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3.3.1 Power Control Activation
Power Control can be activated or deactivated for AMR and non-AMR calls independently using parameters AMRCALLPCALLOWED and NONAMRCALLPCALLOWED. Calls that with Power Control disabled use full power.
3.3.2 Measurement Report Handling
When the PCIII algorithm is applied, a fixed number of MRs are discarded during the initial access of the MS to the network to prevent the impact of inaccurate MRs on the algorithm. The number of discarded MRs is specified by SDMRCUTNUM (SDCCH) and TCHMRCUTNUM (TCH).
Active Power Control is enabled and the MRs are not discarded when parameter PWRBCDALLOWD is set to YES.
The MR processing in the PCIII algorithm involves the following stages:
1. MR interpolation
l If RXLEV values are missing, a value is interpolated linearly.
l If RXQUAL values are missing, the missed value is replaced with a synthetically generated "worst possible" Quality (RXQUAL=7)
l The value of MS/BTS transmit power missing from the MRs is not interpolated. In such a case, MR filtering is not affected, and Power Control procedure proceeds normally.
l The interpolation is not performed in the case that the measurement results are lost.
l If the number of continuously lost MRs is greater than the value of MRMISSNUM, the Power Control procedures stop. The procedures will resume when a new MR is received.
2. MR filtering
MR filtering in the PCIII algorithm involves exponential filtering and sliding window filtering.
In the process of calculation, receive quality is converted into C/I. In MR filtering, exponential filtering and sliding window filtering are performed on C/I and receive level in succession. The measurement value obtained through the filtering is used to decide whether Power Control is performed.
In the PCIII algorithm, the filtering periods are specified by the following parameters:
l Uplink:
ULREXLEVEXPFLTLEN, ULREXQUALEXPFLTLEN, ULREXLEVSLDWINDOW, and ULREXQUALSLDWINDOW
l Downlink:
DLREXLEVEXPFLTLEN, DLREXQUALEXPFLTLEN, DLREXLEVSLDWINDOW, and DLREXQUALSLDWINDOW
3.3.3 Power Control Decision
Power Control decision in the PCIII algorithm involves the following stages:
l If it is within the specified range, Power Control is performed.
l The gain of the channels on the Um interface is obtained through calculation.
l The adjustment step is calculated on the basis of the gain, RxLev, and RxQual after filtering.
l The calculated step will be checked to determine whether it exceeds the maximum step allowed.
1. Decision on whether Power Control should be performed
Power Control is not required when ULREXLEVHIGHTHRED ≥ Rxlev ≥ ULREXLEVLOWTHRED and UL**REXQUALHIGHTHRED ≥ RxQual ≥ UL**REXQUALLOWTHRED.
Otherwise, the calculation of the adjustment step starts.
In Huawei III Power Control algorithm, different quality level thresholds are set for different speech coding schemes. The symbol ** represents full-rate service (FS), half-rate service (HS), AMR full-rate service (AFS), or AMR half-rate service (AHS).
2. Calculation of adjustment step
The PCII algorithm is based on dual thresholds, and increases the power if the channel is below the lower threshold, and reduces the power if it is above the upper threshold.
The PCIII algorithm is quite different and is a P controller. That is to say the adjustment made is simply proportional to the difference (and "error") between a configured setpoint and the current (filtered) control metric.
The error is computed and scaled for both a level and quality term. That is, there is a level setpoint and gain, and a quality setpoint and gain.
The controller computes the adjustment ("step") for each cycle and this is added to the preceding power attenuation to give the power attenuation to be used in this cycle.
Calculating the BTS Power Control Step
In each power control period, the power control adjustment step is calculated on the basis of the receive level and receive quality.
g(k) = p(k) – (ca_filtered(k) + qa_filtered(k) – 10 x log10 (1 + 10^( qa_filtered(k)/10)))
SThr = (SThrUp + SThrDown)/2
QThr = (QThrUp + QThrDown)/2
step(k) = –(sfactor x (BsTxMaxPower – g(k) – SThr) + qfactor x (qa_filtered(k) – QThr))
If step (k) > 0, step (k) = 0.
Where,
SthrUp: indicates downlink receive level upper threshold that is specified by DLRexLevHighThred.
SThrDown: indicates downlink receive level lower threshold that is specified by DLRexLevLowthred.
QThrUp =DL**RexQualHighThred
QthrDown = DL**RexQualLowThred
Sfactor = DLREXLEVADJFCTR
BsTxMaxPowe: the maximum transmit power of the TRX used for the call
Qfactor = DLREXQUALADJFCTR
g (k): gain of the radio channel (referred to as path loss of the channel)
qa_filtered (k): MR of the filtered receive quality (converted to CIR)
ca_filtered(k): MR of the filtered receive level
p(k): transmit power of the BTS
You can calculate the valid level through the CIR and the receive level (including the valid signals and the interference signals), and then calculate the channel gain by distracting the valid level from the transmit power.
To prevent excessive adjustment, control the range of step (k) by setting DLMAXUPSTEP or DLMAXDOWNSTEP. If the value of step (k) is greater than the maximum allowable step length, the power is controlled according to the maximum allowed step set in this parameter. DLMAXUPSTEP indicates maximum step by which to increase downlink power according to signal strength. DLMAXDOWNSTEP indicates maximum step by which to decrease downlink power according to signal strength.
Calculating the MS Power Control Step
In each power control period, the power control adjustment step is calculated on the basis of the receive level and receive quality.
g(k) = p(k) – (ca_filtered(k) + qa_filtered(k) – 10 x log10 (1 + 10^( qa_filtered(k)/10)))
SThr = (SThrUp + SThrDown)/2
QThr = (QThrUp + QThrDown)/2
step(k) = –(sfactor x (MsTxMaxPower– g(k) – SThr) + qfactor x (qa_filtered(k) – QThr))
If step(k) > 0, step(k) = 0.
Where,
SthrUp: indicates uplink receive level upper threshold that is specified by ULRexLevHighThred.
SThrDown: indicates uplink receive level lower threshold that is specified by ULRexLevLowthred.
QThrUp = UL**RexQualHighThred
QThrDown = UL**RexQualLowThred
Sfactor = ULREXLEVADJFCTR
MsTxMaxPower: maximum transmit power in the MS classmark
Qfactor = ULREXQUALADJFCTR
g(k): gain of the radio channel (referred to as path loss of the channel)
qa_filtered (k): filtered receive quality (converted to CIR)
ca_filtered(k): MR of the filtered receive level
p(k): transmit power of the MS
To prevent excessive adjustment, control the range of step (k) by setting ULMAXUPSTEP/ULMAXDOWNSTEP. If the value of step(k) is greater than the allowed maximum step length, the power is controlled according to the maximum allowed step set in this parameter.
By default, the minimum power adjustment step is 2 dB, but some BTS products support higher resolution Power Control, in 0.2 dB steps. This provides enhanced performance. This is controlled by parameter FINESTEPPCALLOWED.
3.4 Optimized Huawei III Power Control Algorithm
The process of the PCIII Opt. algorithm is the same as the process of the PCIII algorithm. The PCIII Opt. algorithm involves MR processing, MR filtering, calculation of the Power Control step, and Power Control execution. The PCIII Opt. algorithm takes effect when PWRCTRLSW is set to PWR3 (Power Control III) and PWRCTRLOPTIMIZEDEN is set to YES.
This section describes the improvements of the PCIII Opt. algorithm over the PCIII algorithm.
3.4.1 Measure Report Handling
1. MR Power Control compensation
MR Power Control compensation aims to compensate the receive level and receive quality so that they reach the measured values at the maximum transmit power.
In the PCIII Opt. algorithm, the receive level and receive quality reported through the MR are compensated. Subsequently, the receive level after compensation and the receive quality after compensation are used as inputs for MR filtering.
The formula for calculating the quality compensation value is as follows:
Quality compensation value = 2 x Power control level
The formula for calculating the level compensation value is as follows:
l When the current CS session is carried on the BCCH TRX:
− If frequency hopping (FH) is not used or the BCCH frequency is not involved in FH, the BSS does not compensate for power control.
− If the BCCH frequency is involved in FH and CANPC is set to YES, Level compensation value = 2 x Power control level; when the BCCH frequency is involved in FH and CANPC is set to NO, Level compensation value = (N-1)/N x Power control level x 2, where N is the number of frequencies involved in FH.
l When the current CS session is not carried on the BCCH TRX:
− If the BCCH frequency is not involved in FH, Level compensation value = 2 x Power control level.
− If the BCCH frequency is involved in FH and CANPC is set to YES, Level compensation value = 2 x Power control level; when the BCCH frequency is involved in FH and CANPC is set to NO, Level compensation value = (N-1)/N x Power control level x 2, where N is the number of frequencies involved in FH.
If baseband FH is used and the BCCH frequency is involved, it is recommended that PCHOCMPCON be set to ON. By doing this, power control accuracy is improved. This also reduces the number of ping-pang handovers caused by the inconsistency between power control compensation and handover compensation.
2. Dual-coefficient MR filtering algorithm
The PCIII Opt. algorithm adopts an exponential filtering algorithm and MR filtering adopts the dual-coefficient filtering algorithm. The dual-coefficient filtering algorithm concerns the receive level and the receive quality.
This algorithm has a strong correlation with the filtering period K and the filter adjustment factor FiltAdjustFactor.
The values of K and FiltAdjustFactor vary with the measured receive level and receive quality:
− The value of K depends on ULREXLEVEXPFLTLEN/DLREXLEVEXPFLTLEN and ULREXQUALEXPFLTLEN/DLREXQUALEXPFLTLEN.
− The value of FiltAdjustFactor, can be adjusted using parameter ULFILTADJFACTOR.
In this section, the symbol / separates two independent parameters. For example, ULREXLEVEXPFLTLEN/DLREXLEVEXPFLTLEN indicates ULREXLEVEXPFLTLEN or DLREXLEVEXPFLTLEN. ULREXLEVEXPFLTLEN and DLREXLEVEXPFLTLEN take effect in uplink Power Control and downlink Power Control respectively.
In the dual-coefficient exponential filtering algorithm, the filter response rate increases when the radio propagation environment deteriorates. In this case, the filter length is K. The rate of increasing the filtering value decreases when the radio propagation environment becomes better. In this case, the filter length is K x FiltAdjustFactor.
3.4.2 Calculation of the Power Control Step
The Power Control step of the PCIII Opt. algorithm is calculated on the basis of two step factors: output1(k) and output2(k). The methods of calculating power control step are similar in the uplink and downlink. This section uses the uplink as an example.
output1(k) is determined by RexLev_pf, RexQual_pf, STarget, and QTarget. The calculation formula is as follows:
output1(k) = - {RexLev_pf x (ca_filtered(k) - STarget) + RexQual_pf x(qa_filtered(k) - QTarget)}
Where,
RexLev_pf indicates ULRXLEVPROTECTFACTOR.
ca_filtered(k) indicates the measured receive level after the filtering.
STarget = ULREXLEVHIGHTHRED.
RexQual_pf = ULRXQUALPROTECTFACTOR.
qa_filtered(k) indicates the measured receive quality after the filtering.
QTarget = ULFSREXQUALHIGHTHRED.
output2(k) is determined by sfactor, qfactor, STarget, and QTarget. The calculation formula is as follows:
output2(k) = - {sfactor x (ca_filtered(k) - STarget) + qfactor x (qa_filtered(k) - QTarget)}
Where,
sfactor indicates RxLev Adjustment Factor ULREXLEVADJFCTR.
ca_filtered(k) indicates the measured receive level after the filtering.
STarget indicates RxLev setpoint, ULREXLEVHIGHTHRED.
qfactor indicates RxQual Adjustment Factor, ULREXQUALADJFCTR.
qa_filtered(k) indicates the measured receive quality after the filtering.
QTarget indicates RxQual setpoint, ULFSREXQUALHIGHTHRED.
The step factor output(k) is determined according to the formula
output(k) = max(output1(k), output2(k)).
Subsequently, based on this step factor, Power Control adjustment is performed. If output(k) is greater than 0, then output(k) is set equal to 0, that is, transmit power is not adjusted.
By default, the minimum power adjustment step is 2 dB, but some BTS products support higher resolution Power Control, in 0.2 dB steps. This provides enhanced performance. This is controlled by parameter FINESTEPPCALLOWED.
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