Mean Opinion Score(MOS) KPI

Network Quality & Performance Division

“Monitoring the End User Quality of

Experience using the derivative Mean

Opinion Score (MOS) KPI”

Effect of transmission performance on Multimedia Quality of Service 17 - 19 June 2008 - Prague, Czech Republic

Paper Authors: Konstantinos Vlahodimitropoulos PhD, Evangelos Katsaros

Presentation: Filippos Kyriazidis


Objectives:

� Indicate the importance of MOS to the end user perceived speech quality.

� Introduce the MOS derivative Key Performance Indicator (KPI) which comes from Drive Tests Data and Network Statistics.


Statistics.

� Implement a mathematical formalism in order systemize the MOS calculation procedure.

� Compare different speech codecs implementations in BSC areas using MOS distribution patterns.


Contents:

•• MOS concept & dependencies.MOS concept & dependencies.

• Average MOS calculation in Cell & BSC level combining drive tests data & OSS measurements.


• Cell MOS distribution patterns for different speech codecs. EFR vs AMR codec comparison.

• Effect of MS technology on different speech codecs share.

• Evaluating speech codec effectiveness using quality and speech codec distribution patterns


Mean Opinion Score (MOS) concept description:• A common benchmark used to determine sound quality. • In voice telephony, represents a measure of human speech quality, at the

destination end of the circuit. • It is an important factor in determining the QoS.

MOS Measurement: 1. A pool of listeners rate a series of audio files using a five-grade scale ranging

from 1 to 5.2. The average or Mean Opinion Score (MOS) for each audio file is calculated.


2. The average or Mean Opinion Score (MOS) for each audio file is calculated.

Conditions:• 16 or more listeners (adequate sample).• Quiet environment.

�To reduce variability, tests commonly include reference files that have "industry accepted" MOS scores.


MOS dependencies in a mobile network:

�Speech Codec �Radio Interface Conditions


MOS classification according to ASCOM scale

53.5

ExcellentGood

2.72.1

FairPoor

0

Bad

1.5

Full Rate (FR)Half Rate (HR)

Enhanced Full Rate (EFR)Adaptive Multi Rate (AMR)

Signal Qualityi.e.: BER, FER


•• MOS concept & dependencies.MOS concept & dependencies.

•• Average MOS calculation in Cell & BSC level Average MOS calculation in Cell & BSC level combining drive tests data & OSS measurements.combining drive tests data & OSS measurements.

• Cell MOS distribution patterns for different speech codecs.






• Basic principle of extracting a MOS derivative KPI:

Perform Drive Tests

Process results & create MOS Quality &

Query OSS

Export Speech Codec usage Matrix


create MOS Quality & Speech Codec Matrix

Matrix Export Quality class statistics

Matrix

Perform Matrix Operations to calculate

Cell/BSC MOS value

Data Merge


Drive Tests Reference Table:

Speech Codec degradation direction

(5 speech codecs)

Quality degradation direction (8 quality classes)

Speech Codec / DL Quality class 0 1 2 3 4 5 6 7AMR FR MOS 3,71 3,56 3,31 3,05 2,72 2,49 2,12 1,70AMR HR MOS 3,36 3,24 3,04 2,88 2,71 2,47 2,11 1,40

EFR MOS 3,76 3,68 3,43 3,08 2,72 2,34 2,01 1,44FR MOS 3,19 3,14 3,03 2,77 2,58 2,22 1,82 1,45HR MOS 2,92 2,83 2,68 2,59 2,43 2,13 1,66 1,41


Speech Share of BSC Table

AMR FR AMR HR EFR FR HR33.95% 13.96% 39.46% 0.39% 12.23%

Speech Codec Share

Quality Class Share of BSC

DL Quality Samples ShareQUAL_0 80.17%QUAL_1 3.73%QUAL_2 3.68%QUAL_3 3.67%QUAL_4 3.22%QUAL_5 2.72%QUAL_6 1.89%QUAL_7 0.91%

OSS Derived Tables


BSC MOS calculation example:

DL Quality Samples ShareQUAL_0 80.17%QUAL_1 3.73%QUAL_2 3.68%QUAL_3 3.67%QUAL_4 3.22%QUAL_5 2.72%QUAL_6 1.89%QUAL_7 0.91%

Spech Codec / DL Quality class 0 1 2 3 4 5 6 7AMR FR MOS 3.71 3.56 3.31 3.05 2.72 2.49 2.12 1.70AMR HR MOS 3.36 3.24 3.04 2.88 2.71 2.47 2.11 1.40

EFR MOS 3.76 3.68 3.43 3.08 2.72 2.34 2.01 1.44FR MOS 3.19 3.14 3.03 2.77 2.58 2.22 1.82 1.45HR MOS 2.92 2.83 2.68 2.59 2.43 2.13 1.66 1.41

X =

Dimension: 5X8

Dimension: 8X1

Speech Codec Weighted MOS ValueAMR FR MOS 3.55AMR HR MOS 3.24

EFR MOS 3.59FR MOS 3.08HR MOS 2.82

Dimension: 5X1


Speech Codec Weighted MOS ValueAMR FR MOS 3.55AMR HR MOS 3.24

EFR MOS 3.59FR MOS 3.08HR MOS 2.82

BSC MOS = X

Dimension: 5X1

Dimension: 1X5

= 3.43AMR FR AMR HR EFR FR HR33.95% 13.96% 39.46% 0.39% 12.23%

Speech Codec Share


Generalized calculation procedure:The (m x n) (m codecs, n quality classes) matrix is multiplied with the (n x1)

quality classes matrix as in (1):

(1)

...

...

...

...

......

............

............

......1

0

1

0

000

=

×

n SC

SC

Q

Q

MM

MM


............

0

mm

mnm SCQMM

The product of (1), (m x 1) is further multiplied with the (1 x m) speech codecs matrix to obtain a single average MOS value, as in (2):

[ ] (2) _.........

...

...

...

0

0

MOSAverageCC

SC

SC

m

m

=×


Key issues:• Process can be easily implemented in a performance

monitoring system.• Can be applied in Cell, BSC or any other network

structure. • Cells with Poor or Bad MOS can be isolated and be further

investigated.


investigated.• A single average MOS value of a cell group (i.e. BSC

area) may not be essential. The comparison of different network areas provides QoS indicative results.


• MOS concept & dependencies.


•• Cell MOS distribution patterns for different speech Cell MOS distribution patterns for different speech


•• Cell MOS distribution patterns for different speech Cell MOS distribution patterns for different speech codecs. EFR vs AMR codec comparison.codecs. EFR vs AMR codec comparison.




MOS distribution:•Derives from cell level MOS calculation of a group of cells

•Gives a brief description of the end user perceived speech quality in a specific network area.

60

7053.5

ExcellentGood

2.72.1

FairPoor

0

Bad

1.5


0

10

20

30

40

50

2,5

2,58

2,66

2,74

2,82 2,

92,

983,

063,

143,

22 3,3

3,38

3,46

3,54

3,62 3,

73,

783,

863,

94

MOS classification

Nu

mb

er o

f ce

lls


MOS improvement pattern:•The distance between distributions shows the MOS improvement

between two different states of a group of cells.

50

60

70FR/HR codec

AMR codec (together with EFR &FR/HR)


0

10

20

30

40

50

2,5

2,58

2,66

2,74

2,82 2,

92,

983,

063,

143,

22 3,3

3,38

3,46

3,54

3,62 3,

73,

783,

863,

94 >4

MOS classification

Nu

mb

er o

f ce

lls

53.5

ExcellentGood

2.72.1

FairPoor

0

Bad

1.5


EFR versus AMR:•EFR achieves highest but also lowest MOS values in comparison to AMR.

•EFR distribution has a larger standard deviation than AMR.

•AMR is subsequently, a preferable speech codec.

120

140

160

EFR codec (together with FR/HR)

AMR codec (together with EFR/FR/HR)

53.52.72.10 1.5


0

20

40

60

80

100

120

2,5

2,58

2,66

2,74

2,82 2,

92,

983,

063,

143,

22 3,3

3,38

3,46

3,54

3,62 3,

73,

783,

863,

94 >4

MOS classification

Nu

mb

er o

f ce

lls

53.5

ExcellentGood

2.72.1

FairPoor

0

Bad

1.5







•• Effect of MS technology on different speech codecs Effect of MS technology on different speech codecs share.share.



The role of Mobile Station technology

� The following speech codecs share matrix is involved in all MOS calculations:

]..........[0 m

CCSC =

According to the previous example:


� The existence of old-technology mobiles in a network area, which do not support ‘modern’ speech codecs, will affect codecs’ shares against EFR & AMR percentages. This will degrade average MOS of BTSs.

]%23.12%39.0%46.39%96.13%95.33[=SC

� Promotion of latest technology MSs to existing subscribers could be a key issue of marketing strategy in order to optimize speech quality.

AMRFR AMRHR EFR FR HR








•• Evaluating speech codec effectiveness using quality Evaluating speech codec effectiveness using quality and speech codec distribution patternsand speech codec distribution patterns


Quality & Speech codec distribution patterns:

� An equivalent way of deciding speech codecs’ effectiveness is to calculate the percentage of samples in each MOS class, i.e. create a graph with the following information:

35%

40%

45%


To achieve this aim drive tests data should be post-processed differently with regard to the original data.

0%

5%

10%

15%

20%

25%

30%

Excellent Good Fair Poor Bad

Sam

ple

s sh

are


Reference Table Quality & Speech codec distribution patterns:

SC MOS Class 0 1 2 3 4 5 6 7AMR FR E 87.79% 75.78% 55.38% 35.41% 15.51% 7.77% 0.00% 0.00%AMR FR G 7.33% 13.66% 22.58% 31.91% 33.16% 30.10% 19.28% 0.00%AMR FR F 4.31% 7.45% 16.94% 21.40% 32.09% 33.01% 30.12% 22.86%AMR FR P 0.57% 3.11% 4.30% 9.73% 17.11% 24.27% 31.33% 34.29%AMR FR B 0.00% 0.00% 0.81% 1.56% 2.14% 4.85% 19.28% 42.86%AMR HR E 38.71% 20.81% 15.63% 10.59% 12.50% 10.81% 0.00% 0.00%

Post-Processed Drive Tests Data


AMR HR E 38.71% 20.81% 15.63% 10.59% 12.50% 10.81% 0.00% 0.00%AMR HR G 53.12% 68.79% 58.75% 54.12% 35.00% 18.92% 12.50% 0.00%AMR HR F 7.10% 7.72% 18.13% 23.53% 35.00% 29.73% 31.25% 11.11%AMR HR P 1.08% 2.68% 6.88% 11.76% 12.50% 37.84% 43.75% 11.11%AMR HR B 0.00% 0.00% 0.63% 0.00% 5.00% 2.70% 12.50% 77.78%

EFR E 91.48% 87.06% 68.26% 41.13% 15.69% 6.15% 0.00% 0.00%EFR G 7.05% 9.90% 19.90% 30.65% 39.87% 18.46% 16.67% 0.00%EFR F 1.25% 2.08% 8.82% 21.77% 29.41% 43.08% 21.43% 15.00%EFR P 0.00% 0.80% 2.77% 5.24% 7.84% 23.85% 38.10% 15.00%EFR B 0.23% 0.16% 0.25% 1.21% 7.19% 8.46% 23.81% 70.00%FR E 0.00% 0.21% 0.00% 0.00% 0.67% 0.00% 0.00% 0.00%FR G 96.14% 92.31% 84.43% 63.30% 43.33% 18.92% 4.00% 0.00%FR F 3.34% 6.44% 12.11% 25.00% 38.00% 36.94% 24.00% 10.00%FR P 0.39% 1.04% 3.11% 9.57% 16.67% 34.23% 45.33% 25.00%FR B 0.13% 0.00% 0.35% 2.13% 1.33% 9.91% 26.67% 65.00%HR E 0.16% 0.42% 1.31% 1.72% 1.32% 0.00% 0.00% 0.00%HR G 92.54% 81.89% 60.93% 49.68% 32.34% 9.83% 1.82% 0.00%HR F 5.40% 13.63% 26.24% 32.47% 39.27% 43.35% 13.64% 8.51%HR P 1.90% 3.95% 11.08% 14.41% 24.09% 37.57% 44.55% 19.15%HR B 0.00% 0.10% 0.44% 1.72% 2.97% 9.25% 40.00% 72.34%


Calculation example in a BSC area with AMR /EFR/FR/HR enabled:

QUAL_0 QUAL_1 QUAL_2 QUAL_3 QUAL_4 QUAL_5 QUAL_6 QUAL_7

� Calculation Procedure: � Drive Tests data are weighted according to quality class

share, that is the following table:


QUAL_0 QUAL_1 QUAL_2 QUAL_3 QUAL_4 QUAL_5 QUAL_6 QUAL_783.58% 3.12% 2.97% 2.93% 2.52% 2.23% 1.71% 0.94%

� The resulting table is further transformed according to speech encoding share:

AMRFR 37.43%AMRHR 8.73%EFR 46.12%FR 0.44%HR 7.28%



� After all transformations (multiplications) the Drive tests table becomes:

SC MOS Class 0 1 2 3 4 5 6 7 TotalAMR FR E 27.213% 0.897% 0.663% 0.425% 0.160% 0.068% 0.000% 0.000% 29.427%AMR FR G 2.292% 0.159% 0.251% 0.350% 0.312% 0.251% 0.123% 0.000% 3.740%AMR FR F 1.348% 0.087% 0.188% 0.235% 0.302% 0.275% 0.193% 0.081% 2.710%AMR FR P 0.180% 0.036% 0.048% 0.107% 0.161% 0.202% 0.201% 0.121% 1.056%AMR FR B 0.000% 0.000% 0.009% 0.017% 0.020% 0.040% 0.123% 0.151% 0.361%AMR HR E 2.825% 0.057% 0.041% 0.027% 0.027% 0.021% 0.000% 0.000% 2.998%


AMR HR E 2.825% 0.057% 0.041% 0.027% 0.027% 0.021% 0.000% 0.000% 2.998%AMR HR G 3.876% 0.187% 0.152% 0.138% 0.077% 0.037% 0.019% 0.000% 4.487%AMR HR F 0.518% 0.021% 0.047% 0.060% 0.077% 0.058% 0.047% 0.009% 0.837%AMR HR P 0.078% 0.007% 0.018% 0.030% 0.027% 0.074% 0.065% 0.009% 0.309%AMR HR B 0.000% 0.000% 0.002% 0.000% 0.011% 0.005% 0.019% 0.064% 0.101%

EFR E 35.261% 1.251% 0.936% 0.555% 0.182% 0.063% 0.000% 0.000% 38.248%EFR G 2.716% 0.142% 0.273% 0.414% 0.463% 0.190% 0.132% 0.000% 4.329%EFR F 0.482% 0.030% 0.121% 0.294% 0.342% 0.443% 0.169% 0.065% 1.945%EFR P 0.000% 0.011% 0.038% 0.071% 0.091% 0.245% 0.301% 0.065% 0.822%EFR B 0.088% 0.002% 0.003% 0.016% 0.083% 0.087% 0.188% 0.304% 0.772%FR E 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000%FR G 0.354% 0.013% 0.011% 0.008% 0.005% 0.002% 0.000% 0.000% 0.392%FR F 0.012% 0.001% 0.002% 0.003% 0.004% 0.004% 0.002% 0.000% 0.028%FR P 0.001% 0.000% 0.000% 0.001% 0.002% 0.003% 0.003% 0.001% 0.013%FR B 0.000% 0.000% 0.000% 0.000% 0.000% 0.001% 0.002% 0.003% 0.007%HR E 0.010% 0.001% 0.003% 0.004% 0.002% 0.000% 0.000% 0.000% 0.020%HR G 5.634% 0.186% 0.132% 0.106% 0.059% 0.016% 0.002% 0.000% 6.136%HR F 0.329% 0.031% 0.057% 0.069% 0.072% 0.070% 0.017% 0.006% 0.651%HR P 0.116% 0.009% 0.024% 0.031% 0.044% 0.061% 0.056% 0.013% 0.354%HR B 0.000% 0.000% 0.001% 0.004% 0.005% 0.015% 0.050% 0.050% 0.125%



MOS Class Samples ShareExcellent 70.69%

Good 19.08%Fair 6.17%Poor 2.55%Bad 1.37%

� A grouping by the MOS class yields the MOS class distribution of samples within the BSC area:


Bad 1.37%

0%

10%

20%

30%

40%

50%

60%

70%

80%


MOS Class

Sam

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erce

nta

ge

Samples Share


Comparative evaluation of three different network states:

MOS Class ΑΜR/EFR/FR/HR EFR/FR/HR FR/HRExcellent 70.69% 56.98% 0.11%

Good 19.08% 33.65% 87.36%Fair 6.17% 5.32% 7.23%Poor 2.55% 2.47% 3.61%Bad 1.37% 1.58% 1.59%

100%


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


MOS Class

Sam

ple

s p

erce

nta

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ΑΜR/EFR/FR/HR EFR/FR/HR FR/HR


Thank you for your attention


Thank you for your attention

Documents

Mean Opinion Score(MOS) KPI