OMD0560 Power control ISSUE1.1Adjust the transmitting power of BTS and MS when needed.
Based on measurement reports of BTS and MS
Purpose
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.
1. During handover, MS will access the target cell with the maximum transmitting power (associated handover command) allowed by the target cell. But if “MS power prediction after HO” is enable, then MS will use the optimized power to access the target cell.
2. During intra-cell handover, the current power will be retained.
3. Power control can be implemented on TCH carriers only, BCCH carrier is not allowed power control. Because MS needs to measure the receiving level of BCCH from the adjacent cell. It will be inaccurate when power control is performed on BCCH.
4. Power control is performed independently for each channel.
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It takes 3 measurement report periods(480ms/period) from command sending to execution.
SA0
SA1
SA0
SA0
SA1
SA1
SA2
SA2
SA2
SA3
SA3
SA3
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.
When MS accesses the network via RACH channel, its transmitting power is the “MS max. TX power level” get from the system information sent on BCCH. MS send the first message on dedicated channel also uses the “MS max TX power level” ,this is not under the control of the system before the power control command which carried on SACCH of SDCCH or TCH. The implementation procedure is as follows:
1. According to the uplink receiving level and receiving quality reported by BTS, consider the maximum transmitting power of MS, BSC calculates the proper transmitting power for the MS.
2. Power control command and the TA value will be transmitted to MS at layer 1 header carried by each downlink SACCH block.
3. MS receives the power control command carried by SACCH header at the end of each SACCH report period, Then MS will carry out the command in the beginning of next report period. MS can change power 2dB per 13 frames (60ms) maximum.
4. After MS executed the power control command, it will set the current power class at the layer 1 message header of the next uplink SACCH, and transmit it to BTS in the measurement report. Therefore, it will take 3 measurement report periods for the new power class (in each power control command) to be available.
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Power Control Overview
Huawei power control algorithm: HW I and HW II power control
Measurement report pre-processing
Power control algorithm
algorithm
HWII power control is developed based on HWI. It’s more sensitive and the data configuration is simpler. For details, see later sections.
Huawei can support GSM0508 power control algorithm.
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Power Control Overview
Power control judgment and the selection of HWI algorithm or HWII algorithm
Power control algorithm selected in power control data table
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.
Set pre-processing “yes” is to reduce the signaling load in Abis interface.
i.e.:
1.If Abis E1 is in 15:1 mode, it should be set “yes”, otherwise the Abis capacity for speed is not enough;
2.BTS22C 0110 version should be set “No”;
3.Satellite transmission BTS should be set “yes”;
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MR pre-processing
comparison of uplink power control with downlink power control
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Measurement report pre-processing
HW I Power Control
In HWI power control, after the BSC or BTS performs pre-processing (interpolation and filtering) on the original measurement report, it will start HWI power control algorithm, and send the power control command.
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Network
HW I Power Control
The original data of power control is from measurement report. MS submits a measurement report to the network on SACCH channel every 480ms, the content reported by MS is the downlink measurement values which received by MS.
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Uplink measurement report
Downlink measurement report
There are two kind of measurement report for system: FULL (full measurement) and SUB (sub measurement).
FULL--Averaging over 100 TCH bursts(except four idle frames of four 26-multiframes).
SUB--Averaging over 12 bursts(four SACCH bursts, eight TCH bursts).
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Measurement report pre-processing -- interpolation
Each measurement report has a serial number. When the serial numbers are discontinuous, this indicates that some measurement reports must be missed. In this case, the network will fill up the measurement report according to interpolation algorithm.
HW I Power Control
Measurement report serial number n+4
Consecutive measurement report flow
3 missing measurement reports
The network receives the measurement reports n and n+4, which are with discontinuous serial numbers. Therefore the three missed measurement reports n+1, n+2 and n+3 will be filled up with some algorithm.
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Calculate average results of several consecutive measurement reports to obtain the current information, reduce the influence of some abnormal measurement reports for the judgment of power control.
HW I Power Control
Filter
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[BTS power control table]
HW I Power Control
The parameter configuration for HW I includes two sheets: [BTS power control table] and [MS power control table] for downlink and uplink power control. When the “HW_1” in “PC algorithm ” is selected, the network will perform power control according to these two sheets.
Only some of key parameters are listed above.
Parameter name
DL RX_LEV Expected
The expected signal level of MS in stable status, Expected stable downlink signal level > downlink edge HO thresholdOtherwise, ping-pang HO will be caused.
063
DL RX_LEV Compensation
The power adjustment value varies with this parameter. The adjustment value caused by power level equal to the difference between the expected signal level and the actual receiving signal level multiply this factor.
0100
DL Qual. Expected
07 Levels
DL Qual.Compensation
The power adjustment value varies with this parameter. The adjustment value caused by signal quality equal to 10*difference between the expected signal quality level and the actual receiving signal quality level multiply this factor.
0100
MAX PC Step
Levels 0~16, 2dB each step
8
24.unknown
Period
Time interval for implementing two power control commands (unit count of SACCH period)
110
Filter length for DL RX_LEV
Content: indicating the number of measurement reports in which the average of uplink signal strength is taken before MS power adjustment at stable stage. The purpose is to remove the influence of some abnormal reports. When the filter length is too long, the influence due to abnormal reports will be weakened, but the MS power adjustment is not timely.
132
Indicating the minimum transmitting power value supported by the BTS
0~36
Indicating the maximum transmitting power value supported by the BTS.
0~56
HW I Power Control
Parameter name
initial RX_LEV expected
The expected BTS receiving signal level in the initial stage when MS access the network.
0~63dBm
Stable EX_LEV Expected
The expected BTS receiving signal level in stable status. Expected stable signal level > uplink margin HO threshold (HO parameter). Otherwise, “ping-pang” HO will be caused.
0~63dBm
UL RX_LEV compensation
Give an adjustment for the power control level value, the actual power level value MS should change is the result of this parameter multiply the difference between the expected uplink signal level and the actual BTS receiving signal level.
0~100
UL Qual. compensation
The power adjustment value varies with this parameter. The adjustment value caused by signal quality equal to 10*difference between the expected signal quality level and the actual receiving signal quality level times this factor.
0100
Max PC step
The maximum level of MS power that can be dynamically adjusted.
Level 1~16, 2dB/level.
Value range
Value recommended
PC interval
Time interval between the implementations of two power control algorithms; unit: SACCH period
0~30
Filter length for Initial RX_LEV
This is the number of measurement reports required for predicting the signal strength at the initial stage. Unit: Measurement reports
1~32
Filter length for stable RX_LEV
This is the number of measurement reports required for predicting the signal strength at the stable power control stage. Unit: Measurement reports
1-31
5
Filter length for Qual.
This is the number of the measurement reports required for assessing signal quality at the stable stage. Unit: Number of measurement reports
1~30
HW I power control judgment
The adjustment on the current output power=(Expected signal strength in stable status - strength of signal currently received) * up (down) link compensating factor +[quality of uplink(downlink) currently received - expected uplink(downlink) quality]*10* uplink(downlink) quality compensating factor
The final adjustment power level should be no more than the maximum power control step size, the formula for stable level is: stable level = currently level + the adjustment value on current out put power
HW I Power Control
HW I Power Control
Power control will not occur in case of these three conditions
Both level and quality equal to the setting values (HW I power control), or level and quality are within threshold band(HW II power control)
Adjusting range less than error tolerance
Adjusting range less than minimum power control step
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HW I power control judgment
Before judging the signal level to be adjusted, query the error tolerance table according to the current transmitting power level. Adjustment will not be done if the power adjustment value is less than the error tolerance value.
Error tolerance table for 900M and 1800M is as follows:
HW I Power Control
Error tolerance: Measured in dB, varies with MS transmitting power.
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Similarity:
1. To avoid frequently changes of signal level, the PC interval time between the two consecutive uplink and downlink power control are limited.
2. To reduce the influence caused by abnormal reports, all measurement reports should be filtered.
3. Both uplink and downlink power controls include level-specific and quality-specific power controls.
4. Both uplink and downlink power controls have maximum power control step size limit and compensating factor.
HW I Power Control
Differentia:
1. Including power control for the stable status, MS also has power control when MS access the network, thus to reduce transmitting power of MS as soon as possible.
2. For uplink, precautions are ready for increase MS transmitting power in case HO fails.
3. For downlink, there are maximum and minimum transmitting power limits in power control data configuration.
HW I Power Control
Given conditions:
900M MS transmitting at the maximum power, uplink receiving level of the 900M BTS is –60dBm, uplink quality level is always 0.
Parameter configuration in [BTS power/MS power control table] is as follows – “stable RX_LEV Expected” is 35, “UL RX_LEV Compensation” is 80, “UL Qual. expected ” is 1, and “UL Qual. compensation” is 20, and the max. PC step is 16dB.
HW I Power Control
Question:
1. Suppose that power control will no longer be done once the power value to be adjusted is less than 2dB, what is the approximate stable power value after power control with the above data configuration?
2. According to the error tolerance list, suppose the initial MS transmitting power is level 3, what is the maximum uplink receiving level in stable status after power control?
Exercise
Answers for question 1:
Stable level = current actual level + [(expected signal intensity in stable status – current actual level) * uplink path loss compensating factor] + [actual current quality – expected uplink signal quality) * 10 * uplink quality compensating factor] = -60+[(-75-(-60))*80]+[(0-1)*10*20] = -60-12-2 -74dBm. Now it’s necessary to adjust -14dB (no larger than the maximum power control step size), but it needs further adjustment because it fails to reach -75dBm, the “expected signal level in stable status”. Use -74 in the above formula again for calculation, and the power to be adjusted is -2.8dB. Because no power control adjustment will be done when the power value to be adjusted is smaller than -2, it still needs to be changed 2dB lower, so the uplink receiving level is -76dBm at last.
Exercise
Answers for question 2:
Query the error tolerance table, the tolerance of level 3 is 4dB, the power to be adjusted for the second time is 2.8, which is less than 4 and up to the requirement, so the final uplink receiving level is -74dBm in stable status.
Exercise
Power control algorithm implementation
HW I I Power Control
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Measurement report pre-processing
General power control judgement
The power control demand according to receiving quality
HWII power control is performed in four steps.
Pre-processing of the measurement reports (interpolation and filtering),
2. Calculate power control demand according to the receiving level,
3. Calculate power control demand according to the receiving quality,
4. Make comprehensive judgment on the receiving level and receiving quality.
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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 adjusting the transmitting power according to the receiving level, so as to achieve the expected level as soon as possible.
HW I I Power Control
When power control is performed based on the receiving level, it adopts three step sizes respectively for different receiving qualities band:
“MAX. Adj. Value for Qual. Zone 0 (receiving quality level 0)
“MAX. Adj. Value for Qual. Zone 1 (receiving quality level 1~2)
“MAX. Adj. Value for Qual. Zone 2 (receiving quality level 3~7)
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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
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 I I Power Control
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Note:
1. Control as required when either level or quality needs to be controlled.
2. When the controls based on signal level and quality are in an opposite direction, and the level requires decreasing power, so no action should be performed for power control; when the level requires increasing power, then just perform as level required.
3. When they work in the same direction, perform according to the larger value.
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
Power control algorithm implementation
HW I I Power Control
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Measurement report compensation -- 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
HW II Power Control
Measurement report compensation
Purpose: Ensure the accuracy of selection of the history measurement report before filtering.
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 compensation, 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
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The expected receiving signal level: 30
The power control will be more effective with measurement report compensation.
HW II Power Control
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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Purpose
to 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 OMC.
3. Filter the interpolated, compensated and predicted measurement reports, and implement power control judgment.
HW II Power Control
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The expected receiving signal level: 30
The power control with prediction filter will be more effective than that with mean filter
HW II Power Control
Mean filter power control
Prediction filter power control
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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).
HW II Power Control
Automatic adjustable step size:
When the power control caused by receiving level in HWII power control algorithm, the power control will be performed also considering the receiving quality which are set into three quality zones (0, 1~2, ≥3). Each quality zone allow different maximum adjustment step size. The worse the quality is, the less the adjustable step size will be.
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Power control within the upper/lower thresholds
As for HW II power control in case of calculating power control step size according to signal level and quality, the signal level and quality have upper/lower thresholds. Power control will not execute if the signal level and quality is within the threshold bands.
Avoid the signal level up-and-down caused by power control.
HW II Power Control
DL RX_LEV upper thrsh/lower thrsh
UL Qual upper thrsh/lower thrsh
DL Qual upper threh/lower threh
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Simple parameter configuration
All needed to do is to configure simple parameters as follows:
Signal level and quality upper/lower thresholds of up/down link
Three kinds of step sizes for adjustment by level
Step size for adjustment by quality
HW II Power Control
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HW II Power Control
filter length for UL RX_LEV
How many uplink measurement reports obtained for the average uplink signal level to be used for uplink power control adjustment.
1~20
filter length for DL RX_LEV
How many downlink measurement reports obtained for the average downlink signal level to be used for downlink power control adjustment.
1~20
filter length for UL Qual.
How many uplink measurement reports obtained for the average uplink quality level to be used for uplink power control adjustment.
1~20
filter length for DL Qual.
How many downlink measurement reports obtained for the average downlink quality level to be used for downlink power control adjustment.
1~20
MR compensation allowed
If “yes”, System put the currently received measurement report into the measurement report compensation queue, and record the transmitting power information according to MS and BTS power values. And then interpolation, compensate the receiving level value of the record measurement report according to the power change information.
Yes, no
UL MR number predicted
The number of uplink pred. MR in the filter using for power control judgment.
0~3 reports
DL MR number predicted
The number of downlink pred. MR in the filter using for power control judgment.
0~3 reports
HW II Power Control
Note: when configuring s-strength thresholds that: upper/lower thresholds> edge handover threshold + inter-cell handover hysteresis.
This is designed to avoid handover caused by improper power control.
Parameter name
1~30
(SACCH period)
UL RX_LEV upper threshold
This parameter specifies the uplink signal level upper threshold. When the signal level higher than this value, calculate a power decrement [=receiving level - (upper threshold + lower threshold)/2]. This decrement value should consider together with the maximum step size allowed for different quality zone which the receiving signal quality located.
0~63
UL RX_LEV lower threshold
This parameter specifies the uplink signal level lower threshold. When the signal level higher than this value, calculate a power increase [= (upper threshold + lower threshold)/2- receiving level]. This increase also consider together with the maximum step size allowed for different quality zone which the receiving signal quality located.
0~63
Level 0~7
UL Qual. lower threshold
This parameter specifies the uplink quality lower threshold for power control
Level 0~7
HW II Power Control
DL RX_LEV upper threshold
This parameter specifies the downlink signal level upper threshold. When the signal level higher than this value, calculate a power decrement [=receiving level – (upper threshold + lower threshold)/2]. This decrement should consider together with the maximum step size allowed for different quality zone which the receiving signal quality located.
0~63
DL EX_LEV lower threshold
This parameter specifies the downlink signal level lower threshold. When the signal level higher than this value, calculate a power increase [= (upper threshold + lower threshold)/2- receiving level]. This increase also consider together with the maximum step size allowed for different quality zone which the receiving signal quality located.
0~63
DL Qual. upper threshold
This parameter specifies the downlink quality upper threshold for power control
Level 0~7
DL Qual. lower threshold
This parameter specifies the downlink quality lower threshold for power control
Level 0~7
HW II Power Control
max. adj. value for Qual. Zone 0
This parameter specifies the maximum power adj. step size allowed when adj. the power according to the signal level when the Rx quality is 0.
0~30dB
max. adj. value for Qual. Zone 1
This parameter specifies the maximum power adj. step size allowed when adj. the power according to the signal level when the Rx quality is 1 or 2.
0~30dB
max. adj. value for Qual. Zone 2
This parameter specifies the maximum power adj. step size allowed when adj. the power according to the signal level when the Rx quality is equal to or more than 3.
0~30dB
adj. PC value by Rx Qual.
Specifying the adj. step size allowed when the power control is adjusted according the receiving signal quality. That is to say, the step size is constant for power control by quality, but the step size varies with quality in case of power control by signal level.
0~4dB
Given conditions:
The uplink receiving level is -85dBm, the quality is level 4. 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 0. Uplink signal lower quality threshold: level 2. The adjustable step size of quality band 0 is 16dB, of quality band 1 is 8dB, and of quality 2 is 4 dB. The adjustable step size for power control by quality is 4dB.
Question: What will be the uplink stable receiving level after power control?
Exercise
Answer.
First, transmitting power to be added according to receiving level = (uplink signal level upper threshold + uplink signal level lower threshold)/2-actual receiving level (-60 + (-80))/2-(-85)(-70)-(-85)15dB. As the receiving quality is level 4, only adjustable step size of quality band 2 can be used -- increase 4dB.
Second, the transmitting power to be increased according to receiving quality = as “power control adjustment step size by quality” is 4dB, thus increase 4dB, the same as adjustment by signal level.
Therefore, according to the general judgement on power control, 4dB should be increased for adjustment either by level or by quality.
Exercise
Answer .
After the implementation of step 1 power control, the receiving level becomes: -85dBm + 4dB=-81dBm, Suppose the quality reach already in level 2 here, it still fails within the expected band -80dBm~-60dBm. Therefore, it needs to be adjusted.
First: adjust by level -- repeat the previous step: adjustment by level = (-70) – (-81) = 11db, i.e. to increase 11dB. If the receiving quality has been improved to level 2, and the adjustable step size with quality band 1 is 8dB. Then, the result of adjustment by level is to increase 8dB.
Second: adjustment by quality--as the receiving quality value is between 0 and 2, Needn’t adjust.
Therefore, the uplink stable receiving level = (-81) + 8 = -73dBm.
Exercise
and quality
↓ AdjStep_Lev ↓ AdjStep_Qul ↓
Parameter
name
The expected signal level of MS in stable status, Expected
stable downlink signal level > downlink edge HO threshold
Otherwise, ping-pang HO will be caused.
063
adjustment value caused by power level equal to the difference
between the expected signal level and the act ual receiving
signal level multiply this factor.
0100 80
07
adjustment value caused by signal quality equal to
10*difference between the expected signal quality level and the
actual receiving signal quality level multiply this factor.
0100 20
command
Levels
(unit count of SACCH period)
110
Content: indicating the number of measurement reports in
which the average of uplink signal strength is taken before MS
power adjustment at stable stage. The purpose is to remove
the influence of some abnormal reports . When the filter length
is too long, the influence due to abnormal reports will be
weakened, but the MS power adjustment is not timely .
132
the BTS
by the BTS.
The expected BTS receiving signal level in the initial stage
when MS access the network.
0~63dBm 30
Expected stable signal level > uplink margin HO threshold
(HO parameter). Otherwise, “ping -pang” HO will be caused.
0~63dBm 30
Give an adjustment for the power control level value, the
actual power level value MS should change is the result of
this parameter multiply the difference between the expected
uplink signal level and the actual BTS receiving signal level.
0~100 80
UL Qual.
adjustment value caused by signal quality equal to
10*difference between the expected signal quality level and
the actual receiving signal quality level times this factor.
0100 20
The maximum level of MS power that can be dynamically
adjusted.
How many uplink measurement report s obtained for the average
uplink signal level to be used for uplink power control adjustment.
1~20 6
How many downlink measurement report s obtained for the average
downlink signal level to be used for downlink power control
adjustment.
How many uplink measurement report s obtained for the average
uplink quality level to be used fo r uplink power control adjustment.
1~20 6
How many downlink measurement report s obtained for the average
downlink quality level to be used for downlink power control
adjustment.
If “yes”, System put the currently received measurement report into
the measurement report compensation queue, and record the
transmitting power information according to MS and BTS power
values. And then interpolation, compensate the receiving level
value of the record meas urement report according to the power
change information.
number
predicted
The number of uplink pred. MR in the filter using for power control
judgment.
number
predicted
The number of downlink pred. MR in the filter using for power
control judgment.
calculate a power decrement [=receiving level – (upper
threshold + lower threshold)/2 ]. This decrement should
consider together with the maximum step size allowed for
different quality zone which the receiving signal quality
located.
calculate a power increase [= (uppe r threshold + lower
threshold)/2- receiving level]. This increase also consider
together with the maximum step size allowed for different
quality zone which the receiving signal quality located.
0~63 30
DL Qual. upper
threshold for power control
Level 0~7 0
threshold for power control
Level 0~7 2
range
Recommended
value
PC interval Time between two power control command implementation 1~30
(SACCH
period)
5
This parameter specifies the uplink signal level upper threshold.
When the signal level higher than this value, calculate a power
decrement [=receiving level - (upper threshold + lower
threshold)/2]. This decrement value should consider together with
the maximum step size allowed for different quality zone which
the receiving signal quality located.
0~63 35
This parameter specifies the uplink signal level low er threshold.
When the signal level higher than this value, calculate a power
increase [= (upper threshold + lower threshold )/2- receiving level].
This increase also consider together with the maximum step size
allowed for different quality zone which the receiving signal
quality located.
0~7
power control