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V00R01
GSM BSS Network KPI (MOS) Optimization
Manual
For internal use only
Prepared by
GSM&UMTS Network
Per
formance Research
Department
Dong
Xuan
Date
2008
2
21
Reviewed by
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yyyy
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dd
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yyyy
mm
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Granted by
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Huawei Technologies Co., Ltd.
All rights reserved
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Revision Record
Date
Revision
Version
Change Descripti
on
Author
2008
1
21
0.9
Draft completed.
Dong Xuan
2008
3
20
1.0
The document is modified
according to review comments.
Wang Fei
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GSM BSS
Network KPI (MOS) Optimization Manual
Ke
y words: MOS, interference, BER, C/I, power control, DTX, frequency hopping
,
PESQ,
PSQM /PSQM+, PAMS
Abstract: With the development of the radio network, mobile operators become
more
focused on end users’ experience instead of key performance indicators (K
PIs). The
improvement of the end users’ experience and the improvement of the network
capacity
are regarded as KPIs. Therefore, Huawei must pay close attention to the
improvement of
the soft capability of the network quality as well as the fulfillment of K
PIs. At present,
there are three methods of evaluating the speech quality: subjective evaluation,
objective
evaluation, and estimation. Among the three methods, objective evaluation is the
most
accurate. The PESQ algorithm defined by the ITU can objectivel
y evaluate the speech
quality of the communication network. This document uses
the
mean opinion score
(
MOS
)
to label the speech quality after objective evaluation.
This document describes the factors of MOS, the impact of each factor on the
MOS,
and
the m
ethods of improving the network QoS and then the speech quality. It also
describes
the attention points during the test of speech quality of the existing network and
the
device capability value of the lab test. In addition, this document introduces the
dif
ferences between the speech test tools. The methods and principles of using the
test
tools are omitted. This document serves as a reference to the acceptance of
network
KPIs and the marketing bidding.
Reference
s
: ITU
T P.800
\
ITU
T P.830
\
ITU
T P.861
\
IT
U
-
T P.862
\
ITU
T P.853
List of acronyms:
Acronym
Expansion
MOS
Mean Opinion Score
PESQ
Perceptual
Evaluation
of
Speech Quality
PSQM
Perceptual Speech Quality Measurement
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PAMS
Perceptual Analyse Measurement Sytem
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Contents
1
Basic P
rinciples of MOS
................................
................................
................................
...........
9
1.1
Subjective Speech Quality Evaluation
................................
................................
..........
9
1.2 Objective Speech Quality Evaluation
................................
................................
...............
10
1.2.1 PSQM (P.861) Recommendation or Algorithm
................................
................................
....
10
1.2.2 PESQ (P.862) Recommendation or Algorithm
................................
................................
.....
10
1.2.3 P862.1 Recommendation (Mapping Function for Transforming)
................................
.........
11
1.2.4 P.563 Recommendation
................................
................................
................................
.......
12
1.3 S
peech Processing of Involved NEs
................................
................................
..................
13
1.3.2
MS
14
1.3.3
BTS
15
1.3.4
BSC
15
1.3.5
UMG
16
2 Factors That Affect th
e MOS in GSM
................................
................................
.........................
17
2.1 Introduction to GSM Speech Acoustic Principles
................................
.............................
17
2.2 Impact of Field Intensity and C/I on the Speech Quality
................................
..................
18
2.3 Impact of Handover on the Speech
Quality
................................
................................
......
18
2.4 Impact of DTX on the Speech Quality
................................
................................
..............
18
2.5 Impact of Speed (Frequency Deviation) on the Speech Quality
................................
.......
19
2.6 Impact of Speech Coding Rate on the Speech
Quality
................................
.....................
20
2.7 Impact of Transmission Quality on the Speech Quality
................................
....................
20
3 Method of Analyzing the Problem of Low MOS
................................
................................
.........
21
3.1 Process of Analyzing the Problem of Low MOS
................................
..............................
21
3.2 Method of Solving the Problem of Low MOS
................................
................................
..
23
3.2.1 Consistency Check and Sample Check
................................
................................
...............
23
3.2.2 Um Interface Check
................................
................................
................................
..............
24
3.2.3 BTS Check
................................
................................
................................
............................
27
3.2.4 Abis Transmission Check
................................
................................
................................
.....
28
3.2.5 BSC Check
................................
................................
................................
...........................
28
3.2.6 A Interface Transmission Check
................................
................................
..........................
29
3.2.7 MGW Check
................................
................................
................................
.........................
29
3.2.8 Miscellaneous (Comparison of MOS Before and After Network
Replacement)
..................
29
4 Test Methods and Suggestions
................................
................................
................................
.....
31
4.1 Test Tool Selection and Test Suggestions
................................
................................
.........
31
4.2 Sug
gestions on the Test of the Existing Network
................................
.............................
32
5 MOS Cases
................................
................................
................................
................................
...
32
5.1 Differences Between Speech Signal Process and Signaling Process
................................
32
5.1.1 GSM Speech Signal Process
................................
................................
...............................
32
5.1.2 Signaling Process
................................
................................
................................
.................
33
5.2
Identified MOS Problems
................................
................................
................................
.
33
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6 Feedback on MOS or Speech Problems
................................
................................
.......................
36
6.1
Test Requirements
................................
................................
................................
.............
36
6.2
Requirements for Configuration Data in Existing Network
................................
..............
38
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Tables
T
ABLE
1
R
ELATIONS BETWEEN THE
QUALITY GRADE
,
SCORE
,
AND LISTENING EFFECT
SCALE
..........
9
T
ABLE
2
I
MPACT OF
DTX
ON THE SPEECH QUALIT
Y
................................
................................
........
19
T
ABLE
3
M
APPING BETWEEN THE S
PEECH CODING SCHEME
AND THE
MOS
VALUE
.........................
20
T
ABLE
4
M
APPING BETWEEN SPEEC
H SAMPLE AND
MOS
................................
................................
23
T
ABLE
5
I
MPACT OF
TFO
ON THE IMPROVEMENT O
F SPEECH QUALITY
(GSM
R
EC
.
06.85)
.............
28
T
ABLE
6
I
DENTIFIED
MOS
PROBLEMS
................................
................................
.............................
34
T
ABLE
7
N
ETWORK CONFIGURATION
PARAMETERS TO BE PRO
VIDED
................................
..............
38
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Although the formal subjective listening test is the most reliable evaluation
method and
the network performance and any coding/decoding algorithm can be evaluated,
the test
result varies from listener to listener. In add
ition, the factors such as the listening
environment, listeners, and speech materials should be strictly controlled during
the test.
As a result, this method consumes a lot of time and money. Therefore, several
objective
evaluation methods, such as
PSQM, P
ESQ, and P862.1,
are introduced. For details
about the objective evaluation methods, see the next section.
1.2
Objective Speech Quality Evaluation
1.2.1
PSQM (P.861) Recommendation or Algorithm
The perceptual speech quality measurement (PSQM) recommendation or alg
orithm
introduces the system of five quality grades, with each grade further classified in
the
form of percentages through the %PoW (Percent Poor or Worse) and %GoB
(Percent
Good or Better) scales. Although the PSQM involves subclassification, it is still
one of
the subjective evaluation methods. At present, someone uses a computer to
generate a
wave file. Through the changes in the wave file before and after network
transmission,
the quality grade is obtained to evaluate the speech quality. In 1996, the PS
QM was
accepted as Recommendation P.861 by the ITU
T. In 1998, an optional system based on
measuring normalizing blocks (MNBs) was added to P.861 as an attachment.
1.2.2
PESQ (P.862) Recommendation or Algorithm
Jointly developed by British Telecom and KPN, the
Perceptual Evaluation
of
Speech
Quality
(PESQ) was accepted as ITU
T Recommendation P.862 in 2001. The PESQ
compares an original signal with a degraded signal and then provides an MOS.
The
MOS is similar to the result of a subjective listening test. The PE
SQ is an intrusive test
algorithm. The algorithm is powerful enough to test both the performance of a
network
element (NE) such as decoder and end
to
end speech quality. In addition, the algorithm
can give test results by degradation causes, such as codec
distortion, error, packet loss,
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delay, jitter, and filtering. The PESQ is the industry’s best standard algorithm that
has
been commercially used.
F
igure
1
shows the PESQ process.
Figure 1
PESQ process
For both the PSQM and the PAMS, a s
peech reference signal should be transmitted on
the telephone network. At the other end of the network, the sample signal and
the
received signal should be compared through the use of digit signal processing so
that the
speech quality of the network can be
estimated. The PESQ incorporates the advantages
of both the PSQM and the PAMS. It improves the VoIP and hybrid end
to
end
applications and modifies the MOS and MOS
LQ calculation methods. Initially, these
methods are used to measure the coding algorithm.
Afterwards, they are also used to
measure the VoIP network system.
1.2.3
P862.1 Recommendation (Mapping Function for Transforming)
The perceptual evaluation of speech quality (PESQ) is a method of objectively
evaluating the speech quality of the
communication n
etwork
. It is developed on the basis
of the PSQM+ and PAMS. In February 2001, the PESQ was accepted as ITU
T
Recommendation P.862. Afterwards, P.862.1 (mapping function for transforming)
was
added. Not an independent protocol, P.862.1 is only the mapping o
f P862. P.862.1
simulates the human ear’s perception of speech more exactly than P.862.
Therefore,
P.862.1 is more comparable to a subjective listening test than P.862. The high
scores
obtained according to P.862.1 are higher than those obtained according
to P.862. The
low scores obtained according to P.862.1 are lower than those obtained
according to