08-wcdma rno power control_20051214

Huawei Confidential

WCDMA Power Control Principle

WCDMA Power Control Principle

23/4/18 2

Chapter 1 Power OverviewChapter 1 Power Overview

Chapter 2 Power Control AlgorithmChapter 2 Power Control Algorithm

23/4/18 3

Purpose of power control

• Purpose of power control

Power control of the uplink channel is mainly to overcome

the near-far effect.

Downlink channel power control is to overcome fast fading and the

interferences of adjacent cells.

• Power control must be used in CDMA system to

ensure every user transmit by minimum power and

the network capacity can get maximum.

• The purpose of inner loop power control (in the UL UE

to Node B) of the WCDMA system is to maintain a

certain signal-to-interference ratio (SIR target) of

transmission signal power when the signals reach the

receiving end.

• However, in different multi-path environments, even if

the mean signal-to-interference ratio is kept above a

certain threshold, the communication quality

requirement (BER or FER or BLER) can not be always

satisfied .

23/4/18 4

The Relationship between Transmitted Power and Received Power after Power Control Methods

Introduced

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

23/4/18 5

Benefit from Power Control

• Benefit from power control

Power control is known to be essential in a CDMA-based system due to

the uplink near-far problem

Adjust transmission power to ensure communication quality of uplink

and downlink.

Power control can well overcome the influences of unfavorable factors

such as fast fading, slow fading on radio channels

Decrease network interference, increase the capacity and quality of

network

In a word, the purpose of power control is to ensure the QoS with

minimum power in the CDMA system.

23/4/18 6

Power control classification

Power control classification ：• Open loop Power control

• Closed loop Power control is divided into two main parts:

• Inner power control UE-Node B

• Outer power control Node B-RNC

– Uplink inner power control

– Downlink inner-power control

– Uplink outer power control

– Downlink outer power control

UE NodeB RNC

SIR Target

Bler/BerSIR

TPC Command

Outer Loop Power Control

Inner Loop Power Control

Open Loop Power Control

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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 －－－ X

SCCPCH －－－ X

PRACH X －－－

AICH －－－ X

PICH －－－ X

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Chapter 1 Power OverviewChapter 1 Power Overview


23/4/18 9

1.Open loop power control1.Open loop power control

2.Inner-loop power control2.Inner-loop power control

3.Outer loop power control3.Outer loop power control


23/4/18 10

Open Loop Power Control Overview

• Purpose the UE estimates the power loss of signals on the propagation

path by measuring the downlink channel signals (CPICH-Tx

power), 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.

23/4/18 11

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 more

serious than that caused by propagation loss. Therefore, open

loop power control is applied only at the beginning of connection

setup, generally in setting the initial power value.

23/4/18 12

Open Loop Power Control of PRACH

The random access procedure of PRACH is shown in above

figure: UE transmit a preamble using the selected uplink access

slot, signature, and preamble transmission power. After

that ,UTARN will response AI if the preamble is received. Then the

UE will transmit the message part if the AI is received. But, if UE

does not receive the AI from UTRAN in τp-p period, a next

preamble will be transmitted. The process won’t stop until the AI

received by UE. Set as 8 times

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.

23/4/18 13

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

• Parameters explanation

The values of PCPICH DL TX power 、 UL interference and Constant

Value are given in system information.

The value of CPICH_RSCP is measured by UE

PCPICH DL TX power is very closed to the downlink coverage ability,

which is already given in cell setup.

UL interference can be measured by NodeB, then it will be reported to RNC.

Constant Value is the threshold of preamble message. This value has to be

analysed very carefully.

23/4/18 14

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

Preamble_Initial_power

23/4/18 15


• Different Constant Values for different stage of

WCDMA network

lifecycle. Take the beginning stage for example:

Constant Value could be greater (-16dB or -15dB) so that the preamble

message can be received easier by UTRAN

The power ramp step could be greater so that the possibility which the

preamble message can be received correctly will be higher

• With the development of network, the number of

users increased

very fast. On this stage, the Constant value could be

less 1dB.

23/4/18 16

Open loop power control of PRACH Open loop power control of PRACH

Application scenariosApplication scenarios1. CCCH : RRC Connection Request


5. Downlink Synchronisation

UE Node BServing RNS

Serving RNC

DCH - FP

Allocate RNTISelect L1 and L2parameters

RRC RRC

NBAP NBAP

3. Radio Link Setup Response

NBAP NBAP

2. Radio Link Setup Request

RRC RRC

7. CCCH : RRC Connection Set up

Start RX description

Start TX description

4. ALCAP Iub Data Transport Bearer Setup

RRC RRC

9. DCCH : RRC Connection Setup Complete

6. Uplink Synchronisation

NBAP NBAP

8. Radio Link Restore Indication

DCH - FP

DCH - FP

DCH - FP

23/4/18 17

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 + PCPICH

• Parameters explanation

(Ec/Io)req is the required Ec/Io, which should satisfied UE can receive

the message from the dedicated channel correctly

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

PCPICH is the transmission power of CPICH

• Comments

Similar to UL, the (Ec/Io)Req value should be considered very carefully

Because there is not power ramp in the initial DL DPCCH, the initial

power should be satisfied with the requirements. Therefore, this value

can be

greater than the one from simulation to ensure the success ratio

23/4/18 18

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

Application scenariosApplication scenarios

1. CCCH : RRC Connection Request

Open loop power control of DPCCH



Serving RNC

DCH - FP

Allocate RNTISelect L1 and L2 parameters

RRC RRC

NBAP NBAP


NBAP NBAP


RRC RRC





RRC RRC



NBAP NBAP


DCH - FP

DCH - FP

DCH - FP

23/4/18 19

Open loop power control of UL DPCCH

• The UL DPCCH open loop power control can be

calculated by the

following formula:

DPCCH_Initial_power ＝ PCPICH DL TX power - CPICH_RSCP

+ UL interference + DPCCH_SIRtarget

• References explanation PCPICH DL TX power is the transmission power of CPICH

CPICH_RSCP can be measured by UE

UL interference can be measured by NodeB

• Comments The DPCCH_SIR target value should be considered very carefully.

It reflects the lowest requirement for decoding the DPCCH in a

certain multiple path environment

23/4/18 20

Open loop power control of UL DPCCH Open loop power control of UL DPCCH

Application scenariosApplication scenarios

1. CCCH : RRC Connection Request

Open loop power control of DPCCH



Serving RNC

DCH - FP

Allocate RNTISelect L1 and L2parameters

RRC RRC

NBAP NBAP


NBAP NBAP


RRC RRC





RRC RRC



NBAP NBAP


DCH - FP

DCH - FP

DCH - FP

23/4/18 21





23/4/18 22

Close loop power control

• The deficiencies of open loop power control

the open loop power control can decided the initial power, but it’s 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 neededWhy the close loop power control is needed

23/4/18 23

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

• TPC is sent in each time slot that means the

frequency of TCP is 1500 repetition per second

15/10ms

The principle for Inner-loop power controlThe principle for Inner-loop power control

23/4/18 24

Inner-loop power control

• In 3GPP protocol, two algorithms are adopted in the

inner-loop

power control of uplink DPCCH

PCA1(Power Control Algorithm) ， uplink power control step is

tpc=△ 1dB or 2dB

PCA2 ， uplink power control step is tpc=△ 1dB

• The power control adjustment range in DPCCH is

△ DPCCH= tpc× TPC_cmd△ TPC_cmd is achieved by different algorithm

• The power offset shows the difference of

transmission power of UL

DPDCH and UL DPDCH

• The adjustment range of DPDCH is the same as the

DPCCH.

The power offset is decided by the signaling from

higher layer

IInner-loop power control Algorithmnner-loop power control Algorithm

23/4/18 25

Uplink-inner loop power control

• NodeB compares the measured signal-to-

interference ratio

to the preset target signal-to-interference ratio

(SIRtarget).

NodeB

UETransmit TPC

Inner-loop

set SIRtar

1500Hz 1500Hz

Each UE has own loop Each UE has own loop

23/4/18 26


2

2

d

c

DPDCH/DPCCH structureDPDCH/DPCCH structure

The power ratio of DPCCH to DPDCH is

Pilot N pilot bits

TPC NTPC bits

DataNdata bits

Slot #0 Slot #1 Slot #i Slot #14

Tslot = 2560 chips, 10 bits

1 radio frame: T f = 10 ms

DPDCH

DPCCHFBI

N FBI bitsTFCI

N TFCI bits

Tslot = 2560 chips, N data = 10*2 k bits (k=0..6)

23/4/18 27


• The uplink DPCCH SIR should be estimated by

different serving cells.

In each time slot, the TPC can be generated by the

following rules:

No soft handover

• If SIR estimation is greater than SIR target, the TPC is 0 to

decrease the transmission power

• If SIR estimation is less than SIR target, the TPC is 1 to

increase the transmission power

Soft handover

• In one time slot, UE received several TPC, then combine then.

• Comments

in the last situation, the PCA decides how the TPC_cmd are combined.

The PCA has two methods. UTRAN decides which one is used.

TPCTPC

23/4/18 28


• UE can adjust the UL DPCCH transmission

power with △ tpc step

according to the received TPC_cmd

• The step △ tpc can be 1dB or 2dB, which is

decided by UTRAN

If the TPC_cmd is 1 ， the UL DPCCH and UL

DPDCH transmission power should be increased

△ tpc

If the TPC_cmd is -1 ， the UL DPCCH and UL

DPDCH transmission power should be decreased

△ tpc

If the TPC_cmd is 0 ， the UL DPCCH and UL

DPDCH transmission power should be decreased

△ tpc

23/4/18 29


• UE only can receive one TPC in non-soft handover

situation,

If TPC ＝ 0 ， TPC_cmd= -1

If TPC ＝ 1 ， TPC_cmd= 1

PCA1PCA1

23/4/18 30


• When UE is in soft handover

UE can receive several TPCs in one time slot and combine

them to get one TPC_cmd by the following two steps:

• First, combine the TPCs from one RLS

• Then, combine the TPCs from different RLS

• Comments

The TPC from RLSi is Wi

PCA1PCA1

23/4/18 31


• Wi can be achieved by the following rules

If the TPC is 0, Wi=0

If the TPC is 1, Wi ＝ 1

Assume UE has N RLSes ， N TPC can be obtained after

combination, W1 、 W2…WN. The combination method for these

N TPCs from N RLSes can be described as following formula

TPC_cmd = γ (W1, W2, … WN)

• γ function should satisfied:

If one Wi is 0, TPC_cmd is -1

If all Wi are 1 ， TPC_cmd is 1

PCA1PCA1

23/4/18 32


• If UE is not in soft handover

Only one TPC is received in one time slot. The power control can be done

once by each 5 time slots. Each frame is divided 3 groups with 5 time

slots. In the first 4 time slots, the TPC_cmds are 0, which means the

power does not change. In the 5th time slot, the TPC_cmd can be

achieved by the following rules:

• If all the TPC are 0, the TPC_cmd is -1 and the transmission will decrease

1dB;

• If all the TPC are 1, the TPC_cmd is 1 and the transmission will increase

1dB;

• Otherwise, TPC_cmd=0.

TPC （ RX） TPC_cmd

0000 0 0000 -1

1111 1 0000 1

else 0000 0

PCA2PCA2

23/4/18 33


• When UE is in soft handover, the TPC_cmd can be

achieved by the

following two steps

First, combine the TPC from a same RLS

• N TPCi (i = 1,2......N) can be achieved from N RLSes in each time slot

• The N TPC_cmds from different RLS can be achieved by the above

mentioned rules. So the first 4 time slot, the TPC_cmd is 0. And the

each final TPC_cmd is decided in the 5th time slot

• Assume the each final TPC_cmd from N RLS are TPC_tempi （ i =

1,2......N ）

• The first 4 time slots, all TPC_tempi = 0

• Take the average.

• the TPC_cmd in fifth time slot can get by the following ruls ：

– Mathematic average for N TPC_temps. If it is greater than 0.5,

TPC_cmd=1. If it is less than -0.5, TPC_cmd=-1, otherwise TPC_cmd=0

PCA2PCA2

23/4/18 34


• The control frequency

TPC1, the power control frequency is 1500Hz

TPC2, the power control frequency is 300Hz

• Application scenarios

When UE is moving with high speed (80Km/h), the fast inner-loop

power control can not catch up with the fast fading, which produce

negative gain. In this situation, PCA2 is preferred.

Comparison between PCA1 and PCA2Comparison between PCA1 and PCA2

23/4/18 35

Downlink Inner-loop power control

NodeB

Set SIRtar

Transmit TPC

Measure SIR and compare

Inner-loop

1500Hz

23/4/18 36

Downlink inner-loop power control

The inner-loop power control of downlink DPCCH include two typies: one is the inner-loop power control in compressed mode, the other is the inner-loop power control in non-compressed mode.

Timeslot structure of Downlink DPCH :

－ PO1 defines the power offset of the TFCI bit in the downlink

DPCCH to DPDCH.

－ PO2 defines the power offset of the TPC bit in the downlink

DPCCH to DPDCH.

－ PO3 defines the power offset of the Pilot bit in the downlink

DPCCH to DPDCH.

－ The values of PO1 、 PO2 and PO3 are defined by RNC.

23/4/18 37


• Firstly, UE should estimate the downlink

DPDCH/DPCCH power and the current SIR

• Then, UE can generate TPC by comparing the

estimated SIR to target SIR

If the estimated SIR is greater than the target one, TPC is 0 (decrease

power)

If the estimated SIR is less than the target one, TPC is 1 (increase

power)

• The step of DL inner-loop power control could be

0.5 、 1 、 1.5 or 2dB

23/4/18 38


• 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

• As for responding to the receiving TPC, UTRAN will

adjust the downlink power of DPCCH/DPDCH. But the

transmission power can not higher than

Maximum_DL_Power, and not less than

Minimum_DL_Power neither.

Power control in different statePower control in different state

23/4/18 39

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 too much, it will

command the DPB process

• The initiation and stop of

DPB

The power offset of two RL is

greater than the DPB initial

threshold, the DPB process is

initiated

The power offset of two RL is less

than the DPB stop threshold, the

DPB process is stopped

NodeB

NodeB

Initiate the DPB process

DPB process

23/4/18 40





23/4/18 41

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

23/4/18 42

Uplink outer loop power control

NodeB UE

Transmit TPC

Measure and compare SIR

Inner-loop

Set SIRtar

get the good quality service data get the good quality service data

Out loop

RNC

Measure received data and

compare BLER in the TrCH

Set BLERtar

10-100Hz

23/4/18 43

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

23/4/18 44

outer loop power control

SIR target SIR target adjustment step adjustment step

etBLERt

etBLERtBLERmeastepSIRAdjustSoefficientSIRAdjustcSIRtar

arg

arg**

23/4/18 45

Outter loop power control

Uplink outer loop power control command transmit to

NodeB through DCH-FP

Node B SRNC

……

OUTER LOOP PC

23/4/18 46

Thank You

08-wcdma rno power control_20051214

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