SIST ETS 300 728 E1:2003

Digital cellular telecommunications system; Comfort noise aspects for Enhanced Full Rate (EFR) speech traffic channels (GSM 06.62)

This European Telecommunication Standard (ETS) gives the detailed requirements for the correct operation of the background acoustic noise evaluation, noise parameter encoding/decoding and comfort noise generation in Mobile Stations (MSs) and Base Station Systems (BSSs) during Discontinuous Transmission (DTX) on enhanced full rate speech traffic channels. The requirements described in this ETS are mandatory for implementation in all GSM MSs capable of supporting the enhanced full rate speech traffic channel. The receiver requirements are mandatory for implementation in all GSM BSSs capable of supporting the enhanced full rate speech traffic channel, the transmitter requirements only for those where downlink DTX will be used.

Digitalni celični telekomunikacijski sistem – Vidiki znosnega šuma v kanalih za prometne kanale izboljšanega govora s polno hitrostjo (EFR) (GSM 06.62)

General Information

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.070.50 - Global System for Mobile Communication (GSM)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Mandate: T-172
• Ref Project: ETSI ETS 300 728 ed.1 (1997-03) - Digital cellular telecommunications system; Comfort noise aspects for Enhanced Full Rate (EFR) speech traffic channels (GSM 06.62)

Standards Content (Sample)

SLOVENSKI STANDARD
01-december-2003
'LJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHP±9LGLNL]QRVQHJDãXPDYNDQDOLK]D
SURPHWQHNDQDOHL]EROMãDQHJDJRYRUDVSROQRKLWURVWMR()5*60
Digital cellular telecommunications system; Comfort noise aspects for Enhanced Full
Rate (EFR) speech traffic channels (GSM 06.62)
Ta slovenski standard je istoveten z: ETS 300 728 Edition 1
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 728
TELECOMMUNICATION March 1997
STANDARD
Source: ETSI TC-SMG Reference: DE/SMG-020662
ICS: 33.020
Key words: EFR, digital cellular telecommunications system, Global System for Mobile communications
(GSM), speech
R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS
Digital cellular telecommunications system;
Comfort noise aspects for Enhanced Full Rate (EFR)
speech traffic channels
(GSM 06.62)
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
X.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: [e-mail]
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1997. All rights reserved.

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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions, symbols and abbreviations.8
3.1 Definitions .8
3.2 Symbols .8
3.3 Abbreviations .9
4 General.9
5 Functions on the transmit (TX) side .10
5.1 Background acoustic noise evaluation .11
5.2 Modification of the speech encoding algorithm during SID frame generation .14
5.3 SID-frame encoding.15
6 Functions on the receive (RX) side .16
6.1 Averaging and decoding of the LP and fixed codebook gain parameters .16
6.2 Comfort noise generation and updating.18
7 Computational details.18
History.19

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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
Foreword
This European Telecommunication Standard (ETS) has been produced by the Special Mobile Group
(SMG) Technical Committee of the European Telecommunications Standards Institute (ETSI).
This ETS defines operation of the background acoustic noise evaluation, noise parameter
encoding/decoding and comfort noise generation in Mobile Stations (MSs) and Base Station Systems
(BSSs) during Discontinuous Transmission (DTX) on Enhanced Full Rate speech traffic channels within
the digital cellular telecommunications system.
This ETS corresponds to GSM technical specification, GSM 06.62, version 5.1.2
Transposition dates
Date of adoption: 28 February 1997
Date of latest announcement of this ETS (doa): 30 June 1997
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 December 1997
Date of withdrawal of any conflicting National Standard (dow): 31 December 1997

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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
1 Scope
This European Telecommunication Standard (ETS) gives the detailed requirements for the correct
operation of the background acoustic noise evaluation, noise parameter encoding/decoding and comfort
noise generation in Mobile Stations (MSs) and Base Station Systems (BSSs) during Discontinuous
Transmission (DTX) on Enhanced Full Rate speech traffic channels.
The requirements described in this ETS are mandatory for implementation in all GSM MSs capable of
supporting the Enhanced Full Rate speech traffic channel.
The receiver requirements are mandatory for implementation in all GSM BSSs capable of supporting the
Enhanced Full Rate speech traffic channel, the transmitter requirements only for those where downlink
DTX will be used.
In case of discrepancy between the requirements described in this ETS and the fixed point computational
description of these requirements contained in GSM 06.53 (ETS 300 724) [2], the description in
GSM 06.53 (ETS 300 724) [2] will prevail.
2 Normative references
This ETS incorporates by dated and undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references, the
latest edition of the publication referred to applies.
[1] GSM 01.04 (ETR 100): "Digital cellular telecommunications system (Phase 2);
Abbreviations and acronyms".
[2] GSM 06.53 (ETS 300 724): "Digital cellular telecommunications system; ANSI-C
code for the GSM Enhanced Full Rate (EFR) speech codec".
[3] GSM 06.60 (ETS 300 726): "Digital cellular telecommunications system;
Enhanced Full Rate (EFR) speech transcoding".
[4] GSM 06.61 (ETS 300 727): "Digital cellular telecommunications system;
Substitution and muting of lost frame for Enhanced Full Rate (EFR) speech
traffic channels".
[5] GSM 06.81 (ETS 300 729): "Digital cellular telecommunications system;
Discontinuous transmission (DTX) for Enhanced Full Rate (EFR) speech traffic
channels".
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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of this ETS, the following definitions apply.
frame: Time interval of 20 ms corresponding to the time segmentation of the Enhanced Full Rate speech
transcoder, also used as a short term traffic frame.
SID frame: Frame characterized by the SID (SIlence Descriptor) codeword. It conveys information on the
acoustic background noise.
SID codeword: Fixed bit pattern for labelling a traffic frame as a SID frame.
SID field: The bit positions of the SID codeword within a SID frame.
speech frame: Traffic frame that cannot be classified as a SID frame.
VAD flag: Voice Activity Detection flag.
SP flag: SPeech flag.
Other definitions of terms used in this ETS can be found in GSM 06.60 (ETS 300 726) [3] and GSM 06.81
(ETS 300 729) [5]. The overall operation of DTX is described in GSM 06.81 (ETS 300 729) [5].
3.2 Symbols
For the purposes of this ETS, the following symbols apply. Boldface symbols are used for vector variables.
T
f = ff .f Unquantized LSF vector
[]
12 10
T
� �� �
f = ff .f Quantized LSF vector
[]12 10
()m
f mth unquantized LSF vector of the frame
()m
�
f mth quantized LSF vector of the frame
ref
�
f Reference LSF parameter vector
mean
f Averaged LSF parameter vector
g Unquantized fixed codebook gain
c
g� Quantized fixed codebook gain
c
ref
g� Reference fixed codebook gain
c
mean
g Averaged fixed codebook gain
c
e Linear prediction residual signal
LP
e Computed LSF parameter prediction residual
e� Quantized LSF parameter prediction residual

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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
γ
Computed fixed codebook gain correction factor
�
γ Quantized fixed codebook gain correction factor
b
xn() =+xa() xa(+11)+�+xb(− )+xb( )
∑
=
na
3.3 Abbreviations
For the purposes of this ETS, the following abbreviations apply.
BSS Base Station Subsystem
DTX Discontinuous Transmission
MS Mobile Station
SID SIlence Descriptor
LP Linear Prediction
LSP Line Spectral Pair
LSF Line Spectral Frequency
RX Receive
TX Transmit
VAD Voice Activity Detector
For abbreviations not given in this subclause, see GSM 01.04 (ETR 100) [1].
4 General
A basic problem when using DTX is that the background acoustic noise, which is transmitted together with
the speech, would disappear when the radio transmission is cut, resulting in discontinuities of the
background noise. Since the DTX switching can take place rapidly, it has been found that this effect can
be very annoying for the listener - especially in a car environment with high background noise levels. In
bad cases, the speech may be hardly intelligible.
This ETS specifies the way to overcome this problem by generating on the receive (RX) side synthetic
noise similar to the transmit (TX) side background noise. The comfort noise parameters are estimated on
the TX side and transmitted to the RX side before the radio transmission is switched off and at a regular
low rate afterwards. This allows the comfort noise to adapt to the changes of the noise on the TX side.

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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
5 Functions on the transmit (TX) side
The comfort noise evaluation algorithm uses the following parameters of the GSM Enhanced Full Rate
speech encoder, defined in GSM 06.60 (ETS 300 726) [3]:
- the unquantized and quantized Linear Prediction (LP) parameters, using the Line Spectral Pair
(LSP) representation, where the unquantized Line Spectral Frequency (LSF) vector is given by
T T
�� �
�
f = ff .f , the quantized LSF vector is given by f = ff .f , and the two sets of
[]
12 10 []12 10
()1 ()2 ()1
�
unquantized and quantized LSF vectors (one for each half of a frame) are given by f , f , f
()2
�
and f , respectively;
�
- the quantized fixed-codebook gain g .
c
The algorithm also computes the following parameters to assist in comfort noise generation:
ref
�
- the reference LSF parameter vector f (average of the quantized LSF parameters of the
hangover period);
mean
- the averaged LSF parameter vector f (average of the LSF parameters of the eight most recent
frames);
ref
�
- the reference fixed codebook gain g (average of the quantized fixed codebook gain values of
c
the hangover period);
mean
- the averaged fixed codebook gain g (average of the fixed codebook gain values of the eight
c
most recent frames);
- the unquantized fixed codebook gain g .
c
ref mean ()1 ()2 ()1
�
� �
These parameters give information on the level ( g , g , g , g ) and the spectrum ( f , f , f ,
c c c c
()2 ref mean
� �
f , f , f ) of the background noise.
mean mean
Two of the evaluated comfort noise parameters (f and g ) are encoded into a special frame,
c
called a Silence Descriptor (SID) frame, for transmission to the RX side. Since the reference LSF
ref ref
�
f g�
parameter vector and the reference fixed codebook gain can be evaluated in the same way in
c
the encoder and decoder, as given in subclause 5.1, no transmission of these parameters is necessary.
mean mean
The averaged LSF parameter and fixed codebook gain values, f and g , are computed in the
c
encoder using both quantized and unquantized parameter values if the period of the eight most recent
frames (the SID averaging period) is overlapping with the hangover period (the parameters from the
frames overlapping with the hangover period have quantized values, while the parameters of the more
recent frames of the SID averaging period have unquantized values). If the period of the eight most recent
frames is non-overlapping with the hangover period, the averaged LSF parameter and fixed codebook
gain values are computed using only unquantized parameter values.
The SID frame also serves to initiate the comfort noise generation on the receive side, as a SID frame is
always sent at the end of a speech burst, i.e., before the radio transmission is terminated.
The scheduling of SID or speech frames on the radio path is described in GSM 06.81 (ETS 300 729) [5].

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ETS 300 728 (GSM 06.62 version 5.1.2): March 1997
5.1 Background acoustic noise evaluation
The comfort noise parameters to be encoded into a SID frame are calculated over N = 8 consecutive
frames marked with VAD = 0, as follows:
mean
The averaged LSF parameter vector f i of the frame i shall be computed according to the equation:
()
7 2
 
mean ()m
ffii=− n (1)
() ()
∑∑
 
n=0 m=1
where:
()m
f i is the mth (unquantized) LSF parameter vector of the current frame i (n = 0);
()
()m
f ()in− is the mth (quantized or unquantized) LSF parameter vector of one of the last frames
(n = 1,., 7);
n is the averaging period index (n = 0, 1,., 7);
m is the LSF parameter vector index within a frame (1 or 2);
is the frame index.
i
NOTE: When the averaging is performed at the end of the hangover period (first SID update),
()m
all of the LSF parameter vectors f ()in− of the 7 previous frames (the hangover
()m
period) have quantized values, while the LSF parameter vectors f ()i of the current
frame i have unquantized values. In the subsequent SID updates, the LSF parameter
vectors of the SID averaging period in the frames overlapping with the hangover period
have quantized values, while the parameter vectors of the more recent frames of the
SID averaging period have unquantized values.
mean
f i
The averaged LSF parameter vector () of the frame i is encoded using the same encoding tables
that are also used by the GSM Enhanced Full Rate speech codec for the encoding of the non-averaged
LSF parameter vectors in ordinary speech encoding mode, but the quantization algorithm is modified in
order to support the quantization of comfort noise. The LSF parameter prediction residual to be quantized
is obtained according to the following equation:
mean ref
�
efii=−f (2)
() ()
where:
mean
f i
() is the averaged LSF parameter vector at the current frame I
ref
�
f is the reference LSF parameter vector
e i is the computed LSF parameter prediction residual at the current frame I
()
i is the frame index;
NOTE: This prediction residual is used for both halves of the frame in the quantization
ref
�
algorithm. The computation of the reference LSF parameter vector f is made o
...