omf810003 gsm power control issue2.01
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Copyright © 2009 Huawei Technologies Co., Ltd. All rights reserved.
GSM Power Control
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Contents1. Power Control Overview2. HWⅡPower Control3. HWⅢPower Control
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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
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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
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Power Control Overview Up link and Down link power
control can be enabled
independently
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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.
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Data Configuration of Power Control Period
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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
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Data Configuration of MR Preprocessing(1)
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Data Configuration of MR Preprocessing(1)
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Contents1. Power Control Overview2. HWⅡ Power Control3. HWⅢPower Control
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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
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HW II Power Control Original data of power control -- Measurement Report(M
R)
Network
Downlink MRDownlink MR
Uplink MRUplink MR
BTS
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HW II Power Control Measurement report
Uplink Uplink measurement measurement
reportreport
Downlink Downlink measurement measurement
reportreport
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MR. preprocessing in HW II PC algorithm consists of four steps Interpolation Compensation (optional) Prediction (optional) Filter
HW II Power Control
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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)
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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
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Data Configuration of MR Preprocessing
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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.
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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
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Data Configuration of MR. Compensation
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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.
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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
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Data Configuration of MR. Prediction
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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
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Data Configuration of MR. filter
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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.
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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.
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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
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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.
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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.
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Data Configuration for UL Rx_Lev Upper/Lower Threshold
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Data Configuration for UL Upper/Lower Quality Threshold
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Data Configuration for DL Rx_Lev Upper/Lower Threshold
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Data Configuration for DL Upper/Lower Quality Threshold
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Data Configuration of Power Control (Rx_Lev)
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Data Configuration of Power Control (Rx_Lev)
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Data Configuration of Power Control (Rx_Lev)
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Data Configuration for UL/DL Bad Quality
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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
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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?
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Exercise Exercises for HW II power control
Answer. First, transmitting power to be reduced according to receiving level = a
ctual 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.
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Exercise Exercises for HW II power control
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.
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Content1. Power Control Overview2. HWⅡPower Control3. HWⅢPower Control
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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
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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
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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.
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Data Configuration of Initial Discarded MR. Number
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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
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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
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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
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Data Configuration of Filter(DL)
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Data Configuration of Filter(UL)
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Power Control Judgment During HW III power control judgment, system will calcul
ate radio channel gain. Suppose: In SACCH period k, useful signal is c(k), interferenc
e 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)
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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
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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
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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;
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Data Configuration of Power Control Judgment
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Data Configuration of Power Control Judgment
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Data Configuration of Power Control Judgment
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Data Configuration of Power Control Judgment
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Data Configuration of Power Control Judgment
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Data Configuration of Power Control Adjust Factor
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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).
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Data Configuration of Power Control Step
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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
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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.
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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
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Answer:step(k) = - ( sfactor×( MsTxMaxPower - 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
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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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