GBC_005_E0_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
i
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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1 GSM Handover Principles
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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GBC_005_E0_0 GSM Handover and Power Control
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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1 GSM Handover Principles
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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GBC_005_E0_0 GSM Handover and Power Control
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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1 GSM Handover Principles
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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GBC_005_E0_0 GSM Handover and Power Control
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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1 GSM Handover Principles
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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GBC_005_E0_0 GSM Handover and Power Control
1.4.2.2 IntraHoDlLevThs, IntraHoDlLevP, IntraHoDlLevN
Description
According to GSM specifications, handover decision is performed after a series of
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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1 GSM Handover Principles
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 Relevant Parameters
1.4.4.1 HoUlQualThs, HoUlQualP, HoUlQualN
Description
According to GSM specifications, handover decision is performed after a series of
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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GBC_005_E0_0 GSM Handover and Power Control
Reference
GSM05.08 A.3.2.2 NED2.7
1.4.4.2 HoDlQualThs, HoDlQualP, HoDlQualN
Description
According to GSM specifications, handover decision is performed after a series of
average values are obtained. Downlink receiving quality is one of the handover
causes. The judgment process is as follows:
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
(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.
Reference
GSM05.08 A.3.2.2 NED2.7
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1 GSM Handover Principles
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 Relevant Parameters
1.4.6.1 HoUlLevThs, HoUlLevP, HoUlLevN
Description
According to GSM specifications, handover decision is performed after a series of
average values are obtained. Uplink receiving strength is one of the handover
causes. The judgment process is as follows:
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
(increase). In other words, perform power control first, and then perform handover
if the power control has no effect. The default value can be 15 (i.e. -96 dBm ~ -95
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GBC_005_E0_0 GSM Handover and Power Control
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
According to GSM specifications, handover decision is performed after a series of
average values are obtained. Downlink receiving strength is one of the handover
causes. The judgment process is as follows:
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
(increase). In other words, perform power control first, and then perform handover
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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1 GSM Handover Principles
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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1 GSM Handover Principles
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
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GBC_005_E0_0 GSM Handover and Power Control
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
1 GSM Handover Principles
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
According to GSM specifications, power control decision is performed after a
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
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GBC_005_E0_0 GSM Handover and Power Control
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
2.4.3 PcUlRedLevThs, PcUlRedLevP, PcUlRedLevN
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 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
The default threshold value can be 22 (i.e. -89 dBm ~ -88 dBm). The default value
of P can be 3 and the default value of N can be 4.
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1 GSM Handover Principles
Reference
GSM05.08 A.3.2.1 NED 2.7 10.9
2.4.4 PcDlRedLevThs, PcDlRedLevP, PcDlRedLevN
Description
According to GSM specifications, power control decision is performed after a
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
The default threshold value can be 22 (i.e. -89 dBm ~ -88 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
23
GBC_005_E0_0 GSM Handover and Power Control
2.4.5 PcUlInclQualThs, PcUlInclQualP, PcUlInclQualN
Description
According to GSM specifications, power control decision is performed after a
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
According to GSM specifications, power control decision is performed after a
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
24
1 GSM Handover Principles
follows:
If P of the latest N average values of downlink signal quality are larger than
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
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
2.4.7 PcUlRedQualThs, PcUlRedQualP, PcUlRedQualN
Description
According to GSM specifications, power control decision is performed after a
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
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GBC_005_E0_0 GSM Handover and Power Control
PcUlRedQualN: defines relevant N values
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
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
2.4.8 PcDlRedQualThs, PcDlRedQualP, PcDlRedQualN
Description
According to GSM specifications, power control decision is performed after a
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
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1 GSM Handover Principles
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
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
27