Tech-invite3GPPspaceIETFspace
21222324252627282931323334353637384‑5x

Content for  TS 26.447  Word version:  17.1.0

Top   Top   None   None   Next
1…   5…

 

1  Scopep. 6

The present document defines a frame loss concealment procedure, also termed frame substitution and muting procedure, which is executed by the Enhanced Voice Services (EVS) decoder when one or more frames (speech or audio or SID frames) are unavailable for decoding due to e.g. packet loss, corruption of a packet or late arrival of a packet.

2  Referencesp. 6

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]
TR 21.905: "Vocabulary for 3GPP Specifications".
[2]
TS 26.441: "Codec for Enhanced Voice Services (EVS); General Overview".
[3]
TS 26.442: "Codec for Enhanced Voice Services (EVS); ANSI C code (fixed-point)".
[4]
TS 26.444: "Codec for Enhanced Voice Services (EVS); Test Sequences".
[5]
TS 26.445: "Codec for Enhanced Voice Services (EVS); Detailed Algorithmic Description".
[6]
TS 26.446: "Codec for Enhanced Voice Services (EVS); AMR-WB Backward Compatible Functions".
[7]
R. Martin, Noise Power Spectral Density Estimation Based on Optimal Smoothing and Minimum Statistics, 2001
[8]
TS 26.443: "Codec for Enhanced Voice Services (EVS); ANSI C code (floating-point)"
[9]
TS 26.452: "Codec for Enhanced Voice Services (EVS); ANSI C code; Alternative fixed-point using updated basic operators".
Up

3  Definitions, symbols and abbreviationsp. 6

3.1  Definitionsp. 6

For the purposes of the present document, the terms and definitions given in TR 21.905 and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905.
Further EVS codec specific definitions are found in clause 3.1 of TS 26.445.
Up

3.2  Symbolsp. 6

For the purposes of the present document, the following symbols apply:
EVS codec specific symbol definitions may be found in clause 3.2 of TS 26.445.

3.3  Abbreviationsp. 7

For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905.
AMR
Adaptive Multi Rate (codec)
AMR-NB
Adaptive Multi Rate Narrowband (codec) = AMR
AMR-WB
Adaptive Multi Rate Wideband (codec)
EFR
Enhanced Full Rate (codec)
EVS
Enhanced Voice Services
FB
Fullband
FR
(GSM) Full Rate (codec)
HR
(GSM) Half Rate (codec)
JBM
Jitter Buffer Management
MTSI
Multimedia Telephony Service for IMS
NB
Narrowband
PLC
Packet Loss Concealment
PS
Packet Switched
PSTN
Public Switched Telephone Network
SWB
Super Wideband
WB
Wideband
Further EVS codec specific abbreviations may be found in clause 3.3 of TS 26.445.
Up

4  Generalp. 7

The purpose of the frame loss concealment procedure is to conceal the effect of any unavailable EVS frame (speech or audio or SID) for decoding. The concealment of erased frames covers both the reconstruction of missing frames and the techniques to ensure smooth and rapid recovery of normal synthesis after erased segments. The frame loss concealment procedure also covers proper strategies including muting or fading to background noise for the case of multiple frame losses in a row. The purpose of muting the output or fading to background noise in the case of several lost frames in a row is to indicate the breakdown of the channel to the user and to avoid generating possible annoying sounds as a result from the frame loss concealment procedure.
Unless stated differently, fading operations (described in subclause 5.3.4 and subclause 5.4.6) start already with the first lost frame.
Given the architecture and features of the EVS codec (details in [EVS Codec Detailed Algorithmic Description]) the frame loss concealment procedure comprises concealment methods for the various major codec modules, such as signal classification, spectral envelope (LPC), ACELP, MDCT and Bandwidth Extension. A particular feature of the EVS codec is 'guided' frame loss concealment for which the encoder provides specific supplementary data guiding the concealment during erased frames and enhancing the convergence and recovery of the decoder after erased frames. The description in this specification is limited on how to apply the 'guided' frame loss concealment data; the corresponding encoding operations are described as part of the EVS codec algorithmic description TS 26.445.
The procedure of the present document is mandatory for implementation in all network entities and User Equipment (UE)s supporting the EVS decoder.
The present document does not describe the ANSI C code of this procedure. For a description of the two reference fixed-point ANSI C code implementations, using different sets of basic operators, see TS 26.442 and TS 26.452 respectively; for a description of the reference floating-point ANSI C code implementation see TS 26.443.
In the case of discrepancy between the procedure described in the present document and its ANSI-C code specifications contained in TS 26.442 the procedure defined by TS 26.442 prevails. In the case of discrepancy between the procedure described in the present document and its ANSI-C code specifications contained in TS 26.443 the procedure defined by TS 26.443 prevails. In the case of discrepancy between the procedure described in the present document and its ANSI-C code specifications contained in TS 26.452 the procedure defined by TS 26.452 prevails.
Up

Up   Top   ToC