Suitable for staff with P&O skill certificate IV or lower

Issued by GSM Network P&O Dept.

Power Control AlgorithmPower Control Algorithm

The Secrets of GSM AlgorithmsThe Secrets of GSM Algorithms

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Version Introduction

Version

Date Writer Assessor Translator Amendment

recordsV1.0 2009-05-

05Chang Hai

JieZheng Hao Feng Xiao

YingFirst edition

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Brief Introduction

I. Rudiments of Power Control

II. ZTE Power Control Algorithms

III. Setting of Power Control Parameters

IV. Application of Power Control

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1. What is power control? Why we carry out power

control?

2. Classification of power control

3. Difference among various kinds of power control

4. What’s the main object of power control?

5. How to conduct power control?

I. Rudiments of Power Control

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1. What is power control? Why we carry out power control?

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What is power control?

Why should we carry out power control?

Definition: Power control is to adjust the transmitting power of BTS and MS according to real needs.Base: result of UL/DL measurement Goal: to lower transmitting power, reduce interference in the whole network and power consumption, on condition that speech quality is ensured.

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2. Classification of power control

Ordinary power control

Rapid power control

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3. Difference among various kinds of power control

Static power control

Impose restrictions on the max transmitting power of MS or BTS at OMCR

Dynamic power control

Under the non-idle mode, the network flexibly decides the transmitting power of MS or BTS in a dynamic manner according to radio environment.

Ordinary power control

Adopt fixed step to adjust power.

Rapid power control

Adopt non-fixed step to adjust power, i.e. to settle power adjustment at one go.

CS power control

PS power control

Power control in CS service.

Power control in PS service.

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4.What’s the main body of power control?

The main object of power control: TS and MS

Power control is directed at single subscribers, so the main object

of UL power control is single MS; for DL, it’s some timeslot (ST) in

the BTS used by the MS, Note it’s not the whole carrier.

Back

It’s stipulated in the protocol that the transmission must be performed at

full power on the carrier of BCCH, so only UL dynamic power control

(not DL dynamic power control) can be carried out on the carrier of

BCCH.

It’s stipulated in the protocol that the transmission must be performed at

full power on the carrier of BCCH, so only UL dynamic power control

(not DL dynamic power control) can be carried out on the carrier of

BCCH.

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5.How to conduct power control?

Collection of MS/BTS measurement reports

Weighted average of MRs

If the average satisfies conditions of power control decision?

Condition for power increase is satisfied

Condition for power

maintenance is satisfied

Condition for power

decrease is satisfied

Increase MS/BTS transmitting power

Maintain MS/BTS transmitting power

Decrease MS/BTS transmitting power

Save the averageNo

Yes

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1. What power control algorithms are supported in ZTE systems?2. What features do ZTE power control algorithms have?3. What is sliding-window averaging?4. What is Rapid averaging?5. How is the initial state of ZTE power control algorithms defined?6. How is the stable state of ZTE power control algorithms defined ?7. What’s the relation between the initial state and stable state of ZTE power control algorithm

s?8. In which network element is ZTE power control realized?9. How is measurement reports processed in ZTE power control algorithms?10. How to judge conditions for power increase/decrease in ZTE power control algorithms?11. How to decide power increase/decrease value in ZTE power control algorithms (I)?12. How to decide power increase/decrease value in ZTE power control algorithms (II)?13. How to decide power increase/decrease value in ZTE power control algorithms (III)?

14. How to decide power increase/decrease value in ZTE power control algorithms (IV)?15. Why bySub is introduced for the initial state of ZTE power control algorithms?16. How is power control result measured in ZTE systems?

II. ZTE Power Control Algorithms

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1. What power control algorithms are supported in ZTE systems?

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UL and DL Rapid power control are not discriminated in version 6.20 and previous ones.

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2. What features do ZTE power control algorithms have?

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3. What is sliding-window averaging?

Definition: during averaging of measurement reports, when number of MR

reaches the window size (suppose it’s 4), calculate the first 4 MRs and get the

first average value; then calculate MR no.2 -5 and get the second average

value; and so on. Advantage: it can effectively disperse the influence of signal

fluctuation.

Disadvantage: it takes quite a bit of time to get the first average.

Definition: during averaging of measurement reports, when number of MR

reaches the window size (suppose it’s 4), calculate the first 4 MRs and get the

first average value; then calculate MR no.2 -5 and get the second average

value; and so on. Advantage: it can effectively disperse the influence of signal

fluctuation.

Disadvantage: it takes quite a bit of time to get the first average.

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4. What is Rapid averaging? Definition: during averaging of measurement reports, which is not restricted by

average window, the first average value is obtained when the first MR is submitted; and the second average value is obtained by calculating the first and second MRs; when number of MRs reaches the window size, rapid averaging is converted to sliding-window averaging.

Advantage: it reduces the time for triggering the first power control. Disadvantage: its reliability is a bit low, as there are fewer samples of MRs

participating in the decision.

Definition: during averaging of measurement reports, which is not restricted by average window, the first average value is obtained when the first MR is submitted; and the second average value is obtained by calculating the first and second MRs; when number of MRs reaches the window size, rapid averaging is converted to sliding-window averaging.

Advantage: it reduces the time for triggering the first power control. Disadvantage: its reliability is a bit low, as there are fewer samples of MRs

participating in the decision.

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Internal Use Only▲5. How is the initial state of ZTE power control algorithms defined?

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When MS initially accesses into channel (SDCCH or TCH),

the power control status it enters is referred as initial state.When MS initially accesses into channel (SDCCH or TCH),

the power control status it enters is referred as initial state.

Features of this state:

There is a big difference between the max transmitting power MS initially uses

and that actually needed.

It produces heavy influence on MS using other channels.

There is dramatic adjustment on MS and BTS power ranks, so there will be big

changes on MS and BTS power.

Usually it needs several consecutive times of rapid power adjustment.

Features of this state:

There is a big difference between the max transmitting power MS initially uses

and that actually needed.

It produces heavy influence on MS using other channels.

There is dramatic adjustment on MS and BTS power ranks, so there will be big

changes on MS and BTS power.

Usually it needs several consecutive times of rapid power adjustment.

Features of power control algorithm at this state:

Perform power control decision to each MR, adjust MS and BTS power

rank and make it reach the demanded level and quality in the shortest

time.

Features of power control algorithm at this state:

Perform power control decision to each MR, adjust MS and BTS power

rank and make it reach the demanded level and quality in the shortest

time.

Internal Use Only▲6. How is the stable state of ZTE power control algorithms defined?

Back

After experiencing the dramatic adjustment of power, MS reaches the requested UL

level and quality and enters a relatively stable situation, which is called stable state. After experiencing the dramatic adjustment of power, MS reaches the requested UL

level and quality and enters a relatively stable situation, which is called stable state.

Conditions for MS entering stable state from initial state (either 1 or 2 is acceptable):

Condition 1: in most cases, MS power takes downward modulation in initial state; if

it stops downward modulation for N1 times, it’s supposed to have entered stable state.

Condition 2: when the number of measurement reports received reaches N2, MS

directly enters stable state.

Conditions for MS entering stable state from initial state (either 1 or 2 is acceptable):

Condition 1: in most cases, MS power takes downward modulation in initial state; if

it stops downward modulation for N1 times, it’s supposed to have entered stable state.

Condition 2: when the number of measurement reports received reaches N2, MS

directly enters stable state.

Explanations on N1/N2 value:

Principle:N1<N2

Recommended value: N1-4, N2-11

N1 and N2 not only can be set some fixed value according to test result, but also can

be configured at OMCR; in order to maintain the compatibility of OMCR, currently

N1 and N2 are set the default value, and they can be adjusted through hyper-terminal.

Explanations on N1/N2 value:

Principle:N1<N2

Recommended value: N1-4, N2-11

N1 and N2 not only can be set some fixed value according to test result, but also can

be configured at OMCR; in order to maintain the compatibility of OMCR, currently

N1 and N2 are set the default value, and they can be adjusted through hyper-terminal.

Internal Use Only▲7. What’s the relation between the initial state and stable state of ZTE

power control algorithms?

When MS enters initial

state of power control,

it quickly adjusts its

power up to demand;

When MS power

stops downward

modulation for N1

times, or when

number of received

MRs reaches N2, MS

enters stable state;

Initial state and stable

state adopt different

power control

strategies.

When MS enters initial

state of power control,

it quickly adjusts its

power up to demand;

When MS power

stops downward

modulation for N1

times, or when

number of received

MRs reaches N2, MS

enters stable state;

Initial state and stable

state adopt different

power control

strategies.

Back

Initial state

MS power stops downward modulation for N1 times

Stable stateChannel release

Number of MRs received reaches N2

Channel power control enters initial state

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8. In which network element is ZTE power control realized?

In ZTE system, power control is realized in BTS, which masters UL/DL dynamic power control and reports the results to BSC at certain intervals, so that BSC can collect related performance statistics. Refer to the following figure for the logical location of power control elements.

In ZTE system, power control is realized in BTS, which masters UL/DL dynamic power control and reports the results to BSC at certain intervals, so that BSC can collect related performance statistics. Refer to the following figure for the logical location of power control elements.

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Internal Use Only▲9. How is measurement reports processed in ZTE power

control algorithms?

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Internal Use Only▲10. How to judge conditions for power increase/decrease in ZTE power control algorithms?

LEVEL CAUSE

QUAL CAUSE

RESULT

0 0 POWER_STAY

0 1 DECREASE_BYQUALITY

0 2 INCREASE_BYQUALITY

1 0 INCREASE_BYLEVEL

1 1 INCREASE_BYLEVEL

1 2 INCREASE_ BYQUALITY

2 0 DECREASE_BYLEVEL

2 1 DECREASE_BYLEVEL

2 2 INCREASE_BYQUALITYBack

LEVELCAUSE = 1

LEVELCAUSE = 0

LEVELCAUSE = 2

QUALCAUSE = 2

QUALCAUSE = 0

QUALCAUSE = 1

Internal Use Only▲11. How to decide power increase/decrease value in ZTE power

control algorithms (I)?

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Internal Use Only▲12. How to decide power increase/decrease value of in ZTE power control algorithms (II)?

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Power control in initial state:

With the aim to carry out power control effectively, whether power is to increase or decrease, the step shall be the one set for power decrease, which shall be fixed.

1） MS power increase:

a) UL signal is bad, and no MS MR is received. If the difference between the MS power value

(computed through the current power control) and the last valid MS power value exceeds

8dbm, then the current power control decision is valid, and MS power increase shall be

continued;

b) UL signal is good, MS MR is received by BTS; DL signal is bad, the power control value

hasn’t effectively controlled MS power, and the difference (bySub) exceeds 8dbm, then

power control shall not be imposed on MS any more;

2）MS power decrease:

Regardless whether BTS has received MS UL MR or not, once the difference is less than

8dbm, power control shall not be imposed on MS;

3） As in BTS power measurement, the power adjustment benchmark value shall be the power

rank value of current BTS transmitting signal, and the calculation method is the same as

that of power control in stable state.

Internal Use Only▲13. How to decide power increase/decrease value in ZTE power control algorithms (III)?

Rapid power control: power increase/decrease in rapid power control shall be carried out according to the following criteria. For level-related power increase/decrease control, specific conditions are needed in decision; if the conditions are not satisfied, use the ordinary power control method.

Rapid power control: power increase/decrease in rapid power control shall be carried out according to the following criteria. For level-related power increase/decrease control, specific conditions are needed in decision; if the conditions are not satisfied, use the ordinary power control method.

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Internal Use Only▲14. How to decide power increase/decrease value in ZTE power control algorithms (IV)?

Graph of UL ordinary power control:

Graph of UL ordinary power control:

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Graph of UL ordinary power control with rapid averaging adopted:

Graph of UL ordinary power control with rapid averaging adopted:

Graph of UL rapid power control:

Graph of UL rapid power control:

Internal Use Only▲15. Why bySub is introduced for the initial state of ZTE power

control algorithms?

After sending new power rank to MS, it takes an interval of at least three MRs for

BTS to receive MS power rank report, which makes it unable to meet the

requirement for each MR to adjust the last sent power control

value( byMSpowerSet) by 2dB in the initial state of power control.

A variable bySub is introduced, which represents the difference between the

power control value to be sent and the currently received power value, whose limit

is 8dbm.

After sending new power rank to MS, it takes an interval of at least three MRs for

BTS to receive MS power rank report, which makes it unable to meet the

requirement for each MR to adjust the last sent power control

value( byMSpowerSet) by 2dB in the initial state of power control.

A variable bySub is introduced, which represents the difference between the

power control value to be sent and the currently received power value, whose limit

is 8dbm.

Back

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16. How is power control result measured in ZTE systems?

BTS reports power control results to BSC for performance statistics.

Reporting period is controlled by PwrCtrlReportPrd (SACCH multi-frame) .

ZTE power control statistics are in collected in BTS measurement tasks,

including cause and times of power control. For details, please refer to the

fascicule of performance counters in attached manuals.

BTS reports power control results to BSC for performance statistics.

Reporting period is controlled by PwrCtrlReportPrd (SACCH multi-frame) .

ZTE power control statistics are in collected in BTS measurement tasks,

including cause and times of power control. For details, please refer to the

fascicule of performance counters in attached manuals.

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1. What are the general cares of setting power control

parameters?

2. Recommended values of power control parameters

3. What factors influence the speed of dynamic power

control?

III Setting of Power Control Parameters

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Internal Use Only▲1. What are the general cares of setting power control

parameters?

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2. Recommended values of power control parameters

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The recommended values are for reference, please make appropriate adjustment according to actual network situations.

The recommended values are for reference, please make appropriate adjustment according to actual network situations.

ParameterRecommended value

6.20.101e &subsequent versions

6.20.101e&subsequent versions

Average window size 4 4UL/DL RQ increase threshold 3 2UL/DL RQ increase P/N value 2/3 2/3UL/DL RQ decrease threshold 1 0UL/DL RQ decrease P/N value 2/3 2/3

UL/DL level increase /decrease threshold

default default

UL/DL level increase /decrease P/Nvalue

2/3 2/3

Increase step 4db 4db Decrease step 2db 2dbRapid averaging Enabled Disabled

Rapid power control Enabled Disabled

Power decrease limit10 ， 8 ， 6 ， 4 ， 2 ， 2 ，

2 ， 2default

Power control min interval 1 0

MS min power rank18 （ 900M ）、 14 （ 1800

M)18 （ 900M ）、 14 （ 1800M)

BS min power rank 15(900M) 、 14 （ 1800M ） 15(900M) 、 14 （ 1800M ）

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3. What factors influence the speed of dynamic power control?

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1. In which circumstances can power control be appli

ed?

2. Which KPIs will be influenced by power control?

3. In which aspects will power control influence subs

criber’s satisfaction?

IV Application of Power Control

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1. In which circumstances can power control be applied?

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Normally UL ordinary power control is enabled, other power control types are mainly applied in areas with dense sites, which can help reduce interference. The following table is for reference.

Normally UL ordinary power control is enabled, other power control types are mainly applied in areas with dense sites, which can help reduce interference. The following table is for reference.

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2. Which KPIs will be influenced by power control?

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Power control influences transmitting power, which may impose some negative effects on the level of coverage, and result in dramatic decrease in the proportion of level above -75dbm.

Internal Use Only▲3. In which aspects will power control influence subscriber’s

satisfaction?

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