power control wcdma

8/4/2019 Power Control WCDMA

1/21

Power Control WCDMA


2/21

Page 2

Power control methods adopted for various physical channels

Power control methods adopted for various physical channels "X" can be applied, "" not applied

Physical

channel

Open loop

power

control

Inner loop

power

control

Outer loop

power

Control

No power control process,

power is specified by upper

layers.

DPDCH X X DPCCH X X X PCCPCH XSCCPCH XPRACH X AICH XPICH X


3/21

Power Control Classification

UE NodeB RNC

SIR Target

Bler/BerSIR

TPC Command

Outer Loop Power Control

Inner Loop Power Control

Open Loop Power Control

Open Loop Power ControlOpen loop power control is used to determine UEs initial uplink transmit power in PRACH and

NodeBs initial downlink transmit power in DPDCH. It is used to set initial power reference values for

power control.

Outer Loop power controlOuter loop power control is used to maintain the quality of communication at the level of bearer servicequality requirement, while using as low power as possible.

Inner loop power control (also called fast closed loop power control)

Inner loop power control is used toadjustUEs uplink / NodeBs downlink Dpch Power every one slotin accordance with TPC commands. Inner loop power control frequency is 1500Hz.


4/21

Page 4

Chapter 2 Power Control Algorithm

2.1 Open loop power control

2.2 Inner-loop power control

2.3 Outer loop power control


5/21

Page 5

Open Loop Power Control Overview

Purpose the UE estimates the power loss of signals on the

propagation path by measuring the downlinkchannel signals, then calculate the transmission

power of the uplink channel

The open loop power control principal Under the FDD mode, fast fading of the uplink

channel is unrelated to fast fading of the downlink

channel.


6/21

Page 6

Open Loop Power Control Overview

the disadvantage of open loop power control This power control method is rather vague

Application scenarios of open loop power control In the range of a cell, signal fading caused by fast fading

is usually moreserious than that caused by propagation loss. Therefore,open loop power control is applied only at the beginningof connection setup, generally in setting the initial powervalue.


7/21

Page 7

Open loop power control of PRACH

Application scenarios

1. CCCH: RRC Connection Request

Open loop powercontrol of PRACH

5. Downlink Synchronisation

UENode B

Serving RNS

Serving

RNC

DCH - FP

Allocate RNTISelect L1 and L2parameters

RRCRRC

NBAPNBAP

3. Radio Link Setup Response

NBAPNBAP

2. Radio Link Setup Request

RRCRRC7. CCCH: RRC Connection Set up

Start RXdescription

Start TXdescription

4. ALCAP Iub Data Transport Bearer Setup

RRCRRC9. DCCH: RRC Connection Setup Complete

6. Uplink Synchronisation

NBAPNBAP

8. Radio Link Restore Indication

DCH - FP

DCH - FP

DCH - FP


8/21

Page 8

Open loop power control of DL DPCCH



Open loop power

control of DPCCH5. Downlink Synchronisation

UENode B

Serving RNS

Serving

RNC

DCH - FP


RRCRRC

NBAPNBAP


NBAPNBAP



Start RXdescription

Start TXdescription




NBAPNBAP


DCH - FP

DCH - FP

DCH - FP


9/21

Page 9

Open loop power control of UL DPCCH



Open loop power

control of DPCCH

5. Downlink Synchronisation

UE Node B

Serving RNS

Serving

RNC

DCH - FP


RRCRRC

NBAPNBAP


NBAPNBAP



Start RXdescription

Start TXdescription




NBAPNBAP


DCH - FP

DCH - FP

DCH - FP


10/21

Page 10






11/21

Page 11

Close loop power control

The deficiencies of open loop power control

the open loop power control can decided the initial power, but its still

inaccurate

For WCDMA-FDD system, the uplink fading is not related to the downlink

one because of the big frequency interval of them Therefore, the path loss and interference estimated by downlink can not

reflect

the one in uplink completely. But, the close loop power control can solve this

problem

The advantages of close loop power control

Can convergence the transmission power of uplink and downlink very fast, and

decrease interference in system.

Maintains a higher quality of service

Why the close loop power control is needed


12/21

Page 12

Inner-loop power control

The receivers calculate the SIR by estimating the power strengthen

and the current interference. Then, compare this one to SIRtarget,

If less than SIRtarget, the TPC is 1 to tell receivers increase

transmission power

If greater than SIRtarget, the TPC is 0 to tell receivers decrease

transmission power

The receiver which get the TPC will adjust the transmission power

by algorithms. The inner loop power control can convergence the

estimated SIR to SIR target

The principle for Inner-loop power control


13/21

Page 13

Uplink-inner loop power control

NodeB compares the measured signal-to-interference ratioto the preset target signal-to-interference ratio (SIRtarget).

NodeB

UETransmit TPC

Inner-loop

set SIRtar

1500Hz

Each UE has own loop


14/21

Page 14


UE can adjust the UL DPCCH

transmission power withtpc step

according to the received TPC_cmd

The steptpc can be 1dB or 2dB,

which is decided by UTRAN If the TPC_cmd is 1the UL DPCCH and UL DPDCH transmission

power should be increasedtpc

If the TPC_cmd is -1the UL DPCCH and UL DPDCH transmissionpower should be decreasedtpc

If the TPC_cmd is 0the UL DPCCH and UL DPDCH transmission

power should be decreasedtpc


15/21

Page 15


NodeB compares the measured signal-to-interference ratioto the preset target signal-to-interference ratio (SIRtarget).

NodeB

UETransmit TPC

Inner-loop

set SIRtar

1500Hz

Each UE has own loop


16/21

Page 16






17/21

Page 17

Outer-loop power control

The limitation of inner loop power control

The purpose of inner loop power control of the WCDMA system is to

maintain a certain signal-to-interference ratio of transmission signal

power when the signals reach the receiving end.

The character of outer-loop power control

The Qos which NAS provide to CN is BLER, not SIR

The relationship between inner-loop power control and outer-loop power control

SIR target should be satisfied with the requirement of decoding correctly. But

different multiple path radio environment request different SIR

Therefore, the outer-loop power control can adjust the SIR to get a stable BLER in

the changeable radio environment


18/21

Page 18

Uplink outer loop power control

NodeB UE

Transmit TPC

Measure and compare SIR

Inner-loop

Set SIRtar

get the good quality

service data

Out loop

RNC

Measure receiveddata and compareBLER in the TrCH

Set BLERtar

10-100Hz


19/21

Page 19

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


20/21


21/21

UMTS Power Control

Open loop power control is the ability of the UE transmitter to sets its output power to a specific value. It is used for settinginitial uplink and downlink transmission powers when a UE is accessing the network. The open loop power control tolerance is 9 dB (normal conditions) or 12 dB (extreme conditions)

Inner loop power control (also called fast closed loop power control) in the uplink is the ability of the UE transmitter to adjust its

output power in accordance with one or more Transmit Power Control (TPC) commands received in the downlink, in order to keepthe received uplink Signal-to-Interference Ratio (SIR) at a given SIR target. The UE transmitter is capable of changing the outputpower with a step size of 1, 2 and 3 dB, in the slot immediately after the TPC_cmd can be derived. Inner loop power controlfrequency is 1500Hz.

The serving cells estimate SIR of the received uplink DPCH, generate TPC commands (TPC_cmd) and transmit the commands onceper slot according to the following rule: if SIRest > SIRtarget then the TPC command to transmit is "0", while if SIRest < SIRtarget thenthe TPC command to transmit is "1". Upon reception of one or more TPC commands in a slot, the UE derives a single TPCcommand for each slot, combining multiple TPC commands if more than one is received in a slot. Two algorithms are supportedby the UE for deriving a TPC_cmd. Which of these two algorithms is used, is determined by a UE-specific higher-layer parameter,"PowerControlAlgorithm".

Algorithm 1:The power control step is the change in the UE transmitter output power in response to a single TPC command

Algorithm 2:If all five estimated TPC command are "down" the transmit power is reduced by 1 dBIf all five estimated TPC command are "up" the transmit power is increased by 1 dBOtherwise the transmit power is not changed

The transmit power of the downlink channels is determined by the network. The power control step size can take four values: 0.5,1, 1.5 or 2 dB. It is mandatory for UTRAN to support step size of 1 dB, while support of other step sizes is optional. The UE

generates TPC commands to control the network transmit power and send them in the TPC field of the uplink DPCCH. Uponreceiving the TPC commands UTRAN adjusts its downlink DPCCH/DPDCH power accordingly.

Outer loop power control is used to maintain the quality of communication at the level of bearer service quality requirement,while using as low power as possible. The uplink outer loop power control is responsible for setting a target SIR in the Node B foreach individual uplink inner loop power control. This target SIR is updated for each UE according to the estimated uplink quality(BLock Error Ration, Bit Error Ratio) for each Radio Resource Control connection. The downlink outer loop power control is theability of the UE receiverto converge to required link quality (BLER) set by the network (RNC) in downlink.

power control wcdma

Documents