gbc_005_e1_0 gsm handover and power control-31

GBC_005_E1_0 GSM Handover and Power Control

Course Objectives:

Understand GSM system handover types and causes

Grasp common handover algorithms and parameters

Understand basic concepts of GSM system power control

Grasp common settings of power control parameters

Contents

1 GSM Handover Principles...................................................................................................................1

1.1 Overview........................................................................................................................................1

1.2 Handover Types.............................................................................................................................1

1.3 Implementation Methods...............................................................................................................4

1.3.1 Cell Layer Configuration....................................................................................................4

1.3.2 Measurement Report Preprocessing...................................................................................4

1.3.3 Destination Cell Selection..................................................................................................5

1.3.4 Destination Cell Sorting.....................................................................................................6

1.3.5 Handover Penalty Strategies...............................................................................................7

1.4 Basic Handover Algorithms and Parameters..................................................................................8

1.4.1 Uplink/Downlink Handover due to Interference................................................................8

1.4.2 Relevant Parameters...........................................................................................................9

1.4.3 Uplink/Downlink Handover due to Quality......................................................................11

1.4.4 Relevant Parameters.........................................................................................................11

1.4.5 Uplink/Downlink Handover due to Level.........................................................................13

1.4.6 Relevant Parameters.........................................................................................................13

1.4.7 Better Cell (PBGT)...........................................................................................................15

2 Power Control.....................................................................................................................................17

2.1 Overview......................................................................................................................................17

2.2 Power Control Process.................................................................................................................18

2.3 Rapid Power Control....................................................................................................................19

2.4 Power Control Parameters...........................................................................................................20

2.4.1 PcUlInclLevThs, PcUlInclLevP, PcUlInclLevN...............................................................20

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2.4.2 PcDlInclLevThs, PcDlInclLevP, PcDlInclLevN...............................................................21

2.4.3 PcUlRedLevThs, PcUlRedLevP, PcUlRedLevN..............................................................22

2.4.4 PcDlRedLevThs, PcDlRedLevP, PcDlRedLevN..............................................................23

2.4.5 PcUlInclQualThs, PcUlInclQualP, PcUlInclQualN..........................................................23

2.4.6 PcDlInclQualThs, PcDlInclQualP, PcDlInclQualN..........................................................24

2.4.7 PcUlRedQualThs, PcUlRedQualP, PcUlRedQualN.........................................................25

2.4.8 PcDlRedQualThs, PcDlRedQualP, PcDlRedQualN.........................................................26

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1 GSM Handover Principles

1.1 Overview

Handover is a very important function of the cellular mobile system.

In GSM cellular system, the multiplexing technology for radio frequency resource is

fully adopted to realize the coverage by several cells. Thus the concept of cross-cell

handover is introduced.

Handover enables a user to keep continuous conversation during the process of passing

through different cells. Handover also adjusts the traffic of cells. Moreover, handover is

implemented without being noticed by users, and does not require users’ involvement.

The following are some of the handover causes:

Signal strength is too weak

Signal quality is too poor

Signal interference is too large

Mobile user is far away from the base station

Uplink level degrades suddenly

Macro-micro handover

There is a more appropriate cell

1.2 Handover Types

ZXG10 series products are designed with advanced ideas, realizing various types of

effective handover, increasing handover speed, and reducing handover failure ratio.

They also combine with many new technologies to increase the network capacity and

service quality.

1. Handover types

(1) According to the two cells involved before and after handover, ZXG10–BSC

(V2) supports four handover types:

1

Intra-cell handover

The handover is completed by the BSC to which the cell belongs.

Intra-BSC inter-cell handover

The two cells before and after handover are different cells under the same BSC.

The handover does not require MSC and is completed by BSC.

Intra-MSC inter-BSC handover

The two cells before and after handover are under different BSCs, and the two

BSCs are controlled by one MSC.

The handover is completed by MSC and the two BSCs.

Inter-MSC handover

The two cells before and after handover are under different MSCs.

The handover is completed by the two MSCs and two BSCs to which the two

cells belong.

(2) According to how MS establishes connection with the destination cell, ZXG10-

BSC (V2) supports three handover types:

Synchronous handover

MS uses the same Time Advance (TA) in the destination cell and the source cell.

The synchronous handover is fast, and usually occurs inside a cell or between

two sectors of the same site.

Asynchronous handover

MS does not know the TA used in the destination cell. The asynchronous

handover is slow, and is adopted if none of the two cells synchronizes with BSC.

Pseudo-synchronous handover

MS can calculate the TA used in the destination cell. The pseudo-asynchronous

handover is fast, and is adopted if both the cells synchronize with BSC.

2. Special handover functions of ZXG10-BSC (V2)

With the development of various new technologies, some special handover

functions are added to ZXG10-BSC (V2):

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2 Power Control

Concentric circle handover

Network capacity can be increased by using special network planning methods, of

which the concentric circle technology is most commonly used.

The concentric circle means that a common cell is divided into two regions:

exterior layer and interior layer. The exterior layer covers traditional micro cells,

usually adopting the 4×3 multiplexing mode. The interior layer covers the area

near the site and adopts more aggressive multiplexing mode such as 2×3 or 1×3.

The exterior layer and the interior layer share the site address and the same antenna

system. They also use the same BCCH, and the BCCH must belong to the exterior

layer.

There are several types of concentric circle technologies. ZXG10-BSC (V2) adopts

a highly effective C/I-based concentric circle technology, with which specific

handover strategies are designed, and the network capacity is increased by more

than 30%.

Micro-cell handover

Another method to increase network capacity is the micro-cell technology. It is

also an effective way to solve network coverage.

The micro-cell and the macro-cell constitute the multi-layer network. In other

words, the large continuous coverage is realized by the macro-cell, forming the top

layer of the multi-layer network; while the micro cell is used to realize continuous

small-area coverage which is overlapped on the micro-cell, forming the bottom

layer of the multi-layer network. The micro-cell mainly serves low-speed mobile

users. For high-speed mobile users, services are provided by the macro-cell,

avoiding call drops that are caused by too frequent handover or handover failure

due to insufficient time.

ZXG10-BSC (V2) tests MS’s moving speed relative to the site through software

and then performs the speed-based micro-cell handover.

Dual-frequency handover

Network capacity can also be increased by forming the dual-frequency network

through adding 1800 MHz (or 1900 MHz) layer. It can solve the problem of

insufficient 900 MHz frequency points.

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Considering that the capacity of 1800 MHz (or 1900 MHz) layer is not fully used,

make 1800 MHz (or 1900 MHz) cells absorb traffic as much as possible during

handover.

ZXG10-BSC (V2) can manage 900 MHz cells and 1800 MHz (1900 MHz) cells

simultaneously. In addition to enhancing 1800 MHz (or 1900 MHz) cells’ traffic

absorbability by modifying common cell parameters, it can also set special

priorities for handover from 900 MHz cell to 1800 MHz (or 1900 MHz) cell.

1.3 Implementation Methods

1.3.1 Cell Layer Configuration

The concept of relative layer is adopted in cell hierarchy. For each service cell, the

adjacent cell can be configured as undefined layer, upper-layer, co-layer, and lower-

layer.

During the handover process, the cell priority should be considered when sorting

candidate cells. Three factors determine the sequence of candidate cells: priority,

traffic, and radio condition. Priority and traffic have more influences on the sorting,

and radio condition is considered only in cases that the first two factors’ influences are

the same.

1.3.2 Measurement Report Preprocessing

The measurement report provides original data for handover decision. ZXG10-BSC

(V2) adopts the rolling average method, which can have different weights to realize

smooth handover.

The rolling average method has the following features:

The number of measurement reports must reach the average window size before

calculating the average value.

If DTX is enabled, the accuracy of the level and quality value in measurement

report will decrease. Thus when performing the weighted average calculation, the

weight of the measurement report with DTX must be different from that of the

measurement report without using DTX. The fixed weight of the measurement

report when DTX is enabled is 1. The weight of the measurement report when

DTX is disabled can be configured as 1, 2, or 3; if the weight is configured as 1,

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2 Power Control

the measurement report is no different from that when DTX is enabled.

The number of measurement reports that are allowed to be lost is ZeroAllowed

at most. If the number of lost measurement reports is too large, the queue resets,

and those lost measurement reports are taken as of measurement value 0 (i.e. -110

dBm), which are not used in the average calculation. For example, suppose the No.

(K-1) measurement report is lost and the average window size is 8, then the

average value = 1/7 (RXLEV_NCELL(K) + 0 + RXLEV_NCELL (K-2) + ... +

RXLEV_NCELL (K-7)).

After power control is performed, implement power compensation for relevant

handover decision.

1.3.3 Destination Cell Selection

After a comparison succeeds, that is, after BSC decides to perform handover, the

destination cell is selected according to different handover causes.

ZXG10-BSC (V2) can find the most appropriate destination cell according to specific

handover causes.

For intra-cell handover, ZXG10-BSC (V2) specifies the type of the TRX where the

new channel is located according to the handover cause. The TRX types include

macro-cell common TRX, macro-cell special TRX, and other TRX in micro-cell.

For the cause of HO_NEARTOFAR in the extended cell, the type of the TRX where

the new channel is located is the extended carrier. For the cause of HO_FARTONEAR

in the extended cell, the type of the TRX where the new channel is located is the

common carrier.

For inter-cell handover, the destination cell is selected according to the following

formulas:

Selection rule 1:

AvRxLevNCell(n) > RXLEV_MIN(n) + MAX(0,(MS_TXPWR_MAX(n)- P(n)))

Selection rule 2:

PBGT(n) > HO_MARGIN(n)

Selection rule 3:

AvRxLevNCell(n) > avRxLevDL + HO_MARGIN_QUAL(n)

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Selection rule 4:

AvRxLevNCell(n) > avRxLevDL + HO_MARGIN_LEVEL(n)

Parameter Meaning

RXLEV_MIN(N) The minimum level required to handover-in the adjacent cell

PBGT(N) Power budget of the adjacent cell

H0_MARGIN(N) Power budget threshold for handover-in the adjacent cell

HO_MARGIN_QUAL(N) Level threshold for handover-in the adjacent cell

HO_MARGIN_LEVEL(N) BER threshold for handover-in the adjacent cell

MS_TXPWR_MAX(n) The maximum MS power allowed in the adjacent cell

P(n) MS power in the adjacent cell

avRxLevDL The average value of MS’s downlink strength

AvRxLevNcell (N) The average value of the adjacent cell’s downlink strength

Selection rule 1 must be satisfied, that is, the average level of the handover-in adjacent

cell must be larger than the minimum handover-in level. Selection rule 2 is used if the

handover cause is “better cell”. Selection rule 3 is used if the handover cause is

“uplink/downlink quality”. Selection rule 4 is used if the handover cause is

“uplink/downlink strength”.

Except for the case of rapid fading, the destination cell can be decided if the selection

rule and the hierarchical relationship between the destination cell and the service cell

are decided. After being processed by the sorting module, the sorted cell list is

generated. If destination cells contain cells of different layers, concatenate the several

cell lists according to the generating sequence to get the final result.

1.3.4 Destination Cell Sorting

If more than one adjacent cell is found, these adjacent cells should be sorted. After the

sorting is completed, attempt handover according to the sorted list.

The sorting strategy of ZXG10-BSC (V2) is based on priorities and penalties,

improving the handover success ratio and controlling the handover flow.

The sorting rule of adjacent cell list is as follows:

Sort cells according to their dynamic priorities first. If the dynamic priorities of two

cells are the same, then sort the two cells according to their power budgets. In

destination cells, the extended cell’s priority is lower.

The dynamic priority depends on the cell’s static priority and the cell’s resource ratio.

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2 Power Control

The cell’s static priority has eight levels: 0 ~ 7, and the larger the level, the higher the

priority. The cell’s static priority, which can be set according to the traffic statistics,

mainly depends on the cell’s geographical position. For example, the micro cell in a

building and its adjacent cells which are on the same floor are assigned with higher

priorities, while its other adjacent cells on different floors are assigned with lower

priorities. In this way, it guarantees that handover is performed on the same floor,

which decreases interference and improves call quality.

The cell’s resource ratio refers to the percentage of idle TCHs in total TCHs, with a

range of 0 ~ 100. During the handover process, MS only concerns the handover-in

cell’s TCHs. The higher the percentage of available TCHs is, the lighter the cell’s load

is, which indicates a higher handover success ratio.

The sorting flow has the following features:

For the speed-based handover, it is cross-layer handover, thus cells of the same

layer must be removed first.

For the interference-based handover, distinguish different carrier groups in the cell

and handle them respectively.

Adjust the handover candidate cells according to the load: (within the same BSC)

adjust candidate cells’ priorities according to their load, which influences the

destination cell selection and dynamically balancing traffic.

1.3.5 Handover Penalty Strategies

Adopting penalty strategies after handover failure occurs can effectively avoid repeated

failures and increase the handover success ratio.

Inter-cell handover (including BSC-controlled and MSC-controlled)

If handover fails, then during the next handover attempt, manually decrease the

destination cell’s downlink level by an offset of PenaltyLevOffset. After

doing that, if the penalty cell still ranks first (for example, the cell is the only

destination cell, or the cell’s level is much higher than that of other cells), then

perform handover to the cell again.

When performing offset penalty for the destination cell, the counter

PenaltyCount is enabled and set as 1. The counter increments when handover

fails, the offset level increases by PenaltyLevOffset at the same time.

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When the number of handover failures reaches 3 (the maximum attempt times) and

the cell is still in the penalty period, the cell is filtered. The previous penalty

scheme is applied and handover is not attempted towards the cell. In this way,

repeated handover attempts can be avoided and the handover success ratio will not

be influenced.

Intra-cell handover

If a user performs intra-cell handover repeatedly, it indicates that the user is

located where interference is serious and can not find appropriate channel. In this

case, the user should be prohibited to perform handover within a certain period of

time. The judgment method is as follows:

If handover occurs again during the timer TMaxIHo’s interval, it indicates that the

previous handover does not have effect on interference, the counter IHoCount

increments, and TMaxIHo restarts. If handover occurs after TMaxIHo’s interval

expires, it indicates that the previous handover is effective, IHoCount’s value is

cleared. If IHoCount’s value reaches MaxIHo, it indicates that it is unnecessary to

continue the handover attempt within a certain period of time, and intra-cell

handover penalty strategy due to interference can be adopted, that is, the intra-cell

handover attempt due to interference should not be implemented any more.

1.4 Basic Handover Algorithms and Parameters

1.4.1 Uplink/Downlink Handover due to Interference

The handover is caused by:

Poor uplink/downlink receiving quality

High level

MS entering predefined interference area

In the interference area, the higher the level is, the easier it is to find a channel with less

interference. Therefore, the intra-cell handover standard is not unified for all calls in

the cell. In other words, if the level is high, the intra-cell handover can be performed

even if RQ is low; if the level is low, the intra-cell handover is performed only if RQ is

high. In this way, call quality is guaranteed, call drop rate decreases, and ineffective

handovers are avoided.

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2 Power Control

1.4.2 Relevant Parameters

1.4.2.1 IntraHoUlLevThs, IntraHoUlLevP, IntraHoUlLevN

Description

According to GSM specifications, handover decision is performed after a series of

average values are obtained. Uplink co-frequency interference is one of the

handover causes. The judgment process is as follows:

If the uplink quality handover conditions are satisfied, and P of the latest N

average values of uplink signal strength are larger than relevant thresholds, then

handover is performed. The handover is due to too strong uplink co-frequency

interference.

IntraHoUlLevThs: defines relevant threshold values

IntraHoUlLevN: defines relevant N values

IntraHoUlLevP: defines relevant P values

Usually, an intra-cell handover is performed if the handover condition is satisfied.

Values

1 ≤ IntraHoUlLevP ≤ IntraHoUlLevN ≤ 32

IntraHoUlLevThs Corresponding Level Value (dBm)

0 < -110

1 -110 ~ -109

2 -109 ~ -108

61 -50 ~ -49

62 -49 ~ -48

63 > -48

Settings

Usually, the value of IntraHoUlLevThs must be larger than the threshold value

(PcUlRedLevThs in table R_POC) that causes uplink power control (decrease),

to avoid unnecessary intra-cell handover. The default value can be 30 (i.e. -81

dBm ~ -80 dBm). The default value of P can be 3 and the default value of N can be

4.

Reference

GSM05.08 A.3.2.2

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1.4.2.2 IntraHoDlLevThs, IntraHoDlLevP, IntraHoDlLevN

Description


average values are obtained. Downlink co-frequency interference is one of the

handover causes. The judgment process is as follows:

If the downlink quality handover conditions are satisfied, and P of the latest N

average values of downlink signal strength are larger than relevant thresholds, then

handover is performed. The handover is due to too strong downlink (co-frequency)

interference.

IntraHoDlLevThs: defines relevant threshold values

IntraHoDlLevN: defines relevant N values

IntraHoDlLevP: defines relevant P values

Usually, an intra-cell handover is performed if the handover condition is satisfied.

Values

1 ≤ IntraHoDlLevP ≤ IntraHoDlLevN ≤ 32

IntraHoDlLevThs Corresponding Level Value (dBm)

0 < -110

1 -110 ~ -109

2 -109 ~ -108

61 -50 ~ -49

62 -49 ~ -48

63 > -48

Settings

Usually, the value of IntraHoDlLevThs must be less than (or equal to) the

threshold value (PcDlRedLevThs in table R_POC) that causes downlink power

control (decrease), to avoid unnecessary intra-cell handover. The default value can

be 30 (i.e. -81 dBm ~ -80 dBm). The default value of P can be 3 and the default

value of N can be 4.

Reference

GSM05.08 A.3.2.2 NED2.7

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2 Power Control

1.4.3 Uplink/Downlink Handover due to Quality

The handover is caused by poor uplink/downlink receiving quality.

If the receiving quality is so poor that exceeds the predefined value, the handover is

triggered to improve the call quality.


1.4.4.1 HoUlQualThs, HoUlQualP, HoUlQualN

Description


average values are obtained. Uplink receiving quality is one of the handover

causes. The judgment process is as follows:

If P of the latest N average values of uplink signal quality are larger than relevant

thresholds, then handover is performed. The handover is due to too poor uplink

signal quality.

HoUlQualThs: defines relevant threshold values

HoUlQualN: defines relevant N values

HoUlQualP: defines relevant P values

Values

1 ≤ HoUlQualP ≤ HoUlQualN ≤ 32

HoUlQualThs Corresponding Quality Grade Meaning

0 0 BER<0.2%

1 1 0.2%<BER<0.4%

2 2 0.4%<BER<0.8%

6 6 6.4%<BER<12.8%

7 7 12.8%<BER

Settings

Usually, the value of HoUlQualThs must be larger than the threshold value

(PcUlInclQualThs in table R_POC) that causes uplink power control

(increase). In other words, perform power control first, and then perform handover

if the power control has no effect. The default value can be 5. The default value of

P can be 3 and the default value of N can be 4.

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Reference

GSM05.08 A.3.2.2 NED2.7

1.4.4.2 HoDlQualThs, HoDlQualP, HoDlQualN

Description


average values are obtained. Downlink receiving quality is one of the handover


If P of the latest N average values of downlink signal quality are larger than

relevant thresholds, then handover is performed. The handover is due to too poor

downlink signal quality.

HoDlQualThs: defines relevant threshold values

HoDlQualN: defines relevant N values

HoDlQualP: defines relevant P values

Values

1 ≤ HoDlQualP ≤ HoDlQualN ≤ 32

HoDlQualThs Corresponding Quality Grade Meaning

0 0 BER<0.2%

1 1 0.2%<BER<0.4%

2 2 0.4%<BER<0.8%

6 6 6.4%<BER<12.8%

7 7 12.8%<BER

Settings

Usually, the value of HoDlQualThs must be larger than the threshold value

(PcDlInclQualThs in table R_POC) that causes downlink power control


if the power control has no effect. The default value can be 5. The default value of

P can be 3 and the default value of N can be 4.

Reference

GSM05.08 A.3.2.2 NED2.7

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1.4.5 Uplink/Downlink Handover due to Level

The handover is caused by poor uplink/downlink level.

When the level is lower than the predefined value, call drop might occur, and handover

is triggered at the moment to keep the call.


1.4.6.1 HoUlLevThs, HoUlLevP, HoUlLevN

Description


average values are obtained. Uplink receiving strength is one of the handover


If P of the latest N average values of uplink signal strength are less than relevant

thresholds, then handover is performed. The handover is due to too weak uplink

signal strength.

HoUlLevThs: defines relevant threshold values

HoUlLevN: defines relevant N values

HoUlLevP: defines relevant P values

Values

1 ≤ HoUlLevP ≤ HoUlLevN ≤ 32

HoUlLevThs Corresponding Level Value (dBm)

0 < -110

1 -110 ~ -109

2 -109 ~ -108

61 -50 ~ -49

62 -49 ~ -48

63 > -48

Settings

Usually, the value of HoUlLevThs must be less than the threshold value

(PcUlInclLevThs in table R_POC) that causes uplink power control


if the power control has no effect. The default value can be 15 (i.e. -96 dBm ~ -95

13


dBm), and the parameter’s value must be 3 dB larger than the cell’s

RxLevAccessMin. The default value of P can be 3 and the default value of N

can be 4.

Reference

GSM05.08 A.3.2.2 NED2.7

1.4.6.2 HoDlLevThs, HoDlLevP, HoDlLevN

Description


average values are obtained. Downlink receiving strength is one of the handover


If P of the latest N average values of downlink signal strength are less than

relevant thresholds, then handover is performed. The handover is due to too weak

downlink signal strength.

HoDlLevThs: defines relevant threshold values

HoDlLevN: defines relevant N values

HoDlLevP: defines relevant P values

Values

1 ≤ HoDlLevP ≤ HoDlLevN ≤ 32

HoDlLevThs Corresponding Level Value (dBm)

0 < -110

1 -110 ~ -109

2 -109 ~ -108

61 -50 ~ -49

62 -49 ~ -48

63 > -48

Settings

Usually, the value of HoDlLevThs must be less than the threshold value

(PcDlInclLevThs in table R_POC) that causes downlink power control


if the power control has no effect. The default value can be 15 (i.e. -96 dBm ~ -95

dBm), and the parameter’s value must be 3 dB larger than the cell’s

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2 Power Control

RxLevAccessMin. The default value of P can be 3 and the default value of N

can be 4.

Reference

GSM05.08 A.3.2.2 NED2.7

1.4.7 Better Cell (PBGT)

Power Budget (PBGT) handover, also called as edge handover, is the handover that

occurs most frequently in urban area. The purpose of PBGT handover is not to just

keep the call process but to have better call quality. PBGT is calculated each time the

measurement report is received. During the handover decision process, no threshold is

set actually, it only requires that PBGT is larger than 0. PBGT approximately equals the

result of the adjacent cell’s level subtracting the cell’s level.

Check each adjacent cell, if P consecutive average level values of an adjacent cell are

larger than or equal to 0, the PBGT handover condition is satisfied.

It should be emphasized that the PBGT handover has destination frequency bands, and

the parameter is controlled by “layers suitable for standard PBGT handover”. The table

below explains meanings of the parameter (in binary code):

Bit Value & Description

bit1 0: can not perform PBGT handover to co-layer hetero-frequency adjacent cell

1: can perform PBGT handover to co-layer hetero-frequency adjacent cell

bit2 0: can not perform PBGT handover to adjacent cell that has no hierarchical

relationship

1: can perform PBGT handover to adjacent cell that has hierarchical relationship

bit3 0: can not perform PBGT handover to upper-layer adjacent cell

1: can perform PBGT handover to upper-layer adjacent cell

bit4 0: can not perform PBGT handover to lower-layer adjacent cell

1: can perform PBGT handover to lower-layer adjacent cell

bit5~bit8 Reserved, being 0 constantly

It effectively controls the direction of PBGT handover and the network traffic

distribution.

The PBGT handover threshold can be set as a negative value. It can be flexibly applied

in the dual-frequency network to control the handover direction.

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2 Power Control

2.1 Overview

Power control means controlling the actual transmission power of MS or base station in

radio propagation to reduce the transmission power as much as possible. It helps reduce

the power consumption of MS and base station as well as reduce the GSM network

interference. The premise of performing power control is that the call quality is good

during the call process. Figure 2.1-1 shows the power control process.

A B

Figure 2.1-1 Power Control

As shown in Figure 2.1-1, the MS at position A is far from the base station’s antenna.

Because the radio wave propagation loss is in direct proportion of the Nth power of the

distance, a large transmission power is required for MS at position A to guarantee the

call quality. However, the MS at position B is close to the base stations’ antenna, the

propagation loss is less, thus similar call quality can be obtained with a less

transmission power. During the call process, if MS moves from position B to position

A, MS’s transmission power can increase gradually by performing power control.

There are two types of power control: uplink power control and downlink power

control. The two can be implemented independently. The uplink power control is used

to control the transmission power of MS while the downlink power control is used to

control the transmission power of base station. They can reduce uplink/downlink

interference by reducing the transmission power, and also reduce the power

consumption of MS or base station. With the power control technology, the average

call quality of GSM network increases greatly and the usable time of MS’s battery is

17

prolonged.

2.2 Power Control Process

The measurement data of MS and base station are raw data used for making decision in

power control process. These raw data are processed and analyzed before making

relevant control decision. Figure 2.1-2 illustrates the power control process.

Figure 2.1-2 Power Control Process Flow Chart

1. Save measurement data

Measurement data related to the power control include: uplink signal level,

uplink signal quality, downlink signal level, and downlink signal quality.

2. Average measurement data

In order to reduce the influence of complex radio transmission on the

measurement data, the forward average method is often used to realize smooth

processing of measurement data. In other words, multiple average values of

measurement data are used in making power control decision. During the

average process, parameter settings may differ for different measurement data

types, that is, the number of measurement data used may be different.

3. Make power control decision

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2 Power Control

Three parameters are required for power control decision: a threshold, an N

value, and a P value. If P of the latest N average values are larger than the

threshold value, it indicates that the signal level is too high or the signal quality

is too good. If P of the latest N average values are less than the threshold value,

it indicates that the signal level is too low or the signal quality is too poor.

According to the signal level or signal quality, MS or base station can decide

how to control the transmission power. The positive or negative change in

transmission power depends on the predefined value.

4. Send power control command

According to the power control decision, the corresponding control command is

sent to base station, which then executes the command or forwards the

command to MS.

5. Modify measurement data

After power control is performed, the raw measurement data and average values

are useless. To avoid making incorrect power control decision, these data should

either be abandoned or modified before being used.

The most frequent power control can be performed every 480 ms, which is

actually the fastest speed that the measurement data is reported. In other words,

a complete power control process can be executed every 480 ms at the fastest

speed.

2.3 Rapid Power Control

Power control ranges recommended in ETSI specifications are fixed, usually 2 dB or 4

dB. However, in many actual applications, a fixed power control range can not gain an

optimum result.

For example, suppose MS initiates a call in a place very close to the base station’s

antenna, the MS’s initial transmission power is the maximum transmission power

MS_TXPWR_MAX_CCH, which is in the system message broadcasted on BCCH.

Because MS is very close to the antenna, the transmission power should be reduced by

power control as early as possible. However, it can not be realized by the power control

process recommended in ETSI specifications, because such a power control process

can only make MS transmission power reduce by 2 dB or 4 dB each time. There is a

19


certain interval between two power control processes (to collect enough new

measurement data), thus there will be a long period of time before MS transmission

power is reduced to an appropriate value. Things are the same in downlink direction.

Therefore, such strategies can not relieve interference of the entire GSM network.

To solve the above problem, the power control range should be increased, which is the

main idea of rapid power control.

During the rapid power control process, the control range is not fixed but depends on

the actual signal strength and signal quality. It solves the power control problem during

the process of MS’s initial access. In addition to that, rapid power control also solves

many other power control problems in cases that require large power control ranges,

such as a rapidly moving MS, a call process during which interference or obstacles

suddenly occur.

2.4 Power Control Parameters

2.4.1 PcUlInclLevThs, PcUlInclLevP, PcUlInclLevN

Description

According to GSM specifications, power control decision is performed after a

series of average values are obtained. Uplink receiving strength is one of the

reasons that cause MS (uplink) power to increase. The judgment process is as

follows:

If P of the latest N average values of uplink signal strength are less than relevant

thresholds, then increase MS (uplink) transmission power because the uplink

signal strength is too weak.

PcUlInclLevThs: defines relevant threshold values

PcUlInclLevN: defines relevant N values

PcUlInclLevP: defines relevant P values

Values

1 ≤ PcUlInclLevP ≤ PcUlInclLevN ≤ 32

PcUlInclLevThs Corresponding Level Value (dBm)

0 < -110

20

2 Power Control

PcUlInclLevThs Corresponding Level Value (dBm)

1 -110 ~ -109

2 -109 ~ -108

61 -50 ~ -49

62 -49 ~ -48

63 > -48

Settings

The default threshold value can be 18 (i.e. -93 dBm ~ -92 dBm). The default value

of P can be 3 and the default value of N can be 4.

Reference

GSM05.08 A.3.2.1 NED 2.7 10.9

2.4.2 PcDlInclLevThs, PcDlInclLevP, PcDlInclLevN

Description


series of average values are obtained. Downlink receiving strength is one of the

reasons that cause BTS (downlink) power to increase. The judgment process is as

follows:

If P of the latest N average values of downlink signal strength are less than

relevant thresholds, then increase BTS (downlink) transmission power because the

downlink signal strength is too weak.

PcDlInclLevThs: defines relevant threshold values

PcDlInclLevN: defines relevant N values

PcDlInclLevP: defines relevant P values

Values

1 ≤ PcDlInclLevP ≤ PcDlInclLevN ≤ 32

PcDlInclLevThs Corresponding Level Value (dBm)

0 < -110

1 -110 ~ -109

2 -109 ~ -108

61 -50 ~ -49

62 -49 ~ -48

21


63 > -48

22

2 Power Control

Settings



Reference

GSM05.08 A.3.2.1 NED 2.7 10.9

2.4.3 PcUlRedLevThs, PcUlRedLevP, PcUlRedLevN

Description


series of average values are obtained. Uplink receiving strength is one of the

reasons that cause MS (uplink) power to decrease. The judgment process is as

follows:

If P of the latest N average values of uplink signal strength are larger than relevant

thresholds, then decrease MS (uplink) transmission power because the uplink

signal strength is too strong.

PcUlRedLevThs: defines relevant threshold values

PcUlRedLevN: defines relevant N values

PcUlRedLevP: defines relevant P values

Values

1 ≤ PcUlRedLevP ≤ PcUlRedLevN ≤ 32

PcUlRedLevThs Corresponding Level Value (dBm)

0 < -110

1 -110 ~ -109

2 -109 ~ -108

61 -50 ~ -49

62 -49 ~ -48

63 > -48

Settings



Reference

23


GSM05.08 A.3.2.1 NED 2.7 10.9

2.4.4 PcDlRedLevThs, PcDlRedLevP, PcDlRedLevN

Description


series of average values are obtained. Downlink receiving strength is one of the

reasons that cause BTS (downlink) power to decrease. The judgment process is as

follows:

If P of the latest N average values of uplink signal strength are larger than relevant

thresholds, then decrease BTS (downlink) transmission power because the

downlink signal strength is too strong.

PcDlRedLevThs: defines relevant threshold values

PcDlRedLevN: defines relevant N values

PcDlRedLevP: defines relevant P values

Values

1 ≤ PcDlRedLevP ≤ PcDlRedLevN ≤ 32

PcDlRedLevThs Corresponding Level Value (dBm)

0 < -110

1 -110 ~ -109

2 -109 ~ -108

61 -50 ~ -49

62 -49 ~ -48

63 > -48

Settings



Reference

GSM05.08 A.3.2.1 NED 2.7 10.9

2.4.5 PcUlInclQualThs, PcUlInclQualP, PcUlInclQualN

Description

24

2 Power Control


series of average values are obtained. Uplink receiving quality is one of the

reasons that cause MS (uplink) power to increase. The judgment process is as

follows:

If P of the latest N average values of uplink signal quality are larger than relevant

thresholds, then increase MS (uplink) transmission power because the uplink

signal quality is too poor.

PcUlInclQualThs: defines relevant threshold values

PcUlInclQualN: defines relevant N values

PcUlInclQualP: defines relevant P values

Values

1 ≤ PcUlInclQualP ≤ PcUlInclQualN ≤ 32

PcUlInclQualThs Corresponding Quality Grade Meaning

0 0 BER<0.2%

1 1 0.2%<BER<0.4%

2 2 0.4%<BER<0.8%

6 6 6.4%<BER<12.8%

7 7 12.8%<BER

Settings

The default threshold value can be 3. The default value of P can be 3 and the

default value of N can be 4.

Reference

GSM05.08 A.3.2.1 NED 2.7 10.9

2.4.6 PcDlInclQualThs, PcDlInclQualP, PcDlInclQualN

Description


series of average values are obtained. Downlink receiving quality is one of the

reasons that cause BTS (downlink) power to increase. The judgment process is as

follows:

If P of the latest N average values of downlink signal quality are larger than

25


relevant thresholds, then increase BTS (downlink) transmission power because the

downlink signal quality is too poor.

PcDlInclQualThs: defines relevant threshold values

PcDlInclQualN: defines relevant N values

PcDlInclQualP: defines relevant P values

Values

1 ≤ PcDlInclQualP ≤ PcDlInclQualN ≤ 32

PcDlInclQualThs Corresponding Quality Grade Meaning

0 0 BER<0.2%

1 1 0.2%<BER<0.4%

2 2 0.4%<BER<0.8%

6 6 6.4%<BER<12.8%

7 7 12.8%<BER

Settings



Reference

GSM05.08 A.3.2.1 NED 2.7 10.9

2.4.7 PcUlRedQualThs, PcUlRedQualP, PcUlRedQualN

Description


series of average values are obtained. Uplink receiving quality is one of the

reasons that cause MS (uplink) power to decrease. The judgment process is as

follows:

If P of the latest N average values of uplink signal quality are less than relevant

thresholds, then decrease MS (uplink) transmission power because the uplink

signal quality is too good.

PcUlRedQualThs: defines relevant threshold values

PcUlRedQualN: defines relevant N values

26

2 Power Control

PcUlRedQualP: defines relevant P values

Values

1 ≤ PcUlRedQualP ≤ PcUlRedQualN ≤ 32

PcUlRedQualThs Corresponding Quality Grade Meaning

0 0 BER<0.2%

1 1 0.2%<BER<0.4%

2 2 0.4%<BER<0.8%

6 6 6.4%<BER<12.8%

7 7 12.8%<BER

Settings



Reference

GSM05.08 A.3.2.1 NED 2.7 10.9

2.4.8 PcDlRedQualThs, PcDlRedQualP, PcDlRedQualN

Description


series of average values are obtained. Downlink receiving quality is one of the

reasons that cause BTS (downlink) power to decrease. The judgment process is as

follows:

If P of the latest N average values of downlink signal quality are less than relevant

thresholds, then decrease BTS (downlink) transmission power because the

downlink signal quality is too good.

PcDlRedQualThs: defines relevant threshold values

PcDlRedQualN: defines relevant N values

PcDlRedQualP: defines relevant P values

Values

1 ≤ PcDlRedQualP ≤ PcDlRedQualN ≤ 32

27


PcDlRedQualThs Corresponding Quality Grade Meaning

0 0 BER<0.2%

1 1 0.2%<BER<0.4%

2 2 0.4%<BER<0.8%

6 6 6.4%<BER<12.8%

7 7 12.8%<BER

Settings



Reference

GSM05.08 A.3.2.1 NED 2.7 10.9

28

gbc_005_e1_0 gsm handover and power control-31

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