SIST EN 300 730 V6.0.1:2003

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Voice Activity Detector (VAD) for Enhanced Full Rate (EFR) speech traffic channels (GSM 06.82 version 6.0.1 Release 1997)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 300 730 Version 6.0.1SIST EN 300 730 V6.0.1:2003en01-december-2003SIST EN 300 730 V6.0.1:2003SLOVENSKI
STANDARD



SIST EN 300 730 V6.0.1:2003



EN 300 730 V6.0.1 (1999-06)European Standard (Telecommunications series)Digital cellular telecommunications system (Phase 2+);Voice Activity Detector (VAD) for EnhancedFull Rate (EFR) speech traffic channels(GSM 06.82 version 6.0.1 Release 1997)GLOBAL SYSTEM
FOR MOBILE COMMUNICATIONSRSIST EN 300 730 V6.0.1:2003



ETSIEN 300 730 V6.0.1 (1999-06)2(GSM 06.82 version 6.0.1 Release 1997)ReferenceDEN/SMG-020682Q6 (6rc0300o.PDF)KeywordsDigital cellular telecommunications system,Global System for Mobile communications (GSM)ETSIPostal 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° 7803/88Internetsecretariat@etsi.frIndividual copies of this ETSI deliverablecan be downloaded fromhttp://www.etsi.orgIf you find errors in the present document, send yourcomment to: editor@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 1999.All rights reserved.SIST EN 300 730 V6.0.1:2003



ETSIEN 300 730 V6.0.1 (1999-06)3(GSM 06.82 version 6.0.1 Release 1997)ContentsIntellectual Property Rights.4Foreword.41Scope.52References.53Definitions, symbols and abbreviations.53.1Definitions.53.2Symbols.53.2.1Variables.53.2.2Constants.63.2.3Functions.73.3Abbreviations.74General.85Functional description.85.1Overview and principles of operation.85.2Algorithm description.85.2.1Adaptive filtering and energy computation.95.2.2ACF averaging.95.2.3Predictor values computation.105.2.4Spectral comparison.105.2.5Information tone detection.115.2.6Threshold adaptation.115.2.7VAD decision.135.2.8VAD hangover addition.145.2.9Periodicity detection.146Computational description overview.156.1VAD modules.156.2Pseudo-floating point arithmetic.15Annex A (informative):Simplified block filtering operation.17Annex B (informative):Pole frequency calculation.18Annex C (informative):Change Request History.19History.20SIST EN 300 730 V6.0.1:2003



ETSIEN 300 730 V6.0.1 (1999-06)4(GSM 06.82 version 6.0.1 Release 1997)Intellectual 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 SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respectof ETSI standards", which is available free of charge from the ETSI Secretariat. Latest updates are available on theETSI Web server (http://www.etsi.org/ipr).Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guaranteecan be given as to the existence of other IPRs not referenced in SR 000 314 (or the updates on the ETSI Web server)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).The present document specifies the Voice Activity Detector (VAD) to be used in the Discontinuous Transmission(DTX) for Enhanced Full Rate (EFR) speech traffic channels within the digital cellular telecommunications system.The contents of the present document is subject to continuing work within SMG and may change following formal SMGapproval. Should SMG modify the contents of the present document it will be re-released with an identifying change ofrelease date and an increase in version number as follows:Version 6.x.ywhere:6indicates Release 1997 of GSM Phase 2+xthe second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates,etc.ythe third digit is incremented when editorial only changes have been incorporated in the specification.Proposed national transposition datesDate of adoption of this EN:05 June 1999Date of latest announcement of this EN (doa):30 September 1999Date of latest publication of new National Standardor endorsement of this EN (dop/e):31 March 2000Date of withdrawal of any conflicting National Standard (dow):31 March 2000SIST EN 300 730 V6.0.1:2003



ETSIEN 300 730 V6.0.1 (1999-06)5(GSM 06.82 version 6.0.1 Release 1997)1ScopeThe present document specifies the Voice Activity Detector (VAD) to be used in the Discontinuous Transmission(DTX) as described in GSM 06.81 [5] Discontinuous transmission (DTX) for Enhanced Full Rate (EFR) speech trafficchannels.The requirements are mandatory on any VAD to be used either in GSM Mobile Stations (MS)s or Base Station Systems(BSS)s that utilize the enhanced full-rate speech traffic channel.2ReferencesThe following documents contain provisions which, through reference in this text, constitute provisions of the presentdocument.· References are either specific (identified by date of publication, edition number, version number, etc.) ornon-specific.· For a specific reference, subsequent revisions do not apply.· For a non-specific reference, the latest version applies.· A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the samenumber.[1]GSM 01.04: "Digital cellular telecommunications system (Phase 2+); Abbreviations andacronyms".[2]GSM 06.53: "Digital cellular telecommunications system (Phase 2+); ANSI-C code for the GSMEnhanced Full Rate (EFR) speech codec".[3]GSM 06.54: "Digital cellular telecommunications system (Phase 2+); Test vectors for the GSMEnhanced Full Rate (EFR) speech codec".[4]GSM 06.60: "Digital cellular telecommunications system (Phase 2+); Enhanced Full Rate (EFR)speech transcoding".[5]GSM 06.81: "Digital cellular telecommunications system (Phase 2+); Discontinuous transmission(DTX) for Enhanced Full Rate (EFR) speech traffic channels".3Definitions, symbols and abbreviations3.1DefinitionsFor the purposes of the present document, the following definitions apply:noise: The signal component resulting from acoustic environmental noise.mobile environment: Any environment in which mobile stations may be used.3.2SymbolsFor the purposes of the present document, the following symbols apply:3.2.1Variablesaav1filter predictor values, see subclause 5.2.3SIST EN 300 730 V6.0.1:2003



ETSIEN 300 730 V6.0.1 (1999-06)6(GSM 06.82 version 6.0.1 Release 1997)acfthe ACF vector which is calculated in the speech encoder (GSM 06.60 [4])adaptcountsecondary hangover counter, see subclause 5.2.6av0averaged ACF vector, see subclause 5.2.2av1a previous value of av0, see subclause 5.2.2burstcountspeech burst length counter, see subclause 5.2.8dendenominator of left hand side of equation 8 in annex B, see subclause 5.2.5differencedifference between consecutive values of dm, see subclause 5.2.4dmspectral distortion measure, see subclause 5.2.4hangcountprimary hangover counter, see subclause 5.2.8lagcountnumber of subframes in current frame meeting periodicity criterion, see subclause 5.2.9lastdmprevious value of dm, see subclause 5.2.4lagsthe open loop long term predictor lags for the two halves of the speech encoder frame(GSM 06.60 [4])numnumerator of left hand side of equation 8 in annex B, see subclause 5.2.5oldlagcountprevious value of lagcount, see subclause 5.2.9prederrfourth order short term prediction error, see subclause 5.2.5ptchBoolean flag indicating the presence of a periodic signal component, see subclause 5.2.9pvadenergy in the current filtered signal frame, see subclause 5.2.1rav1autocorrelation vector obtained from av1, see subclause 5.2.3rcthe first four unquantized reflection coefficients calculated in the speech encoder (GSM 06.60 [4])rvadautocorrelation vector of the adaptive filter predictor values, see subclause 5.2.6smallagdifference between consecutive lag values, see subclause 5.2.9statBoolean flag indicating that the frequency spectrum of the input signal is stationary, see subclause5.2.4thvadadaptive primary VAD threshold, see subclause 5.2.6toneBoolean flag indicating the presence of an information tone, see subclause 5.2.5vadflagBoolean VAD decision with hangover included, see subclause 5.2.8veryoldlagcountprevious value of oldlagcount, see subclause 5.2.9vvadBoolean VAD decision before hangover, see subclause 5.2.73.2.2Constantsadpnumber of frames of hangover for secondary VAD, see subclause 5.2.6burstconstminimum length of speech burst to which hangover is added, see subclause 5.2.8decdetermines rate of decrease in adaptive threshold, see subclause 5.2.6facdetermines steady state adaptive threshold, see subclause 5.2.6framesnumber of frames over which av0 and av1 are calculated, see subclause 5.2.2SIST EN 300 730 V6.0.1:2003



ETSIEN 300 730 V6.0.1 (1999-06)7(GSM 06.82 version 6.0.1 Release 1997)freqththreshold for pole frequency decision, see subclause 5.2.5hangconstnumber of frames of hangover for primary VAD, see subclause 5.2.8incdetermines rate of increase in adaptive threshold, see subclause 5.2.6lthreshlag difference threshold for periodicity decision, see subclause 5.2.9margindetermines upper limit for adaptive threshold, see subclause 5.2.6nthreshframe count threshold for periodicity decision, see subclause 5.2.9plevlower limit for adaptive threshold, see subclause 5.2.6predththreshold for short term prediction error, see subclause 5.2.5pthenergy threshold, see subclause 5.2.6threshdecision threshold for evaluation of stat flag, see subclause 5.2.43.2.3Functions+addition-subtraction*multiplication/division| x |absolute value of xANDBoolean ANDORBoolean ORbMULT(x(i))the product of the series x(i) for i=a to bi=abSUM(x(i))the sum of the series x(i) for i=a to bi=a3.3AbbreviationsACFAutocorrelation functionANSIAmerican National Standards InstituteDTXDiscontinuous TransmissionLTPLong Term PredictorTXTransmissionVADVoice Activity DetectorFor abbreviations not given in this subclause, see GSM 01.04 [1].SIST EN 300 730 V6.0.1:2003



ETSIEN 300 730 V6.0.1 (1999-06)8(GSM 06.82 version 6.0.1 Release 1997)4GeneralThe function of the VAD is to indicate whether each 20 ms frame produced by the speech encoder contains speech ornot. The output is a Boolean flag (vadflag) which is used by the Transmit (TX) DTX handler defined in GSM 06.81 [5].The present document is organized as follows:Clause 5 describes the principles of operation of the VAD. Clause 6 provides an overview of the computationaldescription of the VAD. The computational details necessary for the fixed point implementation of the VAD algorithmare given in the form of ANSI C program contained in GSM 06.53 [2].The verification of the VAD is based on the use of digital test sequences which are described in GSM 06.54 [3].5Functional descriptionThe purpose of this clause is to give the reader an understanding of the principles of operation of the VAD, whereasGSM 06.53 [2] contains the fixed point computational description of the VAD. In the case of discrepancy between thetwo descriptions, the description in GSM 06.53 [2] will prevail.5.1Overview and principles of operationThe function of the VAD is to distinguish between noise with speech present and noise without speech present. This isachieved by comparing the energy of a filtered version of the input signal with a threshold. The presence of speech isindicated whenever the threshold is exceeded.The detection of speech in a mobile environment is difficult due to the low speech/noise ratios which are encountered,particularly in moving vehicles. To increase the probability of detecting speech the input signal is adaptively filtered(see subclause 5.2.1) to reduce its noise content before the voice activity decision is made (see subclause 5.2.7).The frequency spectrum and level of the noise may vary within a given environment as well as between differentenvironments. It is therefore necessary to adapt the input filter coefficients and energy threshold at regular intervals asdescribed in subclause 5.2.6.5.2Algorithm descriptionThe block diagram of the VAD algorithm is shown in figure 1. The individual blocks are described in the followingsubclauses. The variables shown in the block diagram are described in table 1.Table 1: Description of variables in figure 1VarDescriptionacfThe ACF vector which is calculated in the speech encoder (GSM 06.60 [4]).av0Averaged ACF vector.av1A previous value of av0.lagsThe open loop long term predictor lags for the two halves of the speech encoder frame(GSM 06.60 [4]).ptchBoolean flag indicating the presence of a periodic signal component.pvadEnergy in the current filtered signal frame.rav1Autocorrelati
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