06 wcdma power control issue1.1

HUAWEI TECHNOLOGIES CO., LTD. All rights reserved

www.huawei.com

Internal

OWJ200107 WCDMA Power Control

ISSUE 1.1


Chapter 1 Power Control OverviewChapter 1 Power Control Overview

Chapter 2 Open Loop Power Control Chapter 2 Open Loop Power Control

Chapter 3 Close Loop Power Control Chapter 3 Close Loop Power Control


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


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


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


Power control classification

Power control classification ：

Open loop Power control

Closed loop Power control

− Uplink inner power control

− Downlink inner-power control

− Uplink outer power control

− Downlink outer power control


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



Chapter 2 Open Loop Power ControlChapter 2 Open Loop Power Control



Chapter 2 Open Power Control Chapter 2 Open Power Control

2.1 Open loop power control overview2.1 Open loop power control overview

2.2 PRACH open loop power control2.2 PRACH open loop power control

2.3 DPCCH open loop power control2.3 DPCCH open loop power control


Open Loop Power Control Overview

Purpose

UE estimates the power loss of signals on the propagation path

by measuring the downlink channel signals, then calculate the

transmission power of the uplink channel

The open loop power control principle

Fast fading of the uplink channel is unrelated to fast fading of the

downlink channel


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.

Open loop power control is applied only at the beginning of

connection setup, generally in setting the initial power value.


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.

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.


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.


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



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 increasing of subscribers, the Constant value could be

less 1dB.


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

Application scenariosApplication scenarios

1. 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


Open loop power control of DL DPCCH The DL DPDCH 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 begreater than the one from simulation to ensure the success ratio

With PO1, PO2 and PO3, initial transmission power for DPCCH can be calculated


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



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


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+ Default Constant Value

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

Default Constant Value will decide initial transmission power of Uplink DPCCH

This value is different from the previous “Constant value” for PRACH


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



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



Chapter 2 Open Loop Power Control Chapter 2 Open Loop Power Control




3.1 Close Loop power control overview3.1 Close Loop power control overview

3.2 Uplink inner loop power control3.2 Uplink inner loop power control

3.3 Downlink inner loop power control3.3 Downlink inner loop power control

3.4 Outer loop power control3.4 Outer loop power control


Close loop power control overview

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


Close loop power control overview

Inner loopOuter loop

Control process:BLERmea>BLERtar→SIRtar

BLERmea<BLERtar→SIRtar

Until to BLERmea=BLERtar

SIRtar

Control process ：SIRmea>SIRtar→TPC=0

SIRmea<SIRtar→ TPC=1

Until toSIRmea=SIRtar

TPC

Control process ：TPC=0 Power

TPC=1 Power

Inner loop power control With TPC in DPCCH, the SIR can be ensured to the level of target SIR. Inner loop power control can be done 1500 times in 1 second

Outer loop power control Through adjusting the SIR target value, BLER can be ensured to the QoS requirement

BLERtar

Ensure the QoS with minimum

power


Uplink-inner loop power control

NodeB compares the measured signal-to-interference ratio

to the preset target signal-to-interference ratio (SIRtarget).

NodeB

UE

Transmit TPC

Inner-loop

set SIRtar

1500Hz1500Hz

Each UE has its own loop

Each UE has its own 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


Uplink inner-loop power control

The receivers calculate the SIR by estimating the power strengthen

and the current interference. Then, compare this one with 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

How to produce TPCHow to produce TPC



In 3GPP protocol, UE can get different TPC_cmd (1, 0, -1) based

on different PCA (power control algorithm)

Adjustment on DPCCH

△DPCCH= tpc×TPC_cmd△

− If TPC_cmd=1 ， Uplink DPCCH Tx should increase △ tpc

− If TPC_cmd=-1 ， Uplink DPCCH Tx should decrease △ tpc

− If TPC_cmd=0 ， uplink DPCCH Tx does not change

△tpc

PCA1 ， uplink power control step is tpc=△ 1dB or 2dB

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

TPC_cmdTPC_cmd


Uplink DPDCH power is decided by the offset between DPCCH and DPDCH

This offset is decided by upper layer


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)


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 TS

Power control frequency is 1500HZ

0 1 1 0 1 1 0 1 1 0…… ……

…… ……TPC_CMD

TPC

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

Uplink inner-loop power controlWithout soft handover in PCA1Without soft handover in PCA1


0 1 1 0 1 1 0 1 1 0…… ……

RLS1-TPC (W1)

…… ……RLS2-TPC (W2) 1 0 1 1 0 1 0 1 0 1

…… ……

…… …… Final TPC

0 0 1 0 0 1 1 0 1 1

0 0 1 0 0 1 0 0 0 0

Each TS, combine TPC from different RLS ， then get Wi

CELL1 CELL2

CELL4CELL3

RL11 RL12

RLS1

RLS2 RLS3

RLS3-TPC (W3)

Get TPC_cmd based on

TPC_cmd = γ (W1, W2, … WN)

With soft handover in PCA1With soft handover in PCA1



Each time slot, UE will receive TPC from different RL. UE can get the final

TPC_cmd based on the following steps:

Combine TPC from same RLS. Actually, the TPCs for same RLS are same;

Combine TPC from different RLS. Suppose the TPC for RLSi is W i, and for

each RLS, if

− TPC=0, Wi =0

− TPC=1, Wi =1

About TPC_cmd = γ (W1, W2, … Wn)

If any Wi is 0, TPC_cmd=-1

If all Wi are 1, TPC_cmd=1




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

10ms/frame

Group 2Group 1 Group 3

…… ……

0 0 0 0 -1 0 0 0 0 1 0 0 0 0 0

TPC

TPC_CMD

Transmission power will be controlled in each 5 time slots

The frequency is 300HZ

…… ……

Uplink inner-loop power controlWithout soft handover in PCA2Without soft handover in PCA2


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

Without soft handover in PCA2Without soft handover in PCA2



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=1If 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 power controlWith soft handover in PCA2With soft handover in PCA2



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

− 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




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 1 1 1 0 1 1 1 1 1 1

…… ……

10ms/frameGroup 1 Group 2 Group 3


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 0 0 0 0 0 1

…… ……

TPC

TPC_tempi


0 0 0 0 1 0 0 0 0 -1 0 0 0 0 0…… ……

TPC_CMD

Power is controlled in each 5 time slots

The power control frequency is 300HZ

Uplink-inner loop power controlWith soft handover in PCA2With soft handover in PCA2



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 prefered.

Comparison between PCA1 and PCA2Comparison between PCA1 and PCA2


NodeB

set SIRtar

Transmit TPC

Measure and compare SIR

Measure and compare BLER

Outer loop

Inner loop L1

L3

10-100Hz1500Hz

Downlink close loop power control


Downlink Inner-loop power control

NodeB

Set SIRtar

Transmit TPC in each TS

Measure SIR and compareAdjust Tx power

with 0.5, 1, 1.5 or 2dB

1500Hz


Downlink inner-loop power control

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



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 produce TPCHow to produce TPC


The transmission power can not higher than Maximum_DL_Power, and not less than

Minimum_DL_Power neither.

Downlink power adjustment:

Pk Pk 1PTPCkPbalkWhere

P(k-1) is power of previous

PTPC(k) is the adjustment

Pbal(k) is correction value

Downlink inner-loop power controlHow to adjust powerHow to adjust power


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”


0)(TPCifΔ

1)(TPCifΔ)(P

estTPC

estTPCTPC k

kk


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



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.12 3


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


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


Uplink outer loop power control

NodeB UE

Transmit TPC


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


NodeB

set SIRtar

Transmit TPC


Measure and compare BLER

Outer loop

Inner loop L1

L3

10-100Hz1500Hz

Downlink outer loop power control


outer loop power control

SIR 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


Outer loop power control

Uplink outer loop power control command transmit to NodeB

through DCH-FP

Node B SRNC

……

OUTER LOOP PC

www.huawei.com

Thank You

06 wcdma power control issue1.1

Documents

loop power

tpc ifelimit

rrc connection

initial transmission

fp huawei

transmission

initial power

huawei technologies