10 wcdma power control

HUAWEI TECHNOLOGIES CO., LTD.

www.huawei.com

HUAWEI Confidential

Internal Only

WCDMA Power Control

HUAWEI TECHNOLOGIES CO., LTD. HUAWEI Confidential

Chapter 1 Overview of Power ControlChapter 1 Overview of Power Control

Chapter 2 Introduction to Power Control


Relation between Tx Power and Rx Power after introduction of Power Control

Rx power

Tx power

Fading channel


Purposes of Power Control

Solve the near-far effect

Ensure the uplink/downlink quality by adjusting the transmit power

Overcoming slow fading and fast fading

Decrease interference, and improve system quality and capacity

In short, the purpose of power control in the CDMA system is ensuring

user’s communication quality with minimum transmit power


Power Control Classification

Open loop power controlOpen loop power control

Uplink open loop power control (reverse)

Downlink open loop power control (forward)

Closed loop power controlClosed loop power control

Uplink inner-loop power control

Downlink inner-loop power control

Uplink outer-loop power control

Downlink outer-loop power control


Chapter 1 Overview of Power Control

Chapter 2 Introduction to Power ControlChapter 2 Introduction to Power Control


Chapter 2 Chapter 2 Introduction to Power ControlIntroduction to Power Control

2.1 Open Loop Power Control

2.2 Inner-Loop Power Control

2.3 Outer-Loop Power Control


Principles of Open Loop Power Control

Principle

Assume that path loss for Uplink and Downlink between the transmitter and

the receiver are the same, and the UE or RNC determines the transmit power

according to the received power.

Basic functions

Overcome fading and path loss

Disadvantage

Asymmetry between power of the uplink signal and downlink signal is not

considered, so power control is not very accurate.

Applications scenarios

Uplink: applied on PRACH and DPCCH

Downlink: applied on DPCCH


Open Loop Power Control on PRACH

RACH

BCH: CPICH powerUL interference level

The UE measures received power of the CPICH and calculates initial uplink transmit power


Principle of Open Loop Power Control

Principles of setting initial transmit power (e.g. Uplink)

EcIoXceInterferenRSCPCPICHPowCPICHPowX

PLPLSuppose

ceInterferenPLPowXEcIoX

PLPowCPICHRSCPCPICH

UL

ULDL

ULUL

DL

____

)3......(..................................................:

)2.(....................__

)1........(....................__



Ⅰ

Ⅲ

Ⅱ

I : Tx_power = Preamble_Initial_PowerII : Tx_power = I + PowerRampStepIII : Tx_power = II + PowerRampStepIV : Tx_power = III + PowerOffsetPpm

PRACH

Ⅳ



Preamble_Initial_Power = PCPICH DL TX power - CPICH_RSCP + UL interference +

Constant Value

Notes: UE can get the PCPICH DL TX power, UL interference, and the constant value from the

system information.

CPICH_RSCP is measured by UE itself.

Normally in the initial stages of network lifecycle, coverage is limited, constant value

could be set greater (-16 dB or -15dB) so the preamble message can be received easier

by UTRAN. The power ramp step could also be set greater. (Currently we take the

default setting)

Method for setting the first preamble transmit power on PRACHMethod for setting the first preamble transmit power on PRACH

Default parameters setting:

Constant Value: -20dB PowerRampStep: 2dB

PreambleRetransMax: 20 PowerOffsetPpm: -3 / -2

Mmax: 8


Open Loop Power Control in the Uplink DPCCH

DPCCH_Initial_power = DPCCH_Power_offset - CPICH_RSCP

Notes:

CPICH_RSCP is measured by UE.

DPCCH_Power_offset is DPCCH initial transmission power offset, which is

configured by RNC and delivered to UE in RRC Connection Setup. It is

calculated by the following formula:

DPCCH_Power_offset = Primary CPICH DL TX power + UL

interference +Default Constant Value

Method for setting initial power of the uplink DPCCHMethod for setting initial power of the uplink DPCCH


Open Loop Power Control in the Downlink DPCCH

Method for setting downlink DPCCH initial powerMethod for setting downlink DPCCH initial power

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

Notes:

(Ec/Io)Req: the Ec/Io required to ensure the UE can receive this dedicated channel

CPICH_Ec/Io: PCPICH Ec/Io measured by UE, and It is reported to the UTRAN on RACH.

PCPICH: the PCPICH transmit power.


Chapter 2 Chapter 2 Introduction to Power ControlIntroduction to Power Control

Open Loop Power Control

Inner Loop Power Control

Outer Loop Power Control

Inner Loop Power Control in

Compressed Mode


Closed Loop Power Control

Inner loop power control and outer loop power control together are called closed loop power control.

Inner loop power control

Measure SIR

Power control bits

SIR target

Outer loop power control


Uplink Inner Loop Power Control

NodeB UE

Send TPC bits

Measure SIRs of the received signals

and compare them

Inner loop

Set SIRtar

1500Hz

Purpose of inner loop power control: Make the measured SIR converge to the given SIRtar as soon as possible. Each UE has a

control loop.


Downlink Inner Loop Power Control

NodeB

Set SIRtar

Send the TPC command

Measure SIRs and compare them.

Inner loop

1500Hz


Chapter 2Chapter 2 Introduction to Power ControlIntroduction to Power Control

Open Loop Power Control

Inner Loop Power Control


Inner Loop Power Control in

Compressed Mode



Phenomenon

With the same SIR target, the BLER statistic results of the service in different

environments are different.

Reason

The QoS which the UTRAN provides to NAS is BLER, not SIR.

Purpose of outer loop

Provide link quality that meets a certain BLER target for the NAS.

Basic principle

If the measured BLER/BER is lower than the BLER/BER target, reduce

the SIRtar of the inner loop.

If the measured BLER/BER is higher than the BLER/BER target, increase

the SIRtar of the inner loop.


Uplink Outer Loop Power Control

NodeB UE

Sent TPC

SIR measurement and comparing

Inner loop

SIR target setting

BLER measurement

Outer loop

RNC

Comparing

BLER target setting


Downlink Outer Loop Power Control

NodeB

Set SIRtar

Send TPC

Measure SIRs and compare them.

Measure BLERs and compare them

Outer loop

Inner loop

Physical layer of the UE

Layer 3 of UE

Downlink outer loop and outer loop power control


Appendix: The common configurable table of uplink power control parameters


Appendix: The common configurable table of downlink power control parameters


Appendix: Applicability of Power Control for Each Channel

Physical

ChannelOpen Loop

Close Inner

Loop

Closed Outer

Loop

No Power

Control

PRACH √

DPCCH √ √ √

DPDCH √ √

CPICH √

PCCPCH √

SCCPCH √

AICH √

PICH √

Thank you!www.huawei.com


Uplink Inner Loop Power Control - Detail NodeB side: The NodeB measures uplink DPCCH SIR in every time slot and then

compare it with the SIR target. If the measured SIR is larger than the SIR target, the NodeB sends the TPC = 0; otherwise, the NodeB sends TPC = 1;

UE side: The UE processes the TPC command and computes TPC_cmd; There are two modes of uplink power control:

PCA1, the UE processes the TPC command in every time slot and the step size tpc is 1 △dB or 2 dB;

PCA2, the UE processes the TPC command in every five time slots and the step size tpc △is 1 dB;

Step size adjustment of power control in the DPCCH: dpcch = tpc * △ △TPC_cmd,TPC_cmd is the TPC.

command calculated with the previous formula. tpc is also related to it.△

The proportion of power of the DPCCH and DPDCH is the square of βc/βd.(βc/βd is configured by the higher layer) Cd

Cc

¦ Âd

¦ Âc j

DPDCH

DPCCH

I

Q

I+jQ

Sdpch

S


Inner Power Control in the Uplink DPCCH - Detail

When the UE is not in soft handover, it receives a TPC command in

every time slot.

If TPC ＝ 0, TPC_cmd=-1

If TPC ＝ 1, TPC_cmd=1

When the UE is in soft handover (PCA1)

It combines the TPC commands of the same RLS. It performs

maximum-ratio combining for RLs of different cells and generates a

TPC, and then sends this TPC command to each cell. TPC commands

of all RLs in a RLS are the same.

TPC command processing algorithm1(PCA1)TPC command processing algorithm1(PCA1)



When the UE is in soft handover (PCA1)

It combines TPC commands of different RLS. The combining rules

are as follows: (N: RLS Num)

TPC command processing algorithm1(PCA1)TPC command processing algorithm1(PCA1)

"0",0

"1",1

10,1

1,1) W , W,(W g TPC_cmd

#,

#,

1

1

N21

slotest

slotesti

N

ii

N

ii

TPC

TPCW

N

W

N

W



When the UE is not in soft handover (PCA2)

The UE performs power control in every five time slots. During the first four time slots,

power remains.

In the fifth time slot, the UE decides TPC_est of these five time slots with a hard-

decision algorithm:

otherwise

estTPC

estTPC

ii

ii

,0

15/_,1

05/_,1

slot)h TPC_cmd(5t

5

1

5

1

TPC command processing algorithm 2(PCA2)TPC command processing algorithm 2(PCA2)

TPC_est TPC_cmd

0000 0 0000 -1

1111 1 0000 1

else 0000 0



When the UE is in soft handover (PCA2),

It combines TPC commands of the same RLS. It perform maximum-ratio combining and

generates the TPC command with a hard decision algorithm.

If all 5 hard decisions within a set are "1", TPC_tempi = 1.

If all 5 hard decisions within a set are "0", TPC_tempi = -1.

Otherwise, TPC_tempi = 0.

The UE combines TPC commands of different RLS according to the following rules:

TPC command processing algorithm 2(PCA2)TPC command processing algorithm 2(PCA2)

otherwise

NtempTPC

NtempTPC

N

ii

N

ii

,0

5.0/_,1

5.0/_,1

)TPC_temp ,TPC_temp ,(TPC_temp

slot)h TPC_cmd(5t

1

1

N21



Difference in control rate

TPC command processing algorithm 1: the power control rate is 1500Hz;

TPC command processing algorithm 2: power control rate is 300Hz.

Application scenario

When the UE moves at a high speed (80km/h), fast fading cannot be traced in

fast inner loop power control (one time slot should be longer than the wavelength)

and minus gain occurs. In this situation, algorithm 2 is suggested. For example,

algorithm 2 is recommended for the cells covering a express way.

Comparison between two algorithmsComparison between two algorithms


Downlink Inner Loop Power Control - Detail

UE side: The UE compares the SIR of the pilot in the DPCCH (after

maximum-ratio combining during soft handover) with the SIR target and

generate the TPC command accordingly

If DPC-MODE=0, the UE sends a TPC command in every time slot.

If DPC-MODE=1, the UE sends a same TPC command in every three time slots.

Node B side: The Node B adjusts transmit power of the DPCCH and

DPDCH after receiving the TPC command. Step size is 0.5 dB, 1 dB, 1.5

dB, or 2dB.

If DPC-MODE=0, the Node B adjusts the transmit power in every time slot.

If DPC-MODE=1, the Node B adjusts transmit power in every three time slots.


Downlink Inner Loop Power Control - Detail

Downlink transmit power

P(k) = P(k - 1) + PTPC(k) + Pbal(k)

Limited power increase is not supported (if the value of Limited power Raised Used is "Not

used")

Limited power increase is supported (if the value of Limited power Raised Used is "Used"

, 1

, 0est

TPC

est

TPC TPCP

TPC TPC

i f

i f

and

and

1 _ _

0 1 _ _

0

est sum TPC

TPC est sum TPC

est

TPC TPC Power Raise Limit

P TPC Power Raise Limit

TPC TPC

，I F

， I F

，I F

1k

Size_Window_Averaging_Power_DLkiTPCsum )i(P

10 wcdma power control

Documents

common configurable

compressed

limited power

power control

power control

preamble transmit

power controlhuawei

adjusts transmit