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Revision History
Product Version Document Version Serial Number Reason for Revision
V1.0 First published
iBSC V6.20.200f R2.0
The information ofhandover/resource allocationalgorithm and CA coding hasbeen updated in the version ofiBSC V6.20.200f.
Author
Date Document Version Prepared by Reviewed by Approved by
2009-07-04 V1.0 Chen Chun Zheng Hao Zheng Hao
2010-07-13 R2.0 Hou Shuai Zheng Hao Zheng Hao
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Applicable to: GSM after-sales staff
Proposal:Before reading this document, you had better have the followingknowledge and skills.
SEQ Knowledge and skills Reference material
1 Radio parametersZXG10 iBSC (V6.20.61) Base StationController Radio Parameter Reference
2 Performance countersZXG10 iBSC (V6.20.21) Base StationController Performance Counter Reference
3
Follow-up document: After reading this document, you may need thefollowing information.
SEQ Reference material Information
1 Null Null
2
3
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About This Document
Summary
Chapter Description
1 Overview Overview
2 Handover and Channel AllocationAlgorithms
Handover and channel allocation algorithms
3 Requirements for the LengthLimitations of the Frequencies in theDual Band Co-BCCH Cell
Requirements for the length limitations of the frequencies inthe dual band Co-BCCH cell
4 Subcell Performance Analysis Subcell performance analysis
5 Cases on Configuration of Co-BCCH Parameters
Cases on configuration of Co-BCCH parameters
6 Indicator Performance in Large-Scale Use of Co-BCCH
Indicator performance in large-scale use of Co-BCCH
AppA Radio Parameters Relevantto Co-BCCH
Radio parameters relevant to Co-BCCH
AppB Judgment Standard Relatedto the Co-BCCH Threshold
Judgment standard related to the Co-BCCH threshold
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TABLE OF CONTENTS
1 Overview 11.1 Introduction to the Concept of Co-BCCH.....................................................................11.2 Application Scenarios................................................................................................... 11.2.1 Dual Band Co-BCCH Cell.....................................................................................11.2.2 Requirements for the Wide Coverage..................................................................21.2.3 How to Increase the Capacity of the System........................................................2
2 Handover and Channel Allocation Algorithms............................................................32.1 Handover Algorithms.................................................................................................... 3
2.1.1 Handover Algorithm Based on Path Loss/TA.......................................................32.1.2 Handover Algorithm Based on C/I........................................................................42.1.3 PBGT Algorithm Update.......................................................................................52.2 TCH Allocation Algorithm............................................................................................. 52.2.1 Channel Allocation of the Subcells in the Case of Assignment.............................52.2.2 Channel Allocation of the Subcells in the Case of Handover................................62.3 PDTCH Allocation Algorithm........................................................................................ 72.3.1 Subcell Channel Allocation in the Case of the Initial Allocation............................72.3.2 Subcell Channel Allocation in the Case of the TS Reallocation............................8
3 Requirements for the Length Limitations of the Frequencies in the Dual Band Co-BCCH Cell9
3.1 Overview of the Principles............................................................................................93.1.1 Versions Earlier than iBSC V6.20.200f.................................................................93.1.2 iBSC V6.20.200e and Latter Versions................................................................103.2 Case 11
4 Subcell Performance Analysis.................................................................................... 114.1 Congestion Counters.................................................................................................124.2 Traffic Counters......................................................................................................... 12
5 Cases on Configuration of Co-BCCH Parameters.....................................................135.1 Scenario 1: Most TA = 0............................................................................................. 135.2 Scenario 2: TA = 0 Accounts for About 50%..............................................................15
5.3 Scenario 3: Proportion of TA 1 Equals to Proportion of TA > 1...............................16
6 Indicator Performance in Large-Scale Use of Co-BCCH...........................................176.1 Information of the Software Version...........................................................................176.2 Information of the Hardware Environment..................................................................186.3 Configurations of Co-BCCH Parameters....................................................................186.4 Clarification of Comparison between Indicators.........................................................186.5 Relevant KPI Formulas.............................................................................................. 196.6 Comparison Results of the Indicators......................................................................... 20
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FIGURES
Figure 1-1 Dual-Band Network with Co-BCCH Adopted................................................1
Figure 2-2 Handover Model.............................................................................................. 4
Figure 5-3 TA Distribution of a Co-BCCH Cell..............................................................13
Figure 5-4 TA Distribution of a Co-BCCH Cell..............................................................14
Figure 5-5 TA Distribution of a Co-BCCH Cell..............................................................15
Figure 5-6 TA Distribution of a Co-BCCH Cell..............................................................16
Figure 5-7 TA Distribution of a Co-BCCH Cell..............................................................17
TABLES
Table 4-1 Counters for Congestion in the Inner Circle................................................12
Table 4-2 Counters for Traffic in the Inner Circle.........................................................12
Table 6-3 Value Range of the Frequency Band............................................................22
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1 Overview
1.1 Introduction to the Concept of Co-BCCH
One cell can be divided into two subcells with Co-BCCH function. The two subcells
share one BCCH. Subcell 1 is configured with BCCH; subcell 2 is newly added. This is
also referred as concentric circle; Subcell 1 is also referred as the outer circle, and
Subcell 2, the inner circle. See Figure 1 -1.
Figure 1-1 Dual-Band Network with Co-BCCH Adopted
1.2 Application Scenarios
1.2.1 Dual Band Co-BCCH Cell
Dual band Co-BCCH cell refers to the situation when two TRXs of different frequency
bands are configured in the same cell. Usually, the TRX with frequency band of better
transmission performance is configured in Subcell1 as well as BCCH and SDCCH; the
other TRX is configured in Subcell2. In this situation, the handover algorithm based on
path loss/TA is often adopted. (See Handover and Channel Allocation Algorithms for
details.)
For example, it can be applied to the Co-BCCH cells (where there are both 900M TRXs
and 1800M TRXs), and BCCH and SDCCH should be configured on the 900M
frequency band. The advantage of the Co-BCCH networking is that one BCCH can be
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saved. More importantly, this method makes it possible that the 1800M frequency band
can absorb the traffic of the 900M frequency band without the reselections and
handovers among the dual-band cells. Besides, when the capacity expansion is done for
the network where only GSM900M is used, it is possible to configure the 1800M TRXs in
the 900M cells directly without changing the original relations of the neighbor cells.
1.2.2 Requirements for the Wide Coverage
For the site with the multi-carrier configuration, the coverage radius will be reduced if the
combiners are connected in series. In this case, the technology of concentric circle
should be used. In this way, the outer circle can make the coverage stable. In this
situation, the handover algorithm based on path loss/TA is often adopted. (See
Handover and Channel Allocation Algorithms for details.)
1.2.3 How to Increase the Capacity of the System
Configure the TRXs of a cell in subcell 1 and subcell 2 respectively. Increase the TRXs
of subcell 2 and employ a tighter frequency reuse pattern so as to improve the capacity
of the system. The inner circle and the outer circle adopt a different reuse coefficient:
The inner circle adopts a tighter frequency reuse pattern, for example, 4X3, 3X3, or a
tighter frequency reuse pattern. Usually, the frequency reuse pattern adopted by the
outer circle is 4X3, 5X3, or a less tight frequency reuse pattern.
This scenario can be further divided into the following two categories:
The general concentric circle
Usually, the inner circle reduces the transmission power of TRXs. Compared with
the outer circle, its coverage range is small and it does not absorb the indoor traffic
easily. Therefore, the inner circle mainly provides service for the outdoor
subscribers who are near the base station. In this situation, the handover algorithm
based on path loss/TA is often adopted. (See Handover and Channel Allocation
Algorithms for details.)
The intelligent concentric circle
The inner circle and the outer circle have the same transmission power of TRXs.
The outer circle makes the continuous coverage possible, and it mainly provides
service for the subscribers at the boundaries of the cells. The inner circle can not
provide the continuous coverage (in terms of C/I or carrier-to-interference ratio). It
mainly provides service for those subscribers who are near the base station or in
the buildings and for those who can not enjoy the high quality telecommunications
service due to the fact that the environment they are in is affected by the
interferences or the fast attenuation. In this situation, the handover algorithm based
on C/I is recommended (See Handover and Channel Allocation Algorithms for
details.).
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2 Handover and Channel Allocation
Algorithms
2.1 Handover Algorithms
2.1.1 Handover Algorithm Based on Path Loss/TA
2.1.1.1 Calculation Method of PathLoss
Here is the formula of PahtLoss:
PahtLoss = BSTXPWR - Rxlev_dl
Here,
BSTXPWR is the actual transmission power of BTS;
Rxlev_dl is the current downlink Rxlev.
Here is the formula of BSTXPWR:
BSTXPWR = PowerClass - 2*PwrReduction - 2*BSPower
Here,
PowerClass indicates the maximum transmission power of TRX;
PwrReduction indicates the static power level.
BSPower indicates the dynamic power adjustment grade of TRX.
2.1.1.2 Introduction to the Algorithm
If MS is in subcell 1 and every SubCellP out of SubCellN satisfies both the
conditions of (PATHLOSS = PathLossMax) or the condition (TA > SubCellTAMax), it
is believed that a handover should be made from subcell 2 to subcell 1.
If SubCellTAMax = SubCellTAMin = TAMAX (the maximum TA), the prerequisite
for the handover mentioned above changes and the path loss becomes the only
criterion to be used. Similarly, if PathLossMax = PathLossMin = LMAX (the
maximum path loss), the prerequisite for the handover mentioned above also
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changes and TA becomes the only criterion to be used.
For example, here is a handover model of PahtLoss, as shown in Figure 2 -2.
Figure 2-2 Handover Model
The area which connects PathLossMax and PathLossMin is a protection area. Its
function is to avoid the oscillation which goes back and forth.
2.1.2 Handover Algorithm Based on C/I
2.1.2.1 Calculation Method of C/I
1. Define the interference cells in the neighbor cell relations:
Interference cells are a kind of neighbor cells, which are mainly used to calculate
C/I when there are handovers between the subcells. There is not a crystal clear
definition of this kind of cells. When the neighbor cells are configured, those
neighbor cells which may interfere with the current cells can be configured as the
interference cells. This configuration can be done according to the actual situation.
2. If the received measurement reports show that the current cells have some
interference cells, the Rxlev of the interference cells can be transformed into the
power (unit: W). Then, the power of several interference cells can be summed up.
Besides, the minimum Rxlev of the neighbor cells should be recorded.
3. If the summed magnitude of power of the interference cells is larger than zero, it
can be transformed into Rxlev.
4. If the summed magnitude of power of the interference cells is zero, it is believed
that the interference level of this time is zero.
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5. If no interference cells are defined among the neighbor cells and the reported
number of neighbor cells is smaller than the number of neighbor cells configured in
the database (Here is a typical situation: The number of neighbor cells which are
configured is larger than six while the reported number of neighbor cells is smaller
than six.), it is believed that the interference level of this time is zero. Otherwise, the
interference level is the minimum Rxlev of the neighbor cells, which is shown by the
measurement reports.
6. Finally, the C/I of this time is calculated according to the Rxlev_dl of the serving
cell.
2.1.2.2 Introdution to the Algorithm
For the C/I-based handover, it is necessary to judge whether the subscriber resides in
subcell 1 or subcell 2. If MS is in subcell 1, a handover towards subcell 2 can be made if
C/I is good enough. On the other hand, if MS is in subcell 2, a judgment should be made
to see whether the current C/I is really bad. If so, a handover towards subcell 1 can be
made. Here are the details:
If MS is in subcell 1 and every GoodCiP out of GoodCiN satisfies the condition of
(C/I> GoodCiThs), it is believed that a handover should be made from the outer
circle to the inner circle.
If MS is in subcell 2 and every BadCiP out of BadCiN satisfies the condition of (C/I
< BadCiThs), it is believed that a handover should be made from the inner circle to
the outer circle.
2.1.3 PBGT Algorithm Update
The parameter DuleBandOffset indicates the value to compensate power in second cell
in the dual band Co-BCCH cell. If there are subcells, the two subcells can adopt two
different PBGT handover criteria so as to control the PBGT handover better. If the
current service is in subcell 2, DuleBandOffset should be subtracted from the calculation
results of PBGT margin of the neighbor cells.
2.2 TCH Allocation Algorithm
2.2.1 Channel Allocation of the Subcells in the Case of Assignment
If it is confirmed that the cause for the application for resources is assignment, the
channel allocation of the subcells is completed in the following way:
If the handover algorithm of the subcells is based on path loss, the measurement
results of path loss on SDCCH should be considered: If the intra-cell handover
threshold is satisfied and the handset supports the frequency band of subcell 2, the
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channels of subcell 2 will be chosen first. If the threshold is not satisfied or the
handset does not support the frequency band of subcell 2, only the channels of
subcell 1 can be chosen.
If the handover algorithm of the subcells is based on C/I, the measurement resultsof path loss on SDCCH should be considered: If C/I satisfies the intra-cell handover
threshold and the handset supports the frequency band of subcell 2, the channels
of subcell 2 will be chosen first. If the threshold is not satisfied or the handset does
not support the frequency band of subcell 2, only the channels of subcell 1 can be
chosen.
2.2.2 Channel Allocation of the Subcells in the Case of Handover
If it is confirmed that the cause for the application for resources is handover (including
the directional retry), the channel allocation algorithm of the subcells is completed in thefollowing way:
For the intra-cell handover,
If the cause for the handover is C/I or path loss, the handover is between the
subcells within the cell. If the channel request message indicates that the
original cell is subcell 1, only the channels of subcell 2 can be chosen. If the
channel request message indicates that the original cell is subcell 2, only the
channels of subcell 1 can be chosen.
If the handover decision criteria for subcell 1 and subcell 2 are met but no
channels are available in the target subcell, it takes at least a period ofHoFailPenaltyTime before the handover attempt starts.
If the cause for the handover is the uplink/downlink interference, the handover
is between the subcells. If the channel request message indicates that the
original cell is subcell 1, only the channels of subcell 1 can be chosen. If the
channel request message indicates that the original cell is subcell 2, only the
channels of subcell 2 can be chosen.
For the inter-cell handover or the directional retry (versions earlier than iBSC
V6.20.200f),
The BTS parameter named inHoEnable does not exist.
If the original cell and the target cell are co-sited (with the same SITEID) and
the original cell is in subcell 1, the only choice is to make a handover to the
channels of subcell 1 of the target cell.
Suppose the original cell and the target cell are co-sited (with the same
SITEID), the original cell is in subcell 2, and the handset supports the
frequency band of subcell 2 of the target cell. Then, the first choice is to
make a handover to the channels of subcell 2 of the target cell.
If the original cell and the target cell are not co-sited (with different SITEIDs),
the handover can only be made to the channels of subcell 1 of the target cell
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no matter MS is in subcell 1 or subcell 2 of the original cell.
For the inter-cell handover or the directional retry (iBSC V6.20.200f and the later
versions),
If the original cell and the target cell are co-sited (with the same SITEID) and
the original cell is in subcell 1, the only choice is to make a handover to the
channels of subcell 1 of the target cell.
Suppose the original cell and the target cell are co-sited (with the same
SITEID), the value of inHoEnable of the site is one, the original cell is in
subcell 2, and the handset supports the frequency band of subcell 2 of the
target cell. Then, the first choice is to make a handover to the channels of
subcell 2 of the target cell.
Suppose the original cell and the target cell are co-sited (with the same
SITEID), the value of inHoEnable of the site is zero, and the original cell is insubcell 2. Then, the only choice is to make a handover to the channels of
subcell 1 of the target cell.
If the original cell and the target cell are not co-sited (with different SITEIDs),
the handover can only be made to the channels of subcell 1 of the target cell
no matter the original cell is in subcell 1 or subcell 2.
2.3 PDTCH Allocation Algorithm
2.3.1 Subcell Channel Allocation in the Case of the Initial Allocation
If it is the initial allocation, only the PDTCH of subcell 1 can be allocated to the
subscriber. From this perspective, the following aspects should be paid special attention
to when PDTCH is configured for the Co-BCCH cell.
Subcell 1 must be configured with PDTCH.
If the TS reallocation algorithm based on Rxlev and TA is not used (In other words,
the configuration of the parameter PSALLOCSC_0 is that only subcell 1 is
allowed.), subcell 2 should not be configured with PDTCH. Otherwise, there may be
a waste of resources.
Suppose the TS reallocation algorithm based on Rxlev and TA is used (In other
words, the configuration of the parameter PSALLOCSC_0 is not that only subcell 1
is allowed.). When the cell is initially configured as the Co-BCCH cell, it is
suggested that PDTCH should be mainly configured in subcell 1. Then, some minor
adjustments can be made later according to the TA distribution and the Rxlev
distribution.
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2.3.2 Subcell Channel Allocation in the Case of the TS Reallocation
The TS reallocation algorithm based on Rxlev and TA is enabled from the version iBSC
V6.20.200fp002. Here are the newly added parameters:
PSALLOCSC_0
PSALLOCSC_1
PSALLOCSC_2
Here are the borrowed radio parameter fields:
Wnd
PbcchBlks
PagBlkRes
PrachBlks
Here are some scenarios where the TS reallocation algorithm based on Rxlev and
TA is used or not used:
If the configuration of PSALLOCSC_0 is that only subcell 1 is allowed, only
PDTCH of subcell 1 can be allocated to the PS subscribers during the TS
reallocation.
If the configuration of PSALLOCSC_0 is that subcell 1 or subcell 2 enjoys thepriority, it means that the TS reallocation algorithm based on Rxlev and TA is
enabled. If neither the Rxlev-based judgment standards not the TA-based
judgment standards are met, whether TS is reallocated to subcell 1 or
subcell 2 depends on the value of PSALLOCSC_0.
If subcell 1 is configured with enough PDTCHs, the TS reallocation algorithm
based on Rxlev and TA is not recommended.
The TS reallocation algorithm based on Rxlev:
The original sample of Rxlev is obtained from C_Value of Packet Downlink
Ack/Nack.
The size of the window related to the judgment is defined on basis of Wnd.
The value of N related to the judgment (The value of P does not exist.) is
defined on basis of PbcchBlks. In order to ensure that PbcchBlks is valid, the
parameter Psi1RepPer must be configured as any value which is at least ten
(This is a constraint condition of the system, and it does not have any actual
meanings.).
Currently, the PDTCH occupied by the subscriber is in subcell 2, and the
value of Rxlev, which is calculated on basis of the window and the value of
N, is no larger than PSALLOCSC_1. Therefore, from the perspective of
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Rxlev-based TS reallocation algorithm, the requirements for the TS
reallocation to subcell 1 are satisfied.
Currently, the PDTCH occupied by the subscriber is in subcell 1, and the
value of Rxlev, which is calculated on basis of the window and the value ofN, is equal to or larger than PSALLOCSC_2. Therefore, from the perspective
of Rxlev-based TS reallocation algorithm, the requirements for the TS
reallocation to subcell 2 are satisfied.
The TS reallocation algorithm based on TA:
For TS reallocation algorithm based on Rxlev and TA, the judgment based on
Rxlev is made first. If the judgment based on Rxlev is approved, TA update
will be started via the polling. After the TA update, if it is found that TA also
satisfies the requirements, the TS reallocation will be carried out for the
subcells. If no Packet Control Ack responds to the polling after the Rxlev-
based judgment is approved, the TA which is updated most recently will be
borrowed to be involved in the judgment.
Whether the TA threshold of PS-based TS reallocation to subcell 1 is satisfied
or not is defined on basis of the borrowed PagBlkRes, and the sign of the
judgment is .
Whether the TA threshold of PS-based TS reallocation to subcell 2 is satisfied
or not is defined on basis of the borrowed PrachBlks, and the sign of the
judgment is .
3 Requirements for the Length
Limitations of the Frequencies in the
Dual Band Co-BCCH Cell
3.1 Overview of the Principles
3.1.1 Versions Earlier than iBSC V6.20.200f
The frequencies configured at OMCR are not distinguished according to their subcell. All
of them are put in the CA of the BTS table. Since the system message 1 clarifies the
limitations of the quantity of frequencies, there are some constraint conditions for the
configuration of frequencies of the Co-BCCH cell (subcell 1 + subcell 2):
For system with PGSM900 only:
CA list may at most contain 124 frequencies; and at most 64 frequencies for
each cell.
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For system with mixed frequency bands and system with EGSM or DCS1800 only:
If the difference between the maximum frequency ARFCN and the minimum
frequency ARFCN is smaller than 112, then the CA list may at most contain
112 frequencies, and each cell may at most contain 64 frequencies.
If the difference is smaller than 128, then the CA list my at most contain 29
frequencies.
If the difference is smaller than 256, then the CA list may at most contain 22
frequencies.
If the difference is smaller than 512, then the CA list may at most contain 18
frequencies.
If the difference is NOT smaller than 512, and frequency 0 is included, then
the CA list may at most contain 17 frequencies; if frequency 0 is not
included, then the CA list may at most contain 16 frequencies.
3.1.2 iBSC V6.20.200e and Latter Versions
Changes to the versions:
System message 1 only broadcasts the frequency of Subcell1;
For CS service, CA in system message 1 cannot be used in the channel
assignment of Subcell2; while the frequency list carried by the assignment
message and handover message can be used.
For PS service, CA (Direct Cipher Mode1) in system message 1 and indirect cipher
mode (obtaining frequency list from system message 13) cannot be used in the
channel assignment of Subcell2; while Direct Cipher Mode 2(using the frequency
list carried by assignment and TS reallocation messages) can be used.
Based on the changes to the iBSC versions, the constraint conditions for Subcell1 and
Subcell2 are as follows:
For system with PGSM900 only:
CA list may at most contain 124 frequencies; and at most 64 frequencies for
each cell.
For system with mixed frequency bands and system with EGSM or DCS1800 only:
If the difference between the maximum frequency ARFCN and the minimum
frequency ARFCN is smaller than 112, then the CA list may at most contain
112 frequencies, and each cell may at most contain 64 frequencies.
If the difference is smaller than 128, then the CA list my at most contain 29
frequencies.
If the difference is smaller than 256, then the CA list may at most contain 22
frequencies.
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If the difference is smaller than 512, then the CA list may at most contain 18
frequencies.
If the difference is NOT smaller than 512, and frequency 0 is included, then
the CA list may at most contain 17 frequencies; if frequency 0 is not
included, then the CA list may at most contain 16 frequencies.
3.2 Case
Phenomenon Description
An overseas network adopts 900/1800M dual band Co-BCCH cell; BCCH is
configured on 900M; both the inner circle and the outer circle adopt FH. Large
number of block calls are detected in DT with cause value (47) Resources
unavailable, unspecified.
Cause Analysis
BSC V 6.10 series are used on site. Both 900M and 1800M adopt FH1X1; the
frequency sequence for 900M is 79-86 (8 frequencies); and that for 1800M is 586-
629 (44 frequencies). The difference between the max frequency ARFCN and the
minimum frequency ARFCN is larger than 512 with frequency 0 excluded,
therefore, the total length of FH sequence (No. of frequencies) of the dual-band
subcell shall be no larger than 16. The current frequency length in planning well
exceeds the FH sequence length specified in system, which leads to assignment
failure and block calls.
Solution
After the inspection and analysis, we should make adjustment to FH configuration
and FH sequence length. The adjustment principles are as follows:
900M maintains FH1X1, frequency number in FH sequence is 8;
1800M FH mode is changed to 1X6, frequency number in FH sequence is 8 7.
After the frequencies are adjusted according to the above principles, the problem is
solved.
4 Subcell Performance Analysis
Counters related to subcells are under Subcell Statistical Measurement. When
subcells are configured, the measurement task measures the channels in subcells
and handovers between the subcells, and focuses on the traffic sharing in Subcell2
(inner circle). For detailed introduction to the counters, please refer to the
corresponding users manual. This chapter mainly introduces the counters related
to traffic analysis. For Co-BCCH, what we shall concern about is whether the traffic
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sharing between the two subcells is reasonable.
Currently our system cannot directly output the situation of congestion and traffic in
the two cells. We may temporarily solve the problem by setting up Subcell
Statistical Measurement. From the measurement data, we may obtain the statistics
of congestion and traffic in the inner circle; from performance reports, we obtain the
statistics of congestion and traffic in the cell. We may obtain data about the outer
circle by making subtraction between the two sets of statistics.
4.1 Congestion Counters
The statistics for congestion in the inner circle may be obtained from the following
counters in Table 4 -1.
Table 4-1 Counters for Congestion in the Inner Circle
Counter No.Counter Name
V2 V3
C12033 C901130047No. of TCH/F seizure failures in Subcell2(assignment)
C12036 C901130050No. of TCH/F seizure failures in Subcell2(handover)
C12039 C901130053No. of TCH/H seizure failures in Subcell2(assignment)
C12042 C901130056No. of TCH/H seizure failures in Subcell2(handover)
4.2 Traffic Counters
The statistics for traffic in the inner circle may be obtained from the following counters in
Table 4 -2.
Table 4-2 Counters for Traffic in the Inner CircleCounter No.
Counter NameV2 V3
C12045 C901130059 Total TCH/F busy time in Subcell2
C12046 C901130060 Total TCH/H busy time in Subcell2
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5 Cases on Configuration of Co-BCCH
Parameters
TRX power in Subcell2 drops by 4 dB. Analysis (with RMA) of TA distribution statistics in
Abis interface signaling suggests that Co-BCCH cell falls into two scenarios:
If user TA is equally distributed within the cells service range, we may balance the
traffic in the inner circle through setting TA. With the assistance of handover
algorithm based on path loss, handover to the inner circle can be performed when
the signal is good, and handover to the outer circle can be performed in time when
the signal quality deteriorates.
When users are centered around the site (most TA=0), setting of TA is not useful in
balancing the traffic. In such case, we need to use path loss and limit the innercircles service range with the handover algorithms based on path loss, in order to
reach traffic balance.
5.1 Scenario 1: Most TA = 0
Case 1
Figure 5-3 TA Distribution of a Co-BCCH Cell
The SubCellTAmin/SubCellTAmax of the cell is changed from 3/5 to 1/3, and here is a
comparison of traffic before and after the adjustment.
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Inner CircleTraffic (Erl)
Outer CircleTraffic (Erl)
Percentage of InnerCircle Traffic
BeforeAdjustment
10.44 5.98 63.58%
After Adjustment 11.17 6.56 63.00%
It can be seen that the traffic migration is not obvious when the
SubCellTAmin/SubCellTAmax is adjusted at that moment. However, since the traffic
distribution of the cell is reasonable, no further adjustment is made on basis of Path
Loss-based handover algorithm.
Case 2
Figure 5-4 TA Distribution of a Co-BCCH Cell
The SubCellTAmin/SubCellTAmax of the cell is changed from 3/5 to 1/3, and here is a
comparison of the traffic before and after the adjustment.
Inner Circle
Traffic (Erl)
Outer Circle
Traffic (Erl)
Percentage of Inner
Circle Traffic
Before Adjustment 1.96 0.35 84.85%
After Adjustment 3.79 0.7 84.41%
It can be seen that the traffic migration is not obvious when the
SubCellTAmin/SubCellTAmax is adjusted at that moment. Then, the
PathLossMax/PathLossMin is adjusted, and the effect is evident. Here is a comparison
of the data before and after the adjustment:
PLmin/ PLmaxInner CircleTraffic (Erl)
Outer CircleTraffic (Erl)
Percentage of InnerCircle Traffic
121/131 8.97 1.65 84.46%
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PLmin/ PLmaxInner CircleTraffic (Erl)
Outer CircleTraffic (Erl)
Percentage of InnerCircle Traffic
116/126 4.29 1.24 77.58%113/123 2.94 2.14 57.87%
5.2 Scenario 2: TA = 0 Accounts for About 50%
Case 3
Figure 5-5 TA Distribution of a Co-BCCH Cell
Original configuration: SubCellTAmin = 3, SubCellTAmax = 4
Modified configuration: SubCellTAmin = 1, SubCellTAmax = 3
A comparison of traffic migration before and after the modification:
Inner CircleTraffic (Erl)
Outer CircleTraffic (Erl)
Percentage of InnerCircle Traffic
BeforeAdjustment
49.48 20.74 70.46%
After Adjustment 41.36 33.67 55.12%
Case 4
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Figure 5-6 TA Distribution of a Co-BCCH Cell
Original configuration: SubCellTAmin = 2, SubCellTAmax = 4
Modified configuration: SubCellTamin = 1, SubCellTAmax = 3
A comparison of traffic migration before and after the modification:
Inner CircleTraffic (Erl)
Outer CircleTraffic (Erl)
Percentage of InnerCircle Traffic
BeforeAdjustment
15.81 28.3 35.84%
After Adjustment 24.26 19.65 55.25%
5.3 Scenario 3: Proportion of TA 1 Equals to
Proportion of TA > 1
Case 5
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Figure 5-7 TA Distribution of a Co-BCCH Cell
Original configuration: SubCellTAmin = 3, SubCellTAmax = 5
Modified configuration: SubCellTAmin = 2, SubCellTAmax = 4
A comparison of traffic migration before and after the adjustment:
Inner CircleTraffic (Erl)
Outer CircleTraffic (Erl)
Percentage of InnerCircle Traffic
BeforeAdjustment
8.1 5.04 61.64%
After Adjustment 6.1 6.75 47.47%
6 Indicator Performance in Large-Scale
Use of Co-BCCH
6.1 Information of the Software VersionSoftware Environment Explanation
iOMCR iOMCR V6.20.200e
OMCB OMCB V4.00.200k p003
iBSC iBSC V6.20.200e p002
MINOS V4.10.430d p002
SDR SDR V4.00.210e p07
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after the replacement is finished.
In this network, only 6% of the cells are Co-BCCH cells. In order to avoid the
influence from the worst cells as much as possible, eight cells of non Co-BCCH
part, which are the worst, are filtered, and two cells of Co-BCCH part are filteredbefore the indicators are compared.
The congestion rate indicators are involved in the traffic distribution, so it is not
necessary to make a reference to those indicators.
The replacement of the network is just finished, and the centralized KPI
optimization has not been done yet, so the results of the comparison is only for
your reference and they cannot be taken as a guidance on KPI Q & A.
6.5 Relevant KPI Formulas
KPI Formulas
UL Quality 67 Share
(C900060072+C900060073)/(C900060066+C900060067+C900060068+C900060069+C900060070+C900060071+C900060072+C900060073)
DL Quality 67 Share
(C900060080+C900060081)/(C900060074+C900060075+C900060076+C900060077+C900060078+C900060079+C900060080+C900060081)
UL Quality 01 Share
(C900060066+C900060067)/(C900060066+C900060067+C900060068+C900060069+C900060070+C900060071+C900060072+C900060073)
DL Quality 01 Share
(C900060074+C900060075)/(C900060074+C900060075+C900060076+C900060077+C900060078+C900060079+C900060080+C900060081)
SDCCH assignment SuccessRate
C900060242/C900060241
TCH Assignment SuccessRate
1-(C900060029+C900060037+C900060200+C900060211)/(C900060019+C900060030+C900060042+C900060046+C900060021+C900060032+C900060048+C900060044)
TCH Congestion Rate(Excluding Handover)
(C900060020+C900060031+C900060043+C900060047)/(C900060019+C900060030+C900060042+C900060046)
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KPI Formulas
Handover Success Rate
(C900060098+C900060102+C900060120+C900060094+C900060096)/(C900060097+C900060213+C900060214+C900060215+C900060099+C900060100+C900060101+C900060216+C900060119+C900060093+C900060095)
Inter-cell Handover SuccessRate
(C900060098+C900060102+C900060094+C900060096)/(C900060097+C900060213+C900060214+C900060215+C900060099+C900060100+C900060101+C900060216
+C900060093+C900060095)SDCCH Drop Rate C900060053/C900060004
TCH Call Drop Rate (ExcludingHandover)
(C900060054+C900060055)/(C900060028+C900060036+C900060199+C900060210)
DL TBF EstablishmentSuccess Rate
(C900040007+C900040015+C900040008+C900040016)/(C900040141+C900040142+C900040143+C900040144+C900040145+C900040146+C900040147+C900040148)
UL TBF EstablishmentSuccess Rate
(C900040025+C900040033+C900040026+C900040
034)/(C900040159+C900040160+C900040161+C900040168+C900040163+C900040164+C900040165+C900040166)
6.6 Comparison Results of the Indicators
KPI Co-BCCH non Co-BCCH
UL Quality 6 7 Share 0.42% 0.49%
DL Quality 6 7 Share 0.94% 1.02%
UL Quality 0 1 Share 98.46% 98.00%
DL Quality 0 1 Share 95.91% 95.53%
SDCCH assignment Success Rate 99.24% 97.60%
TCH Assignment Success Rate 99.80% 99.81%
TCH Congestion Rate (Excluding Handover) 0.00% 0.02%
Handover Success Rate 98.44% 96.91%
Inter-cell Handover Success Rate 97.86% 96.90%
SDCCH Drop Rate 0.01% 0.07%
TCH Call Drop Rate (Excluding Handover) 0.38% 0.59%
DL TBF Establishment Success Rate 96.06% 91.79%
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KPI Co-BCCH non Co-BCCH
UL TBF Establishment Success Rate 99.43% 96.43%
The comparison of the indicators shows that the average values of all the indicators ofthe cells where Co-BCCH is enabled are as satisfying as or more satisfying than those
of the cells where Co-BCCH is not enabled. However, it should be noticed that all the
Co-BCCH sites are those in the dense urban areas of the capital and they have a good
coverage. However, some of the non Co-BCCH sites are isolated sites or suburban
sites. Besides, the altitudes of different areas in the suburb vary greatly and the
continuity of the coverage is not good there. Therefore, it can not be concluded that the
performance indicators can be improved when the Co-BCCH function is enabled.
However, the indicators here show that at least they will not deteriorate when Co-BCCH
function is enabled. So Co-BCCH can be enabled for the commercial networks without
any risks.
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AppA Radio Parameters Relevant to Co-BCCH SubcellUsed It indicates whether the cell uses the subcell structure.
Description: It indicates whether the cell uses the subcell structure.
Value range: 0: No 1: Yes
FreqBand The frequency band of subcell 1
Description: The frequency band of subcell 1 refers to the frequency band where all
the frequencies used by subcell 1 are.
Value range: See Table 6 -3.
Table 6-3 Value Range of the Frequency Band
Value Range Explanation
0 P-GSM (ARFCN = 1 124)
1 E-GSM (ARFCN = 0 124, 975 1023)
2 DCS1800 (ARFCN = 512 885)
3 R-GSM (ARFCN = 0 124, 955 1023)
4 GSM1900 (ARFCN = 512 810)
7 GSM850 (ARFCN = 128251)
SubFreqBand The frequency band of subcell 2
Description: The frequency band of subcell 2
Value range: See Table 6 -3 .
DuleBandOffset Power compensation between frequencies
Description: It indicates the value to compensate power in second cell in the dual
band Co-BCCH cell. If there are subcells, the two subcells can adopt two different
PBGT handover criteria so as to control the PBGT handover better. If the currentservice is in subcell 2, DuleBandOffset should be subtracted from the calculation
results of PBGT margin of the neighbor cells.
Value range: 050 dB
Default value: 0
HoControl18 Subcell handover algorithm
Description: This parameter defines two handover modes of subcell handover
algorithm: Handover based on C/I, handover based on path loss and TA.
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Value range: 0: Handover based on C/I; 1: Handover based on path loss and TA
Default value: 0
Note: HoControl8 (The concentric handover is supported.) is used to
control whether the function of intelligent concentric circle is enabled (an
old concept). This parameter is invalid.
PathLossMax The MAX of path loss
Description: It is one of the subcell handover parameters, and it indicates the
maximum path loss.
Value range: 0150 dB
Default value: 126
Note: The judgment standard is .
PathLossMin The MIN of path loss
Description: It is one of the subcell handover parameters, and it indicates the
minimum path loss.
Value range: 0150 dB
Default value: 120
Note: The judgment standard is .
SubCellTAMax The MAX of time advance
Description: It is one of the subcell handover parameters, and it indicates the
maximum time advance.
Value range: 063
Default value: 1
Note: The judgment standard is >.
SubCellTAMin The MIN of time advance
Description: It is one of the subcell handover parameters, and it indicates the
minimum time advance.
Value range: 063
Default value: 0
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Note: The judgment standard is .
GoodCiN Value N (GoodCiN) of the special layer TRX frequency
Description: Please refer to GoodCiThs.
Value range: 131
Default value: 3
GoodCiP Value P (GoodCip) of the special layer TRX frequency
Description: Please refer to GoodCiThs.
Value range: 131
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Default value: 2
BadCiN Bad C/I threshold of the special layer TRX frequency when there is an
outgoing handover
Description: If the paging is on the special layer TRX frequency and P of the latest
N C/I values fall below the bad C/I threshold, then perform a handover from the
special layer TRX frequency to the common layer TRX frequency. The cause for
the handover is Bad C/I.
Value range: 0255
Default value: 130
Note: The judgment standard is
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Note: This parameter is a BTS parameter, and it becomes valid from the version
iBSC V6.20.200f.
PSALLOCSC_0 PS channel allocation subcell choice
Description: When the configuration of subcells is completed, the channel
reallocation strategy of the PS service of the subcells can be controlled via this
parameter. There are three options: Priority subcell 1, priority subcell 2, only subcell
1
Value range: 0: Priority subcell 1; 1: Priority subcell 2; 2: Only subcell 1
Default value: Priority subcell 1
Note: This parameter becomes valid from the version iBSC V6.20.200f
p002.
PSALLOCSC_1 The level threshold of subcell 1 allocated by PS channel
Description: When the configuration of subcells is completed, this parameter can
control the level threshold for choosing subcell 1 when the channel reallocation of
PS service starts. If the PS channel is at subcell 2 and the level is smaller than or
equal to PSALLOCSC_1 and TA value is larger than or equal to PagBlkRes (This
field is borrowed by the version of iBSC V6.20.200f.), it is necessary to transfer to
subcell 1.
Value range: 0 63
0: < -110 dBm;
1: -110 dBm -109 dBm;
2: -109 dBm -108 dBm;
...
62: -49 dBm -48 dBm;
63: > -48 dBm
Default value: 0
Note: This parameter becomes valid from the version iBSC V6.20.200f
p002.
PSALLOCSC_2 The level threshold of subcell 2 allocated by PS channel
Description: When the configuration of subcells is completed, this parameter can
control the level threshold for choosing subcell 2 when the channel reallocation of
PS service starts. If the PS channel is at subcell 1 and the level is larger than or
equal to PSALLOCSC_2 and TA value is smaller than or equal to PagBlkRes (This
field is borrowed by the version of iBSC V6.20.200f.), it is necessary to transfer to
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subcell 2.
Value range: 0 63
0: < -110 dBm;
1: -110 dBm -109 dBm;
2: -109 dBm -108 dBm;
...
62: -49 dBm -48 dBm;
63: > -48 dBm
Default value: 63
Note: This parameter becomes valid from the version iBSC V6.20.200f
p002.
Wnd The size of the sliding window where the measurement reports are kept
Description: When the subcells are configured, this field can be used to decide
whether C_value calculated on basis of PSALLOCSC_1 and PSALLOCSC_2
satisfies the requirements of the window size when the level threshold of the TS
reallocation is reached.
Value range: 18
Default value: 4
Note: The version iBSC V6.20.200f p002 borrows this field first.
PbcchBlks PBCCH reserved blocks
Description: When the subcells are configured, this field can be used to decide
whether C_value calculated on basis of PSALLOCSC_1 and PSALLOCSC_2
reaches the value of N when the level threshold of the TS reallocation is reached.
Value range: 03 (corresponding to the value of N = 4, 1, 2, 3 respectively)
Default value: 3
Note: The version iBSC V6.20.200f p002 borrows this field first.
PagBlkRes PAGCH reserved blocks
Description: When the subcells are configured, this field is used to check whether
the TA threshold of the PS-based TS reallocation is reached so as to enter subcell
1. The judgment standard is .
Value range: 010
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Default value: 5
Note: The version iBSC V6.20.200f p002 borrows this field first.
PrachBlks PRACH reserved blocks
Description: When the subcells are configured, this field is used to check whether
the TA threshold of the PS-based TS reallocation is reached so as to enter subcell
2. The judgment standard is .
Value range: 015
Default value: 2
Note: The version iBSC V6.20.200f p002 borrows this field first.
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AppB Judgment Standard Related to the Co-
BCCH ThresholdParameter Code Range & Unit Default
JudgmentStandard
GoodCiThs0255; 0:-127 dB, 1:-126 dB,...,255:128 dB
133 >
BadCiThs0255; 0:-127 dB, 1:-126 dB,...,255:128 dB
130 =
PathLossMin 0150, dB 120
SubCellTAMin 063 0 -48 dBm
0 -48 dBm
63 >=
l PagBlkRes 010 5 >=
l PrachBlks 015 2