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Content for  TS 26.093  Word version:  16.1.0

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1  ScopeWord‑p. 6

This document describes the Source Controlled Rate (SCR)operation of the Adaptive Multi-Rate speech Codec in Codec Types UMTS_AMR and UMTS_AMR2 for the UMTS system. The implementation of this SCR operation is mandatory in all UMTS equipment.
The description is structured according to the block diagram in figure 1. This structure of distributing the various functions between system entities is not mandatory for implementation, as long as the operation on the speech decoder output remains the same.
Annex A describes the Discontinuous Transmission (DTX) operation of the Adaptive Multi-Rate speech Codec in Codec Types FR_AMR, HR_AMR and OHR_AMR for GERAN. This annex is the former GSM 06.93 (Release 98).
Annexes B to E describe the SCR operation of the Adaptive Multi-Rate speech Codec in Codec Types GSM_EFR, TDMA_EFR, TDMA_US1 and PDC_EFR for the UMTS system.
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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]
TS 26.071: : "AMR Speech Codec; General description".
[2]
TS 26.073: : "AMR Speech Codec; ANSI C code".
[3]
TS 26.074: : "AMR Speech Codec; Test sequences".
[4]
TS 26.090: : "AMR Speech Codec; Transcoding functions".
[5]
TS 26.091: : "AMR Speech Codec; Error concealment of lost frames".
[6]
TS 26.092: : "AMR Speech Codec; Comfort noise aspects".
[7]
TS 26.094: : "AMR Speech Codec; Voice Activity Detector (VAD)".
[8]
TS 26.101: : "AMR Speech Codec; Frame structure".
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3  Definitions, symbols and abbreviations

3.1  Definitions

For the purpose of this document, the following definitions apply.
frame:
Time interval of 20 ms, corresponding to the time segmentation of the Adaptive Multi Rate speech Codec, also used as a short term for a traffic frame.
traffic frame:
Block of 95..244 information bits transmitted on the speech traffic channels.
SID frame:
Frame that conveys information about the acoustic background noise.
speech frame:
Traffic frame that has been classified as SPEECH_GOOD or SPEECH_BAD frame.
VAD flag:
Boolean flag, generated by the VAD algorithm indicating the presence ("1") or the absence ("0") of a speech frame.
RX_TYPE:
classifies the received frame.
TX_TYPE:
classifies the frame to be transmitted.
hangover period:
A period of frames added at the end of a speech burst in which VAD flag ="0" and TX_TYPE is ="SPEECH_GOOD", this period provides the encoder with an extra window to derive the Comfort Noise parameters .
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3.2  SymbolsWord‑p. 7

For the purpose of this document, the following symbols apply.
Nelapsed
Number of elapsed frames since the last updated SID frame.

3.3  Abbreviations

For the purpose of this document , the following abbreviations apply.
AN
Access Network
SCR
Source Controlled Rate operation
TS
Telecommunication Standard, Technical Specification
GSM
Global System for Mobile Telecommunication
GSM-EFR
GSM Enhanced Full Rate speech Codec
UE
User Equipment
PDC-EFR
ARIB PDC-EFR 6.7 kBit/s speech Codec
RAN
Radio Access Network
RX
Receive
SID
Silence Descriptor
TDMA-EFR
TIA IS-641 Enhanced speech Codec
TDMA-US1
TIA TDMA-US1 (12.2 kBit/s Codec, similar to GSM-EFR)
TX
Transmit
VAD
Voice Activity Detector

4  General

Source Controlled Rate operation (SCR) is a mechanism for the AMR Speech Codec, which allows to encode the input signal at a lower average rate by taking speech inactivity into account. The SCR scheme may be used for the following purposes:
  • to save power in the User Equipment;
  • to reduce the overall interference and load in the networks.
SCR in the transmitting path (uplink) shall be in operation in UEs, if commanded so by the network. Note that for UMTS AMR and UMTS AMR2 codec types, the uplink SCR operation shall always be activated. The UE shall handle SCR in the receiving path (downlink) at any time, regardless, whether SCR in the transmitting path is enabled or not.
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4.1  General organisation

The default SCR mechanism described in this document requires the following functions:
  • a Voice Activity Detector (VAD) on the transmit (TX) side;
  • evaluation of the background acoustic noise on the transmit (TX) side, in order to transmit characteristic parameters to the receive (RX) side;
  • generation on the receive (RX) side of a similar noise, called comfort noise, during periods where the transmission is switched off.
The Voice Activity Detector (VAD) is defined in [7] and the AMR-mode comfort noise functions in [6]. Both are based partly on the speech Codec and its internal variables, defined in [4].
In addition to these functions, if the parameters arriving at the RX side are detected to be seriously corrupted by errors, the speech or comfort noise must be generated from substituted data in order to avoid seriously annoying effects for the listener. These functions are defined in [5].
An overall description of the speech processing parts can be found in [1]. An overview of one link SCR operation is shown in Figure 1.
[not reproduced yet]
Figure 1: Block diagram of one link SCR operation
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