner Loop Power Control Mode 

Two DPC_MODE (Downlink Power Control Mode) could be used: 

If DPC_MODE = 0, UE sends a unique TPC in each slot, UTRAN shall derive TPCest to be 0 or 1, and update the power every slot



If DPC_MODE = 1, UE repeats the same TPC over 3 slots, UTRAN shall derive TPCest over three slots to be 0 or 1, and update the power every three slots

Downlink Inner Loop Power Control Mode Parameters 

DpcMode 

Parameter name: Downlink power control mode



Recommended value: SINGLE_TPC, namely DPC_MODE = 0

Downlink Inner Loop Power Control (Cont.) 

After estimating the TPC, NodeB shall set the new downlink power P(k) according to the following formula:

P ( k )  P ( k  1 )  P TPC ( k )  P ba l ( k ) 

Where: 

P(k-1) is (k-1):th downlink transmission power



PTPC(k) is the power adjustment due to TPC est(k)



Pbal (k) is correction value according to the downlink power balance procedure. For a single radio link, P bal (k) equals 0

Downlink Inner Loop Power Control (Cont.) 

PTPC(k) is calculated according to the following: 

If the value of “Limited Power Increase Used ” parameter is

“Not Used”, then:

 TPC P )   TPC ( k   TPC 

if TPC est ( k )  1 if TPC est ( k )  0

Where: 



TPCest (k) is the estimated TPC TPC

is downlink power adjustment step size, it’s determined by

the parameter FddTpcDlStepSize

Downlink Inner Loop Power Control (Cont.) 

If the value of “Limited Power Increase Used ” parameter is “Used”, then:

 TPC if TPC est ( k )  1 and   P ( k ) if TPC est ( k )  1 and 0 TPC    TPC if TPC est ( k )  0



Where:

 sum ( k )  TPC  Power _ Raise _ Limit  sum ( k )  TPC  Power _ Raise _ Limit

k 1

 sum( k ) 

 P TPC ( i ) i  k  DL _ Power _ Average _ Window _ Size

Downlink Inner Loop Power Control Parameters 

PC_INNER_LOOP_LMTED_PWR_INC_SWITCH 

This is one switch in PcSwitch (Power control switch) parameter





Recommended value: 0, namely OFF

FddTpcDlStepSize 

Parameter name: FDD DL power control step size



Recommended value: STEPSIZE_1DB, namely 1dB

Downlink Power Balance 

Purpose 

Monitor the Tx power of NodeBs and start the DPB process

The purpose of this procedure is to reduce power drift between radio links in macro diversity system



The start and stop of DPB when the DPB switch is on 

For the UEs in softer handover, the RNC evaluate the power difference

NodeB

NodeB

of the radio links and decide whether to start or stop DPB 

For the UEs in soft handover, DPB is always active

DPB process

Downlink Power Balance Parameters 

PC_DOWNLINK_POWER_BALANCE_SWITCH 




Recommended value: 1, namely ON


Outer Loop Power Control 

Why we need outer loop power control?

Different curves correspond to different multi-path environment BLER

SIR

Uplink Outer Loop Power Control Measure BLER of received data and compare with the BLER tar

Measure SIR and compare with SIR tar

Out loop

Set BLERtar

Inner loop

Transmit TPC

Set SIRtar

RNC

NodeB

UE

Initial SIR Setting 

The initial SIR target value (Init_SIR_target ) is servicedependent and is provided by the RNC to the NodeB



For the SRB and TRB, the values of SIR target, Max_SIR_target , and Min_SIR_target must fulfill the

following requirement: Min_SIR_target ≤ SIR target ≤ Max_SIR_target

Adjusting the SIR Target 

SIRtar adjustment formula:

  BLERmeas ,i ( n  1 )  BLERtar ,i SIRtar ( n )  MAX  SIRtar ( n  1 )   Stepi  Factor  BLERtar ,i   

Where: 

i is the ith transport channel



n is the nth adjustment period

SIR Target Adjustment Limitation 

The parameters Max_SIR_increase_step and Max_SIR_decrease_step limit the adjustment range of the

SIRtar, and the algorithm is: 

If SIRtar  0 and SIRtar  “Max_SIR_increase_step ”, then SIRtar (n+1) = SIRtar (n) + Max_SIR_increase_step



If SIRtar  0 and ABS (SIRtar)



“Max_SIR_decrease_step ”,

then SIRtar (n+1) = SIRtar (n) - Max_SIR_decrease_step

Parameters Example of BLER-based Uplink Outer Loop Power Control Service

BLER target

Init_SIR _target

Max_SIR _target

Min_SIR _target

OLPC period

SIR_adjust ment_step

Max_SIR_inc rease_step

Max_SIR_dec rease_step

SRB 3.4K

0.01

2 dB

5 dB

–2 dB

40 ms

0.004 dB

0.4 dB

0.2 dB

SRB 13.6K

0.01

4 dB

5 dB

–2 dB

20 ms

0.01 dB

0.5 dB

0.2 dB

AMR 12.2K

0.01

2 dB

5 dB

–2 dB

20 ms

0.005 dB

0.5 dB

0.2 dB

CSD 64K

0.002

4 dB

7 dB

–2 dB

20 ms

0.002 dB

1 dB

0.1 dB

PS I/B 8K

0.01

2 dB

5 dB

–2 dB

40 ms

0.004 dB

0.4 dB

0.2 dB

PS I/B 16K

0.01

2 dB

5 dB

–2 dB

20 ms

0.004 dB

0.4 dB

0.2 dB

PS I/B 32K

0.01

2 dB

5 dB

–2 dB

20 ms

0.004 dB

0.4 dB

0.2 dB

PS I/B 64K

0.01

2 dB

5 dB

–2 dB

20 ms

0.004 dB

0.4 dB

0.2 dB

PS I/B 128K

0.01

2 dB

5 dB

–2 dB

20 ms

0.004 dB

0.4 dB

0.2 dB

PS I/B 144K

0.01

2.5 dB

5.5 dB

–2 dB

20 ms

0.004 dB

0.4 dB

0.2 dB

PS I/B 256K

0.01

4 dB

7 dB

–2 dB

20 ms

0.004 dB

0.4 dB

0.2 dB

PS I/B 384K

0.01

6 dB

9 dB

–2 dB

20 ms

0.004 dB

0.4 dB

0.2 dB

Uplink Outer Loop Power Control Parameters 

PC_OLPC_SWITCH 




Recommended value: 1, namely ON

Uplink Outer-Loop Power Control Based on BER 

The OLPC based on the BER is similar to the OLPC based on the BLER, but the BER is used as the control object.



When the UE is in discontinuous transmission (DTX) mode, the RNC cannot receive data or update the BLER. Therefore, the BER is used to solve this problem.

Downlink Outer Loop Power Control Measure BLER of received data and compare with the

L3

BLER tar

Outer loop Set SIRtar

Inner loop

L1

NodeB

Transmit TPC

UE

Measure SIR and compare with SIR tar

WCDMA Power Control Algorithm and Parameters

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