Speech Quality and MOS

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

Security Level: Internal

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www.huawei.com

Speech Quality and MOS

Alex

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Agenda

• Introduction

• Measurement

• Evaluation

• Optimization


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MOS- Subjective Evaluation Way

MOS test is normally performed on a group of listeners. The listeners listen to the speech material in the same channel environment and give a score. The scores are then averaged to obtain the MOS score. The scores vary largely from listener to listener.





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MOS- Objective Evaluation Way

Objective way compares an original signal with a degraded signal and then outputs a MOS score. The MOS score is like the result of a subjective listening test.





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PESQ(P.862)

• PESQ value is from -0.5 to 4.5

• PESQ algorithm is powerful enough to test end-to-end speech quality.





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MOS-LQO(P.862.1)

• MOS-LQO (Listening Quality Objective) value is from 1.02 to 4.56





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PESQ-LQ Mapping

• This mapping is not adopted by ITU-T

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Agenda

• Introduction

• Measurement

• Evaluation

• Optimization

HUAWEI TECHNOLOGIES Co., Ltd. HUAWEI Confidential

Measurement –Nemo (MS to MS)

Nemo Audio Module: Sending Reference Sample

Nemo Audio Module : Receiving Impaired Sample

MOS Score


QVM-MOS Measurement

QVP-Data Analysis

Measurement –QVoice (MS to PSTN)


MS to PSTN Way

BTSBTS BSCBSC MSCMSC PSTNPSTNMSMS

Reference Sample Impaired Sample

Impaired Sample Reference Sample

Uplink MOSUplink MOS

Downlink MOSDownlink MOS

UL MOS score and DL MOS score is available. The configuration of Testing System is more complicated Required less MS when performing Benchmark

UL MOS score and DL MOS score is available. The configuration of Testing System is more complicated Required less MS when performing Benchmark


UL MOS score and DL MOS score is not available 。 MOS test by MS to MS way is more sensitive for Um interface Using Local switch or TFO can improve MOS (MS to MS way) 。

UL MOS score and DL MOS score is not available 。 MOS test by MS to MS way is more sensitive for Um interface Using Local switch or TFO can improve MOS (MS to MS way) 。

MS1MS1

BTSBTS

MSCMSC

BSCBSC

BSCBSC

BTSBTS

MS2MS2

Reference Sample UplinkUplink

Impaired Sample DownlinkDownlink

MS to MS Way

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Agenda

• Introduction

• Measurement

• Evaluation

• Optimization





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Common Report

Resul ts. l ogservi ce

performance report. rar

MOS

=Average[MOS(all samples)]





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QVoice Report

44 codectypeusage.RAR

Basic Report:

Advanced Report:

43-AMR.RAR

DL MOS = MOS_FR × FR% + MOS_HR × HR% + MOS_EFR × EFR% +

MOS_AFR × AFR% + MOS_AHR × AHR%

UL MOS = MOS_FR × FR% + MOS_HR × HR% + MOS_EFR × EFR% +

MOS_AFR × AFR% + MOS_AHR × AHR%

MOS = (DL_MOS + UL_MOS) / 2

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Agenda

• Introduction

• Measurement

• Evaluation

• Optimization





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Factors of MOS

RF performance （ RxLev, RxQual, C/I, HO,…)RF performance （ RxLev, RxQual, C/I, HO,…)

Transmission (Speech route ， Tran. quality…)Transmission (Speech route ， Tran. quality…)

BSS Features (Codec ， DTX, TFO, PC…) BSS Features (Codec ， DTX, TFO, PC…)

Hardware （ BTS/FTC version ， Fault…）Hardware （ BTS/FTC version ， Fault…）Factors of Factors of

MOS MOS

Consider comprehensively when analyzing MOS Consider comprehensively when analyzing MOS

Others （ FR/HR percentage…）Others （ FR/HR percentage…）

Test Method (Equipment, Testing mode,Speech Sample)Test Method (Equipment, Testing mode,Speech Sample)





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Equipment

Different equipment has different standard (PESQ is preferred)

Do not compare MOS value from different type of equipment.

Testing Mode

MS to MS

MS to PSTN

Speech Sample

Speech Sample should be the same for any compare.

English Speech Sample is preferred

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Test Method





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Um interface(1)

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SQI (Downlink Um)

Note ： SQI is not equal to MOS. SQI is just a factor that can affect MOSNote ： SQI is not equal to MOS. SQI is just a factor that can affect MOS





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Um Interface(2)

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Improve SQI

Uplink Um Quality

Can be evaluated by single user tracing or STS, normally Uplink Um interface should

be a bit better than downlink Um interface. If not, be aware of Uplink interference,

Uplink DTX, link balance.





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Features(1)

Feature Recommend Effect on MOS

Speech VersionActive AMR,

EFR

The descending speech quality of 5 types of Speech Version in GSM is as following:

AMR FR >= EFR > AMR HR >= FR > HR 。Active AMR and EFR will improve MOS remarkably.

UL or DL DTX ？DTX will introduce clipping which is bad for MOS. However, DTX can decrease interference which is good for Um interface.

UL and DL PC Open Power Control will decrease network interference.

Hopping OpenCaused by frequency diversity and interference equalization, FH is helpful for enhancing speech quality.

TFO OpenTFO can cut one encoding and decoding off a conversation , which is helpful for enhancing MOS in MS to MS way.

Local Switch Open

Allowing speech signal to bypass MSC and BSC, which also can cut one encoding and decoding time.

However, if TFO is activated, local switch can only save transmission resources.

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Feature(2)-Codec

AMR FR >= EFR > AMR HR >= FR > HR





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Transmission(1)

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Speech Signal Route

Evaluate how many times for encoding and decoding. There will be 0.2 MOS loss for one

more encoding and decoding.

MS to PSTN

Speech Signal Route ： MS- BTS-BSC-MSC-GMSC-PSTN

Be aware of transmission between MSC and GMSC:

If using IP transmission, NSS part will introduce one time encoding and decoding.

If using TDM transmission, no MOS loss

While performing MOS benchmark, if MS to PSTN test way is adopted, you

should consider the transmission differences between MSC and GMSC.

For example ： If networks all use AMR codec, the maximum MOS value in

network with IP backbone is 3.8 to 3.9, and maximum MOS value in network with

TDM can be 4.0-4.2.

While performing MOS benchmark, if MS to PSTN test way is adopted, you

should consider the transmission differences between MSC and GMSC.

For example ： If networks all use AMR codec, the maximum MOS value in

network with IP backbone is 3.8 to 3.9, and maximum MOS value in network with

TDM can be 4.0-4.2.





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Transmission(2)

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Speech Signal Route

MS to MS

Speech route ： MS-BTS-BSC-MSC-BSC-BTS-MSC

The speech will experience 2 times encoding and decoding.

But if TFO is adopted in the network, only one time encoding and decoding,

which can provide 0.2 MOS increase.

No TFO, 2 times encoding and

decoding

TFO, 1time encoding and decoding

Transmission Quality

Speech quality is also strongly related to transmission quality, especially for microwave

or satellite transmission type, which are more easily affected by weather (raining,

snowing…) and cause MOS degrading.





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Hardware

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For BSS part, BTS and TC can affect the speech quality.

Select the recommended software version.





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Others…

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FR/HR traffic distribution

Suppose score for AMR FR and AMR HR will not change, if the percentage of AFR

raise from 65% to 80%.....

MOS (3.3) = 3.5(AMR FR)* 65% + 3.0(AMR HR) * 35%

MOS (3.4) = 3.5(AMR FR)* 80% + 3.0(AMR HR) * 20%

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Speech Quality and MOS

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