ETSI EN 300 730-2000 Digital Cellular Telecommunications System (Phase 2+) Voice Activity Detector (VAD) for Enhanced Full Rate (EFR) Speech Traffic Channels (GSM 06 82 Version 8 0.pdf

1、ETSI EN 300 730 V8.0.1 (2000-11) European Standard (Telecommunications series) Digital cellular telecommunications system (Phase 2+); Voice Activity Detector (VAD) for Enhanced Full Rate (EFR) speech traffic channels (GSM 06.82 version 8.0.1 Release 1999) COPYRIGHT European Telecommunications Standa

2、rds InstituteLicensed by Information Handling Services(GSM 06.82 version 8.0.1 Release 1999) 2 ETSI EN 300 730 V8.0.1 (2000-1 1) Reference REN/SMG-l10682Q8 Keywords Digital cellular telecommunications system, Global System for Mobile communications (GSM) ETSI 650 Route des Lucioles F-O6921 Sophia An

3、tipolis Cedex - FRANCE Tel.: +33 4 92 94 42 O0 Fax: +33 4 93 65 47 16 Siret No 348 623 562 00017 - NAF 742 C Association but non lucratif enregistre la Sous-prfecture de Grasse (06) No 7803/88 Important notice Individual copies of the present document can be downloaded from: http:/iwww. etsi I oq Th

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6、 the present document, send your comment to: editor etsi.fr Copyright Notification No part may be reproduced except as authorized by written permission. The copyright and the foregoing restriction extend to reproduction in all media. 8 European Telecommunications Standards Institute 2000. All rights

7、 reserved. ETSI COPYRIGHT European Telecommunications Standards InstituteLicensed by Information Handling Services(GSM 06.82 version 8.0.1 Release 1999) 3 ETSI EN 300 730 V8.0.1 (2000-11) Contents Intellectual Property Rights . 4 Foreword 4 1 Scope . 5 2 References . 5 3 Definitions. symbols and abb

8、reviations 5 Definitions 5 3.1 3.2 Symbols 6 3.2.1 Variables . 6 3.2.2 Constants . 6 3.2.3 Functions . 7 3.3 Abbreviations . 7 4 General 7 5 5.1 5.2 5.2.1 5.2.2 5.2.3 5.2.4 5.2.5 5.2.6 5.2.7 5.2.8 5.2.9 Functional description . 7 Overview and principles of operation . 7 Algorithm description . 8 Ada

9、ptive filtering and energy computation . 9 ACF averaging 9 Predictor values computation 9 Spectral comparison 10 Information tone detection 10 Threshold adaptation . 11 VAD decision . 13 VAD hangover addition 13 Periodicity detection . 13 6 6.1 VAD modules . 14 6.2 Annex A (informative): Simplified

10、block filtering operation 16 Annex B (informative): Pole frequency calculation . 17 Annex C (informative): Change Request History . 18 History . 19 Computational description overview . 14 Pseudo-floating point arithmetic 14 ETSI COPYRIGHT European Telecommunications Standards InstituteLicensed by In

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14、the present document. Foreword This European Standard (Telecommunications series) has been produced by ETSI Technical Committee 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)

15、 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 SMG approval. Should SMG modi the contents of the present document it will be re-released with an identiing ch

16、ange of release date and an increase in version number as follows: Version 8.x.y where: 8 indicates Release 1999 of GSM Phase 2+. x the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates, etc. y the third digit is incremented when editorial on

17、ly changes have been incorporated in the specification. National transposition dates Date of adoption of this EN: Date of latest announcement of this EN (doa): Date of latest publication of new National Standard or endorsement of this EN (dop/e): Date of withdrawal of any conflicting National Standa

18、rd (dow): 3 November 2000 28 February 2001 3 1 August 200 1 3 1 August 200 1 ETSI COPYRIGHT European Telecommunications Standards InstituteLicensed by Information Handling Services(GSM 06.82 version 8.0.1 Release 1999) 5 ETSI EN 300 730 V8.0.1 (2000-11) 1 Scope The present document specifies the Voi

19、ce 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 traffic channels. The requirements are mandatory on any VAD to be used either in GSM Mobile Stations (MS)s or Base Station Sy

20、stems (BSS)s that utilize the enhanced full-rate speech traffic channel. 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, ve

21、rsion number, etc.) or non-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 same number. For this Release 1999

22、 document, references to GSM documents are for Release 1999 versions (version 8.x.y). il GSM O 1.04: “Digital cellular telecommunications system (Phase 2+); Abbreviations and acronyms“. GSM 06.53: “Digital cellular telecommunications system (Phase 2+); ANSI-C code for the GSM Enhanced Full Rate (EFR

23、) speech codec“. GSM 06.54: “Digital cellular telecommunications system (Phase 2+); Test vectors for the GSM Enhanced Full Rate (EFR) speech codec“. GSM 06.60: “Digital cellular telecommunications system (Phase 2+); Enhanced Full Rate (EFR) speech transcoding“. GSM 06.8 1 : “Digital cellular telecom

24、munications system (Phase 2+); Discontinuous transmission (DTX) for Enhanced Full Rate (EFR) speech traffic channels“. i21 31 41 51 3 Definitions, symbols and abbreviations 3.1 Definit ions For the purposes of the present document, the following terms and definitions apply: noise: signal component r

25、esulting fi-om acoustic environmental noise. mobile environment: any environment in which mobile stations may be used. ETSI COPYRIGHT European Telecommunications Standards InstituteLicensed by Information Handling Services(GSM 06.82 version 8.0.1 Release 1999) 6 ETSI EN 300 730 V8.0.1 (2000-11) 3.2

26、Symbols For the purposes of the present document, the following symbols apply: 3.2.1 Variables aav 1 acf adaptcount avo av 1 burstcount den difference dm hangcount lagcount lastdm lags num oldlagcount prederr ptch pvad rav 1 rc rvad smallag stat thvad tone vadflag filter predictor values, see clause

27、 5.2.3 the ACF vector which is calculated in the speech encoder (GSM 06.60 4) secondary hangover counter, see clause 5.2.6 averaged ACF vector, see clause 5.2.2 a previous value of avo, see clause 5.2.2 speech burst length counter, see clause 5.2.8 denominator of left hand side of equation 8 in anne

28、x B, see clause 5.2.5 difference between consecutive values of dm, see clause 5.2.4 spectral distortion measure, see clause 5.2.4 primary hangover counter, see clause 5.2.8 number of subframes in current frame meeting periodicity criterion, see clause 5.2.9 previous value of dm, see clause 5.2.4 the

29、 open loop long term predictor lags for the two halves of the speech encoder frame (GSM 06.60 4) numerator of left hand side of equation 8 in annex B, see clause 5.2.5 previous value of lagcount, see clause 5.2.9 fourth order short term prediction error, see clause 5.2.5 Boolean flag indicating the

30、presence of a periodic signal component, see clause 5.2.9 energy in the current filtered signal frame, see clause 5.2.1 autocorrelation vector obtained from avl, see clause 5.2.3 the first four unquantized reflection coefficients calculated in the speech encoder (GSM 06.60 4) autocorrelation vector

31、of the adaptive filter predictor values, see clause 5.2.6 difference between consecutive lag values, see clause 5.2.9 Boolean flag indicating that the frequency spectrum of the input signal is stationary, see clause 5.2.4 adaptive primary VAD threshold, see clause 5.2.6 Boolean flag indicating the p

32、resence of an information tone, see clause 5.2.5 Boolean VAD decision with hangover included, see clause 5.2.8 veryoldlagcount previous value of oldlagcount, see clause 5.2.9 wad Boolean VAD decision before hangover, see clause 5.2.7 3.2.2 Constants adP burstconst dec fac frames freqth hangconst inC

33、 lthresh margin nthresh plev predth thresh Pth number of frames of hangover for secondary VAD, see clause 5.2.6 minimum length of speech burst to which hangover is added, see clause 5.2.8 determines rate of decrease in adaptive threshold, see clause 5.2.6 determines steady state adaptive threshold,

34、see clause 5.2.6 number of frames over which avo and avl are calculated, see clause 5.2.2 threshold for pole frequency decision, see clause 5.2.5 number of frames of hangover for primary VAD, see clause 5.2.8 determines rate of increase in adaptive threshold, see clause 5.2.6 lag difference threshol

35、d for periodicity decision, see clause 5.2.9 determines upper limit for adaptive threshold, see clause 5.2.6 frame count threshold for periodicity decision, see clause 5.2.9 lower limit for adaptive threshold, see clause 5.2.6 threshold for short term prediction error, see clause 5.2.5 energy thresh

36、old, see clause 5.2.6 decision threshold for evaluation of stat flag, see clause 5.2.4 ETSI COPYRIGHT European Telecommunications Standards InstituteLicensed by Information Handling Services(GSM 06.82 version 8.0.1 Release 1999) 7 ETSI EN 300 730 V8.0.1 (2000-11) 3.2.3 Functions + * I AND OR b MULT(

37、x(i) i=a b SUM(x(i) i=a 1x1 addition subtraction multiplication division absolute value of x Boolean AND Boolean OR the product of the series x(i) for i=a to b the sum of the series x(i) for i=a to b 3.3 Abbreviations For the purposes of the present document, the following abbreviations apply: ACF A

38、utocorrelation function ANSI American National Standards Institute DTX Discontinuous Transmission LTP Long Term Predictor TX Transmission VAD Voice Activity Detector For abbreviations not given in this clause, see GSM 01.04 i. 4 Ge ne ra I The function of the VAD is to indicate whether each 20 ms fr

39、ame produced by the speech encoder contains speech or not. The output is a Boolean flag (vadflag) which is used by the Transmit (TX) DTX handler defied 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 overvi

40、ew of the computational description of the VAD. The computational details necessary for the fixed point implementation of the VAD algorithm are 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

41、in GSM 06.54 3. 5 Functional description The purpose of this clause is to give the reader an understanding of the principles of operation of the VAD, whereas GSM 06.53 2 contains the fixed point computational description of the VAD. In the case of discrepancy between the two descriptions, the descri

42、ption in GSM 06.53 2 will prevail. 5.1 Overview and principles of operation The function of the VAD is to distinguish between noise with speech present and noise without speech present. This is achieved by comparing the energy of a filtered version of the input signal with a threshold. The presence

43、of speech is indicated whenever the threshold is exceeded. ETSI COPYRIGHT European Telecommunications Standards InstituteLicensed by Information Handling Services(GSM 06.82 version 8.0.1 Release 1999) 8 ETSI EN 300 730 V8.0.1 (2000-1 1) Var acf avo avl lags ptch pvad rav 1 rc rvad stat thvad tone va

44、dflag wad The detection of speech in a mobile environment is difficult due to the low speechnoise ratios which are encountered, particularly in moving vehicles. To increase the probability of detecting speech the input signal is adaptively filtered (see clause 5.2.1) to reduce its noise content befo

45、re the voice activity decision is made (see clause 5.2.7). The frequency spectrum and level of the noise may vary within a given environment as well as between different environments. It is therefore necessary to adapt the input filter coefficients and energy threshold at regular intervals as descri

46、bed in clause 5.2.6. Description The ACF vector which is calculated in the speech encoder (GSM 06.60 4). Averaged ACF vector. A previous value of avo. The open loop long term predictor lags for the two halves of the speech encoder frame (GSM 06.60 4). Boolean flag indicating the presence of a period

47、ic signal component. Energy in the current filtered signal frame. Autocorrelation vector obtained from avl . The first four reflection coefficients calculated in the speech encoder (GSM 06.60 4). Autocorrelation vector of the adaptive filter predictor values. Boolean flag indicating that the frequen

48、cy spectrum of the input signal is stationary. Adaptive primary VAD threshold. Boolean flag indicating the presence of an information tone. Boolean VAD decision with hangover included. Boolean VAD decision before hanaover. 5.2 Al go rit h m description The block diagram of the VAD algorithm is shown

49、 in figure 1. The individual blocks are described in the following clauses. The variables shown in the block diagram are described in table 1. Table I : Description of variables in figure I Adaptive filtering and energy decision addition computation Threshold - I- Predictor com utation comparison f avl n t avo averaging Figure I: Functional block diagram of the VAD ETSI COPYRIGHT European Telecommunications Standards InstituteLicensed by Information Handling Services(GSM 06.82 version 8.0.1 Release 1999) 9 ETSI EN 300 730 V8.0.1 (2000-11) Constant fr