gsm rno subject-field mos optimization_r2.0
TRANSCRIPT
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Field MOS Optimization
R2.0
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Revision History
Product Version Document Version Serial Number Reason for Revision
R1.0 First published
R2.0The Xi'an case isadded.
Author
Date Document Version Prepared by Reviewed by Approved by
2010-05-17 R1.0Jiang Yi and HouShuai
Zheng Hao, FeiAiping, and ChangHaijie
Zheng Hao
2011-5-31 R2.0Chang Haijie andXiang Fei
Zheng Hao Zheng Hao
Intended audience:GSM network optimization engineers
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About This Document
Summary
Chapter Description
1 Overview Gives an overview about MOS optimization.
2 Principles of MOS Test Describes the MOS test principles.
3 Major Factors Affecting FieldMOSs
Describes the major factors that may affect field MOS values.
4 Three Measures for FieldEngineers to Improve the MOS
Describes the three measures for field engineers to improvethe MOS.
5 General Care for the Use of TestDevices
Describes the general care for the use of test devices.
6 Case Study Describes the typical cases.
AppA Version Requirements forthe AMR + TRO Function
Describes the version requirements for the AMR + TROfunction.
AppB Standard Template of DataCollection for MOS Tests
Describes the standard template of data collection for MOStests.
AppC Glossary Lists the abbreviations and their full names appeared in thisdocument.
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TABLE OF CONTENTS
1
Overview ......................................................................................................... 1
2
Principles of MOS Test ................................................................................... 2
2.1
Basic Concepts ................................................................................................. 2
2.2 MOS Test Principles ......................................................................................... 3
3
Major Factors Affecting Field MOSs.............................................................. 6
3.1
Impact of Handover .......................................................................................... 6
3.2
Impact of Speech Coding Algorithm .................................................................. 7
3.3
Impact of Radio Environment ............................................................................ 8
3.4
TFO Function .................................................................................................... 9
3.5
Impact of CN Signaling Flow ........................................................................... 11
3.6
Impact of Test Vehicle Speed ......................................................................... 12
4
Three Measures for Field Engineers to Improve the MOS ......................... 14
4.1
Optimization of the Coding Modes and HR Traffic Proportions ....................... 20
4.1.1
Optimization of the Speech Coding Modes ..................................................... 20
4.1.2
Optimization of the HR Traffic Proportions ...................................................... 21
4.2
Optimization of the Number of Handovers in the DT ....................................... 24
4.3
Use of the TFO Function ................................................................................ 28
4.4
Use of Other Network Functions ..................................................................... 29
4.4.1
Omission of Optional Parameters in Handover Commands ............................ 294.4.2
IRC Function................................................................................................... 30
4.4.3
Impact of the T3105 Parameter on the Number of Times That the PHYSICALINFORMATION Message Is Delivered ........................................................... 31
4.4.4
Processing of the PHYSICAL INFORMATION Messages by the DBB ............ 32
4.5
RQ Optimization of the Existing Network ........................................................ 32
4.6
Disabling of the Function of Sending Status Query Messages at the CN Side 34
5
General Care for the Use of Test Devices ................................................... 36
5.1
General Care for the Use of Pilot Pioneer ....................................................... 36
5.2
General Care for the Use of NTAS AUTO ....................................................... 37
6
Case Study .................................................................................................... 39
6.1
Scenarios ....................................................................................................... 39
6.2
Test Methods and Devices ............................................................................. 40
6.3
Test Results and Analysis............................................................................... 40
6.3.1
Comparison Results Before and After the T3105 Parameter WasOptimization ................................................................................................... 40
6.3.2
Comparison Tests in Typical Scenarios of ZTE (China Unicom), NSN (ChinaUnicom), and ALU (China Mobile) .................................................................. 43
6.3.3 Comparison Tests Before and After the UL RxLev Handover Threshold andDynamic HR Thresholds of Some Cells Were Modified .................................. 51
6.3.4
Comparison Results Before and After the IRC Function Was Enabled ........... 59
6.4
Conclusion and Suggestions .......................................................................... 64
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AppA
Version Requirements for the AMR + TRO Function ................................. 66
AppB
Standard Template of Data Collection for MOS Tests................................ 67
AppC
Glossary ........................................................................................................ 68
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FIGURES
Figure 2-1 Test principles of PESQ ...................................................................................... 3
Figure 2-2 MOS Test Principles ........................................................................................... 4
Figure 3-1 Consecutive Low MOSs and Call Drops Caused by Consecutive High Bit ErrorRates and Error Frames ......................................................................................................... 9
Figure 3-2 Transcoding Function with TFO Inactivated ...................................................... 10
Figure 3-3 Transcoding Function Bypassed With TFO Activated ........................................ 10
Figure 3-4 Signaling of the Originating MS ......................................................................... 11
Figure 3-5 Signaling of the Terminating MS ....................................................................... 12
Figure 4-1 Delivering a Handover Command in Segments (Green for the Layer-2 Messagesand Blue for the Layer-3 Messages) ..................................................................................... 29
Figure 4-2 Enabling the IRC Function of an SDR Base Station .......................................... 31
Figure 4-3 Asynchronous Handover Signaling on the Um Interface (Blue for the Layer-3Messages and Green for the Layer-2 Messages) ................................................................. 32
Figure 6-1 Um Interface Signaling During the Asynchronous Handover in ZTEs Network. 40
Figure 6-2 Um Interface Signaling During the Asynchronous Handover in NSNs Network41
Figure 6-3 Comparison Between ZTEs Downtown Area and NSNs Downtown Area........ 50
Figure 6-4 Comparison Between ZTEs Suburb and NSNs Suburb................................... 50
TABLES
Table 2-1 MOS Value ........................................................................................................... 2
Table 3-1 Impact of Handover on MOSs Under Different Speech Coding Modes ................. 6
Table 3-2 MOS of Different Speech Coding Algorithms ........................................................ 7
Table 3-3 Impact of Radio Environment on MOS of Different Speech Coding Algorithms .... 8
Table 3-4 MOSs Acquired at Different Vehicle Speeds ...................................................... 12
Table 4-1 Possible Measures and the Verification Results ................................................. 14
Table 4-2 Parameters About the Speech Coding Modes of iBSCs ..................................... 20
Table 4-3 Recommended Values of the Dynamic HR Parameters of iBSCs....................... 22
Table 4-4 Average MOS Values and MOS Distributions of Some Vendors Networks........ 24
Table 4-5 Test Results of ZTEs Network in the Same Scenario (Downtown Area)............ 25
Table 4-6 Recommended Values of the PbgtHoStartThs Parameter .................................. 26
Table 4-7 MOS Values Before and After the TFO Function Was Enabled .......................... 28
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Table 4-8 Major Parameters Involved in the TFO Function ................................................ 28
Table 5-1 C/I Statistical Result (With the SAGEM MS) ....................................................... 37
Table 5-2 Result of the Indicator Comparison Before and After NTAS AUTO Is Properly
Adjusted ............................................................................................................................... 38
Table 6-1 Test Routes in Typical Scenarios ....................................................................... 39
Table 6-2 Networking and Version Information of ZTEs and NSNs Equipment................. 39
Table 6-3 Comparison Results Before and After the T3105 Parameter Is Modified ............ 41
Table 6-4 Comparison Results of DTs in Typical Scenarios of Three Networks ................. 44
Table 6-5 Dynamic HR Cells and Parameter Modification .................................................. 51
Table 6-6 DT Comparison Results of the UL RxLev Handover Threshold and Dynamic HRParameters Before and After Modification ............................................................................ 54
Table 6-7 DT Comparison Results Before and After the IRC Function Was Enabled for SDRBase Stations ....................................................................................................................... 59
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1 Overview
At present, the fundamental service of the GSM network is speech service. Nowadays,
the competition among the operators intensifies and the customers' requirements for the
speech service quality also increase. They will choose the operator on the basis of the
speech service quality, so it has become the focus of the operators. So gradually the
mobile operators begin to pay attention to construct a set of evaluation criteria on the
basis of the QoS requirements for the mobile network, which can be quoted in the
quantitative analysis and evaluation of the speech service quality.
The earliest evaluation criteria for speech quality are based onRxQual, however, in the
actual transmission process of the speech signals, many factors may affect the speech
quality. Therefore, the evaluation criteria based on RxQual or BER is insufficient andcannot fully reflect the end user's perception of the radio network. Now the industry
mainly uses the MOS test method to objectively evaluate the speech quality. In China,
China Mobile and China Unicom also begin to value the MOS values and have fixed the
related DT specifications and MOS value requirements.
In this article, the author collects the experience gained from the MOS tests performed in
the major projects of China and summarizes the encountered problems. Base on this, the
author finds out the major factors that may affect the field MOS values and methods to
enhance the DT MOS values, which can work as a guide for the test and enhancement of
MOS values in other projects and also can contribute to the experience library.
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2 Principles of MOS Test
2.1 Basic Concepts
The evaluation criteria for speech service quality can be divided into subject evaluation
and objective evaluation. In the early time, people judge the speech quality by listening to
phone calls and thus the conclusion is very subjective. The ITU has established the
evaluation criteria for this subject judging method, that is, MOS. MOS is a subjective
evaluation method. During the test, a number of listeners of different genders, ages, and
native languages will be selected within a wide hearing range and they will rate the heard
speech quality of the received phone calls from 1.0 to 5.0, so as to judge the speech
quality.
Table 2-1 MOS Value
Level MOS ValueUser's Satisfaction
Degree
Excellent 5.0Excellent. The speech isvery clear without distortionor delay.
Good 4.0Good. The speech is clearwith a little delay and a fewnoises.
Fair 3.0
Fair. People cannot hearvery clearly. There aredelay, noises, anddistortion.
Poor 2.0
Poor. People cannot hearclearly. There are loudnoises or interruptions. Thedistortion is serious.
Bad 1.0Bad. The call is mute orcannot be understood. The
noises are loud.
Obviously, in real life, it is very difficult to select a group of people and make them answer
phone calls and assess the speech quality, and the cost is high. Meanwhile, it is also very
hard for the operators to trace the speech quality in a long run. Therefore, ITU did much
standardization work to assess the end-to-end speech quality objectively and overcome
the subjective limitation of MOS. Nowadays, the engineers can use objective quantitative
algorithms to evaluate the speech quality and calculate the corresponding level.
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2.2 MOS Test Principles
At present, ITU recommends using PESQ to measure the end-to-end speech quality.
PESQ considers factors that may affect speech perception, like coding and decodingdistortion, error, packet loss, delay, and jitter, and it can evaluate the speech signal
quality objectively. Therefore, PESQ is also called the indicator of clarity and is an
objective evaluation indicator for speech quality. First, speech signals are transmitted
from one end to the other end of the network. Then PESQ analyzes the speech signals
sample-by-sample after an alignment of corresponding reference and test signals and
calculates the speech quality. PESQ is an auditory-model-based speech evaluation
method and can present a relatively objective evaluation of the speech quality.Figure 2-1
illustrates the detailed test principles.
Figure 2-1 Test principles of PESQ
The PESQ score is within the range of 0.5 (lowest) to 4.5 (highest). It is used to
compare the received signals with the transmitted signals and calculates the differences.
Generally, the more the output signals and reference signals differ, the lower the PESQ
score is. PESQ_LQ is an expansion of PESQ, and the output range is between 1.0 and
4.5. This new range is a MOS-like score, which is close to the subjective perception of
the user. In P862.1 of ITU, the mapping function between PESQ and PESQ_LQ is
specified. In China, all MOS tests of China Unicom and most MOS tests of China Mobile
should export the PESQ_LQ value.
The test equipment includes the Pilot Pioneer, NTAS AUTO, and FlyWrieLess. Their
using methods are almost the same.
In MOS DT tests, usually two test mobile stations (MSs) and one MOS speech box are
required. Note: SAGEM OT498 and Nokia N85 are recommended for Pilot Pioneer,
Nokia6720 is recommended for NTAS AUTO, and SAGEM OT498 is recommended for
FlyWrieLess. The MSs are set to make speech calls to each other, and the dialing,
answering, and on-hook are set in automatic mode.Figure 2-2The PESQ score is within
the range of0.5 (lowest) to 4.5 (highest). It is used to compare the received signals with
the transmitted signals and calculates the differences. Generally, the more the output
signals and reference signals differ, the lower the PESQ score is. PESQ_LQ is an
expansion of PESQ, and the output range is between 1.0 and 4.5. This new range is a
MOS-like score, which is close to the subjective perception of the user. In P862.1 of ITU,
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the mapping function between PESQ and PESQ_LQ is specified. In China, all MOS tests
of China Unicom and most MOS tests of China Mobile should export the PESQ_LQ
value.
illustrates the principles of the MOS test.
Figure 2-2 MOS Test Principles
The basic test flow is as follows:
1. The test device and the MSs are connected, and the calling parameter and
templates are set in the MOS test system. Then MS A begins to call MS B.
2. After the call is setup, a standard reference speech sample will be built on the PC
and sent to MS A through the MOS speech box. MS A begins to send this reference
speech sample to MS B. The speech sample is usually 8 s long. In the whole set of
DT test device, the MOS speech box works as a converter of audio signals. Thestandard speech card inside the box converts the audio signal format and the box
will not grade the speech with PESQ.
3. After receiving the speech sample, MS B sends the sample to the MOS speech box,
which converts the audio format and sends it to the PC.
4. The MOS test system compares the speech sample received by MS B and sent by
MS A with PESQ, grades the received sample, and exports PESQ and PESQ_LQ.
5. In the next 8 s, MS B sends a reference speech sample to MS A, and Step 2 to 4 will
be repeated. According to the setting, the test MSs send and receive the test
Audio Cable AudioCable
Data Cable
DataCable
USB Cable
SpeechSampleReceived Speech Signals
MOS Test Software
MOS Speech Box(Plastic Shell)
MSA
MSB
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speech in turns, and one PESQ score and one PESQ_LQ score will be exported
every 8 s till the end.
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3 Major Factors Affecting Field MOSs
According to the MOS tests we have already performed, in a normally operated radio
network without problems like weak coverage or frequency interference, four factors may
lead to low MOSs or most MOSs lower than three. These four factors are whether
functions like TFO, IRC, and handover command optimization that can improve speech
quality are activated, occupancy status of speech coding (like EFR, HR, AMR_HR),
handover frequency, and speed of the test vehicle.
3.1 Impact of Handover
Handover is one of the most fundamental features of the GSM network. Because thehandover happen in GSM is hard handover, an interruption to the speech service when
the MS is handed from the old channel to the new one is unavoidable. Meanwhile, the
necessary FACCH signaling interaction between the BTS and the MS during the
handover will also occupy the TCH speech frames, and the MOS will be impacted and
will decrease. In DT, the engineers may encounter frequent handovers within a short
period. In this case, consecutive low MOSs will be exported. From this, we can see too
many or frequent handovers will greatly impact the MOSs.
The engineers learn from the DT results obtained from some Chinese projects that
handover is the most prominent factor affecting MOS. In some Chinese projects with
favorable radio environment and activated TFO function, the MOS values acquired whenhandovers happen are low, as listed in the table below.
Table 3-1 Impact of Handover on MOSs Under Different Speech Coding Modes
Speech CodingMode
ChannelMode
MOS (OneHandover)
MOS (TwoHandovers)
EFR Full rate 3.58 2.95
HR Half rate 2.96 2.79
In EFR coding mode with TFO activated, the MOS can be 4.25 ideally. If one
handover happens, the MOS will be decreased by 0.6 to 0.7 or even worse if the
speech data is being transmitted when the handover happens. If two handovers
happen when the speech sample is transmitted (both originating and terminating),
the acquired MOS may be lower than three.
In HR coding mode, the acquired MOS is low even under ideal conditions and about
three. If one handover happens, the acquired MOS can be lower than three.
Compared to the impact of successful handovers, the impact of handover failure is more
severe. Because the MS will reconnect the original channel if the handover fails, and the
time consumption equals a successful handover. Therefore, the interruption period of
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speech service occurred during a failed handover is longer than that occurred during a
successful handover and the acquired MOSs are low.
3.2 Impact of Speech Coding Algorithm
In the GSM network, there are five speech coding algorithms. Three are full rate speed,
which are FR, EFR, and AMR_FR; and two are half rate speed, which are HR and
AMR-HR. Because different coding modes have different data compressing styles and
source compression rates, the speeches may be distorted in different degrees. Even in
the same radio environment, the acquired MOSs of different source coding modes and
channel coding modes differ greatly. As to the projects of Chinese operators, FR, EFR,
and HR are the most commonly used speech coding algorithms, especially EFR and HR.
For these three speech coding modes, the source compression modes and the mean
MOS acquired in CQT with favorable radio environment are listed in the table below.
Note: The values listed in the table below are acquired with TFO inactivated and the AMR
tests are performed in the lab so the acquired MOSs are higher than these acquired in
the field tests.
Table 3-2 MOS of Different Speech Coding Algorithms
SpeechCodingMode
ChannelMode
Source CompressionAlgorithm
Speech Rate PESQ LQ
FR Full rate RTE-LTP 13 kbps 3.7*
EFR Full rate ACELP 12.2 kbps 4.17HR Half rate VCELP 5.6 kbps 3.5
AMR Full rate 12.2 kbps 4.17
AMR Full rate 10.2 kbps 4.08
AMRFullrate/halfrate
7.95 kbps 3.98
AMRFullrate/halfrate
7.4 kbps 3.96
AMR
Full
rate/halfrate
6.7 kbps 3.84
AMRFullrate/halfrate
5.9 kbps 3.76
AMRFullrate/halfrate
5.15 kbps 3.59
AMRFullrate/halfrate
4.75 kbps 3.49
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When the TFO function is inactivated, the mean PESQ_LQ value of EFR acquired in
favorable radio environment can be around 4.1 and that of HR can only be around 3.4.
Besides, the anti-interference capability of HR is worse than that of EFR. When
interference exists in the network, HR PESQ may be lower than three. When AMR_HR is
used, the maximum MOS value of single-rate (from 7.95 kbps to 5.9 kbps) is higher than
that of HR. Therefore, it is recommended to activate AMR_HR in the half rate scenario
and to activate EFR in the full rate scenario so as to enhance the MOSs. If the field
version does not support TFO + AMR, the engineers can activate single rate for
AMR_HR. And 7.4 kbps is recommended for the network with good quality and 6.7 kbps
is recommended for the network with poor quality.
In addition, during the handover, the old and new channels will simultaneously send the
speech signals in advance. However, this rule only works for the handover of the same
speech coding algorithm. For HR-FR handover, the speech signals cannot be sent in
advance. Therefore, the interruption period occurred during the EFR-HR handover is
longer than that occurred during the EFR-EFR handover, and the acquired MOSs are
low.
To sum up, the EFR speech coding algorithm is recommended in the field. As to cells
encountering high traffic volume and congestion in busy hours, the engineers can
activate the dynamic HR function, set the HR threshold on the basis of the actual traffic
volume, and activate AMR_HR to improve MOSs.
3.3 Impact of Radio Environment
A favorable radio environment is the guarantee for radio communication. In network withpoor quality, the corresponding speech quality and MOSs will also be poor. Through the
field tests, the engineers found:
When C/I > 13 or RXQUAL < 4, the impact to DL PESQ is small. The impact of
individual RQ problem on MOS is small.
When 10 < C/I < 13 or 4 < RXQUAL < 5, the DL PESQ may be impacted and is
greatly related to the RXQUAL value acquired during the transmission of the test
speech sample.
When C/I < 4 or RXQUAL 6, the DL PESQ decreases greatly.
The following table lists the MOS values of EFR and HR under different C/Is. Note: The
TFO function is activated, and the analysis data is from the MOS tests of the Chinese
projects.
Table 3-3 Impact of Radio Environment on MOS of Different Speech Coding Algorithms
Speech CodingAlgorithm
C/I < 9 9 < C/I < 12 12 < C/I < 20 C/I > 20
EFR 3.03 3.21 4.06 4.25
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Speech CodingAlgorithm
C/I < 9 9 < C/I < 12 12 < C/I < 20 C/I > 20
HR 2.78 2.98 3.23 3.55
Generally, for the radio environment problems on site, the engineers should pay attention
to the following issues:
Co-BCCH or neighbor-BCCH problems caused by improper frequency planning,
which may lead to deterioration of UL and DL RQs
Weak coverage problem, which may lead to low C/I when the DL RXLev is lower
than85 dBm and further leads to the decreasing of RQ
Overshooting problem, which may lead to co-BCCH or neighbor-BCCH and the
isolated island effect and may severely impact RQ
Figure 3-1 shows a typical case of DL RQ deterioration. When DL RxQual was 7, the
MOS value of the speech sample deteriorated greatly and even reached 1.00, an invalid
score.
Figure 3-1 Consecutive Low MOSs and Call Drops Caused by Consecutive High BitError Rates and Error Frames
3.4 TFO Function
The TFO function can help to avoid the speech from been encoded or decoded twice
during the MS-MS (GSM) call, MS-UE (GSM/3G) call, and UE-UE (3G) call. During the
UE-UE call, the speech signals are first encoded in the originating UE and sent to the air
interface, which are further decoded into 64 kbps PCM signals of G.711 A-law or -law by
the local transcoder. Then the PCM signals are encoded by the peer transcoder again
and transmitted to the peer UE through the air interface. After receives the speech
signals, the peer UE decodes them and reconstruct the speech data. Figure 3-2 shows
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the whole call flow. In this configuration, the two transcoders are at the Tandem
Operation status. The speech signals are encoded and decoded twice, which leads to the
deterioration of speech signal quality, especially in the low-rate scenario.
Figure 3-2 Transcoding Function with TFO Inactivated
If the local UE and peer UE use the same speech coder, the speech signals can betransparently transmitted from the local UE to the peer UE without activating the local and
peer transcoders. This is called the TFO.
Figure 3-3 Transcoding Function Bypassed With TFO Activated
Transcoding
Function
Transcoding
Function
Transcoding Functions Bypassed
MS/UEMS/UE
PLMN A PLMN B
En c o din g Deco d in g Compressed Speech
The activation of TFO helps to avoid the Tandem Operation, and thus relieves the
deterioration of speech signal quality and effectively improves the speech quality and the
MOS. Besides, the TFO function also has the following advantages:
The speech compression coding rate in PLMN is only 16 kbps or 8 kbps. With TFO,
the coding rate can be multiplexed and the transmission links are saved. Note: The
64 kbps PCM signals are transmitted to facilitate the speedy seamless handover.
The transcoding function is bypassed, which saves the processing capability and
reduces the end-to-end transmission delay.
Note:
With TFO activated, the engineers only have to activate the decoding function to facilitate
the seamless handover.
MS/UEMS/UE
PLMN A PLMN BTranscoding
Encoding Decoding DecodingEncod ingCompressed Speech Compressed SpeechITU-T G.711 A-Law/ -Law
Transcoding Functions
TranscodingFunction
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For intra-BSC communications, activation of the TFO function can save twice transcoding
for the speech signals no matter the transcoder is installed within the BSC or remotely
and can improve the MOSs.
For inter-BSC communications, the engineers must confirm whether the CN supports
TFO before activating the TFO function.
3.5 Impact of CN Signaling Flow
In ZTE CN, after the MSs are connected, the CN sends Status Enquiry to query the
MSs' status and the MSs returnStatus.Altogether four extra pieces of FACCH signaling
will be sent at the air interface and will steal four TCH speech frames. Therefore, the first
MOS acquired after the MSs are connected is lower than the normal value. The field test
data also shows that the first MOS value is usually around three.
Figure 3-4 Signaling of the Originating MS
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Figure 3-5 Signaling of the Terminating MS
As to the MOS test performed by Chinese operators, the short call mode is adopted and
each call is only 90 s long. Only 11 MOSs can be exported during each call. Therefore,
this signaling flow of the CN will compromise the first acquired MOS value, which may
further influence the mean MOS value.
3.6 Impact of Test Vehicle Speed
Vehicle speed may affect the MOSs greatly. When the speed is high, the possibility that
the MOS is acquired when handover happens is high, which may further affect the mean
MOS and the distribution proportion. The following table lists the mean MOS and the
MOS distribution acquired under different vehicle speeds.
Table 3-4 MOSs Acquired at Different Vehicle Speeds
30 km/h (Vehicle Speed) 60 km/h (Vehicle Speed)
MOS sampling number 323 293Mean MOS 3.75 3.59
Proportion of MOS 3 92.25% 83.62%
MOS samplingnumber/Handover times(including intra-cellhandovers)
3.02 2.40
Handover frequency =Handover times (includingintra-cell handovers)/MOSsampling number
0.33 0.42
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Therefore, it is recommended to keep the vehicle speed under 40 km/h in the urban area.
And China Mobile and China Unicom have made no specific requirements on test vehicle
speed.
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4 Three Measures for Field Engineers to
Improve the MOSAccording to the MOS-related problems discovered during the previous field tests, this
chapter analyzes the factors that may affect the MOS and combines experimental tests
with field tests. At the same time, it puts forward several major measures to improve the
field DT MOS on the basis of the experiences gained through the previous field tests and
research findings on special topics. These measures mainly fall into three categories:
enabling system functions, optimizing radio parameters, and optimizing radio
environments.
Table 4-1 lists some measures and the verification results for reference.
Table 4-1 Possible Measures and the Verification Results
PossibleMeasures
Description
VersionImplementationMethod
EffectsSupportingthe Function
or not
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PossibleMeasures
Description
VersionImplementationMethod
EffectsSupportingthe Function
or notFunctions
1
SimultaneousDL
transmissionandadvancedconnection forE1Ahandover
During thehandover, for thesame speechalgorithm,speeches aretransmittedsimultaneously on
the DLs of both thesource channeland target channel.For differentalgorithms, afterthe handover isdetected,speeches will besent to the targetcell. Thereby, thespeech interruptionwill be shorter andthe MOS can be
improved.
iBSC: V6.20seriesBSC V2:V2.97 series
Version
This measureworks only whenthe speech versionsbefore and after thehandover are thesame. (If AMR isused, the rate setsshould also be thesame.) With thismeasure, the MOScan be improvedobviously.
Currently, all theversions in theexisting networksupport thisfunction.For different speechversions before andafter the handover,if extra coding ordecoding is neededfor simultaneoustransmission,because the DSP
load may beaffected greatly,simultaneoustransmission is notenabled in thiscase.
2
Optimization ofthe EFRcoding
scheme
The codingscheme isimproved and theMOS of EFRspeeches can beimproved by 0.1.
All Version
The improvement isobvious and all thecurrent versionssupport thisfunction. Thepreferred full-ratespeech versionshould be set toFull-rate version 2on the BSC.
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PossibleMeasures
Description
VersionImplementationMethod
EffectsSupportingthe Function
or not
3
Optimization oftheinitialMSpowerafterhandover
The initial MSpower afterhandover isimproved. ForPBGT handover,the initial power ofthe MS on thetarget channel willbe equal to thepower on theoriginal channel.
V6.20 series Switch
For the early plasticspeech boxes, theMOS can beimproved. However,the current speechboxes are wellshielded, so thismeasure hardly hasany impact on theMOS.
4
Omission ofoptionalparameters inhandovercommands
Unnecessaryoptionalparameters (suchas the cipheringfield,synchronizationindication, and
AMR multi-rateparameter) areomitted from thehandovercommands. For the
SAGEM cellphone, the MOScan be improvedby 0.2.
V614CP005 Switch
The probability of
sending handovercommands insegments isdecreased, which isgood to the MOS.Especially, when Bit5 is set to 1in afrequency-hoppingnetwork (forV614CP005 andlater versions), theMALIST dynamicdecoding will beenabled, which cangreatly reduce thenumber of bytesoccupied by theMALIST.
5
Optimization ofUL BTS
decodingcapability (IRC)
The BTS decodingcapability isimproved toenhance theresistance tointerference. Thismeasure can
improve the MOSwhen there is ULinterference.However, it cannotimprove the MOS ifthe radioenvironment isgood.
BTS V2:V5.96.523band laterversionsBTS V3:V6.20.102e
and laterversionsSDR: all. Theswitch shouldbe manuallyturned on onthe OMCB.
SDR:switch
The MOS is
improved undercertain conditions.
BTS V2and V3:version
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PossibleMeasures
Description
VersionImplementationMethod
EffectsSupportingthe Function
or not
6TFOfunction
The number ofspeech coding anddecoding times isreduced by oneand the MOS canbe improved by0.2.
SeeAppAVersionRequirements for the
AMR + TROFunction forversions thatsupport thisfunction.
Switch
The average MOSvalue and MOSdistribution areimproved obviously.
7AHSspeechversion
Compared with the
traditional HRalgorithm, AHS canimprove the MOSof half rates by 0.3.
SeeAppAVersionRequirement
s for theAMR + TROFunction forversions thatsupport thisfunction.
Switch
The MOSdistribution is
improved obviously.It is recommendedto use the singlerate 6.7 Kbps or 7.4Kbps.
8
Processing ofthePHYSICALINFOR
MATIONmessages bythe DBB
The PHYSICALINFORMATIONmessages areprocessed by theDBB and the totalduration of a
handover isshortened by about20 ms. However, ithas little impact onthe MOSimprovement.
SDR: V4.09seriesBTS V3:V6.20.200mand later
versionsBTS V2:V5.96.520Aand laterversions
Version
The total handoverduration can bereduced, but the
MOS cannot beimproved obviously.
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PossibleMeasures
Description
VersionImplementationMethod
EffectsSupportingthe Function
or notParameters
1
Optimization oftheT3105parameter
For cells with goodradioenvironments, theengineers canconsider raisingthe T3105parameter toreduce the numberof times that thePHYSICALINFORMATIONmessages are
delivered. For cellswith bad radioenvironments, theengineers canconsider lowering itto make MSsreceive thePHYSICALINFORMATIONmessages as earlyas possible andreduce thehandover duration.
All
Parameter
settingon theOMC
Compared with 6, 8can reduce thenumber of times ofdelivering thePHYSICALINFORMATIONmessage by oneand thereby reducethe number ofFACCH framestealing times byone, but the MOScannot be improvedobviously.
2
Optimization ofthedynamichalf-ratethreshold
For light-trafficcells, the engineerscan raise thedynamic HRswitching thresholdand avoid usingEFR speeches toimprove the MOS.
iBSC: allBSC V2: Thedynamic HRisrecommended.
Parametersettingon theOMC
Because the HRtraffic proportion isreduced, theaverage MOS valueand the MOSdistribution areobviously improved.
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PossibleMeasures
Description
VersionImplementationMethod
EffectsSupportingthe Function
or not
3
Optimization ofhandov
er-relatedparameters
The purpose is toreduce the numberof handovers(including900M/1800Mpingponghandovers). Theadjustedparameters are:1. 1800M ULreceive levelthreshold (the
HoUlLevThsparameter):changed from 13to6or 82. 1800M PBGThandoverthreshold: changedfrom 53to 353. RxQual marginof neighbor cellsfor 1800M-to-900Mhandovers:increased to 32
iBSC: all theV6.20 seriesThe BSC V2does not
support thePBGThandoverthresholdparameter.
Parameter
settingon theOMC
Because thenumber ofhandovers isreduced, theaverage MOS valueand MOSdistribution areimproved obviously.
Radioenvironments
1
Coverageoptimization
Weak coverage,overshooting, andoverlappedcoverage
All
Analysisandadjustmentbasedon thetest data
There is obviousimprovement forsingle problematicspots.
2RQoptimization
Consecutive poorRxQual (RQ5 orpoorer)
All
Analysisandadjustmentbased
on thetest data
There is obviousimprovement forsingle problematicspots.
Note:
Because the MOS is only one of the numerous field test indicators, the following
adjustment work to optimize the MOS should be conducted gingerly, so as to avoid
negative effects on other important test indicators such as the CSSR, CDR, and HOSR.
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It is recommended to use the Standard Template of Data Collection for MOS Tests (see
AppB Standard Template of Data Collection for MOS Tests during the MOS test and
optimization to record the test data, so as to facilitate the comparison and analysis of the
major factors affecting the MOS and facilitate the troubleshooting by the rear support
engineers.
4.1 Optimization of the Coding Modes and HR TrafficProportions
4.1.1 Optimization of the Speech Coding Modes
Because different coding modes have different data compressing styles, the speeches
may be distorted in different degrees. Usually, the average MOS values of variousspeech coding schemes are as follows: EFR> AMR_FR > AMR_HR > FR > HR.
For FR speech versions, the MOS of ERF is much better than that of FR. Therefore, if
possible, we recommend that the field engineers should set the default values of FR
speech versions to EFRand set those of HR speech versions to AMR_HR.
Table 4-2 Parameters About the Speech Coding Modes of iBSCs
Parameter Name
ParameterCode
ValueRange
and Unit
DefaultValue
Recommended
Value
Description
Preferredspeech
version(half)
PreferSpee
chVer H
Notspecifythepreferredversion,
Half-rateversion 1,andHalf-rateversion 3
Notspecifythe
preferredversion
Half-rate
version 3
Please note thatbecause some clonedcell phones in Chinahave some bugs,when the AMR(including AMR_HR)coding modes areused, there may beassignment failures orhandover failures.Therefore, theengineers should
confirm this operationwith the operatorbefore choosingHalf-rate version 3for Chinas networks.It is unnecessary toconfirm it withoverseas operatorsbecause there are nosuch problems withoverseas networks.
Preferred
speech
PreferSpeeNot
specify
Not
specify
Full-rateBecause full-rate
version 2 (EFR)
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Parameter Name
ParameterCode
ValueRange
and Unit
DefaultValue
RecommendedValue
Description
version
(full)
chVer F the
preferredversion,Full-rateversion 1,Full-rateversion 2,andFull-rateversion 3
the
preferredversion
version 2 provides the best
speech quality. It isrecommended tochoose Full-rateversion 2.
In some fields, it is required to choose AMR-FR. However, generally speaking, most
MOS values of the coding modes provided by AMR-FR are smaller than those provided
by EFR: The MOS value of the highest rate 12.2 Kbps provided by AMR-FR is equal tothat provided by EFR, but the MOS values of the other seven rates provided by AMR-FR
are smaller than those provided by EFR. Therefore, for the scenarios where there are
high demands on the MOS values, such as the VIP areas and MOS test areas, the
coding modes of EFR rather than AMR-FR are recommended.
The MOS values of AMR_HR coding modes are much greater than those of ordinary HR
coding modes. In a network in which the HR traffic takes up a large proportion, AMR_HR
can improve the MOS obviously. Single rates are recommended, such as 6.7 Kbps (for
ordinary radio network environments) or 7.4 Kbps (for good radio network environments),
to improve the average MOS value and MOS distribution obviously. For example, after a
domestic site was changed in this manner, the proportion of MOS values greater thanthree increased by 2%.
Currently, for iBSCs, Half-rate version 3 is recommended for the PreferSpeechVer H
parameter and Full-rate version 2 is recommended for the PreferSpeechVer F
parameter. For AMR_HR, single rates are recommended, such as 6.7 Kbps or 7.4 Kbps.
4.1.2 Optimization of the HR Traffic Proportions
The dynamic HR function can effectively increase the system capacity and improve the
system connection rate. However, because the MOS values of HR coding modes arequite small, excessive use may have a very obvious negative impact on the average
MOS test value and the proportion of MOS values smaller than three.
Therefore, the use of half rates should conform to the following principles:
For iBSCs, use dynamic half rates and avoid using static half rates.
On the premise that the capacity can satisfy the service demand (not causing
congestion), avoid using half rates.
The common methods to reduce the use of half rates mainly include the following ones:
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1. Raise the dynamic HR switch threshold according to the actual traffic of the cell.
The relevant dynamic HR parameters on site mainly include BSC-level and
cell-level dynamic HR switches and HR switch thresholds. Currently, the default
values of the BSC-level and cell-level HR switch thresholds are 60%. For most of
the normal-traffic cells, this value is too low and may cause over-high HR traffic
proportions.
Table 4-3 shows the recommended values of the dynamic HR parameters.
Table 4-3 Recommended Values of the Dynamic HR Parameters of iBSCs
Paramet
er Name
Paramet
er CodeLevel
ValueRange
and Unit
Defaul
t ValueRecommended Value
DynamicHRsupportindication
DynaHREnable
BSC Yes/No No Yes
Threshold for FRto HR
HRThs BSC0~100, %()
60
80% or a greater value isrecommended for theBSC-level HRThs, so that thedemands of normal-trafficcells can be satisfied. Forheavy-traffic cells withcongestion, the cell-levelHRThs can be set separately.
Threshold of AMRHR
AmrHRThs
BSC1~100, %()
50
Dynamic AMR switches arepreferred. The thresholdshould not be lower than thethreshold of the dynamic HR,and it will not take effectunless AMR is enabled. It isrecommended that thisthreshold should be slightlylower than the HRThs, forexample, 78%.
DynamicHRsupportindication
DynaHREnable
Cell Yes/No No
This function should beenabled for heavy-traffic cellsthat have large trafficvolumes per channel andmay have congestion.
Use celldynamicHRparameter
UseCellDynHRPara
Cell Yes/No No
If this parameter is used, theengineers can set the HRswitch threshold more flexiblyaccording to the actual trafficvolume per channel and thecongestion rate of the cell.
Threshol HRThs Cell 1~100, %( 60 The cell-level HRThs should
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Parameter Name
Parameter Code
LevelValueRange
and Unit
Default Value
Recommended Value
d for TRXswitchedfrom FRto HR
) be set prudently according tothe traffic volume perchannel, congestion rate,and HR traffic proportion ofthe cell and should not affectthe cell congestion rate. Forcells with slight congestion, itis recommended that thecell-level HRThs should beset to 80% or a greater value,so as to reduce the HR traffic
proportion.
Threshold of AMRHR
AmrHRThs
Cell1~100, %()
50
Dynamic AMR switches arepreferred. The thresholdshould not be lower than thethreshold of the dynamic HR,and it will not take effectunless AMR is enabled. It isrecommended that thisthreshold should be slightlylower than the HRThs, forexample, 78%.
HRchannelpercentagethreshold
HRTsPercentage
Cell1~100, %()
50
The greater the value of this
parameter is, the higher thepercentage of available HRresources is. It isrecommended to set it to10%~20% on the premisethat there is no congestion.
2. Reduce the use of half rates by means of traffic balancing.
For heavy-traffic cells with high HR traffic proportions, the engineers can shift some
traffic to the surrounding cells through traffic balancing, thereby reducing the traffic
and HR use of the local cells.
The means of traffic balancing mainly include the following ones:
Set the cell selection parameter RxLevAccessMin and the cell reselection
parameters CROand PTto reduce the idle service coverage of busy cells.
Set the PBGT switch threshold to let some service handed over from busy cells
to the surrounding cells.
For a dual-band network, if there is obvious congestion in 900M cells but the
traffic of 1800M cells is not heavy, the engineers can enable the macro-micro
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handover (MacroMicroHo) algorithm and traffic handover (TrafficHO) algorithm
to balance the cell traffic and reduce the traffic of 900M cells.
Adjust the antenna downtilts, antenna azimuths, or carrier transmission power
of busy cells to reduce the actual coverage ranges and the traffic of the serving
cells.
4.2 Optimization of the Number of Handovers in theDT
Excessive handovers during the DT may affect the MOS test result. Therefore,
unnecessary handovers should be avoided, so as to improve the MOS.
Target of handover control: Handover frequency = Number of handovers (includingintra-cell handovers)/Number of MOS samples 0.45
Table 4-4 compares the average MOS values and MOS distributions of some vendors
networks.Table 4-4 Average MOS Values and MOS Distributions of Some VendorsNetworks
Typical Scenario
ZTE,Downtown Area,Test onMay 16
NSN,Downtown Area,Test onMay 17
ALU,DowntownArea (ChinaMobile), Test
on May 18
Average MOS(PESQ_LQ) Average MOS 3.57 3.66 3.47
Proportion ofMOS 3
Proportion of MOS 3 82.44% 84.63% 81.29%
Proportion ofeach speechversion
EFR 76.16% 77.04% 84.27%
HR 23.84% 22.96% 0.00%
AMR-FR 0.00% 0.00% 0.00%
AMR-HR 0.00% 0.00% 15.73%
Handover
frequency
Handover frequency =Number of handovers(including intra-cell
handovers)/Number ofMOS samples
0.60 0.45 1.09
Table 4-4 shows that the EFR traffic proportions of NSNs network and ZTEs network
were similar, but because NSNs handover frequency was smaller than ZTEs, NSNs
average MOS value and MOS distribution were better especially the proportion of
MOSs greater than three, which was 2% larger than ZTEs. As for ALUs network, though
AMR_HR was enabled and the EFR traffic proportion was the largest, because the
handover frequency was too great, ALUs average MOS value and MOS distribution were
the worst.
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Table 4-5 compares the test results of ZTEs network in the same scenario.Table 4-5Test Results of ZTEs Network in the Same Scenario(Downtown Area)
Typical Scenario
ZTE,
DowntownArea, Retest onMay 23
(Modifying theUL RxLevhandover
threshold andthe dynamic
HR parameterof some cells)
ZTE,Downtown Area,
Retest onMay 24
(Enablingthe IRC
function)
ZTE,Downtown
Area,Retest
on June3 (No
modification)
Average MOS(PESQ_LQ)
Average MOS 3.64 3.71 3.78
Proportion ofMOS 3 Proportion of MOS
3 83.32% 85.81% 90.42%
Proportion ofeach speechversion
EFR 82.00% 85.90% 82.27%
HR 18.00% 14.10% 17.73%
AMR-FR 0.00% 0.00% 0.00%
AMR-HR 0.00% 0.00% 0.00%
Handover
Handover frequency =Number of handovers(including intra-cellhandovers)/Number ofMOS samples
0.57 0.55 0.51
Table 4-5 shows that the EFR traffic proportions on the three days were similar, but
because the handover frequencies decreased, the average MOS values and MOS
distributions were improved obviously.
Currently, the following measures can be taken to avoid unnecessary handovers:
1. Check the handover parameter settings. The parameter-check function of the
CNO-G can be used.
Check the HoMarginPbgtparameters of neighbor cell pairs and ensure that
the sum of PBGT (A to B) and PBGT (B to A) is greater than 52 (56
recommended), so as to avoid pingpong handovers based on PBGT.
Check the cell reselection parameters CRO and PT of co-site cells in the
dual-band network and the inter-band HoMarginPBGTparameter (the PBGT
handover threshold) and ensure that they are all set properly, so as to avoid
unnecessary handovers: When an MS completes reselection in idle state and
initiates a call, it will immediately perform a handover to another cell of a
different band.
Check the relation between the minimum RxLev for A-to-B handovers and the
DL receive level threshold (the HoDlLevThs parameter) of Cell B. The
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HoDlLevThs parameter of Cell B should be lower than or equal to the
minimum RxLev for A-to-B handovers. Otherwise, after an A-to-B handover is
completed, an outgoing handover from Cell B will be initiated immediately due
to an emergency DL-RxLev-triggered handover, which will increase the
number of extra handovers.
Check the relation between the A-to-B macro-micro handover threshold and
the HoDlLevThsparameter of Cell B. The HoDlLevThsparameter of Cell B
should be lower than the A-to-B macro-micro handover threshold, better with a
difference of 10 dB for protection. Otherwise, after an A-to-B macro-micro
handover is completed, an outgoing handover from Cell B will be initiated
immediately due to an emergency DL-RxLev-triggered handover, which will
increase the number of extra handovers.
2. Optimize handovers of the existing network.
Set the PbgtHoStartThsparameter (the PBGT handover threshold) to a reasonable
and small value, so as to avoid unnecessary handovers when the DL RxLevs are
very good. Table 4-6 lists the recommended values.Table 4-6 RecommendedValues of the PbgtHoStartThs Parameter
Parameter Name
Recommended Value
RemarksDenseUrbanArea
Ordinary
UrbanArea
Suburbs
Countrysideand
OpenArea
Expressway
PbgtHoStartThs
50 45 35 30 45
This parameter shouldbe set on the basis of acomprehensiveconsideration of thecoverage andinterference conditions.It should be set to avalue as small aspossible on the premisethat there is nointerference increasecaused by handover
delay, so as to avoidunnecessary handovers.
Note:
Some operators may request a coverage rate of RxLevs greater than 75 dBm in
dedicate mode. The engineers can communicate with the operator to persuade them that
the request is unreasonable because in dedicated mode, the speech quality assessment
requires a less strict demand on the coverage rate for example, RxLevs greater than
90 dBm and it can be changed to a request in idle mode. If the operator persists, the
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engineers should set the PBGT handover threshold to 40or a greater value (to reserve a
space of 5 dB or more).
Pay special attention to the test and optimization of main roads. Categorize the
cells that cover main roads as road-covering cells and separately adjust the
handover parameters for them. Optimize the handover parameters according
to the actual environment, so as to avoid frequent handovers.
For a 900M/1800M dual-band network, the engineers can use dual-layer
network setting for continuous coverage areas of the 1800M network and at
the same time disable 900M/1800M PGBT handovers, so as to avoid
unnecessary handovers. However, before disabling PBGT handovers, make
sure that the operation will not lead to network congestion or degradation of
call quality.
For a 900M/1800M dual-band network, the engineers can appropriately raise
the RxQual margin of neighbor cells for 1800M-to-900M handovers, for
example, setting it to 32 to make it 6 dB to 8 dB greater than the RxQual
margin of neighbor cells for 1800M-to-1800M handovers (usually 24~26), so
that there will be fewer handovers (first 1800M-to-900M RxQual-triggered
handovers and then 900M-to-1900M macro-micro handovers).
Check the UL receive level threshold (the HoUlLevThs parameter).Usually,
as long as the UL RxQual is good, avoid triggering forcible UL handovers, so
as to reduce pingpong handovers. The default value of the HoUlLevThs
parameter is 15 (95 dBm), which is too great and may cause excessive
UL-RxLev-triggered handovers. It is recommended to change it to 7 (104
dBm, to trigger emergency UL-RxLev-triggered handovers) for the 900M
network and to 6 (105 dBm, to trigger emergency UL-RxLev-triggered
handovers) for the 1800M network.
It is not recommended to disable emergency UL-RxLev-triggered handovers. A
field test showed that after emergency UL-RxLev-triggered handovers are
disabled, not only the call drop rate but also the distributions of the UL and DL
RQ values were affected.
For frequency-hopping networks, the engineers should check whether there
are intra-cell handovers caused by UL or DL interference. If there are, disable
this kind of handovers.
Check the cells whose TCH assignment requests (including handovers) are far
more than the TCH assignment requests (not including handovers). For
example, the former are over five times of the latter. This kind of cells may
have over-frequent handovers. The engineers should observe the
AdjacentCellHandoverMeasurement task on the OMC, especially the settings
of handover and reselection parameters.
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ParameterName
ParameterCode
DefaultValue
Recommended Value
enable supported by the BSC supports it, thesystem will change the algorithm to
perform the TFO.
AMRoptimizationmode
TFOControl_3
Don'tsupport
ACSvariations
NO. Usually, it is not recommended toenable the AMR function. Therefore, therecommended setting is Don't supportACS variations.
4.4 Use of Other Network Functions
4.4.1 Omission of Optional Parameters in Handover Commands
According to the protocol, the standard length of a handover command is 23 bytes. If a
handover command is longer than 23 bytes, it will be delivered in segments. As a result,
an extra frame (Frame I) will be transmitted through the UL FACCH over the Um interface
(see I (***) inFigure 4-1), and the MS will reply with an extra RRF on the UL. During a
handover, there will be a speech loss of 20 ms both on the UL and DL, as shown in
Figure 4-1.
Figure 4-1 Delivering a Handover Command in Segments (Green for the Layer-2Messages and Blue for the Layer-3 Messages)
Remarks:
To shorten the handover command, ZTE has designed an OldToNewctrlparameter on
the OMC. The engineers can set whether to let the handover command carry optional
fields and whether to optimize the frequency-hopping MALIST coding scheme.
The OldToNewctrlparameter controls the contents to be delivered during each outgoing
handover; the contents are in the Old BSS to New BSS information information
element of the HANDOVER REQUIRED message. Four items Synchronization
Indication, Cipher Mode Setting, Multi-Rate Configuration, and Frequency List are
controlled by the following high bits of the OldToNewCtrlsystem control parameter:
Bit 3: whether to transmit the multi-rate configuration information. 0:No; 1:Yes.
Bit 5: whether to fill the frequency-hopping parameter in FreqList structure. 0:No; 1:
Yes.
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Bit 6: whether to optimize the filling of the AMR multi-frequency configuration
parameter. 0:No; 1:Yes.
Bit 7: whether to optimize the filling of the ciphering information parameter. 0:No; 1:
Yes.
Bit 8: whether to optimize the synchronization information parameter. 0:No; 1:Yes.
The above optimization switches are compatible: They can take effect at the same time,
either for intra-BSC or inter-BSC handovers. The default value of the OldToNewctrl
parameter on the OMC is a decimalnumber,which corresponds to a binary number. For
example, 240 (a decimalnumber)= 11110000 (a binary number), which means that the
functions corresponding to Bits 5 to 8 are enabled.
The ciphering information can be omitted only during intra-BSC handovers.
Please note that during inter-BSC outgoing handovers, the peer BSC should send the
multi-rate configuration information in the handover request, so that the local BSC can
check the AMR parameter and decide whether to carry AMR to the peer BSC. In this
case, the switch deciding whether to transmit the multi-rate configuration information
must be turned on, that is, Bit 3 must be set to 1.
Bit 5 is quite important to the length of a handover command.
The MALIST code in the network is in the form of Cell Channel Description or Frequency
List After Time. Cell Channel Description has a fixed length of 17 bytes and currently it is
used by default, which may cause the handover command to exceed 23 bytes easily.Frequency List After Time is a length-variable field in TLV format (4~131 bytes). When
Frequency List After Time is adopted (Bit 5 is set to 1), the length of the handover
command will be obviously shorter. Therefore, it is recommended to set Bit 5 to 1.
Note:
Bit 5 is applicable to iBSC V6.20.614CP005 and later versions only.
4.4.2 IRC Function
The IRC function can suppress interference in scenarios of dense frequency reuse and
large traffic, improve the UL RxQual and MOS, and reduce the handovers due to poor UL
RxQual. Because the software versions of the BTS V2 and V3 have been designed with
this function, no switch is needed. For SDR base stations, the engineers should choose
whether to use IRC or not on the OMCB, and Use IRC is recommended, as shown in
Figure 4-2.
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Figure 4-2 Enabling the IRC Function of an SDR Base Station
For the MOS comparative test before and after the IRC function was enabled, see
Chapter6 Case Study.
4.4.3 Impact of the T3105 Parameter on the Number of Times That thePHYSICAL INFORMATION Message Is Delivered
The setting of the T3105parameter may affect the number of times that the PHYSICAL
INFORMATION message is delivered. Because the PHYSICAL INFORMATION
message is delivered through FACCH frame stealing over the Um interface, probably
there will be an extra speech loss of 20 ms during the handover when one more
PHYSICAL INFORMATIONmessage is delivered. As a result, the MOS may be affected
during the handover. A field test showed that when the T3105parameter was set to 6,
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basically the PHYSICAL INFORMATION message was delivered for three times, as
shown inFigure 4-3 .
Figure 4-3 Asynchronous Handover Signaling on the Um Interface (Blue for the Layer-3Messages and Green for the Layer-2 Messages)
A lab test showed that the period after the BTS delivered the first PHYSICAL
INFORMATIONmessage and before it received the SABM message from the MS was
120 ms. Therefore, it is recommended to set the T3105 parameter to 8, so that one
PHYSICAL INFORMATION message can be omitted. However, a comparative test
showed that after the modification, the MOS was not improved obviously.
For the MOS comparative test before and after the T3105parameter was changed from 6
to 8, see Chapter6 Case Study.
4.4.4 Processing of the PHYSICAL INFORMATION Messages by the DBB
The PHYSICAL INFORMATION messages are processed by the DBB and the total
duration of a handover is shortened by about 20 ms. However, it has little impact on the
MOS improvement.
This function can be used between BTS and SDR versions. And the applicable versions
are as follows:
SDR: V4.09 series
BTS V3: V6.20.200m and later versions
BTS V2: V5.96.520A and later versions
It is recommended that if conditions permit, the engineers should upgrade the base
stations to the above versions.
4.5 RQ Optimization of the Existing Network
Usually, the speech quality and MOS values in poor radio environments are poor. Internal
frequency interference may affect the signal quality and lead to frequent handovers,
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thereby affecting the MOS test results. Therefore, optimizing the radio environment and
improving the RQ indicator of the existing network are vital to the MOS improvement. In
particular, it is required to make thorough optimization and adjustments for the sections
where the RQ is poor during the DT.
Usually, RQ optimization should be considered from the following three aspects:
1. Handling of the poorest-RQ cells
On the basis of the performance statistics on the OMC, find the cells of the poorest
UL and DL RQ and handle them as follows:
For cells of which the RQ values from six through seven take up a large
proportion (for example, larger than 20%), it is recommended to check the cell
alarms first, so as to judge whether there is any alarm about the combiner,
splitter, TRX, power amplifier, transmission, TMA, or repeater. If there is any
alarm, handle the alarm first.
Check for internal interference and external interference. Observe the
carrier-level indicators of poor-RQ cells to find the carriers of the poorest RQ,
use the frequency planning software to judge whether there are obvious
problems with the planning of ARFCNs, BSICs, MAIOs, and HSNs, and
optimize the frequency parameters. Observe cell-level and carrier-level UL
interference band indicators to judge whether there is obvious external
interference. By optimizing ARFCNs and locating interference sources, solve
the problems of poor RQ caused by external interference.
Check whether the poor-RQ cells have obvious problems of overshooting or
weak coverage. The RMA tool or DT data can be used. For a weak-coverage
cell, it is recommended to check the setting of the carrier transmission power
parameter and the connections of the RF cables and antenna feeder system
and check whether there is any hidden trouble with the TRX and combiner. For
an overshooting cell, it is recommended to properly control the cell coverage
range by adjusting the cell transmission power and the antenna downtilt and
azimuth and conducting DTs.
Use the OMC performance data and RMA tool to check whether the cells have
obvious problems of UL-DL imbalance. For cells whose ULs or DLs are poor,
check whether the external TMAs and repeaters work normally, whether the
feeders, jumpers, antennas, and cables of the RF parts are connected
securely, and whether the carriers and CDU boards work normally step by
step.
2. Optimization for sections where the RQ is poor during the DT, which requires
special attention
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For sections where the RQ is poor (consecutively poorer than RQ5) during the
routine network test, analyze the DT data and the performance data and alarms on
the OMC, and then perform optimization as follows:
Analyze the test data and frequency planning data to judge whether the poor
RQ is caused by frequency interference and solve the problem of ARFCN
interference by optimizing the ARFCNs.
Analyze the test data to judge whether the poor RQ is caused by improper
coverage, such as overshooting and weak coverage. Adjust the antenna
downtilt, azimuth, and carrier transmission power to optimize the cell coverage
and ensure a stable serving cell.
Analyze the test data to judge whether the handover parameters and neighbor
cell parameters are properly set and whether the poor RQ is caused by
over-slow handover triggering speed or omission of better neighbor cells. Then
properly configure the neighbor cells and optimize the handover parameters to
improve the speech quality.
3. Handling of network interference
The overall RQ of a network is mainly related to the C/I level of a network. Usually,
the field engineers can adopt a proper frequency planning scheme or enable power
control and optimize power control parameters to reduce the overall network
interference and improve the RQ.
Replan the frequencies of the whole network to reduce the interference. The
automatic frequency planning tool based on MRs can help design more
reasonable and more accurate frequency planning schemes. If the frequency
reuse in the existing network is too dense and the frequency interference is
conspicuous, it is required to take this measure (if conditions permit).
Enable power control and optimize power control parameters to reduce the
interference and improve the RQ. Usually, this method is more effective for
networks with dense frequency reuse. In most cases, it is recommended to
enable the UL power control. For the DL power control, judge whether to
enable it according to actual conditions of the network interference. If the
interference is small and the DL RQ is good (Proportion of RQ0~3 > 98%),
probably the DL power control will have no obvious impact on the RQ
improvement.
4.6 Disabling of the Function of Sending StatusQuery Messages at the CN Side
The CN side will have a new switch in the later V9.10 series to control the status query
process. A lab test showed that after this process was cancelled, the first MOS value
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after the origination increased by 0.15 averagely. Therefore, it is recommended to
persuade the CN engineers to try to cancel this process, so that the relevant signaling
flow will not affect the first MOS value.
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5 General Care for the Use of Test
DevicesThe engineers use the test device properly and troubleshoot the problem during the DT,
which can guarantee that the MOS will not drop due to abnormal conditions of the test
device or human errors.
5.1 General Care for the Use of Pilot Pioneer
According to the experience gained and problems discovered during the previous field
tests, the basic DT flow and troubleshooting flow with Pilot Pioneer are as follows:
1. For the Pilot Pioneer device of the early version, the engineers should calibrate its
volume and waveform with the test portable computer, because the volume and
waveform can affect the MOS. The best calibration values in different computers are
various. After the calibration is completed, the engineers perform the frequency-lock
CQTs. If the average PESQ_LQ of the EFR algorithm is above 4.0, it indicates that
the device is calibrated to the best state.
2. Currently, it is unnecessary to calibrate most of the Pilot Pioneer devices.
3. It is necessary for the engineers to check the device cables and MS port before
performing the CQTs. They should check whether the connections between cables
and ports are poor. The typical feature of poor connections is that the MOS is
always 1.0. The engineers should pay attention to it.
4. The engineers should pay attention to the consecutive abnormal low MOSs in the
DT. In the normal network, it is abnormal that several consecutive MOSs are low.
With the DT device, the engineers can judge whether the handover frequently
happens or there are handover failures during the period of time. If yes, the
engineers should record the road sections, sites, and cell information and report
them to the RNO engineers. The RNO engineers should solve the problems by
adjusting network parameters or optimizing the network coverage.
5. If the MOSs of some cells or TRXs are low, the engineers should analyze the RQ of
the cell or TRX. They should judge whether the RQ affects the MOS. If yes, the
engineers should record the problematic cell and TRX information and report them
to the RNO engineers for troubleshooting interference and performing optimization
to solve the problem. If the RQ is good but the MOS is low, the engineers should
record the problematic cell, TRX information, and Abis interface signaling and report
them to the RNO engineers for further analysis and troubleshooting.
Besides, the C/I collected with the SAGEM testing MS has problems. The engineers
should pay attention to it when the C/I is collected in some fields.
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The engineers performed tests with the Nokia N85 MS (enabling and disabling the DL
DTX) for comparison in a certain home office. The proportions of C/I 12 dB were
99.22% (enabling the DL DTX) and 99.16% (disabling the DL DTX). There was only one
statistical result, no matter whether the MS occupied the BCCH TRX or TCH TRX.
The result of the test performed by the engineers with the SAGEM OT498 was worse
than that with the Nokia N85 MS. The proportions of C/I 12 dB for the placement tests
(enabling and disabling the DL DTX) are listed inTable 5-1 .
Table 5-1 C/I Statistical Result (With the SAGEM MS)
BCCH C/I (12 dB) TCH C/I (12 dB)
Test 1 (enabling DTX) 95.36% 85.49%
Test 2 (disabling DTX) 93.81% 54.92
5.2 General Care for the Use of NTAS AUTO
According to the experience gained and problems discovered during the previous field
tests, the engineers should perform adjustments when using NTAS AUTO.
1. The volume of the Nokia MS should be set to 9instead of 6.
2. For the MOS test setting, the engineers should not set 6 Recordto 10of the play
setting in the gain setting; instead, they should set 3 Recordto 12.
3. When performing the MOS test, the engineers should use the MOS box in which the
audio input and output are separated. The MOS box in which the audio input and
output are not separated should be replaced.
4. The test software version should be updated to the latest version.
5. It is recommended to use Nokia 6720 for the test.
6. There are four ports on the NTAS speech box. Port 1 and Port 2 are formed one pair
and Port 3 and Port 4 are formed the other pair. Those two pairs of ports are
independent. The engineers can check which pair of ports has problem by replacingthe ports.
7. During the CQT, the MOSs are always good and bad by turns. It is a very important
way to judge whether the audio cable has problem or the connection is loose,
especially for the speech box in which the audio input and output are separated.
If the engineers do not perform the setting on the basis of the above points, the following
problems may happen during the field test:
The MOSs fluctuate greatly. They are good and bad by turns
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The peak MOS is too low.
Sometimes, the MOS is 1.0, which is invalid.
In a same road section in China, the engineers compare the test result on the basis of the
above four points with that without the above four points and the comparison results are
listed in the following table. (Other indicators do not fluctuate.)
Table 5-2 Result of the Indicator Comparison Before and After NTAS AUTO Is ProperlyAdjusted
Peak MOS Average MOSProportion of MOS
3
NTAS AUTO is notcalibrated
reasonably
4.15 3.46 20.00%
NTAS AUTO iscalibratedreasonably
4.29 3.87 3.81%
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6 Case Study
6.1 Scenarios
Three typical DT scenarios are selected for the test. They are the main road, downtown
area, and expressway in the suburb. Select the areas which belong to ZTE and NSN
(they are the manufacturers in the existing network of Xian Unicom) respectively and
meet the requirement of scenarios for the DTs.Table 6-1 lists the routes in detail.
Table 6-1 Test Routes in Typical Scenarios
Manufacturer
Main Road Downtown Area Suburb
ZTE
Da Qing Road
(YuxiangGateWest SecondRing)
East FenggaoRoad-WestGuanzheng Street
West GateWestSecond Ring
West Third Ring
(Entrance of Xihu HighWayExit of Airport HighWay)
NSN
Tangyan Road
West SecondRingEastZhangba Road
Keji Road
(TangyanRoadHanguangRoad)
West Furong Road
Xiying RoadYannan No.4Road
The networking and version information in ZTEs and NSNs test areas are listed inTable
6-2.
Table 6-2 Networking and Version Information of ZTEs and NSNs Equipment
ZTE Networking and Version Information
Type and version of the CN ZTEs CN
BSC version V6.20.200F/V6.20.614Cp001
BTS versionBTSV2: V5.96.520ABTSV3: V6.20.200E
SDR: V47.00.3007P09
A interface (IPA or E1A) Optical port and E1. They are both E1A.
Abis interface (IPOverE1 or others) E1
BTS type (SDR, BTSV3, and BTSV2) BTSV2, BTSV3, and SDR
Speech version configuration anduse condition
EFR and HR
Whether TFO or TrFO is used TFO is used.
Whether the inter-MSC handover isperformed at the test spot
Yes
Whether the inter-BSC handover is Yes
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ZTE Networking and Version Information
performed at the test spot
NSN Networking and Version Information
Type and version of the CN ZTEs CN
BSS manufacturer and version Nokia-Siemens
Speech version configuration anduse condition
EFR and HR
Whether TFO or TrFO is used TFO is used
Network coverage area Downtown area
6.2 Test Methods and Devices
Pilot Pioneer and Nokia N85 are used in the test. The short call is used in the DT and thecall duration is 90 s. The call setup duration and call interval are both 20 s. In order to
make each DT result stable, the number of MOS samples collected in each scenario
should be about 300.
6.3 Test Results and Analysis
6.3.1 Comparison Results Before and After the T3105 Parameter WasOptimization
On May 16, the engineers performed a placement test for the first time. Meanwhile, the
engineers saved and recorded the handover signaling on the Um interface with a
SAGEM MS. They found that the MS received th