Substitution and muting of lost frames for full rate speech channels

3GPP TS 46.011 V9.0.0 (2009-12)
Technical Specification
3rd Generation Partnership Project;
Technical Specification Group Services and System Aspects;
Full rate speech;
Substitution and muting of lost frames for
full rate speech channels
(Release 9)

 EMBED Word.Picture.6  	
The present document has been developed within the 3rd Generation Partnership Project (3GPP TM) and may be further elaborated for the purposes of 3GPP.	 
The present document has not been subject to any approval process by the 3GPP Organizational Partners and shall not be implemented.	 
This Specification is provided for future development work within 3GPP only. The Organizational Partners accept no liability for any use of this Specification.
Specifications and reports for implementation of the 3GPP TM system should be obtained via the 3GPP Organizational Partners' Publications Offices.



Keywords
GSM, speech, codec

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Contents
 TOC \o "1-9" Foreword	 PAGEREF _Toc248307461 \h 4
1	Scope	 PAGEREF _Toc248307462 \h 5
2	References	 PAGEREF _Toc248307463 \h 5
3	Definitions and abbreviations	 PAGEREF _Toc248307464 \h 5
4	General	 PAGEREF _Toc248307465 \h 5
5	Requirements	 PAGEREF _Toc248307466 \h 5
5.1	First lost speech frame	 PAGEREF _Toc248307467 \h 5
5.2	Subsequent lost speech frames	 PAGEREF _Toc248307468 \h 6
5.3	First lost SID frame	 PAGEREF _Toc248307469 \h 6
5.4	Subsequent lost SID frame	 PAGEREF _Toc248307470 \h 6
6	Example solution	 PAGEREF _Toc248307471 \h 6
Annex A (informative):	Change history	 PAGEREF _Toc248307472 \h 8

Foreword
This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x	the first digit:
1	presented to TSG for information;
2	presented to TSG for approval;
3	or greater indicates TSG approved document under change control.
y	the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates, etc.
z	the third digit is incremented when editorial only changes have been incorporated in the document.
1	Scope
The present document defines a frame substitution and muting procedure which shall be used by the RX DTX handler when one or more lost speech or SID frames are received from the radio subsystem.
The requirements of the present document are mandatory for implementation in all GSM Base Station Systems (BSS) and Mobile Stations (MS).
2	References
The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific.
For a specific reference, subsequent revisions do not apply.
For a non-specific reference, the latest version applies.  In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1]	GSM 01.04: "Digital cellular telecommunications system (Phase 2+); Abbreviations and acronyms".
[2]	GSM 06.10: "Digital cellular telecommunications system (Phase 2+); Full rate speech; Transcoding".
[3]	GSM 06.31: "Digital cellular telecommunications system (Phase 2+); Full rate speech; Discontinuous Transmission (DTX) for full rate speech traffic channel".
3	Definitions and abbreviations 
Abbreviations used in the present document are listed in GSM 01.04 [1].
The definitions of terms used in the present document can be found in GSM 06.31 [3].
4	General
The purpose of the frame substitution is to conceal the effect of lost frames.
The purpose of muting the output in the case of several lost frames is to indicate the breakdown of the channel to the user.
5	Requirements
5.1	First lost speech frame
Normal decoding of lost speech frames would result in very unpleasant noise effects. In order to improve the subjective quality, the first lost speech frame shall be substituted with either a repetition or an extrapolation of the previous good speech frame(s). Lost speech frames shall not be delivered to the speech decoder, nor shall the output be muted directly.
5.2	Subsequent lost speech frames
For subsequent lost speech frames, a muting technique shall be used that will gradually decrease the output level, resulting in silencing of the output after a maximum of 320 ms. Clause 6 gives an example solution.
5.3	First lost SID frame
A single lost SID frame shall be substituted by the last valid SID frame and the procedure for valid SID frames be applied as described in GSM 06.31 [3].
5.4	Subsequent lost SID frame
For the second lost SID frame, a muting technique shall be used on the comfort noise that will gradually decrease the output level, resulting in silencing of the output after a maximum of 320 ms. Clause 6 gives an example solution.
For subsequent lost SID frames, the muting of the output shall be maintained.
6	Example solution
For guidance, an example solution is given.
The first lost speech frame is replaced at the speech decoder input by the previous good speech frame. Normal decoding is then performed.
The muting procedure to be used in the case of subsequent lost speech frames or for comfort noise frames following the second lost SID frame is as follows: 
The pseudo‑logarithmic encoded block amplitude Xmaxcr (GSM 06.10 [2]), coded on the interval from 0 to 63, is decreased with a constant value d=4 in each frame, down to the lowest possible value. Consequently, Xmaxcr will be reduced gradually, and the output muted after a maximum of 320 ms. The grid position parameters are chosen randomly between 0 and 3 during this time.
For subsequent unusable frames, after the frame where Xmaxcr reached the lowest possible value, "silence frames" are passed from the RX DTX handler to the speech decoder to guarantee a low output level under all conditions. The silence frame is defined in table 1.
Table 1: Encoded parameters (GSM 06.10) of the silence frame
   Log area ratio 1   =   42

   Log area ratio 2   = 39

   Log area ratio 3   = 21

   Log area ratio 4   = 10

   Log area ratio 5   = 9

   Log area ratio 6   = 4

   Log area ratio 7   = 3

   Log area ratio 8   = 2

_

    LTP gain             = 0

    LTP lag               = 40



    Grid position        = 1

    Block amplitude  = 0



    RPE pulse no. 1  = 3

    RPE pulse no. 2  = 4

    RPE pulse no. 3  = 3

    RPE pulse no. 4  = 4

    RPE pulse no. 5  = 4


‑ repeated for each subsegment
    RPE pulse no. 6  = 3

    RPE pulse no. 7  = 3

    RPE pulse no. 8  = 3

    RPE pulse no. 9  = 3

    RPE pulse no. 10 = 4

    RPE pulse no. 11 = 4

    RPE pulse no. 12 = 3

    RPE pulse no. 13 = 3            _


Annex A (informative):
Change history

Change history
SMG No.
TDoc. No.
CR. No.
Section affected
New version
Subject/Comments
SMG#07



4.0.4
ETSI Publication
SMG#20



5.0.1
Release 1996 version
SMG#27



6.0.0
Release 1997 version
SMG#28



6.0.1
ETSI Publication
SMG#29



7.0.0
Specification version 6.0.0 upgrade to Release 1998 version 7.0.0




7.0.1
Version update for Publication
SMG#31



8.0.0
Release 1999 version


Change history
DateTSG #TSG Doc.CRRevSubject/CommentOldNew03-200111Version for Release 44.0.006-200216Version for Release 54.0.05.0.012-200426Version for Release 65.0.06.0.006-200736Version for Release 76.0.07.0.012-200842Version for Release 87.0.08.0.012-200946Version for Release 98.0.09.0.0




















 STYLEREF ZA 3GPP TS 46.011 V9.0.0 (2009-12)
 PAGE 3
 STYLEREF ZGSM Release 9


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