4- OMO111040 BSC6000 GSM V9R8C01 Power Control Algorithm and Parameters ISSUE2.01

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GSM Power Control

Copyright © 2009 Huawei Technologies Co., Ltd. All rights reserved. Page2

Contents1. Power Control Overview

2. HWⅡPower Control3. 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 Overview 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


Power Control Overview Process of power control commands

It takes 3 measurement report periods(480ms/period) from command sending to getting the feedback.

SA0 SA1SA0 SA0SA1SA1 SA2SA2SA2 SA3SA3SA3

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 Overview 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)


Contents1. Power Control Overview2. HWⅡ 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

BTS


HW II Power Control Measurement report

Uplink Uplink measurement measurement

reportreport

Downlink Downlink measurement measurement

reportreport


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.


HW II Power Control MR. compensation

The expected receiving signal level: 30

The power control will be more effective with measurement report compensation.

X axis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

0

10

20

30

40

50

60

70

Y ax

is

Power control diagram when there is measurement report compensation

Diagram when there is no power control

Power control diagram when there is no measurement report compensation

Power control effect diagram of measurement report compensation


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 procedure1. 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.


HW II Power Control MR. prediction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

X axis

1520253035404550

Y ax

is

No power control

Mean filter power control

Prediction filter power control

Diagram of power control effect comparison between prediction filter and mean filter

The expected receiving signal level: 30

The power control with prediction filter will be more effective than that with mean 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 MR

MR

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 Judgment General power control judgment

Power control by receiving

level Power control by receiving

quality

Power control by signal level and quality

↓ AdjStep_Lev ↓ AdjStep_Qul ↓ max(AdjStep_Lev,AdjStep_Qul)

↓ AdjStep_Lev ↑ AdjStep_Qul No action

↓ AdjStep_Lev No action ↓ AdjStep_Lev

↑ AdjStep_Lev ↓ AdjStep_Qul ↑ AdjStep_Lev

↑ AdjStep_Lev ↑ AdjStep_Qul ↑ max(AdjStep_Lev,AdjStep_Qul)

↑ AdjStep_Lev No action ↑ AdjStep_Lev

No action ↓ AdjStep_Qul ↓ AdjStep_A

No action ↑ AdjStep_Qul ↑ AdjStep_B

No action No action No action


HW II Power Control Feature Adaptive power control:

Adaptive power control refers to changeable power control strategy according to the communication environment, it makes power control more effective and stable.

Automatically change the adjustable maximum step size of power control according to different communication environment (different receiving quality).

Adopt different power control strategies according to different communication environments (different receiving quality and level).

Max. step is different between increase and decrease.


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_Lev Upper/Lower Threshold


Data Configuration for UL Upper/Lower Quality Threshold


Data Configuration for DL Rx_Lev Upper/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


Exercise Exercises for HW II power control

Given conditions: The uplink receiving level is -55dBm, the quality is level 0. Power control

algorithm is HW II. Data configuration is as follows: Uplink signal level upper threshold: -

60dBm, uplink signal level lower threshold: - 80dBm. Uplink signal upper quality threshold: level 1. Uplink signal lower quality threshold: level 2. The downward adjustable step size of quality band 0 is 16dB, of quality band 1 is 8dB, and of quality 2 is 4 dB. The upward adjustable step size of receiving level is 16dB. The upward or downward adjustable step size for power control by quality are both 4dB.

Question: What will be the uplink stable receiving level after power control?



Answer. First, transmitting power to be reduced according to receiving level

= actual receiving level -(uplink signal level upper threshold + uplink signal level lower threshold)/2 ＝ -55- (-60 + (-80))/2 ＝ (-55)-(-70) ＝15dB. As the receiving quality is level 0, downward adjustable step size of quality band 0 can be used -- decrease 16dB.

Second, the transmitting power to be decreased according to receiving quality = as “power control adjustment step size by quality” is 4dB, thus decrease 4dB.

Therefore, according to the general judgement on power control, 15dB should be decreased.



Answer . After the implementation of step 1 power control, the

receiving level becomes: -55dBm-15dB= -70dBm, Suppose the quality reach already in level 1 here.

First: the receiving level value is between -80dBm~-60dBm, needn’t adjust.

Second: the receiving quality value is between 0 and 2, needn’t adjust.

Therefore, the uplink stable receiving level =-70dBm.


Content1. Power Control Overview2. HWⅡPower Control3. HWⅢPower Control


HW III Power Control Flow

Number of lost MR. > N?Yes

Stop PC, waiting the next MR.

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

No

Calculate the power control step for BTS and

MS

No

Exponent Filter

Slide Window Filter

MR. Interpolation

Initial MR. process

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


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


Measurement Report Preprocessing 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.

Quality Class 0 1 2 3 4 5 6 7

CIR (dB) 22 18 16 14 12 9 6 4


Measurement Report Preprocessing 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


Measurement Report Preprocessing 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)(_

10kfilteredca

10)(

10kc

10)(

10kI

Rx_levRx_lev Useful signelUseful signel 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


Power Control Judgment BTS power control step calculation:

step(k) = - ( sfactor*( BsTxMaxPower - g(k) - SThr) + qfactor*( qa_filtered(k) + QOffFh - QThr) );SThr = (SThrUp + SThrDown) / 2; Physical meaning is received useful signal.QThr = (QThrUp + QThrDown) / 2; Physical meaning is received CIR without

hopping. If step(k) >0, so step(k) =0;Notes:sfactor ：【 HWIII DL RexLev Adjust Factor 】

qfactor ：【 HWIII DL Rex Qual. Adjust Factor 】

BsTxMaxPower ： the maximum power level of occupied carrierSThr ： the mean level of expected receiving level windowQThr ： the mean level of expected receiving quality windowQOffFh ： frequency hopping gain


Power Control Judgment MS power control step calculation:

step(k) = - ( sfactor*( MsTxMaxPower - g(k) - SThr) + qfactor*( qa_filtered(k) + QOffFh - QThr) );SThr = (SThrUp + SThrDown) / 2;QThr = (QThrUp + QThrDown) / 2;If step(k) >0 ， then step(k) =0;


Data Configuration of Power Control Judgment










Data Configuration of Power Control Adjust Factor


Power Control Judgment Adjustment protection

For avoiding too rapid adjustment, parameter [HWIII DL/UL MAX DownStep/UpStep] is used to control the maximum power control step.

If the difference between power control step(k) and previous one step(k-1) is bigger than maximum power control step configured above, just take the maximum power control step as the difference between them, so as to limit the current power control command step(k).


Data Configuration of Power Control Step


Power Control Judgment If Rx_lev upper threshold >= Rx_Lev >= Rx_lev lower

threshold and Rx_qual upper threshold >= [RxQual + QOffFh] >=

Rx_qual lower threshold, step(k)=step(k-1) QOffFh is depended on hopping gain table

Number of MA 1 2 3 4 5 6 7 >=8

QOffFh (dB) 0 2 3 4 4.3 4.7 5.0 5.3


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.


Given condition ： The current UL_Re_Level: -75dBm ， UL_Re_Quality: 4(qa_filtered (k)

=12) ， Radio channel gain(g(k)): 110dB, there are 7 hopping frequency, Max power output of MS is 2W(33dBm)

HWIII is available ， data configuration is as following: 【 [HWIII UL RexLev Upper Threshold] 】： 30 【 HWIII UL RexLev Lower Threshold 】： 20 【 HWIII DL FS Rex Qual. Upper Threshold(dB)] 】： 22 【 HWIII UL FS Rex Qual. Lower Threshold(dB)] 】： 16 【 HWIII UL RexLev Adjust Factor 】： 4 【 HWIII UL Rex Qual.Adjust Factor 】：

6 【 HWIII UL MAX DownStep(dB) 】： 8 【 HWIII UL MAX UpStep(dB) 】： 8

Question ： What will be the power output of MS after power control ？

Quality Class 0 1 2 3 4 5 6 7

CIR (dB) 22 18 16 14 12 9 6 4

Number of MA 1 2 3 4 5 6 7 8

QOffFh (dB) 0 2 3 4 4.3 4.7 5.0 5.3

Question


Answer:step(k) = - ( sfactor×( BsTxMaxPower - g(k) - SThr)

＋ qfactor×( qa_filtered(k) + QOffFh - QThr) )

After power control ：Power output of MS: 33-2=31dBmSuppose the current g(k)=115dB, current quality:3(CIR=14dB) ， thenFor level ： -90dBm<31-115<-80dBmFor quality ： 16<14+5<22So power control stops ， the power output of MS 33-2=31dBm

dB2

)}2

1622512(6.0)]}1102

2030(11033[4.0{{

Question


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

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4- OMO111040 BSC6000 GSM V9R8C01 Power Control Algorithm and Parameters ISSUE2.01