SIST EN 301 247 V4.0.1:2003
(Main)Digital cellular telecommunications system (Phase 2) (GSM); Comfort noise aspects for Enhanced Full Rate (EFR) speech traffic channels (GSM 06.62 version 4.0.1)
Digital cellular telecommunications system (Phase 2) (GSM); Comfort noise aspects for Enhanced Full Rate (EFR) speech traffic channels (GSM 06.62 version 4.0.1)
EN created for GSM Phase2 MS type approval purposes (a revision of GSM Phase 2+ ETS)
Digitalni celični telekomunikacijski sistem (faza 2) – Vidiki znosnega šuma pri prometnih kanalih za izboljšani govor s polno hitrostjo (EFR) (GSM 06.62, različica 4.0.1)
General Information
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2) (GSM); Comfort noise aspects for Enhanced Full Rate (EFR) speech traffic channels (GSM 06.62 version 4.0.1)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 301 247 Version 4.0.1SIST EN 301 247 V4.0.1:2003en01-december-2003SIST EN 301 247 V4.0.1:2003SLOVENSKI
STANDARD
SIST EN 301 247 V4.0.1:2003
European Telecommunications Standards InstituteEN 301 247 V4.0.1 (1997-12)European Standard (Telecommunications series)Digital cellular telecommunications system (Phase 2);Comfort noise aspects for Enhanced Full Rate (EFR)speech traffic channels(GSM 06.62 version 4.0.1)GLOBAL SYSTEM
FOR MOBILE COMMUNICATIONSRSIST EN 301 247 V4.0.1:2003
EN 301 247 V4.0.1 (1997-12)2GSM 06.62 version 4.0.1ReferenceDEN/SMG-110662P (bjo0200o.PDF)KeywordsEFR, digital cellular telecommunications system,Global System for Mobile communications(GSM), speechETSI SecretariatPostal addressF-06921 Sophia Antipolis Cedex - FRANCEOffice address650 Route des Lucioles - Sophia AntipolisValbonne - FRANCETel.: +33 4 92 94 42 00
Fax: +33 4 93 65 47 16Siret N° 348 623 562 00017 - NAF 742 CAssociation à but non lucratif enregistrée à laSous-Préfecture de Grasse (06) N° 7803/88X.400c= fr; a=atlas; p=etsi; s=secretariatInternetsecretariat@etsi.frhttp://www.etsi.frCopyright NotificationNo 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.SIST EN 301 247 V4.0.1:2003
EN 301 247 V4.0.1 (1997-12)3GSM 06.62 version 4.0.1ContentsIntellectual Property Rights.4Foreword.41Scope.52Normative references.53Definitions, symbols and abbreviations.53.1Definitions.53.2Symbols.63.3Abbreviations.64General.75Functions on the transmit (TX) side.75.1Background acoustic noise evaluation.85.2Modification of the speech encoding algorithm during SID frame generation.115.3SID-frame encoding.116Functions on the receive (RX) side.126.1Averaging and decoding of the LP and fixed codebook gain parameters.126.2Comfort noise generation and updating.147Computational details.15History.16SIST EN 301 247 V4.0.1:2003
EN 301 247 V4.0.1 (1997-12)4GSM 06.62 version 4.0.1Intellectual Property RightsIPRs essential or potentially essential to the present document may have been declared to ETSI. The informationpertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be foundin ETR 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect ofETSI standards", which is available free of charge from the ETSI Secretariat. Latest updates are available on the ETSIWeb server (http://www.etsi.fr/ipr).Pursuant to the ETSI Interim IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. Noguarantee can be given as to the existence of other IPRs not referenced in ETR 314 (or the updates onhttp://www.etsi.fr/ipr) which are, or may be, or may become, essential to the present document.ForewordThis European Standard (Telecommunications series) has been produced by the Special Mobile Group (SMG)Technical Committee of the European Telecommunications Standards Institute (ETSI).This EN defines operation of the background acoustic noise evaluation, noise parameter encoding/decoding and comfortnoise 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 EN corresponds to GSM technical specification, GSM 06.62, version 5.1.2.National transposition datesDate of adoption of this EN:19 December 1997Date of latest announcement of this EN (doa):31 March 1998Date of latest publication of new National Standardor endorsement of this EN (dop/e):30 September 1998Date of withdrawal of any conflicting National Standard (dow):30 September 1998SIST EN 301 247 V4.0.1:2003
EN 301 247 V4.0.1 (1997-12)5GSM 06.62 version 4.0.11ScopeThis EN gives the detailed requirements for the correct operation of the background acoustic noise evaluation, noiseparameter 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 EN are mandatory for implementation in all GSM MSs capable of supporting theEnhanced Full Rate speech traffic channel.The receiver requirements are mandatory for implementation in all GSM BSSs capable of supporting the Enhanced FullRate 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 EN and the fixed point computational description ofthese requirements contained in GSM 06.53 (EN 301 244) [2], the description in GSM 06.53 (EN 301 244) [2] willprevail.2Normative referencesThis EN incorporates by dated and undated reference, provisions from other publications. These normative referencesare cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequentamendments to or revisions of any of these publications apply to this EN only when incorporated in it by amendment orrevision. 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 andacronyms".[2]GSM 06.53 (EN 301 244): "Digital cellular telecommunications system; ANSI-C code for theGSM Enhanced Full Rate (EFR) speech codec".[3]GSM 06.60 (EN 301 245): "Digital cellular telecommunications system; Enhanced Full Rate(EFR) speech transcoding".[4]GSM 06.61 (EN 301 246): "Digital cellular telecommunications system; Substitution and mutingof lost frame for Enhanced Full Rate (EFR) speech traffic channels".[5]GSM 06.81 (EN 301 248): "Digital cellular telecommunications system; Discontinuoustransmission (DTX) for Enhanced Full Rate (EFR) speech traffic channels".3Definitions, symbols and abbreviations3.1DefinitionsFor the purposes of this EN, 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 acousticbackground 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.SIST EN 301 247 V4.0.1:2003
EN 301 247 V4.0.1 (1997-12)6GSM 06.62 version 4.0.1SP flag: SPeech flag.Other definitions of terms used in this EN can be found in GSM 06.60 (EN 301 245) [3] and GSM 06.81(EN 301 248) [5]. The overall operation of DTX is described in GSM 06.81 (EN 301 248) [5].3.2SymbolsFor the purposes of this EN, the following symbols apply. Boldface symbols are used for vector variables.[]fTfff=1210.Unquantized LSF vector[].fTfff=1210Quantized LSF vectorf()mmth unquantized LSF vector of the framef()mmth quantized LSF vector of the framefrefReference LSF parameter vectorfmeanAveraged LSF parameter vectorgcUnquantized fixed codebook gaingcQuantized fixed codebook gaingcrefReference fixed codebook gaingcmeanAveraged fixed codebook gaineLPLinear prediction residual signaleComputed LSF parameter prediction residualeQuantized LSF parameter prediction residualgComputed fixed codebook gain correction factorgQuantized fixed codebook gain correction factorxnnab()=å()()()()=++++-+xaxaxbxb113.3AbbreviationsFor the purposes of this EN, the following abbreviations apply:BSSBase Station SubsystemDTXDiscontinuous TransmissionMSMobile StationSIDSIlence DescriptorLPLinear PredictionLSPLine Spectral PairLSFLine Spectral FrequencyRXReceiveTXTransmitSIST EN 301 247 V4.0.1:2003
EN 301 247 V4.0.1 (1997-12)7GSM 06.62 version 4.0.1VADVoice Activity DetectorFor abbreviations not given in this subclause, see GSM 01.04 (ETR 100) [1].4GeneralA 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 DTXswitching can take place rapidly, it has been found that this effect can be very annoying for the listener - especially in acar environment with high background noise levels. In bad cases, the speech may be hardly intelligible.This EN specifies the way to overcome this problem by generating on the receive (RX) side synthetic noise similar tothe transmit (TX) side background noise. The comfort noise parameters are estimated on the TX side and transmitted tothe RX side before the radio transmission is switched off and at a regular low rate afterwards. This allows the comfortnoise to adapt to the changes of the noise on the TX side.5Functions on the transmit (TX) sideThe comfort noise evaluation algorithm uses the following parameters of the GSM Enhanced Full Rate speech encoder,defined in GSM 06.60 (EN 301 245) [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 []fTfff=1210.,the quantized LSF vector is given by [].fTfff=1210, and the two sets of unquantized and quantized LSFvectors (one for each half of a frame) are given by f()1, f()2, f()1 and f()2, respectively;-the quantized fixed-codebook gain gc.The algorithm also computes the following parameters to assist in comfort noise generation:-the reference LSF parameter vector fref (average of the quantized LSF parameters of the hangover period);-the averaged LSF parameter vector fmean (average of the LSF parameters of the eight most recent frames);-the reference fixed codebook gain gcref (average of the quantized fixed codebook gain values of the hangoverperiod);-the averaged fixed codebook gain gcmean (average of the fixed codebook gain values of the eight most recentframes);-the unquantized fixed codebook gain gc.These parameters give information on the level (gc, gc, gcref, gcmean) and the spectrum (f()1, f()2, f()1, f()2, fref,fmean) of the background noise.Two of the evaluated comfort noise parameters (fmean and gcmean) are encoded into a special frame, called a SilenceDescriptor (SID) frame, for transmission to the RX side. Since the reference LSF parameter vector fref and thereference fixed codebook gain gcref can be evaluated in the same way in the encoder and decoder, as given in subclause5.1, no transmission of these parameters is necessary.The averaged LSF parameter and fixed codebook gain values, fmean and gcmean, are computed in the encoder usingboth quantized and unquantized parameter values if the period of the eight most recent frames (the SID averagingSIST EN 301 247 V4.0.1:2003
EN 301 247 V4.0.1 (1997-12)8GSM 06.62 version 4.0.1period) is overlapping with the hangover period (the parameters from the frames overlapping with the hangover periodhave quantized values, while the parameters of the more recent frames of the SID averaging period have unquantizedvalues). If the period of the eight most recent frames is non-overlapping with the hangover period, the averaged LSFparameter 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 atthe 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 (EN 301 248) [5].5.1Background acoustic noise evaluationThe comfort noise parameters to be encoded into a SID frame are calculated over N = 8 consecutive frames marked withVAD = 0, as follows:The averaged LSF parameter vector ()fmeani of the frame i shall be computed according to the equation:()()ffmeanmmniin=-æèçöø÷==åå18121207()(1)where:()f()mi is the mth (unquantized) LSF parameter vector of the current frame i (n = 0);()f()min-is the mth (quantized or unquantized) LSF parameter vector of one of the last frames (n = 1,., 7);nis the averaging period index (n = 0, 1,., 7);mis the LSF parameter vector index within a frame (1 or 2);iis the frame index.NOTE:When the averaging is performed at the end of the hangover period (first SID update), all of the LSFparameter vectors ()f()min- of the 7 previous frames (the hangover period) have quantized values,while the LSF parameter vectors ()f()mi of the current frame i have unquantized values. In thesubsequent SID updates, the LSF parameter vectors of the SID averaging period in the frames overlappingwith the hangover period have quantized values, while the parameter vectors of the more recent frames ofthe SID averaging period have unquantized values.The averaged LSF parameter vector ()fmeani of the frame i is encoded using the same encoding tables that are alsoused by the GSM Enhanced Full Rate speech codec for the encoding of the non-averaged LSF parameter vectors inordinary speech encoding mode, but the quantization algorithm is modified in order to support the quantization ofcomfort noise. The LSF parameter prediction residual to be quantized is obtained according to the following equation:()()effiimeanref=-(2)where:()fmeaniis the averaged LSF parameter vector
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.