08-wcdma power control.ppt

8/10/2019 08-WCDMA Power Control.ppt

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Huawei Confidential. All Rights Reserved

WCDMA Power Control Principle

ISSUE 1.0


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Internal Use2

Chapter 1 Power Overview

Chapter 2 Power Control Algorithm


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Internal Use3

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 transmitby minimum power and the network capacity can get maximum.

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. 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 .


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Internal Use4

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)

Relativepower

(dB)

Channel

Transmitted power

Received power


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Internal Use5

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.


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Internal Use6

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


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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

powercontrol

Inner loop

powercontrol

Outer loop

powerControl

No power control process,

power is specified by upperlayers.

DPDCH

DPCCH

PCCPCH

SCCPCH

PRACH

AICH

PICH


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Chapter 1 Power Overview

Chapter 2 Power Control Algorithm


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1.Open loop power control

2.Inner-loop power control

3.Outer loop power control

Chapter 2 Power Control Algor ithm


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Open Loop Power Control Overview

Purpose

the 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

Under the FDD mode, fast fading of the uplink channel is unrelated to

fast fading of the downlink channel.


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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.


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Internal Use12

Open Loop Power Control of PRACH

The random access procedure of PRACH is shown in above figure: UE transmit apreamble 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 p-p period, a next preamble will be transmitted. The process wont stop until

the AI received by UE.

AICH access

slots RX at UE

PRACH accessslots TX at UE

One access slot

p-a

p-mp-p

Pre-

amble

Pre-

ambleMessage part

Acq.Ind.


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Internal Use13

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 powerUL 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.


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Internal Use14

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


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Internal Use15


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.


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Internal Use16


Appl ication scenar ios

1. CCCH: RRC Connection Request

Open loop powercontrol of PRACH

5. Downlink Synchronisation

UE Node BServing RNS

ServingRNC

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

NBAPNBAP8. Radio Link Restore Indication

DCH - FP

DCH - FP

DCH - FP


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Internal Use17

Open loop power control of DL DPCCH

The DL DPCCH open loop power control can be calculated by the

following formula:

P=Ec/IoReq-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


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Internal Use18

Open loop power control of DL DPCCH



Open loop power

control of DPCCH5. Downlink Synchronisation


ServingRNC

DCH - FP


RRCRRC

NBAPNBAP


NBAPNBAP



Start RXdescription

Start TXdescription





DCH - FP

DCH - FP

DCH - FP


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Internal Use19

Open loop power control of UL DPCCH

The UL DPCCH open loop power control can be calculated by the

following formula:DPCCH_Initial_powerPCPICH 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_SIRtarget value should be considered very carefully.

It reflects the lowest requirement for decoding the DPCCH in a

certain multiple path environment


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Internal Use20

Open loop power control of UL DPCCH



Open loop power

control of DPCCH

5. Downlink Synchronisation


ServingRNC

DCH - FP


RRCRRC

NBAPNBAP


NBAPNBAP



Start RXdescription

Start TXdescription





DCH - FP

DCH - FP

DCH - FP


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Internal Use21


2.I nner-loop power control




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Internal Use22

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, anddecrease interference in system.

Maintains a higher quality of service

Why the close loop power control is needed


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Internal Use23

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 I nner-loop power control


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Internal Use24

Inner-loop power control

In 3GPP protocol, two algorithms are adopted in the inner-loop

power control of uplink DPCCH

PCA1uplink power control step istpc=1dB or 2dB

PCA2uplink power control step is tpc=1dB

The power control adjustment range in DPCCH is

DPCCH=tpcTPC_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

I nner-loop power control Algor ithm


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Internal Use25

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

Each UE has own loop

U li k i l t l


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Internal Use26


2

2

d

c

DPDCH/DPCCH structure

The power ratio of DPCCH to DPDCH is

Pilot

N pilot bits

TPC

NTPCbits

Data

Ndata bits

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

Tslot

= 2560 chips, 10 bits

1 radio frame: Tf

= 10 ms

DPDCH

DPCCHFBI

N

FBI

bitsTFCI

N

TFCI

bits

Tslot

= 2560 chips, Ndata

= 10*2 kbits (k=0..6)


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Internal Use27


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.

TPC


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Internal Use28


UE can adjust the UL DPCCH transmission power with tpc 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 transmission

power should be decreasedtpc

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

power should be decreasedtpc


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Internal Use29


UE only can receive one TPC in non-soft handover situation,

If TPC0TPC_cmd= -1

If TPC1TPC_cmd= 1

PCA1


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Internal Use30


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

PCA1


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Internal Use31


Wi can be achieved by the following rules

If the TPC is 0, Wi=0

If the TPC is 1, Wi1

Assume UE has N RLSesN TPC can be obtained after

combination, W1W2WN. The combination method for these

N TPCs from N RLSes can be described as following formula

TPC_cmd = (W1, W2, WN)

function should satisfied:

If one Wi is 0, TPC_cmd is -1

If all Wi are 1TPC_cmd is 1

PCA1


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Internal Use32


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

PCA2

U li k i l l


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Internal Use33


When UE is in soft handover, the TPC_cmd can be achieved by thefollowing 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 abovementioned 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_tempii = 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

PCA2

U li k i l t l


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Internal Use34


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.

Compari son between PCA1 and PCA2

D li k I l t l


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Internal Use35

Downlink Inner-loop power control

NodeB

Set SIRtar

Transmit TPC

Measure SIR and compare

Inner-loop

1500Hz

D li k i l t l


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Internal Use36

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 PO1PO2 and PO3 are defined by RNC.

D li k i l t l


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Internal Use37


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 0.511.5 or 2dB

D li k i l t l


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Internal Use38


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_MODE0UE will transmit TPC in every slot

DPC_MODE1UE 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 di ff erent state

Do nlink Po er Balance


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Internal Use39

Downlink Power Balance

Downlink power balance process

SRNC can monitor every single NodeBs

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

NodeBNodeB

Initiate the DPB

process

DPB process


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Internal Use40


2.Inner-loop power control



Outer loop power control


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Internal Use41

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


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Internal Use42

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

compare BLER inthe TrCH

Set BLERtar

10-100Hz

Downlink outer loop power control


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Internal Use43

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

outer loop power control


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Internal Use44

outer loop power control

SIR target adjustment step

etBLERt

etBLERtBLERmeastepSIRAdjustSoefficientSIRAdjustcSIRtar

arg

arg**



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Internal Use45


Uplink outer loop power control command transmit to NodeB through DCH-FP

Node B SRNC

OUTER LOOP PC


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08-wcdma power control.ppt

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