SIST EN 301 249 V4.0.1:2003

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 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 301 249 Version 4.0.1SIST EN 301 249 V4.0.1:2003en01-december-2003SIST EN 301 249 V4.0.1:2003SLOVENSKI
STANDARD
European Telecommunications Standards InstituteEN 301 249 V4.0.1 (1997-12)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 4.0.1)GLOBAL SYSTEM
FOR MOBILE COMMUNICATIONSRSIST EN 301 249 V4.0.1:2003

EN 301 249 V4.0.1 (1997-12)2GSM 06.82 version 4.0.1ReferenceDEN/SMG-110682P (bkc0200o.PDF)KeywordsEFR, VAD, digital cellular telecommunicationssystem, Global System for Mobilecommunications (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 301 249 V4.0.1:2003

EN 301 249 V4.0.1 (1997-12)3GSM 06.82 version 4.0.1ContentsIntellectual Property Rights.4Foreword.41Scope.52Normative references.53Definitions, symbols and abbreviations.53.1Definitions.53.2Symbols.53.2.1Variables.53.2.2Constants.63.2.3Functions.73.3Abbreviations.74General.75Functional 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.18History.19SIST EN 301 249 V4.0.1:2003

EN 301 249 V4.0.1 (1997-12)4GSM 06.82 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 specifies the Voice Activity Detector (VAD) to be used in the Discontinuous Transmission (DTX) forEnhanced Full Rate (EFR) speech traffic channels within the digital cellular telecommunications system.This EN corresponds to GSM technical specification, GSM 06.82, version 4.0.0.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 301 249 V4.0.1:2003

EN 301 249 V4.0.1 (1997-12)5GSM 06.82 version 4.0.11ScopeThis EN specifies the Voice Activity Detector (VAD) to be used in the Discontinuous Transmission (DTX) as describedin GSM 06.81 (EN 301 248) [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.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 (Phase 2); ANSI-C codefor the GSM Enhanced Full Rate (EFR) speech codec".[3]GSM 06.54 (EN 301 250): "Digital cellular telecommunications system (Phase 2); Test vectors forthe GSM Enhanced Full Rate (EFR) speech codec".[4]GSM 06.60 (EN 301 245): "Digital cellular telecommunications system (Phase 2); Enhanced FullRate (EFR) speech transcoding".[5]GSM 06.81 (EN 301 248): "Digital cellular telecommunications system (Phase 2); Discontinuoustransmission (DTX) for Enhanced Full Rate (EFR) speech traffic channels".3Definitions, symbols and abbreviations3.1DefinitionsFor the purposes of this EN, 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 this EN, the following symbols apply:3.2.1Variablesaav1filter predictor values, see subclause 5.2.3acfthe ACF vector which is calculated in the speech encoder (GSM 06.60 (EN 301 245) [4])adaptcountsecondary hangover counter, see subclause 5.2.6av0averaged ACF vector, see subclause 5.2.2av1a previous value of av0, see subclause 5.2.2SIST EN 301 249 V4.0.1:2003

EN 301 249 V4.0.1 (1997-12)6GSM 06.82 version 4.0.1burstcountspeech 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(EN 301 245) [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(EN 301 245) [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 5.2.2freqththreshold 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 5.2.6SIST EN 301 249 V4.0.1:2003

EN 301 249 V4.0.1 (1997-12)7GSM 06.82 version 4.0.1lthreshlag 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 (ETR 100) [1].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(EN 301 248) [5].This EN is organized as follows:SIST EN 301 249 V4.0.1:2003

EN 301 249 V4.0.1 (1997-12)8GSM 06.82 version 4.0.1Clause 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 (EN 301 244) [2].The verification of the VAD is based on the use of digital test sequences which are described in GSM 06.54(EN 301 250) [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 (EN 301 244) [2] contains the fixed point computational description of the VAD. In the case of discrepancybetween the two descriptions, the description in GSM 06.53 (EN 301 244) [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 (EN 301 245) [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 (EN 301 245) [4]).ptchBoolean flag indicating the presence of a periodic signal component.pvadEnergy in the current filtered signal frame.rav1Autocorrelation vector obta
...