gsm rno subject-power control algorithms_r2.0

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Power Control Algorithms

R2.0



Power Control Algorithms Internal Use Only▲

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ZTE Confidential Proprietary © 2014 ZTE CORPORATION. All rights reserved. II

Revision History

Product Version Document Version Serial Number Reason for Revision

R1.0 First published

R1.1 Parameters and applicationscenarios were added; figuredescription of some problems wasadded.

R2.0

A description about the new powercontrol algorithms for SDRV4.09.21.08 and later versions wasadded.

Author

Date Document Version Prepared by Reviewed by Approved by

2009-05-12 R1.0 Chang HaiJjie Zheng Hao



Intended audience: GSM network optimization engineers




ZTE Confidential Proprietary © 2014 ZTE CORPORATION. All rights reserved. III

About This Document

Summary

Chapter Description

1 Overview Describes the purpose of power control.

2 Features of Power Control Describes the features of power control.

3 Application Scenarios of PowerControl

Describes the application scenarios of power control.

4 Theories of Power Control Describes the theories of power control.

5 CS Power Control Parametersand Reference Values

Describes the basic CS power control parameters.

6 Setting of Power ControlParameters in Different Scenarios

Describes the setting of power control parameters indifference scenarios.

7 Examples of Power Control Gives some examples of power control.




ZTE Confidential Proprietary © 2014 ZTE CORPORATION. All rights reserved. IV

TABLE OF CONTENTS

1

Overview ......................................................................................................... 1

2

Features of Power Control ............................................................................. 2

3

Application Scenarios of Power Control ....................................................... 3

4

Theories of Power Control ............................................................................. 4

4.1

Location of Power Control Module in the System .............................................. 4

4.2

Overall Flow of CS Power Control .................................................................... 5

4.3

Descriptions of Power Control Process ............................................................. 6

4.3.1

Storage of Measurement Data .......................................................................... 6

4.3.2

Calculation of Averages .................................................................................... 7

4.3.3

Window, Average and Threshold ...................................................................... 9

4.3.4

Power Control Step Size ................................................................................. 11

4.3.5

Performance Measurement ............................................................................ 12

4.3.6

Power Control Indication ................................................................................. 12

4.4

BTS V6.20.102e Improvement on Power Control Algorithms .......................... 13

4.4.1

Comparison of Algorithms Before/After Improvement ..................................... 13

4.4.2

Initial State of Power Control .......................................................................... 13

4.4.3

UL Level and Quality Decision and Step Size ................................................. 15

4.4.4

Power Level Control ....................................................................................... 16

4.4.5

Conversion of Power Control States ............................................................... 18 4.4.6

Clear MR Queues and Counters ..................................................................... 19

4.5

Improvement of SDR V4.09.21.08 and Later Versions on Power Control Algorithms ...................................................................................................... 20

4.5.1

Amendments to the Power Control Algorithms ................................................ 20

4.5.2

Presetting of the UL Power ............................................................................. 21

4.5.3

Amendment to the UL/DL Sliding-Window Filter Algorithm ............................. 21

4.5.4

UL/DL Index Filter Algorithm ........................................................................... 22

4.5.5

UL and DL RxLev Optimization Algorithms ..................................................... 23

4.5.6

Respective Settings of Minimum UL and DL Power Control Intervals ............. 24

4.5.7

Respective Settings of Minimum UL and DL Power Control Step Sizes .......... 24

4.5.8 Addition of DL Power Control Over BCCH Carriers......................................... 24

4.5.9

Setting of Thresholds by Coding Scheme ....................................................... 25

4.5.10

Introduction to Newly Added Key Parameters ................................................. 25

4.6

PS Power Control Theories ............................................................................ 29

4.6.1

MS Power Control Algorithm ........................................................................... 29

4.6.2

Power Control Algorithm of BTS ..................................................................... 31

5

CS Power Control Parameters and Reference Values ............................... 33

5.1

UL/DL Power Control ...................................................................................... 33

5.2

Received Signal Level and Quality Threshold ................................................. 33

5.2.1

Received Signal Level .................................................................................... 34

5.2.2

Received Signal Quality .................................................................................. 34

5.3

Power Control Period ...................................................................................... 35




ZTE Confidential Proprietary © 2014 ZTE CORPORATION. All rights reserved. V

5.3.1

Sample Count (Window) and Weight (Weight) ................................................ 35

5.3.2

Number of Power Control Samples N and P ................................................... 35

5.4

Power Adjustment Step .................................................................................. 36

5.5

Criteria of Power Control State Conversion — N1 and N2 .............................. 37

5.6

Maximum Power Levels of MS and BTS for Initial Access .............................. 37

5.7

Rapid Power Control ....................................................................................... 38

5.8 Fast Averaging ............................................................................................... 38

5.9

Setting of Power Control Parameters .............................................................. 40

6

Setting of Power Control Parameters in Different Scenarios .................... 42

6.1

Setting of Signal Quality Threshold (Under Poor DL Radio Environment) ....... 42

6.2

Setting of UL/DL Power Control Period ........................................................... 42

6.3 Handover Threshold ....................................................................................... 42

6.4

Highway/Railway ............................................................................................ 43

6.5

Building ........................................................................................................... 43

7

Examples of Power Control ......................................................................... 44




ZTE Confidential Proprietary © 2014 ZTE CORPORATION. All rights reserved. VI

FIGURES

Figure 4-1 Location of POWCTRL in System ....................................................................... 4

Figure 4-2 Simple Flowchart of Power Control ..................................................................... 6

Figure 4-3 Comparison of MR Processing ............................................................................ 8

Figure 4-4 Power Control Decision ....................................................................................... 9

Figure 4-5 Power Control I ................................................................................................. 14

Figure 4-6 Power Control II ................................................................................................ 14

Figure 4-7 Pingpong Power Control ................................................................................... 17

Figure 4-8 Conversion of Power Control States ................................................................. 19

Figure 4-9 Window Mechanism of Power Control ............................................................... 20

Figure 4-10 Amendment to the UL/DL Sliding-Window Filter Algorithm .............................. 22

Figure 4-11 Index Filter Algorithm ...................................................................................... 23

Figure 7-1 Graph of UL Ordinary Power Control ................................................................ 44

Figure 7-2 Graph of UL Ordinary Power Control With Fast Averaging ................................ 44

Figure 7-3 Graph of UL Rapid Power Control ..................................................................... 45

Figure 7-4 Graph of DL Ordinary Power Control ................................................................ 45

Figure 7-5 Graph of DL Ordinary Power Control With Fast Averaging Adopted .................. 46

Figure 7-6 Graph of DL Rapid Power Control ..................................................................... 46

Figure 7-7 Graph of DL Rapid Power Control With Fast Averaging Adopted ...................... 47

TABLES

Table 3-1 Application Scenarios of Power Control ................................................................ 3

Table 4-1 Components of POWCTRL .................................................................................. 4

Table 4-2 MS Power Control Strategy ................................................................................ 10




ZTE Confidential Proprietary © 2014 ZTE CORPORATION. All rights reserved. 1

1 Overview

Power control is divided into static power control and dynamic power control. Static

power control is to restrict the maximum transmitting power of MS or BTS; dynamic

power control is for the network to dynamically decide the maximum transmitting power of

MS or BTS according to radio environment around subscribers. The power control

discussed in this manual belongs to the scope of dynamic power control.

The main function of power control is to optimize the transmitting power of MS and BTS

without affecting radio transmission quality, so as to improve frequency efficiency as well

as reducing the average transmitting power of MS and BTS, and to reduce interference to

other communications. In mobile systems, to reduce interference means to have high

spectrum efficiency, which means increase of capacity. In the system, power control ofuplink and downlink is independent to each other. MS power control is to adjust the

output power of MS, so that BTS can get stable receive signal level, interference from

other MS using the same channel will be restricted, MS power consumption will be

lowered, and MS average useful time will be extended; BTS power control is to make MS

get stable receive signal level, to restrict interference from MS using the same channel,

and to lower BTS power consumption.





2 Features of Power Control

According to the amount of measurement data, power control makes weighted average

of the data respectively, then compares the averages with corresponding thresholds, and

then makes MS and BTS power control according to result of the comparison. In order to

meet requirements of power control speed on site, ZTE provides fast averaging, rapid

power control, etc. to accelerate power control speed.

Uplink and downlink power control is performed separately.

CS and PS power control is performed separately.

In Version 6.20.101e and the subsequent versions, dynamic power control algorithmshave been optimized. Having combined the speed and stability of power control, power

control is divided into two states: initial state and stable state. Initial state is to adjust

power to the proper level; stable state is to prevent frequent adjustment of frequency, so

as to keep power output stable.

The dynamic power control algorithms for SDR V4.09.21.08 and later versions were

optimized: Index filtration and level optimization functions were added to enhance the

sensitivity and efficiency of power control.





3 Application Scenarios of Power Control

UL ordinary power control is usually enabled; other types of power control are mainly

used in areas with dense sites, for only in areas with dense sites, can power control work

well to reduce interference. Here is a table of application scenarios of power control for

reference.

Table 3-1 Application Scenarios of Power Control

Algorithm

Scenario

UL OrdinaryPower

Control

UL RapidPower

Control

DL OrdinaryPower

Control

DL RapidPower

Control

Urban area ▲ ▲

Dense urban area ▲ ▲ ▲ ▲

Suburb ▲ ▲

Wide coveragearea

▲





4 Theories of Power Control

4.1 Location of Power Control Module in the System

Power control is performed on BTS. Location of CS power control module POWCTRL in

the system is shown in Figure 4-1 (marked in red).

Figure 4-1 Location of POWCTRL in System

Refer to Table 4-1 for explanations on components and interfaces related to POWCTRL.

Table 4-1 Components of POWCTRL

Components Functions Interface

CMM

It’s the manager of BTS and the proxy of

remote operation and maintenance of BSC,it performs operation and maintenance ofthe BTS it belongs to:

1. Configuration of parameters

2. Management of status and alarms

3. Management of software versions

4. Test of equipment

It completesconfiguration ofPwrCtrl parameters,receives and transmitsPwrCtrl performancemeasurement reports.

CHP

It realizes processing of all basebandchannels in BTS and controlling of somerelated parts.

UL: demodulation, equalization,de-interleaving, channel decoding, rate

It reports ULmeasurementstatistics, and receivesorders SET MSPOWER and SET BS





Components Functions Interface

adaptation;

DL: rate adaptation, channel coding,interleaving, etc.

POWER of POWCTRLmodule.

DCHMIt’s the special channel processingsub-module of FURRM, handling messageprocessing of SDCCH or TECH.

It invokes POWCTRLmodule, and transmitsUL/DL MRs toPOWCTRL.

CS power control module POWCTRL is located in the application layer of FUC

subsystem. According to the amount of measurement data, power control makes

weighted average of the data respectively, then compares the averages with

corresponding thresholds, and then makes MS and BTS power control according to

result of the comparison.

4.2 Overall Flow of CS Power Control

After power control parameters are set at OMCR, they will be transmitted to the OAMM

module on FUC through CMM; OAMM configures related parameters at the start or

during the operation of FURRM process; FURRM saves these parameters in its global

variables.

During calls, FURRM periodically receives CHP MEASUREMENT IND message reported

by CHP and MS MEASUREMENT REPORT reported by LAPDm. DCHM decides

whether to perform power control according to the parameters saved in FURRM. If power

control is to be carried out, after the number of received CHP MEASUREMENT IND from

DCHM reaches Hqave, POWCTRL will make weighted average of UL measurement data,

then compares the average with the corresponding threshold, then according to result of

the comparison confirms whether to control MS power. If MS power control is necessary,

then send the new power to CHP through CHP SET MS POWER message. After the

number of received MS MEASUREMENT REPORT reaches Hqave, POWCTRL starts

weighted average of DL measurement data, and then compares the average with the

corresponding threshold, and then according to result of the comparison it confirms

whether to control BTS power. If BTS power control is necessary, then send the new

power to CHP through CHP SET BS POWER message. These processes can be

repeated again and again. In the meantime, POWCTRL module can also conduct power

control performance measurement according to configuration of related parameters. A

simple flowchart of power control is shown bellow.





Figure 4-2 Simple Flowchart of Power Control

Collection of MS/BTS

measurement reports

Weighted averaging of

MRs

Increase MS/BTS

transmitting power

If no. of averages meets

conditions of power

control decision?

Save the averagesNo

Yes

Maintain MS/BTS

transmitting power

Conditions for

power increase

satisfied

Yes

Conditions for

power decrease

satisfied

Yes

Decrease MS/BTS

transmitting power

Conditions for

power

maintenance

satisfied

Judge and adjust step size Judge and adjust step size

4.3 Descriptions of Power Control Process

4.3.1 Storage of Measurement Data

MR data are saved in the circular table structured with arrays. When the circular table is

filled with data for the first time, new MR data will cover the old data. We can use a

counter to record the number of received MRs, and get the location of latest MR data in

the table. The counter will be refreshed after power control is completed successfully,

and won’t be started until next power control (a certain number PCMinInterval of MRs in

the process will be abandoned; and a certain number PCMinInterval of MRs at the

beginning of the process will also be abandoned, because the first several MRs are not

accurate at the beginning of channel activation). Measurement data and averages of

uplink and downlink are stored separately. According to protocol 05.08, the number of

measurement data and averages of uplink and downlink can at most reach 32.





4.3.2 Calculation of Averages

We make weighted average but not the simple averaging calculation of MRs, because

discontinuous transmission (DTX) exists. In order to increase MR weight when DTX is off,

we can set the weight to be 1 when DTX is on; the weight of DTX Off can be set at OMCR.

These averages are saved in the circular arrays, and use of the data is controlled by

counters. When fast averaging is adopted, the first average is the first datum, the second

average is calculated from the first and the second data, and so on. If rapid isn’t adopted,

the first average is obtained only when the number of data reaches Hqave.

Suppose the number of MRs in the window is n during DTX Off, receive signal level is

Levoff ; and the number of MRs in the window is m during DTX On, and receive signal level

is Levon:

Sum of receive levels = ∑Levoff × Weight + ∑Levon × 1;

Weighted average = Sum/(n × weight + m × 1).

For example, the current window size is 3, its weight is 2; take receive signal level as an

example, the levels reported by the three MRs are –80 dBm(DTX off), –70 dBm(DTX on),

–82 dBm(DTX off);

Weighted average = [( –80) × 2 + ( –82) × 2 + ( –70) × 1]/(2 + 2 + 1) = –78.8 dBm

Comparison of ordinary averaging and fast averaging is shown below:





Figure 4-3 Comparison of MR Processing





The comparison in Figure 4-3 shows that 7 MRs are needed for obtaining 4 averages in

ordinary averaging process, while only 4 MRs are needed in fast averaging process.

4.3.3 Window, Average and Threshold

Power control decision can be made according to the status of MS/BTS signal level and

quality. As shown in the following figure, lower signal Rxqual level on the horizontal

ordinate leads to lower signal error rate and better signal quality. For example, when the

receive signal level and quality values are within the range of corresponding thresholds,

the result of power control decision is not to make power control adjustment; when the

receive signal level value is lower than corresponding threshold, and the receive signal

quality is within the range of corresponding threshold, the power control decision result is

to increase power due to level; when the receive signal level is higher than the ―High

level‖, and receive signal quality is higher than the ―High Rxqual level‖, the p ower control

decision result is to increase power due to quality.

When setting receive signal level and quality thresholds, we must pay attention to the

relation between power control threshold and handover threshold. The low level

threshold of power control must be larger than level handover threshold, while the high

quality threshold of power control must be smaller than quality handover threshold, as the

stripped area shown in Figure 4-4.

Figure 4-4 Power Control Decision

High level

Low level

Low quality rank High quality rank

Level handover

threshold

Quality handover threhsold

Increase power

Decrease power

Maintain power

Margin

Note:

Low Rxqual level represents good signal quality; high Rxqual level represents poor

quality.





The strategy of MS power control is the same with that of BTS power control. Take MS

power control as an example, suppose LEVELCAUSE records the current level situation,

and QUALCAUSE records the current situation of error rate, and:

Normal level: LEVELCAUSE = 0

Low level: LEVELCAUSE = 1

High level: LEVELCAUSE = 2

Normal error rate: QUALCAUSE = 0

Low error rate: QUALCAUSE = 1

High error rate: QUALCAUSE = 2

Suppose the level ranges from 0 to 63 (low to high), L_RXLEV is tending to be 0,

U_RXLEV is tending to be 63; error rate class (0~7) represents signal quality (high to

low), L_RXQUAL is tending to be 7, U_RXQUAL is tending to be 0. The average of UL

measurement data and corresponding threshold values and the comparison between

them area as follows:

If at least a certain number PCULIncrLevP among a certain number PCULIncrLevN

of RXLEV_UL are lower than the low limit L_RXLEV_UL, LEVELCAUSE = 1;

If at least a certain number PCULDecrLevP among a certain number PCULDecrLev

of RXLEV_UL are higher than the high limit U_RXLEV_UL, LEVELCAUSE = 2;

For other situations, LEVELCAUSE = 0

If at least a certain number PCULDecrQualP among a certain number

PCULDecrQualN of RXQUAL_UL are lower than the high limit U_RXQUAL_UL,

QUALCAUSE = 1;

If at least a certain number PCULIncrQualP among a certain number

PCULIncrQualN of RXQUAL_UL are higher than the low limit L_RXQUAL_UL,

QUALCAUSE = 2;

For other situations, QUALCAUSE = 0

Compassion of DL data is similar to the description above; just the eight parameters are

marked with DL, like PCDLIncrLevN.

Table 4-2 MS Power Control Strategy

LEVELCAUSE QUALCAUSE Conclusion

0 0 MS_POWER_STAY

0 1 DECREASE_BYQUALITY





LEVELCAUSE QUALCAUSE Conclusion

0 2 INCREASE_BYQUALITY

1 0 INCREASE_BYLEVEL

1 1 MS_POWER_STAY

1 2 INCREASE_ BYQUALITY

2 0 DECREASE_BYLEVEL

2 1 DECREASE_BYLEVEL

2 2 INCREASE_BYQUALITY

BTS power control strategy: similar to MS power control strategy.

4.3.4 Power Control Step Size

4.3.4.1 MS Power Control Step Size

According to parameter bRapidPCInd from OMU, MS decides whether to adopt rapid

power control.

If ordinary power control is adopted, STEP is INCREASESTEP or DECREASESTEP.

If rapid power control is adopted, it should be performed according to the following

principles. Specific conditions are still needed in deciding control over level

increase/decrease. If the conditions are not satisfied, only ordinary power control can be

performed.

1. INCREASE_BYLEVE:

If LEV_UL + 2 × INCREASESTEP < L_RXLEV_UL, then STEP = L_RXLEV_UL –

LEV_UL, LEV_UL is the current value, but not the average value.

2. DECREASE_BYLEVEL:

If LEV_UL – 2 × DECREASESTEP > U_LEV_UL, then STEP = Min(PwrDecrLimit,

LEV_UL – U_RXLEV_UL), LEV_UL is the current value, but not the average value.

3. INCREASE_BYQUALITY:

If LEV_UL + 2 × INCREASESTEP < L_RXLEV_UL

STEP = Max((1 + Max(0, Qa)) × INCREASESTEP, L_RXLEV_UL – LEV_UL)

Or

STEP = (1 + Max(0, Qa)) × INCREASESTEP





Qa = QUAL_UL – L_RXQUAL_UL; QUAL_UL is the current signal quality, LEV_UL

is the current signal level, and neither of them is the average value.

4. DECREASE_BYQUALITY:

For power decrease caused by signal quality, we should be conservative with the

step. size.

Therefore:

If LEV_UL – 2 × DECREASESTEP > U_LEV_UL,

STEP = Min(PwrDecrLimit, LEV_UL – U_ RXLEV_UL, (1 + Max(0, Qa)) ×

DECREASESTEP);

Or

STEP = DECREASESTEP.

LEV_UL is the current signal level, but not the average value.

Qa = U_RXQUAL_UL – AV_QUAL_UL.

AV_QUAL_UL is the signal quality average.

4.3.4.2 BTS Power Control Step Size

The calculation and adjustment of BTS power control step size is the same as that of MS,

only change UL in parameters to DL.

4.3.5 Performance Measurement

During BTS power control, it needs to report related performance data to BSC, and all the

statistical data is stored in PowerMeasData.

4.3.6 Power Control Indication

In order to optimize handover algorithms, after power control of MS or BTS, BSC will be

notified the direction (downlink or uplink) of power control by a message POWER

CONTROL IND, and then BSC will clear the corresponding buffer area based on this

message. After each time of power control, the queue of MRs reported will be cleared to

0. The first average value will not be obtained again until the number of MRs reported

reaches Hqave (non-rapid power control).





4.4 BTS V6.20.102e Improvement on Power ControlAlgorithms

4.4.1 Comparison of Algorithms Before/After Improvement

The existing power control strategy cannot simultaneously satisfy the following situations:

1. Make rapid power control of MS, and make MS UL level and quality meet

requirements in the shortest time;

2. After required UL level and quality are satisfied, MS power control can perform

stably, and no adjustment of power is needed only because of one or two minor

problems.

The improved power control algorithm: power control falls into two states — initial state

and stable state. Power control is carried out in over channels. The initialization of

channel power control status is initial state. After a number of power controls, MS UL

level and quality satisfy the expected values, the channel power control status enters

stable state, and it remains in stable state until the channel is released, and then the

status returns to initial state.

4.4.2 Initial State of Power Control

When MS accesses the channel (SDCCH or TCH), both the MS and BTS are transmitting

signals with their respective maximum power predefined for the network. If power control

period is too long, it will bring interference to subscribers using other channels. Therefore,

in order to realize rapid control of MS and BTS power, we carry out power control

decision to every MR, and make adjustments of MS and BTS power level to make MS

and BTS level and quality meet the requirements.

When MS or BTS initially accesses into channels, it transmits signals in the maximum

power level. In this case, power control usually tends to decrease MS or BTS transmitting

power, until level and quality reach the expected values and enter stable state.

According to MS uplink receive signal level and quality contained in the MRs reported by

CHP, BTS judges the uplink signal state and sends the new power level to MS after

power control decision. Due to coding problems and air interface delay, MS will not

immediately report the next MR with the new power level, but report the MR with the new

power level after a delay of three MRs. As shown in Figure 4-5, if BTS makes power

control decision only after it receives the new power level that it sends to MS, the power

control is of poor efficiency and timeliness.





Figure 4-5 Power Control I

BTS

P1 P1 P1 P1 P2 P2

P0 P0 P1P0P0 P1

MS

A delay of three MRs

In order to perform power control decision each time an MR is received, we add a

variable (MS PowerSet) to record the latest MS power level value, and then make poweradjustment based on the value. For example: as shown in Figure 4-6, if the new power

level sent by BTS (after receiving the last MR) is P1 (MS PowerSet), while the current

received MS power level is P0 , then power adjustment will be performed from P1 to P2 ,

while will be sent to MS. When another MR is received, power value will be adjusted with

P2 as the benchmark, and then a new power level value P3 will be sent to MS.

Figure 4-6 Power Control II

P1 P5P4P2 P3 P6

P0 P0 P0 P0 P1 P2

BTS

MS

……

……

MS Power=P0

MS PowerSet=P0

MS Power=P0

MS PowerSet=P1

MS Power=P0

MS PowerSet=P2

Each adjustment of MS power is based on the latest power level value, but not the actual

power value that MS uses to report. Because of the complexity and instability of radio

environment, the power level sent by BTS may be lost if downlink signal is bad. When

there is great difference between the new power level and the actual one, we take the

new one as benchmark in power adjustment, or power control adjustment will be invalid.





With the aim to ensure the validity of new power level, we impose specific decision

conditions before new MS power level is sent.

Power adjustment of BTS is usually effective and in time, and air interface delay and loss

of power level won’t happen, therefore each time an MR is received correctly, adjustment

of power control decision can be performed.

4.4.3 UL Level and Quality Decision and Step Size

In the initial state of power control, before making power control of each UL MR reported

by MS, we need to judge the situation of UL signal level and quality.

1. Compare each signal level in the UL MR with the threshold (byL_RXLEV_UL)which

causes increase of UL power and the threshold (byU_RELEV_UL) which causes

decrease of UL power:

byRxLevel < byL_RXLEV_UL;

byUpLevCause = 1;

or:

byRxLevl > byU_RELEV_UL;

byUpLevCause = 2;

if the level value is within the threshold range, byUpLevCause = 0;

2. Compare each signal quality in the UL MR with the threshold

(byL_RXQUAL_UL)which causes increase of UL power and the threshold

(byU_REQUAL_UL) which causes decrease of UL power:

byRxQuality > byL_RXQUAL_UL;

byUpQuaCause = 2;

or:

byRxQuality < byU_RXQUAL_UL;

byUpQuaCause = 1;

If the quality value is within the threshold range, byUpQuaCause = 0.

MS power control decision is performed based on the conditions of signal level and

quality abyMSPowDecision[byUpLevCause][byUpQuaCause]. In order to realize

effective and stable power control in the initial state, regardless power control mode

(INCREASE/DECREASE), the adjustment step size should be set:





STEP = DECREASESTEP.

Adjustment method for step size of BTS power control is the same with that of MS power

control.

4.4.4 Power Level Control

In the adjustment procedure of MS/BTS transmitting power level (changeMS/BSpower),

the same power level control strategy is used in both the initial state and stable state.

In adjustment of MS power, a variable (byMSpowerSet) is added to save the power

control adjustment value which is sent by BTS. Power control adjustment should be

based on the last power control adjustment value (byMSpowerSet), but not the currently

received MS power level (byMSpower).

During adjustment, no matter to increase or decrease power, a comparison with the

maximum and minimum power values allowed in the serving cell. For power increase,

power adjustment value =

MIN2(awGSMPowerCtrlLevel[byMSpowerSet] + byStep, byMS_TXPWR_MAX)

byStep is power adjustment step size;

byMS_TXPWR_MAX: maximum MS transmitting power (dbm) allowed in the

serving cell.

MAX2(awGSMPowerCtrlLevel[byTempMSpowerSet] – byStep,

byMS_TXPWR_MIN)

byMS_TXPWR_MIN: minimum MS transmitting power (dbm) allowed in the

serving cell.

After power adjustment value is confirmed, we need to judge its practicability. When

uplink signal is bad, BTS cannot receive the power level reported by MS. In this case, a

variable (bReceiveMSpower) is added to display whether BTS has received the power

level reported. If MS power level is successfully received, set the variable to 1, and clear

it to 0 after each power control.

MS power adjustment takes the latest power level value (MS PowerSet) sent by BTS as

benchmark. The new MS power level sent by BTS can be reported by MS only after an

interval of three MRs, so there is a difference (sub) between the new power level to be

sent and the MS power level (MS Power) in the currently reported MR. In order to prevent

Sub becoming too large, a limit value of 8db is added in the adjustment of power

decrease; if Sub value exceeds 8db, power adjustment won’t be performed.

In the process of power control, the following situations may be encountered:





1. When the received signal quality is good, and the received signal level is larger than

and close to the high level threshold, power decrease will be performed according to

power control decision. Only after an interval of three MRs, the new power level

value (P) can be reported, at this time, the received signal level may be lower than

the low level threshold. In this case, power needs to be improved, which leads to

Pingpong power control (increase-decrease).

Figure 4-7 Pingpong Power Control

Pn

Power control decision: decrease power,

send new power rank P

P

Power control decision: increase power

High level

Low level

2. UL received signal level is within the threshold range and close to the low level

threshold, while the received signal quality is very good and lower than the low level

threshold. In this case, power control decision is: power decrease due to quality.

After the power control, UL received signal level will be lower than the low level

threshold. In this case, power control decision is: power increase due to level. In

these cases, Pingpong power control (increase-decrease) can also be caused.

In order to avoid this kind of Pingpong power control, a Margin value is added when

power control decision is to decrease power, which means to make compensation to the

actual power value and judge whether it will be lower than the threshold after power

control decision is made. The algorithm is: current received signal level value minus the

power difference value (sub), if the result is lower than the low level threshold, power

control will not be performed; if not, continue the power control adjustment.

if (byRxLevel < byL_RXLEV_UL + bySub)

byL_RXLEV_UL: low threshold of RXLEV, which cause increase of UL power.

If the condition is satisfied, power control will not be performed.





For example: suppose current received level (byRxLevel) = –79 dBm,

byL_RXLEV_UL = –88 dBm, bySub = 8 dBm; if power adjustment is made under

this situation, the result will be lower than the threshold. Therefore, Margin value is

added to prevent the unfavorable result.

When power adjustment value is finally confirmed, a new power level will be sent to MS.

In BTS power measurement, the current power level value of BTS transmitting signal is

used as the benchmark value of power adjustment. The calculation method is the same

as that in the stable state of power control.

4.4.5 Conversion of Power Control States

No matter it is MS or BTS power control, they need to enter the stable state from the

initial state. In order to judge the conversion, we set two values (Num1—the number of―no power decrease‖, Num2—total number of MRs) and a counter

(dwPCToStableCount)to MS and BTS. In most cases, the power is adjusted downward

when MS or BTS initially access into channels (SDCCH or TCH). When the required UL

level and quality are achieved, the downward adjustment will be ended. After each power

control decision (byPowDecision), if it’s not needed to decrease MS or BTS power value,

the counter (dwPCToStableCount) will be increased by 1. If Num1 is achieved, it is

decided that power control enters the stable state. In order to ensure that all power

controls will enter stable state from initial state, we decide that if the number of reported

MRs reaches Num2, power control directly enters stable state, and Num1 < Num2.

Meanwhile, change power control state indication byPCStateInd = INIT_PC_STATE to

byPCStateInd = INIT_PC_STATE. Hereafter, when the next MR is received, UL power

control will be performed according to the power control strategy of stable state.





Figure 4-8 Conversion of Power Control States

Initial state

MS power stops downward modulation for N1 times

Stable stateChannel release

Number of MR received reaches N2

Channel control enters

initial state

4.4.6 Clear MR Queues and Counters

When power control enters stable state, MR queues and counters will be cleared to 0.

The reason is when power control initially enters stable state, MRs reported before stable

state will be used in the sliding-window averaging, and the average value obtained is not

accurate, which cannot be used in the measurement judgment of stable state.

In the original strategy, the reported MR queues and counters are cleared to 0 after each

power control, and the first average value cannot be obtained until the number reported

MRs reaches Hqave (non-rapid power control). In the improved strategy, each reported

MR is saved. After one time of power control, with the first MS MR reported to BTS and

the (Hqave – 1) MRs saved before, a weighted average can be performed immediately,

and the first average value needed in the power control will be obtained; after the second

MR is received, with the (Hqave – 1) MRs saved before this one, weighted average will

be continued and the second average value will be obtained. When byPCDLIncrLevN

MRs are received, byPCDLIncrLevN average values will be obtained, with which the first

power control decision can be performed. In this way, power control decision period is

greatly shortened. As shown in the following figure, after power control enters stable state,

the time for the first power control decision is the time used for reporting (W + N – 1) MRs;

from the second power control decision, power control interval is the time used for

reporting N MRs.





Figure 4-9 Window Mechanism of Power Control

W

1st average

1st power control duration under stable state:

(W+N-1)MRs

2nd average

Nth average

1st average

Nth average

……

……

2nd power control duration:

no. of MRs (N)

W

Power control

duration

No. of received MRs

(N)No. of received MRs

(N)

4.5 Improvement of SDR V4.09.21.08 and LaterVersions on Power Control Algorithms

4.5.1 Amendments to the Power Control Algorithms

The existing power control strategy cannot meet the following two demands at the same

time:

1. Quickly controlling the MS power to make the MS have the required UL RxLev and

RxQual in the shortest time

2. Keeping the MS power stable after the MS has the required UL RxLev and RxQual,

so as to avoid any power adjustment due to one or two burrs

Amendments to the power control algorithms include:

1. The UL power can be preset to accelerate the reduction of the MS power.

2. The sliding-window filtration mechanism has been improved, so that the

measurement reports before the power control will be kept to participate in the

sliding-window averaging after the power control and accelerate the power control.

3. An index filtration mechanism has been introduced to make the RxLev values closer

to the actual conditions and to reduce the burrs.





4. An RxLev optimization switch is added when rapid power control is enabled, so that

the power can be reduced rapidly.

5. A switch is added to enable or disable the DL power control over BCCH carriers, so

as to reduce the interference to BCCH carriers.

6. Different thresholds can be set for different coding schemes, so the power control

parameters can be set more flexibly.

7. UL and DL power modulation step sizes can be set separately. The UL power can

be adjusted by unit of 0.5 dB, so the power control step sizes can be adjusted more

flexibly.

4.5.2 Presetting of the UL Power

According to the UL RxLev and RxQual in the measurement report, the BTS performs

power control decision and then sends the new power level to the MS. Because of the

coding and signal delay on the Um interface, the MS will not immediately report the new

power level in the next measurement report. Instead, it will report it in the third

measurement report. Therefore, the power control based on the new power level will not

be performed on the MS until the third measurement report arrives.

To adjust the MS power level more quickly, the third generation of power control

algorithms does not use the mode of waiting for the MS reporting the new power level.

After the new power level P1 obtained in the UL power control decision is sent to the MS

and the next decision is made, a power adjustment will be made directly on the basis ofthe new power level P1 and the power level P2 will be sent to the MS, which is similar to

the stable state in the power control algorithms of BTS V6.20.102e. As a protection, the

same decision conditions should be observed during the sending process (see Section

4.4.4, Power Level Control).

4.5.3 Amendment to the UL/DL Sliding-Window Filter Algorithm

The filter algorithms earlier than the third generation of power control algorithms all use

the mechanism of power control decision based on the sliding-window weighted average

values and are mainly related to three parameters: W (Window), P , and N . Before everytime of power control decision, the system collects W measurement reports, calculates

the weighted average value, and gets a weighted average sample. After it gets N

weighted average samples, it will perform power control decision, judge whether there

are P samples meeting the threshold conditions, and remove the saved original

measurement reports. Therefore, a power control decision period is equal to the duration

of (W + N – 1) measurement reports.

The third generation of power control algorithms uses a similar mechanism but the

original measurement reports are not removed. Thus after every time of power control

decision, the system calculates the weighted average value of the latest measurement





report and the earlier (W – 1) measurement reports and gets an average value sample.

Except for the first time of power control decision, each power control decision period is

(W – 1) measurement reports shorter, which is similar to the sliding-window processing in

stable state in the power control algorithms of BTS V6.20.102e.

Figure 4-10 Amendment to the UL/DL Sliding-Window Filter Algorithm

W

The 1st average value

Duration of the 1st time of power control:

(W + N – 1) MRs

The 2nd

average value

The Nth average value

The 1st average value

The Nth average value

……

……

Duration of the 2nd

time of

power control: N MRs

W

Power control

duration

Reception of N MRs Reception of N MRs

4.5.4 UL/DL Index Filter Algorithm

As a counterpart to the sliding-window filter stated in Section 4.5.3, the index filter

provides a filtration function similar to weighted averaging. Once the index filter is

enabled, the sliding-window filter will be disabled automatically.

The index filter processes the UL and DL RxLev and RxQual values in the measurement

reports. The data samples obtained after the index filtration still use N and P for power

control decision, and the decision method remains unchanged.

RxlevelFilter(k) = Rxlevel(0); k = 0

RxlevelFilter(k) = a × Rxleve(k) + (1 – a) × RxlevelFilter(k – 1) k > 0

RxqualityFilter(0) = Rxquality(0); k = 0

RxqualityFilter(k) = a × Rxquality(k) + (1 – a) × RxqualityFilter(k – 1) k > 0

Here a is the index filter coefficient, a = 1/(2^(W/2)), and W is the filter period. The index

filter period is equal to the value of the Window parameter.





The value of W may change the weight of the RxLev and RxQual measurement results in

the newly received measurement report. The larger W is, the smaller the weight of the

latest measurement results is. The default value of W is 4, so a = 0.25 and the weight of

the latest measurement report is 0.25 and that of the earlier ones is 0.75. As a result, a

stable RxLev can be achieved through index filtration. Usually, we recommend changing

the value of W to 1 or 2 to raise the weight of the latest measurement report.

For example, the first measurement report has the first filter value (Filter 1), the second

measurement report has the second filter value (Filter 2) according to the relevant

formula, …., and the N th measurement report has the N

th filter value (Filter N ). The

system uses the N filter values to perform the first time of N/P power control decision.

After the power adjustment, the system deletes the index filter queue but keeps the

measurement report queue. Although the measurement report queue is kept, these

measurement reports will not be used for subsequent filter calculation, that is, the first

filter value after the power control will be calculated with the formula of ―k = 0‖.)

If there is no interval for power control, after the system receives the (N + 1)th

measurement report, it will get the (N + 1)th filter value (Filter (N + 1)). When it gets Filter

(N + N ), it will perform power control decision again.

The engineer can set the parameter of minimum power control interval to control the

interval between two consecutive power control commands. However, this parameter in

the sliding-window filter is invalid.

Figure 4-11 Index Filter Algorithm

N

Duration of the 1st time of power control: N

Filter 1 Filter 2 Filter 3 Filter N

N

Filter

(N + 1)

Filter

(N + 3)

Filter

(N + 2)

Filter

(N + N)

Duration of the 2nd

time of power control: NInterval

Compared with the average filter, the index filter can filter burrs more effectively and the

RxLev values are closer to the actual conditions, but the disadvantage is that the RxLev

processing of the index filter has hysteresis, which means that the sensitivity is

decreased and the change of the radio environment cannot be presented in time.

4.5.5 UL and DL RxLev Optimization Algorithms

Two UL and DL RxLev optimization switches are added: OptimumRxLevDL (DL RxLev

optimization) and OptimumRxLevUL (UL RxLev optimization). They play a role in the

step size calculation when signal quality leads to a power decrease during rapid power

control. If high quality leads to a decline of the UL or DL transmission power level when





rapid power control is adopted and the UL or DL RxLev optimization switch is turned on,

the target value of the power control should be the value of the corresponding

OptimumRxLevUL or OptimumRxLevDL parameter, that is, a medial value between

the upper and lower RxLev thresholds (to replace the upper UL or DL RxLev thresholds

in the earlier algorithms. See Section 4.3.4.1.)

The OptimumRxLevDL and OptimumRxLevUL parameters respectively control the UL

and DL, which makes the setting more flexible.

4.5.6 Respective Settings of Minimum UL and DL Power Control Intervals

In the algorithms earlier than the third generation of power control algorithms, the

minimum UL and DL power control intervals are defined through a same parameter: the

Minimum FR/HR/AMR FR/AMR HR Interval parameter.

Because in the index filter algorithm, a parameter of minimum power control interval

should be set to control the interval between two consecutive power control commands, it

is required to set the minimum UL and DL power control interval parameters respectively:

the Minimum BTS_FR/HR/AMR FR/AMR HR Interval and Minimum MS_FR/HR/AMR

FR/AMR HR Interval parameters.

The measurement reports during every minimum power control interval will not be listed

in the measurement report queue for index filter calculation.

In the sliding-window filter algorithm, because the measurement reports after power

control will participate in the subsequent weighted averaging, it is unnecessary to use theparameters of minimum power control intervals.

4.5.7 Respective Settings of Minimum UL and DL Power Control StepSizes

The UL and DL power control step sizes can be set respectively.

The increase and decrease of the DL power step size can be adjusted by unit of 0.5 dB.

The value range has changed to 1, 2, 4, 8, and 12, which mean 0.5 dB, 1 dB, 2 dB, 4 dB,

and 6 dB respectively.

4.5.8 Addition of DL Power Control Over BCCH Carriers

A switch is added to enable or disable the DL power control over BCCH carriers, so as to

reduce the interference to BCCH carriers.

The engineer can set a maximal value for the BCCH carrier power decrease separately

or set the transmission power for idle BCCH time slots.

This new function can prevent frequency interference to BCCH carriers to some extent.





4.5.9 Setting of Thresholds by Coding Scheme

The engineer can set different thresholds according to the coding schemes (FR, EFR, HR,

AMR_FR, and AMR_HR), so the power control parameters can be set more flexibly.

4.5.10 Introduction to Newly Added Key Parameters

4.5.10.1 Uplink Power Level

Full Name Uplink power level

Abbreviation PcUlLevWindow

DescriptionThe parameter PcUlLevWindow represents the window size (thatis, the number of sample values) used to calculate the averagevalue of uplink signal strength.

Managed Object Cell

Value Range 1~31

Unit None

Default Value 4

4.5.10.2 Downlink Power Level

Full Name Downlink power level

Abbreviation PcdlLevWindow

Description

PcUlLevWindow calculates the uplink signal strength.

The window size for the average calculation is the number ofsamples.

Managed Object Cell

Value Range 1~31

Unit None

Default Value 4

4.5.10.3 Uplink Quality Level

Full Name Uplink quality level

Abbreviation PcUlQualWindow

Description

The parameter PcUlLevWindow represents the window size (thatis, the

number of sample values) used to calculate the average value ofuplink

signal strength.

Managed Object Cell

Value Range 1~31

Unit None

Default Value 4





4.5.10.4 Downlink Quality Level

Full Name Downlink quality level

Abbreviation PcDlQualWindow

Description

The parameter PcUlLevWindow represents the window size (thatis, the

number of sample values) used to calculate the average value ofdownlink

signal quality.

Managed Object Cell

Value Range 1~31

Unit None

Default Value 4

4.5.10.5 BCCH Power Control Downlink

Full Name BCCH power control downlink

Abbreviation BCCHPwrControlDL

DescriptionThis parameter determines whether to implement power controlfor the dedicated channel on the BCCH carrier according tovarious network requirements.

Managed Object Cell

Value Range0: No

1: Yes

Unit None

Default Value No

BSC Version 6.20.710a

4.5.10.6 BCCH Maximum Power Decrease

Full Name BCCH maximum power decrease

Abbreviation BCCHMaxPwrDec

DescriptionWhen the BCCH carrier participates in the downlink power control,this parameter determines the maximum deteriorated value of thededicated channel on the BCCH carrier.

Managed Object Cell

Value Range 0~60

Unit dBm

Default Value 6 dBm


4.5.10.7 BCCH Idle Burst Power

Full Name BCCH idle burst power

Abbreviation BCCHIdleBurstPwr





DescriptionThis parameter determines whether to decrease the output powerof idle timeslots on the BCCH carrier according to various networkrequirements.

Managed Object Cell

Value Range0..61

Step: 0.5

Unit dBm

Default Value 0


4.5.10.8 Uplink Exponential Filter

Full Name Uplink exponential filter

Abbreviation ULExpFilter

DescriptionThis parameter determines whether to process the uplink level andquality through exponential filtering during uplink power controland use the processed data for uplink power control judgment.

Managed Object Cell

Value Range0: No

1: Yes

Unit None

Default Value No


4.5.10.9 Downlink Exponential Filter

Full Name Downlink exponential filter

Abbreviation DLExpFilter

Description

This parameter determines whether to process the downlink leveland quality through exponential filtering during downlink powercontrol and use the processed data for downlink power control

judgment.

Managed Object Cell

Value Range0: No

1: YesUnit None

Default Value No


4.5.10.10 Uplink Level Optimization

Full Name Uplink level optimization

Abbreviation ULLevOptim





Description

This parameter determines whether to use the optimized uplinklevel as the expected level for uplink power control. The optimizeduplink level is a value between the threshold of uplink powerincrease and the threshold of uplink power decrease.

Managed Object Cell

Value Range0: No

1: Yes

Unit None

Default Value No


4.5.10.11 Downlink Level Optimization

Full Name Downlink level optimization

Abbreviation DLLevOptim

Description

This parameter determines whether to use the optimized downlinklevel as the expected level for downlink power control. Theoptimized downlink level is a value between the threshold ofdownlink power increase and the threshold of downlink powerdecrease.

Managed Object Cell

Value Range0: No

1: Yes

Unit None

Default Value NoBSC Version 6.20.710a

4.5.10.12 Downlink Power Increase Step

Full Name Downlink power increase step

Abbreviation DLPWRINCSTEP

DescriptionThis parameter determines the step of downlink power increase.The values for increase during downlink power control are FR, HR,

AMR FR, AMR HR, AMR WFS, AMR OWFR, and AMR OWHR.

Managed Object Cell

Value Range 1/2/4/8/12

Unit 0.5 dB

Default Value 4


4.5.10.13 Downlink Power Reduction Step

Full Name Downlink power reduction step

Abbreviation DLPWRREDSTEP





Description

This parameter determines the step of downlink power decrease.The values for decrease during downlink power control are FR,HR, AMR FR, AMR HR, AMR WFS, AMR OWFR, and AMROWHR.

Managed Object Cell

Value Range 1/2/4/8/12

Unit 0.5 dB

Default Value 4


4.5.10.14 Downlink Power Control Minimum Interval

Full Name Downlink power control minimum interval

Abbreviation PCMININTERVAL

DescriptionThe values for downlink power control minimum interval are FR,HR, AMR FR, AMR HR, AMR WFS, AMR OWFR, and AMROWHR.

Managed Object Cell

Value Range 1..32

Unit None

Default Value 2


4.6 PS Power Control Theories

4.6.1 MS Power Control Algorithm

MS calculates its output power according to each UL PDCH (which means if MS occupies

more than one UL PDCHs, the transmitting power for each PDCH can be different). The

principle of power control is the output power of all channels should remain lowest on

condition that good communication quality is ensured.

MS calculates its output power according to the power control parameters provided by

network. Besides, MS output power is also decided by the maximum received power foraccess to the cell, MS power level and its received signal level. The power control

algorithm adopted by MS on each independent UL PDCH is as follows:

0( ( 48), )CH CH

P MIN C PMAX (6.1)

CH

P : MS transmitting power on each UL PDCH, its unit is dBm;

0

: 39 dBm for GSM900; 36 dBm for DCS1800;





CH

: power control parameter of MS and some specific channel, which is sent to

MS through control message of RLC/MAC (i.e. Packet UL assignment), its unit is

dBm;

: system parameter, which can be broadcasted on PBCCH and sent to MS

through control message of RLC/MAC;

C : standard MS received signal level, which is the average of the received levels

on the four common burst pulses (which make up the message block);

PMAX : maximum output power allowed in the cell; if PBCCH exists, it =

GPRS_MS_TXPWR_MAX_CCH; if not, it = MS_ TXPWR_MAX_CCH, with the unit

being dBm.

andCH are power control parameters provided by PCU.

After receiving the message block with new andCH

values, after a delay of two

radio blocks,CH

P will be updated based on the above formula.

Open-loop power control: at the initial period of GPRS network construction, MS may

choose open-loop power control mode. Implementation of the mode is to set to be 1,

and keep the continuity ofCH

values. BTS power attenuation value Pb can be set 0

(i.e. DL power control is not adopted). MS power control algorithm is changed to:

0( 48, )CH CH

P MIN C PMAX (6.2)

Value ofCH

is calculated with BTS received signal level SSb. MS received signal

level is:

m BTS bSS P P L

(6.3)

BTS

P : maximum BTS output power;

b

P : BTS power attenuation value for power control;

L: path loss

Then value of C (quantification of received signal level):

m b BTS C SS P P L

(6.4)

So MS output power 0 048 48CH CH BTS

P C P L





0 48b CH BTS

SS P L P (6.5)

So value ofCH

is:

0 48

CH BTS b P SS (6.6)

MS uses the same output power for the four burst pulses contained in one radio block.

After entering a new cell, MS uses the output power defined by PMAX before it receives

the first new power control parameter.

4.6.2 Power Control Algorithm of BTS

In GPRS network, DL power control will be enabled only when the PDCH used by MS

and BCCH are on the same carrier. On PDCH which contains PBCCH or PCCCH, BTS

will use the constant output power, which may be lower than the output power used on

BCCH. The power attenuation value of PCCCH relative to BCCH is Pb, which is

broadcasted on PBCCH.

As for PTCCH/D, BTS usually uses the same output power as that used on PBCCH or

BCCH (if PBCCH is not available).

DL power control can also be used on other PDCH blocks. Except for the burst pulses on

PBCCH carriers, BTS uses the same output power for the four burst pulses contained in

one radio block on other carriers.

DL power control falls into two modes: mode A and mode B. Mode A is applies to all

allocation models; while mode B only applies to the fixed allocation model. Parameter

BTS_PWR_CTRL_MODE defines which mode to be applied in the network.

Both mode A and mode B use parameter P0 , which is the power attenuation value

(relative to BCCH) and is contained in the packet channel assignment message. Usually

P0 is not allowed to be changed under packet transmission mode. MS can have only one

P0 value at some point of time.

On each PDTCH/D, the PR of MAC head indicates the power decrease level of current

RLC data block. Coding of PR domain depends on the value of parameter

BTS_PWR_CTRL_MODE. Because of different power control modes, coding of PR

domain is different. Besides, value of PR is calculated based on P0 of the target MS.

If power control mode A is adopted, BTS will restrict the block power sent to MS and keep

MS level within (BCCH level – P0 – 10 ) dB~(BCCH level – P0 ) dB. Output power for other

blocks shall not exceed (BCCH level – P0 ) dB.

If power control mode B is adopted, the overall output power range of BTS will be

involved. In this case, BTS will take (BCCH level – P0 ) dB as its initial downlink output





power, and all the blocks it sends to a multi-slot MS shall use the same power within one

TDMA frame.





5 CS Power Control Parameters and

Reference ValuesPower control parameters are set with cells as controlled object; each cell is configured

with a series of adjustable power control parameters.

All the parameters described in this chapter are parameters in the algorithms earlier than

SDR V4.09.21.08.

5.1 UL/DL Power Control

We can choose power control object according to network demands. If adjustment of MS

transmitting power is needed, enable Uplink power control (PweControlUl); if control over

BTS power is needed, enable downlink power control (PweControlDl). This parameter is

set on the Others tab, as shown in the following figure.

5.2 Received Signal Level and Quality Threshold

To judge whether to make power control of the current received signal, to increase or

decrease its power, we need criteria, which can be used to measure whether the

received signal condition is as what we expect. The criteria consist of two aspects:

received signal level, received signal quality.

Setting of this parameter is shown in the following figure.





5.2.1 Received Signal Level

For MS uplink received signal level, there are two parameter values: power increase

uplink level and power decrease uplink level, which are corresponding values to the low

level threshold and high level threshold of the expected signal level range. Expected

signal level = Parameter value – 110 dBm, as shown in the above figure, i.e. [ –88 dBm,

–82 dBm].

Similarly, for BTS downlink received signal level, there are also two parameter values:

power increase downlink level and power decrease downlink level. The expected

received signal level = Parameter value – 110 dBm, as shown in the above figure, i.e.

[ –84 dBm, –78 dBm].

5.2.2 Received Signal Quality

For UL/DL received signal quality, there are power increase uplink quality and power

decrease uplink quality. Higher received Rxqual level means poorer received signal

quality. The corresponding relationship between signal Rxqual level and error rate isshown below:

Rxqual Level Error Rate

0 < 0.2%

1 [0.2%, 0.4%)

2 [0.4%, 0.8%)

3 [0.8%, 1.6%)

4 [1.6%, 3.2%)

5 [3.2%, 6.4%)

6 [6.4%, 12.8%)





Rxqual Level Error Rate

7 ≥ 12.8%

5.3 Power Control Period

5.3.1 Sample Count (Window) and Weight (Weight)

5.3.2 Number of Power Control Samples N and P

As shown in the above figure, this parameter is configured under ―Power adjust

threshold‖. The precondition of power control is to collect N averages (number of

averages reaches N); then compare the averages with the expected threshold values to

judge the state of UL/DL received signal.

N represents the number of averages needed in power control decision;





P represents the threshold used for judging the level and quality state of the

averages.

5.4 Power Adjustment Step

If power control is needed after power control decision, make adjustment of MS and/or

BTS power. Except for rapid power control, the range of each power adjustment is a fixed

value, which is referred to power control step.

This parameter is set on the Others tab, as shown in the following figure.

―Power decreasing step‖ is usually set 2. Fast power decrease may cause received

signal level to become lower than the threshold or cause quality to deteriorate, which may

lead to call drops due to sharp decrease in power, therefore, power decreasing step shall

not be set a large value. ―Power increasing step‖ is usually set to be 4 dBm or 6 dBm. It’s

not appropriate to set it with a large value, or the signal level may be larger than the level

threshold after power control, which may lead to ―Pingpong‖ power control.





5.5 Criteria of Power Control State Conversion — N1and N2

Parameter N1 is a fixed value 4. Parameter N2 is adjustable, which is currently adjusted

through parameter (PcMinInterval) in OMCR.

The default of minimum interval of power control (PcMinInterval) is 2. When

PcMinInterval < 4, accordingly the value of N2 is 11 MRs; when PcMinInterval > 17,

accordingly the value of N2 is fixed to be 17 MRs; for other situations, N2 is the value

configured in OMCR. Therefore, N2 can be set within 5~17 MRs. The time length power

control entering the stable state can be adjusted according to actual power control

situations. Suggestion: PcMinInterval = 2.

5.6 Maximum Power Levels of MS and BTS for InitialAccess

Usually, for GSM900, the maximum power level of MS is 5, and the minimum is 16; for

DCS1800, the maximum power level of MS is 0, and the minimum is 11. No matter inGSM900 or DCS1800, the maximum transmitting power level of the BTS is 0.

The parameter of power level is set on the Others tab, as shown in the figures below.

GSM900:

DCS1800:





5.7 Rapid Power Control

Rapid power control is to make immediate adjustment of power according to the different

between the received signal level/quality and the corresponding threshold values; eachpower control step is not a fixed value, but an integral multiple of power

increasing/decreasing step. Rapid power control can satisfy the needs of dynamic control

of MS power, but it can also lead to sudden increase or decrease of MS transmitting

power and affect signal stability. This parameter is set on the Power control tab, as

shown in the following figure.

The power decreasing limit: the maximum limit of power decrease corresponding to

different Rxqual level.

5.8 Fast Averaging

This parameter is set on the Service process additional parameter tab, as shown in

the following figure.





Fast averaging works only when power control enters stable state from initial state,

waiting for the first average of window samples, and Window > 1.

As shown in the following figure, suppose W = 5, N = 3. After power control enters stable

state, average the first MR, then the first average value is obtained; after the second MR

is received, make weighted average of the first two MRs, then the second average value

is obtained; then the third MR is received and the third average value is obtained. AfterN(3) average values are obtained, make the first power control decision. After the fourth

MR is received, average of the four MRs. When the fifth MR is received, i.e. window size

W = 5, return to the common power control algorithm (sampling average), make weighted

average of these (W) MRs, and the second average value is obtained.





1st average

3rd average2nd average

1st PwrCtrl duration

1st average of 2nd pwrCtrl decision

2nd PwrCtrl

1rd average of 2nd pwrCtrl decision

2nd average of 2nd pwrCtrl decision

After power control enters stable state, if the first power control decision takes a long time,

it may lead to sudden deterioration in signal; in this case, fast averaging can make

prompt adjustment on power.

5.9 Setting of Power Control Parameters

Recommended values of power control parameters are shown in the table, appropriate

adjustment can be made according to actual network conditions.

Parameter

Recommended Value

Versions Earlier ThanV6.20.101e

V6.20.101e and LaterVersions

Average window size 4 3

UL/DL RQ increase threshold 3 2UL/DL RQ increase P/N value 2/3 2/3

UL/DL RQ decrease threshold 1 0

UL/DL RQ decrease P/N value 2/3 2/3

UL/DL level increase/decreasethreshold

Default Default

UL/DL level increase/decreaseP/N value

2/3 3/4

Increase step 4db 4db

Decrease step 2db 2db





Parameter

Recommended Value

Versions Earlier ThanV6.20.101e

V6.20.101e and LaterVersions

Rapid averaging Enabled Disabled

Rapid power control Enabled Disabled

Power decrease limit 10, 8, 6, 4, 2, 2, 2, 2 Default

Power control minimum interval 1 Default

MS minimum power level 18 (900M), 14 (1800M) 18 (900M), 14 (1800M)

BS minimum power level 15 (900M), 14 (1800M) 15 (900M), 14 (1800M)





6 Setting of Power Control Parameters in

Different Scenarios

6.1 Setting of Signal Quality Threshold (Under PoorDL Radio Environment)

During operation of power control, what affects network performance seriously is the

distribution of uplink and downlink RQ (0~7). Due to the complexity of network, uplink

/downlink received signal quality threshold is usually set [0, 2], which can help increase

the proportion of network performance indicator RQ (0~3).

Signal quality threshold range can be changed according to the actual UL/DL radio

environment. If radio environment is not good, we can change the quality threshold range

to [0, 1]. However, increase in quality threshold may lead to increase of UL/DL signal

power, and hence the interference between uplink and downlink signals will increase,

especially the interference in downlink. Because of power control, the proportion of

network performance indicator RQ (0~3) remains high. When optimizing related

parameters, we need to weigh increase of the proportion of RQ (0~3) against increase of

interference.

6.2 Setting of UL/DL Power Control Period

Because the interference of uplink and downlink signals is different, we can adjust UL/DL

power control parameters separately. The new power control strategy features fast

frequency and timely adjustment. If radio environment is good, the downlink power

control frequency can be appropriately slowed down, that is to increase power control

decision time N. When making sliding-window averaging, if too many MRs reported with

the last sent power level are used, the proportion of MRs reported with new power level

will be low, thus the averaged level and quality values will be affected, and the accuracy

of new power control decision will be lowered, therefore, the number of samples (window)

should be reduced. The recommended values of related downlink parameters are listed

in the following table.

Sample Count (W) Value N Value P

2 5 3

6.3 Handover Threshold

When adjusting the range of UL/DL received signal level and quality thresholds, we must

ensure that there should be no conflicts with thresholds related to BSC handover

algorithms. The level threshold which causes power increase should NOT be lower than





the handover level threshold; the quality threshold which causes power increase should

be lower than the quality handover threshold. If quality handover threshold = 4, N = 1,

then the high limit of power control threshold should not exceed 2. If power control can be

performed, optimize signal level through power control; if not, carry out handover.

Besides, power control parameters can be adjusted according to network performance

indicators, like handover success rate, call drop rate, etc..

6.4 Highway/Railway

On highways and railways, MS/BTS power control should be performed in fast frequency

and timely manner, so value N should not be a large value; meanwhile, number of

samples (W) should be reduced to improve accuracy; and we should not use too many

MRs reported with the last sent power level in the averaging process.

Sample Count (W) Value N Value P1 3 2

6.5 Building

In office buildings and apartment buildings, MS moves in a slow speed, or stays still. In

this case, the basic setting of power control parameters can be adopted, and power

control duration N can also be extended.





7 Examples of Power Control

Figure 7-1 Graph of UL Ordinary Power Control

Figure 7-2 Graph of UL Ordinary Power Control With Fast Averaging





Figure 7-3 Graph of UL Rapid Power Control

Figure 7-4 Graph of DL Ordinary Power Control





Figure 7-5 Graph of DL Ordinary Power Control With Fast Averaging Adopted

Figure 7-6 Graph of DL Rapid Power Control





Figure 7-7 Graph of DL Rapid Power Control With Fast Averaging Adopted

Experiment 1, see Figure 7-1, Graph of UL ordinary power control

Conditions: ordinary power control over uplink, step = 2 dB; no power control

over downlink; MS stays 5 m away from the BS after the call finished.

Result analysis: the graphs shows that MS power is adjusted from 39 dBm

(time: 16:01:34.577) to 13 dBm (time: 16:02:38.934), the adjustment time is64.357 s, adjustment period is 4.801s/2dB. Besides, the graph shows that MS

power remains steady after the adjustment.

Experiment 2, see Figure 7-2, Graph of UL ordinary power control with fast

averaging

Conditions: ordinary power control with fast averaging is adopted over uplink;

no power control over downlink; MS stays 5m away from the BS after the call is

finished.

Result analysis: the graph shows that MS power is adjusted from 39 dBm (time:

19:49:54.524) to 13 dBm (time: 19:50:29.525), the adjustment time is 35.001 s,

adjustment period is 2.399s/2dB. Compared with experiment 1, the adjustment

period in the experiment is only half of that in experiment 1; power control

speed is greatly increased.

Experiment 3, see Figure 7-3, Graph of UL rapid power control

Conditions: rapid power control over uplink; no power control over downlink;

MS stays 5m away from the BS after the call is finished.





Result analysis: the graph shows that MS power is adjusted from 39 dBm (time:

19:16:20.903) to 13 dBm (time: 19:16:26.648), the adjustment time is 5.745 s.

Compared with experiment 1 and 2, the adjustment time is noticeably shorter

than that in the previous experiments.

Experiment 4, see Figure 7-4, Graph of DL ordinary power control

Conditions: ordinary power control over downlink; no power control over uplink;

MS stays 5m away from the site when the call starts; after a while, MS moves

far away from the BS.

Result analysis: the graph shows that BS power is adjusted from 0 dB (time:

15:52:52.833) to –30 dB (time: 15:54:07.261), the adjustment time is 74.428 s,

adjustment period is 4.799s/2dB. When MS stays near the BS, BS power is

gradually adjusted to the minimum value; when MS moves far away from the

BS, its received signal level drops and voice quality deteriorates, so BS keeps

increasing its transmitting power.

Experiment 5, see Figure 7-5, Graph of DL ordinary power control with fast

averaging adopted

Conditions: ordinary power control with fast averaging over downlink; no power

control over uplink; MS stays 5m away from the site when the call starts; after a

while, MS moves far away from the BS; finally, MS returns to BS.


16:52:35.329) to –30 dB (time: 16:53:15.631), the adjustment time is 40.302 s,

adjustment period is1.934s/2dB. When MS stays near the BS, BS power is

gradually adjusted to the minimum value; when MS moves far away from the

BS, its received signal level drops and voice quality deteriorates, so BS keeps

increasing its transmitting power; when MS returns to stay near BS, BS adjusts

its power back to the original value. Compared with experiment 4, both the

adjustment time and period are shortened to a great extent experiment 5.

Experiment 6, see Figure 7-6, Graph of DL rapid power control

Conditions: rapid power control over downlink; no power control over uplink;

MS stays 5m away from the site when the call starts; after a while, MS moves

far away from the BS; finally, MS returns to BS.


17:08:00.626) to –30dB (time: 17:08:16.964), the adjustment time is 16.338 s.

When MS stays near the BS, BS power is gradually adjusted to the minimum

value; when MS moves far away from the BS, its received signal level drops

and voice quality deteriorates, so BS keeps increasing its transmitting power

and makes compensation to the fast attenuation of signal level; when MS

returns to stay near BS, BS adjusts its power back to the original value and




keeps MS received signal level and quality stable. Compared with experiment

4 and 5, the adjustment time is noticeably shortened in experiment 6.

Experiment 6, see Figure 7-7, Graph of DL rapid power control with fast averaging

adopted

Conditions: rapid power control with fast averaging over downlink; no power

control over uplink; MS stays 5m away from the site when the call starts; after a

while, MS moves far away from the BS; finally, MS returns to BS.


17:19:57.659) to –30 dB (time: 17:20:07.259), the adjustment time is 9.6 s.

When MS stays near the BS, BS power is gradually adjusted to the minimum

value; when MS moves far away from the BS, its received signal level drops

and voice quality deteriorates, so BS keeps increasing its transmitting power

and makes compensation to the fast attenuation of signal level; when MS

returns to stay near BS, BS adjusts its power back to the original value and

keeps MS received signal level and quality stable. Especially at around

17:21:03, when fast attenuation occurs to MS RxLev, and higher error rate

occurs to MS RxQual, BS immediately increases its power to save the call.

Compared with the salvage of call at 17:09:30 in experiment 6, the one in

experiment 7 is even faster. Compared with experiment 4, 5 and 6, the

adjustment time is noticeably shortened in experiment 7.

gsm rno subject-power control algorithms_r2.0

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