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GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
Product Name Confidentiality Level
G3BSC INTERNAL
Product Version Total 44 pages
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual
(For internal use only)
Prepared by WCDMA & GSM Network
Performance Research Dept.
Su Shi
Date
2008-6-28
Reviewed by Date
Reviewed by Date
Granted by Date
Huawei Technologies Co., Ltd.
All rights reserved
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
Contents
1 Overview of the TCH Call Drop Rate....................................6
1.1 Meaning.................................................................................................................................................6
1.2 Recommended Formulas.......................................................................................................................6
1.3 Signaling Procedure and Measurement Points......................................................................................8
2 Factors That Affect the TCH Call Drop Rate........................11
2.1 Hardware Failure.................................................................................................................................11
2.2 Transmission Problem.........................................................................................................................11
2.3 Version Upgrade..................................................................................................................................12
2.4 Parameter Setting.................................................................................................................................12
2.5 Intra-Network and Inter-Network Interference...................................................................................13
2.6 Coverage Problem..............................................................................................................................13
2.7 Antenna System Problem....................................................................................................................14
2.8 Imbalance Between Uplink and Downlink..........................................................................................14
2.9 Repeater Problem................................................................................................................................14
3 Analysis of and Solutions to High TCH Call Drop Rate.........15
3.1 Solutions to High TCH Call Drop Rate...............................................................................................18
3.1.1 Checking the Hardware.................................................................................................................18
3.1.2 Checking the Transmission............................................................................................................19
3.1.3 Checking the BSC and BTS Version Upgrade..............................................................................20
3.1.4 Checking the Parameter Settings...................................................................................................20
3.1.5 Checking the Interference..............................................................................................................25
3.1.6 Checking the Coverage..................................................................................................................26
3.1.7 Checking the Antenna System.......................................................................................................27
3.1.8 Checking the Balance Between Uplink and Downlink.................................................................28
3.1.9 Checking the Repeaters.................................................................................................................29
4 Test Methods....................................................................30
5 Remarks About the Signaling Analysis of the TCH Call Drop Rate....................................................................................30
6 Cases for TCH Call Drop Rate Optimization.........................33
6.1 Case 1: Call Drop Due to Interference................................................................................................33
6.2 Case 2: Call Drop Due to Imbalance Between Uplink and Downlink................................................34
6.3 Case 3: Call Drop Due to Repeater Problem.......................................................................................34
6.4 Case 4: Call Drop Due to Coverage....................................................................................................35
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
6.5 Case 5: Reduction of Call Drops by Optimizing Handover Parameters.............................................36
6.6 Case 6: Call Drop Due to Inappropriate Parameter Setting................................................................36
6.7 Case 7: Call Drop Due to TRX Board Fault........................................................................................37
6.8 Case 8: Call Drop Due to Antenna System Problem...........................................................................38
6.9 Case 9: Call Drop Due to Transmission Problem...............................................................................38
6.10 Case 10: Call Drop Rate Doubled in a CoBCCH Network After Upgrade from V9R1 to V9R3.....39
6.11 Case 11: Increase in Call Drop Rate Due to Inactivity of T305 and T308........................................40
6.12 Case 12: Increase in Call Drop Rate Due to Change of TR1N on the MSC Side.............................40
7 Feedback Form for the TCH Call Drop Rate ........................41
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
Figures
Figure 1.1Immediate assignment procedure............................8
Figure 1.2Assignment procedure............................................8
Figure 1.3 Intra-BSC handover procedure................................9
Figure 1.4 Incoming BSC handover procedure..........................9
Figure 1.5Procedures for analyzing high TCH call drop rate....16
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
Revision Record
Date Revision Version Change Description Author
2008-6-28 0.8 Draft completed. Su Shi
2008-7-26 1.0 The document is modified according
to review comments.
Su Shi
References
SN
Document Name Author Date
1 G-Guide to Eliminating Interference - 20050311-A-1.0 Chen
Baolin
2005-3-11
2 GSM BSS Network KPI (Network Coverage) Optimization Manual
Xie Haibin 2008-6-18
3 GSM BSS Network KPI (TCH Call Drop Rate) Baseline Wu Zhen 2007-6-22
4 GSM BSS Network KPI (Uplink and Downlink Balance) Optimization Manual
Yang
Jixiang
2008-3-26
5 Guide to Solving Call Drop Problems Yang Bin 2002-3-7
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual
Keywords: TCH call drop rate, KPI
Abstract: This document provides the definition and describes the test method and
optimization method of TCH call drop rate.
Acronyms:
The following table lists the acronyms and their expansion:
Acronym Expansion
TCH Traffic Channel
MS Mobile Station
BSC Base Station Controller
KPI Key Performance Indicator
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
1 Overview of the TCH Call
Drop Rate
1.1 MeaningThe TCH call drop rate refers to the ratio of call drops to successful TCH seizures
after the BSC successfully assigns TCHs to MSs. The TCH call drop rate can be
measured from the following aspects:
TCH call drop rate (including handover)
TCH call drop rate (excluding handover)
The TCH call drop rate, one of the most significant KPIs for telecom operators, is
related to retainability. It indicates the probability of call drops due to various
reasons after MSs access TCHs. A too high TCH call drop rate adversely affects
the user's experience.
1.2 Recommended Formulas
BSC32:
TCH call drop rate (including handover) = (Number of TCH call drops + Number
of TCH call drops during very early assignment)/Number of successful TCH
seizures x 100%
TCH call drop rate (excluding handover) = Number of call drops on TCH/(Number
of successful TCH seizures + Number of successful incoming internal inter-cell
handovers + Number of successful incoming external inter-cell handovers –
Number of successful outgoing internal inter-cell handover] – Number of
successful outgoing external inter-cell handovers) x 100%
BSC6000:
TCH call drop rate (including handover) = Number of call drops on TCH/(Number
of successful TCH seizures (signaling channel) + Number of successful TCH
seizures (TCH) + Number of successful TCH Seizures in TCH handovers (TCH))
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
x 100%
TCH call drop rate (excluding handover) = Number of call drops on TCH/Number
of successful TCH seizures (TCH) x 100%
Through the analysis of each pair of formulas, you can find out that the TCH call
drop rate (including handover) is lower than the TCH call drop rate (excluding
handover) irrespective of the BSC model (BSC32 or BSC6000). The following
takes the formulas for the BSC32 as an example. The number of call drops on TCH
is small during the very early assignment procedure. Therefore, the difference
between the numerator of the formula for the TCH call drop rate (including
handover) and that of the formula for the TCH call drop rate (excluding handover)
can be omitted. Including the TCH seizures in the case of handovers, the
denominator of the formula for the TCH call drop rate (including handover) is
greater than the denominator of the formula for the TCH call drop rate (excluding
handover). Therefore, the result of the formula for the TCH call drop rate
(including handover) is smaller than that of the formula for the TCH call drop rate
(excluding handover).
For details, refer to the GSM BSS Network KPI (TCH Call Drop Rate) Baseline.
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
1.3 Signaling Procedure and Measurement Points
Figure 1.1 Immediate assignment procedure
Figure 1.2 Assignment procedure
GSM BSS Network KPI (TCH Call Drop Rate) Optimization Manual INTERNAL
Figure 1.3 Intra-BSC handover procedure
Figure 1.4 Incoming BSC handover procedure
The meanings of the measurement points in the these figures are as follows:
TCH-SUCC-A: indicates the number of successful TCH seizures.
TCH-SUCC-B: indicates the number of successful incoming internal inter-cell handovers plus the number of successful internal intra-cell handovers.
