04 GSM Power Control ISSUE1.0

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Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

GSM Power Control

Page2Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Contents

1. Power Control Overview

2. HWⅡPower Control

3. HWⅢPower Control


Power Control Overview

� Power control

� Adjust the transmitting power of BTS and MS when needed.

� Based on measurement reports of BTS and MS

� Purpose

� Save the power of BTS and MS

� Reduce the interference of the network

� Increase the quality of the network



� Power control includes uplink power control and downlink

power control, Which are performed independently

� Uplink power control: Adjust TX power of MS to let BTS receive

stable signal, reduce the uplink co-channel and adjacent

channel interference, reduce power consumption of MS

� Downlink power control: Adjust BTS TX power to let MS receive

stable signal, reduce the downlink co-channel and adjacent

channel interference, reduce power consumption of BTS


Power Control Overview� Up link and Down link power

control can be enabled

independently



� Process of power control commands

� It takes 3 measurement report periods(480ms/period) from

command sending to execution.

SA0SA0SA0SA0 SA1SA1SA1SA1SA0SA0SA0SA0 SA0SA0SA0SA0SA1SA1SA1SA1SA1SA1SA1SA1 SA2SA2SA2SA2SA2SA2SA2SA2SA2SA2SA2SA2 SA3SA3SA3SA3SA3SA3SA3SA3SA3SA3SA3SA3

BTS sends the command for power

control and TA in SACCH header.

MS obtains SACCH

block

MS begins to send the

measurement report of the

last multi-frame.

In the 26 multi-frames,

frame 12 sends

SACCH.

BTS receives the

measurement report

SACCCH report period:

26X4=104 frames (480ms)

MS adopts the new

power level and TA

MS begins to set up a new SACCH header

to report the new TA and power control

message.


Data Configuration of Power Control Period



� Power control judgment

� Power control judgment is controlled by BTS measurement

report pre-processing item which can be selected in handover

control data table

� MR. Pre-process (measurement report pre-processing): This

switch decide where power control be processed. If

measurement report pre-processing is “yes”, power control is

processed in BTS, and when setting it “no”, power control is

processed in BSC


Data Configuration of MR Preprocessing(1)


Data Configuration of MR Preprocessing(1)


Contents


2. HWⅡⅡⅡⅡ Power Control

3. HWⅢPower Control


HW II Power Control

� Power control judgment process

The power control

demand according to

receiving level

General power control

judgment

Send the power control

command

The power control

demand according to

receiving quality

MR. preprocessing


HW II Power Control

� Original data of power control -- Measurement Report(MR)

Network

Downlink MRDownlink MR

Uplink MRUplink MR

BTSBTSBTSBTS


HW II Power Control

� Measurement report

Uplink Uplink

measuremenmeasuremen

t reportt report

Downlink Downlink

measuremenmeasuremen

t reportt report


� MR. preprocessing in HW II PC algorithm consists of four steps

� Interpolation

� Compensation (optional)

� Prediction (optional)

� Filter

HW II Power Control


HW II Power Control

� MR Interpolation – recover the lost measurement report

� BTS may fail to receive the MR from MS, and it needs to

recover the lost measurement reports. If the lost MR amount is

within the allowed range (Allowed MR Number Lost), then

recovers the lost MR according to the specific algorithm.

� Service cell: linear algorithm

� Neighboring cell: the lowest value defined in GSM specification (-

110dBm)


HW II Power Control

MR

MR

No. n

No. n+4

Continuous MR Flow

MRMR

MR

Missing by

some reasons

…

…

� MR Interpolation – recover the lost measurement report


Data Configuration of MR Preprocessing


HW II Power Control

� MR. compensation

� Purpose: Ensure the accuracy of selection of the history measurement

report before filter.

� Implementation steps:

� 1. Put the current receiving measurement report into the measurement report

compensation queue.

� 2. Record the changed information of the transmitting power according to the

MS and BTS power levels in the measurement report.

� 3. After finish the measurement report interpolation, system will compensate

the receiving level of the history measurement report according to the power

change information. The compensated measurement reports will be the

original data in the filter process.

� 4. Filter the compensated measurement reports.

Pag

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HW

II Pow

er C

ontro

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MR

. com

pensa

tionTh

e e

xp

ec

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rec

eiv

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sig

na

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l: 30

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ill be

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.

X axis

111122223333444455556666777788889999

1010101011111111121212121313131314141414151515151616161617171717181818181919191920202020212121212222222223232323242424242525252526262626272727272828282829292929303030303131313132323232333333333434343435353535363636363737373738383838393939394040404041414141424242424343434344444444454545454646464647474747484848484949494950505050

000 0

10

1010

10 20

2020

20 30

3030

30 40

4040

40 50

5050

50 60

6060

60 70

7070

70

Y axis

Po

we

r co

ntro

l dia

gra

m w

hen

the

re is

m

ea

su

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t rep

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om

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re is

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atio

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Data Configuration of MR. Compensation


HW II Power Control

� MR. prediction

� Purpose: Avoid power control later than needed, the delay is

dangerous in case of poor level or bad quality

� Implementation procedure

1. Analyze the tendency of MR by the historical measurement

reports after interpolation.

2. Guide by the tendency, to predict the values of measurement

report to be received. There are 0~3 measurement reports

prediction, which are configured on LMT.

3. Filter the interpolated, compensated and predicted measurement

reports, and implement power control judgment.

Pag

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Cop

yrig

ht ©

2006 H

uaw

ei Tech

nolo

gies C

o., L

td. A

ll rights reserv

ed.

HW

II Pow

er C

ontro

l�

MR

. pre

dic

tion

111122223333444455556666777788889999

1010101011111111121212121313131314141414151515151616161617171717181818181919191920202020212121212222222223232323242424242525252526262626272727272828282829292929303030303131313132323232333333333434343435353535363636363737373738383838393939394040404041414141424242424343434344444444454545454646464647474747484848484949494950505050

X axis

15

151515 20

202020 25

252525 30

303030 35

353535 40

404040 45

454545 50

505050

Y axis

No

po

we

r co

ntro

l

Mean

filter p

ow

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Pre

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filter p

ow

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filter


Data Configuration of MR. Prediction


HW II Power Control

� MR. filter – Smooth the instantaneous fading point

� Calculate the average value within the filter window

MR

MRContinuous MR Flow

MRMR

MR

…

…

Filter----Average several consecutive MRs

MR


Data Configuration of MR. filter


HW II Power Control Judgment

� Power control demand based on receiving level.

� After measurement report pre-processing, the power control

module makes a comparison between the expected signal

level and the current receiving signal level.

� Calculate the transmitting power level step size to be adjusted,

making the receiving level value closer to the expected value.

� Adopt variable step size when decreasing the transmitting

power according to the receiving level, so as to achieve the

expected level as soon as possible.


HW II Power Control Judgment

� Power control demand based on receiving quality

� After measurement report pre-processing, the power control

module makes comparison between the expected quality level

and the current receiving quality level.

� Calculate the step size of the transmitting power level to be

adjusted: increase the transmitting power in case of poor

receiving quality, and decrease the transmitting power in case

of good receiving quality.

� Adopt fixed step size when adjust the transmitting power

according to the receiving quality.


HW II Power Control Feature

� Power control within the upper/lower thresholds

� Power control will not execute if the signal level and quality

is within the threshold bands.

� Avoid the signal level fluctuation caused by power control.

� The upper threshold can be increased dynamically in case of

bad quality.


Data Configuration for UL Rx_LevUpper/Lower Threshold


Data Configuration for UL Upper/Lower Quality Threshold


Data Configuration for DL Rx_LevUpper/Lower Threshold


Data Configuration for DL Upper/Lower Quality Threshold


Data Configuration of Power Control (Rx_Lev)






Data Configuration for UL/DL Bad Quality


HW II Power Control Advantages

� Measurement report compensation – to makes power control

judgment more accurate

� Measurement report prediction --to avoid power control later

than needed, the delay is dangerous in case of poor level or

bad quality

� Power control expected signal level and quality threshold

falls within a band, this avoids receiving signal level

fluctuate up and down frequently


Content


2. HWⅡPower Control

3. HWⅢⅢⅢⅢPower Control


HW III Power Control Flow

Number of lost MR. > N?Number of lost MR. > N?Yes

Stop PC, waiting the next MR.

Rx_lev&(Qual.+FH gain) are within expected window?

Rx_lev&(Qual.+FH gain) are within expected window?

No

Calculate the power

control step for BTS

and MS

Calculate the power

control step for BTS

and MS

No

Exponent FilterExponent Filter

Slide Window FilterSlide Window Filter

MR. InterpolationMR. Interpolation

Initial MR. processInitial MR. process

Power control

implement

Power control

implement

Yes

No Power Control

MR. Preprocessing


� For the measurement report preprocessing, there are three

differences between HW II and HW III power control：

� Initial discarded MR. number

� Interpolation method

� Filter calculation

Measurement Report Preprocessing



� Initial discarded MR. number

� Avoiding the access period measurement report influence power

control accuracy, system discards some initial measurement report.

� HW II: discard 4 initial MR. fixedly.

� HW III: set it via Signal/Traffic Channel Discard MR. Number.

� MR. interpolation method

� Rx_lev: If Rx_lev(k) is lost, recover it as Rx_lev(k-1).

� Rx_qual: If Rx_qual is lost, recover it as quality lever 7.


Data Configuration of Initial Discarded MR. Number



� MR. filter calculation

� Quality filter

� Quality class value will be converted to BER and set up the

correspondence relationship with CIR as below table.

� Calculate the average CIR according to the selected filter method.

4691214161822CIR (dB)

76543210Quality Class



� MR. filter calculation

� filter algorithm: exponent filter and slide window filter

� Exponent filter

– ca_filtered1 (1)=ca(1) k=1

– ca_filtered1 (k)=a*ca(k)+(1-a)*ca_filtered1 (k-1) k>1

~ ca: original receiving level or quality

~ ca_filtered1: receiving level or quality after exponent filter calculation

~ k: serial number of measurement report

~ a: exponent filter coefficient, a=1 / (2^(w/2)), and w is exponent filter length



� Filter algorithm

� Slide window filter

� ca_filtered (1) = ca_filtered1 (1) k=1

� ca_filtered (k) = [ca_filtered 1(1)+…+ca_filtered1 (k)] / k 1<k<w

� ca_filtered (k) = [ca_filtered1 (k-w+1)+...+ca_filtered1 (k)] / w k>=w

– ca_filtered1: receiving level or quality after exponent filter

– ca_filtered: receiving level or quality after window filter

– k: serial number of measurement report

– w: slide filter window


Data Configuration of Filter(DL)


Data Configuration of Filter(UL)


Power Control Judgment

� During HW III power control judgment, system will calculate

radio channel gain.

� Suppose: In SACCH period k, useful signal is c(k), interference

is I(k), radio channel gain is g(k) and transmit power for BTS or

MS is p(k). The below formulas are calculated by logarithm:

=10

)(_

10

kfilteredca

+10

)(

10

kc

10

)(

10

kI

Rx_levRx_lev Useful Useful signelsignel InterferenceInterference

C/IC/I�� qa_filtered(k) = c(k) – I(k) (2)

c(k) = p(k) – g(k) (3)

(1)


Power Control Judgment

� Radio channel gain calculation:

� According to (1) and (2), we can get c(k)

� Input c(k) to (3), get g(k) = p(k) – c(k). So calculate the g(k)

for BTS and MS

)101lg(10)(_)(_)( 10

)(_ kfilteredqa

kfilterqakfiltercakc +×−+=


Data Configuration of Power Control Judgment










Data Configuration of Power Control Adjust Factor


HW III Power Control Features

� Exponent filter enhance the measurement report process speed.

� In HW II PC, receive level and quality be considered independently

and then general power control judgment will be done. While in

HW III PC, the final result will be got from the general formula.

� Difference quality threshold be set for the difference service, such

as AMR, FS and HS.

� Hopping gain also be considered.


Summary

� In this course, we have learned:

� Power control procedure

� HW II power control algorithm

� HW III power control algorithm

� Data Configuration of HWII and HWIII

Thank youwww.huawei.com

Documents

04 GSM Power Control ISSUE1.0