gsm rno subject-field mos optimization_r2.0

7/27/2019 GSM RNO Subject-Field MOS Optimization_R2.0

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Field MOS Optimization

R2.0


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Field MOS Optimization Internal Use Only

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ZTE Confidential Proprietary 2014 ZTE CORPORATION. All rights reserved. II

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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ZTE Confidential Proprietary 2014 ZTE CORPORATION. All rights reserved. III

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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ZTE Confidential Proprietary 2014 ZTE CORPORATION. All rights reserved. IV

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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ZTE Confidential Proprietary 2014 ZTE CORPORATION. All rights reserved. V

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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ZTE Confidential Proprietary 2014 ZTE CORPORATION. All rights reserved. VI

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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ZTE Confidential Proprietary 2014 ZTE CORPORATION. All rights reserved. VII

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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ZTE Confidential Proprietary 2014 ZTE CORPORATION. All rights reserved. 1

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


7.4 kbps 3.96

AMR

Full

rate/halfrate

6.7 kbps 3.84


5.9 kbps 3.76


5.15 kbps 3.59


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



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



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



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



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



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.
http://www.iciba.com/number/http://www.iciba.com/number/http://www.iciba.com/number/http://www.iciba.com/number/


39/77



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

gsm rno subject-field mos optimization_r2.0

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