1、ETSI EN 301 705 V7.1 .I (2000-04) European Standard (Telecomm unica tions series) Digital cellular telecommunications system (Phase 2+); Substitution and muting of lost frames for Adaptive Multi Rate (AMR) speech traffic channels (GSM 06.91 version 7.1 .I Release 1998) (GSM 06.91 version 7.1.1 Relea
2、se 1998) 2 ETSI EN 301 705 V7.1.1 (2000-04) Reference RENEMG-1 10691 Q7R1 Keywords Digital cellular telecommunications system, Global System for Mobile communications (GSM), AMR ETSI 650 Route des Lucioles F-O6921 Sophia Antipolis Cedex - FRANCE Tel.: +33 4 92 94 42 O0 Fax: +33 4 93 65 47 16 Siret N
3、o 348 623 562 0001 7 - NAF 742 C Association but non lucratif enregistre la Sous-prfecture de Grasse (06) No 7803/88 Important notice The pre ent d Individual copies of the present document can be downloaded from: http:/w.etsi.aq cument mav be made available in more than one electronic version or in
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6、.fr Coovriaht Notification No part may be reproduced except as authorized by written permission. The copyright and the foregoing restriction extend to reproduction in all media. O European Telecommunications Standards Institute 2000. All rights reserved. ETSI (GSM 06.91 version 7.1.1 Release 1998) 3
7、 ETSI EN 301 705 V7.1.1 (2000-04) Contents Intellectual Property Rights 4 Foreword 4 1 2 3 3.1 3.2 4 5 5.1 5.2 5.3 5.4 6 6.1 6.2 6.2.1 6.2.2 6.2.3 6.2.3.1 6.2.3.2 6.3 6.3.1 6.3.2 6.3.2.1 6.3.2.2 6.3.3 6.4 Scope 5 References 5 Definitions and abbreviations 5 Definitions 5 Abbreviations . 6 General .
8、6 Requirements 6 Error detection 6 Lost speech frames . 6 First lost SID frame 6 Subsequent lost SID frames 7 Example ECU/BFH Solution 1 7 State Machine . 7 Assumed Active Speech Frame Error Concealment Unit Actions 8 BFI = O. prevBFI = O. State = O 8 BFI = O. prevBFI = 1. State = O or 5 . 8 BFI = 1
9、, prevBFI = O or 1, State = 1 . . 9 LTP-lag update 9 Innovation sequence 9 Assumed Non-Active Speech Signal Error Concealment Unit Actions 10 General 10 Detectors . 10 Background detector . 10 Voicing detector 10 Background ECU Actions . 10 Substitution and muting of lost SID frames 10 7 Example ECU
10、/BFH Solution 2 11 7.1 State Machine . 11 7.2 Substitution and muting of lost speech frames . 11 7.2.1 BFI = O. prevBFI = O. State = O 11 7.2.2 BFI = O. prevBFI = 1. State = O or 5 . 11 7.2.3 BFI = 1, prevBFI = O or 1, State = 1 . . 12 7.2.3.1 LTP-lag update 12 7.2.4 Innovation sequence . 12 7.3 Sub
11、stitution and muting of lost SID frames 12 Annex A (informative): Document change history 13 History 14 ETSI (GSM 06.91 version 7.1.1 Release 1998) 4 ETSI EN 301 705 V7.1.1 (2000-04) Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared t
12、o ETSI. The information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found in SR O00 3 14: “Intellectual Propero Rights (IPRs); Essential, or potentially Essential, IPRs notifed to ETSI in respect of ETSI standards“, which is availabl
13、e from the ETSI Secretariat. Latest updates are available on the ETSI Web server (h ttix/www.etsi. ocdini). Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in SR O00 31
14、4 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This European Standard (Telecommunications series) has been produced by the Special Mobile Group (SMG). The present document introduces the Adaptive Multi-Rate (AMR) speech traf
15、fic 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 modify the contents of the present document it will be re-released with an identifying change of
16、release date and an increase in version number as follows: Version 7.x.y where: 7 indicates Release 1998 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 only chang
17、es 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 Standard (dow)
18、: 31 March 2000 30June2000 3 1 December 2000 3 1 December 2000 ETSI (GSM 06.91 version 7.1.1 Release 1998) 5 ETSI EN 301 705 V7.1.1 (2000-04) 1 Scope The present document defines a frame substitution and muting procedure which shall be used by the Receive (RX) Discontinuous Transmission (DTX) handle
19、r when one or more lost speech or Silence Descriptor (SID) frames are received from the Radio Sub System (RSS). The requirements of the present document are mandatory for implementation in all GSM Base Station Systems (BSS)s and Mobile Stations (MS)s capable of supporting the AMR speech traffic chan
20、nel. It is not mandatory to follow the bit exact implementation outlined in the present document and the corresponding C source code. 2 References The following documents contain provisions which, through reference in this text, constitute provisions of the present document. References are either sp
21、ecific (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. A non-specific reference to an ETS shall also be taken to refer to later versions p
22、ublished as an EN with the same number. For this Release 1998 document, references to GSM documents are for Release 1998 versions (version 7.x.y). il GSM 05.03: “Digital cellular telecommunications system (Phase 2+); Channel coding“. Pl 31 GSM 06.90: “Digital cellular telecommunications system (Phas
23、e 2+); AMR speech transcoding“. GSM 06.93: “Digital cellular telecommunications system (Phase 2+); Discontinuous transmission (DTX) for Adaptive Multi Rate (AMR) speech traffic channels“. GSM 08.60: “Digital cellular telecommunications system (Phase 2+); Inband control of remote transcoders and rate
24、 adaptors for AMR, Enhanced Full Rate (EFR) and Full Rate traffic channels“. GSM 08.6 1: “Digital cellular telecommunications system (Phase 2+); Inband control of remote transcoders and rate adaptors for Half Rate traffic channels“. 41 51 3 3.1 Definitions and abbreviations Definitions For the purpo
25、ses of the present document, the following terms and definitions apply. N-point median operation: Consists of sorting the N elements belonging to the set for which the median operation is to be performed in an ascending order according to their values, and selecting the (int (N/2) + 1) -the largest
26、value of the sorted set as the median value. Further definitions of terms used in the present document can be found in GSM 06.90 2, GSM 06.93 3, GSM 05.03 i and GSM 08.60 4. ETSI (GSM 06.91 version 7.1.1 Release 1998) 6 ETSI EN 301 705 V7.1.1 (2000-04) 3.2 Abbreviations For the purposes of the prese
27、nt document, the following abbreviations apply: BFI BSIAbis prevBFI PDFI RSS Rx DTX SID CRC ccu ECU BFH medianN TRAU Bad Frame Indication from Radio Sub System Bad Sub-block Indication obtained from A-bis CRC checks Bad Frame Indication of previous frame Potentially Degraded Frame Indication from RS
28、S Radio Sub System Receive Discontinuous Transmission SIlence Descriptor frame (Background descriptor) Cyclic Redundancy Check Channel Coding Unit Error Concealment Unit Bad Frame Handling N-point median operation Transcoding Rate Adaptation Unit 4 General The purpose of frame substitution is to con
29、ceal the effect of lost frames. The purpose of muting the output in the case of several lost frames is to indicate the breakdown of the channel to the user and to avoid generating possible annoying sounds as a result from the frame substitution procedure. The RSS indicates lost speech or lost SID fr
30、ames by setting its Bad Frame Indication flag (BFI) based on CRCs and possibly other error detection mechanisms. The TRAU calculates from the CRCs inserted by the CCU in the TRAU frames one BSIAbis flag for every sub-block of speech parameters. If either one or both of these flags are set, the speec
31、h decoder shall perform parameter substitution to conceal errors. The RSS also indicates potentially degraded frames using the flag PDFI. This flag is derived from the soft output of the channel decoder. It may be used by the speech decoder selectively depending on the estimated signal type. The exa
32、mple solutions provided in paragraphs 6 and 7 apply only to bad frame handling on a complete speech frame basis. However some parts could be modified for substitution of only bad sub-blocks. 5 Requirements 5.1 Error detection An error is detected and the BFI flag is set by the RSS.0. The PDFI flag i
33、s set appropriately using the soft output from the channel decoder. 5.2 Lost speech frames Normal decoding of lost speech frames would result in very unpleasant noise effects. In order to improve the subjective quality, lost speech frames shall be substituted with either a repetition or an extrapola
34、tion of the previous good speech frame(s). This substitution is done so that it gradually will decrease the output level, resulting in silence at the output. Subclauses 6, and 7 provide example solutions. 5.3 First lost SID frame A lost SID frame shall be substituted by using the SID information fro
35、m earlier received valid SID frames and the procedure for valid SID frames be applied as described in GSM 06.93 3. ETSI (GSM 06.91 version 7.1.1 Release 1998) 7 ETSI EN 301 705 V7.1.1 (2000-04) 5.4 Subsequent lost SID frames For many subsequent lost SID frames, a muting technique shall be applied to
36、 the comfort noise that will gradually decrease the output level. For subsequent lost SID frames, the muting of the output shall be maintained. Subclauses 6 and 7 provide example solutions. 6 Example ECU/BFH Solution 1 The C code of the following example is embedded in the bit exact software of the
37、codec. In the code the ECU is designed to allow subframe-by-subframe synthesis, thereby reducing the speech synthesis delay to a minimum. 6.1 State Machine This example solution for substitution and muting is based on a state machine with seven states (Figure 1). The system starts in state O. Each t
38、ime a bad frame is detected, the state counter is incremented by one and is saturated when it reaches 6. Each time a good speech frame is detected, the state counter is reset to zero, except when we are in state 6, where we set the state counter to 5. The state indicates the quality of the channel:
39、the larger the value of the state counter, the worse the channel quality is. The control flow of the state machine can be described by the following C code (BPI = bad frame indicator, State = state variable): if(BFI != O ) State = State + 1 ; else if(State = 6) State = 5; else State = O; if(State 6
40、) State = 6; In addition to this state machine, the Bad Frame Flag from the previous frame is checked (prevBF1). The processing depends on the value of the State-variable. In states O and 5, the processing depends also on the two flags BPI and prevBF1. ETSI (GSM 06.91 version 7.1.1 Release 1998) 8 E
41、TSI EN 301 705 V7.1.1 (2000-04) The procedure can be described as follows: z STATE = O BFI=O PevBFI = O or 1 I 1 + Badframe (BFI=l) Good frame (BH=O) U Figure 1: State machine for controlling the bad frame substitution 6.2 Assumed Active Speech Frame Error Concealment Unit Act ions 6.2.1 BFI = O, pr
42、evBFI = O, State = O No error is detected in the received or in the previous received speech frame. The received speech parameters are used in the normal way in the speech synthesis. The current frame of speech parameters is saved. 6.2.2 BFI = O, prevBFI = 1, State = O or 5 No error is detected in t
43、he received speech frame, but the previous received speech frame was bad. The LTP gain and fixed codebook gain are limited below the values used for the last received good subframe: gp I g“-i) gp = :;-i), gp g“-i) ETSI (GSM 06.91 version 7.1.1 Release 1998) 9 ETSI EN 301 705 V7.1.1 (2000-04) where g
44、p = current decoded LTP gain, gp (-1) = LTP gain used for the last good subframe (BFI = O), and g I g(-i) g = ;Il), g g(-i) where g = current decoded fixed codebook gain and g (-1) = fixed codebook gain used for the last good subframe (BFI = O). The rest of the received speech parameters are used no
45、rmally in the speech synthesis. The current frame of speech parameters is saved. 6.2.3 BFI = 1, prevBFI = O or 1, State = 1.6 An error is detected in the received speech frame and the substitution and muting procedure is started. The LTP gain and fixed codebook gain are replaced by attenuated values
46、 from the previous subframes: P(state) gp(-i), P( state) medians( gp (-1), . . . , gp (-S), gp (-1) I medians( g (-1), . . . , gp (-5) gp (-1) medians( gp (-1), . . . , gp (-5) (3) where gp = current decoded LTP gain, g median50 = 5-point median operation, P(state) = attenuation factor (P(1) = 0.98,
47、 P(2) = 0.98, P(3) = 0.8, P(4) = 0.3, P(5) = 0.2, P(6) = 0.2), state = state number, and C(state) g(-i), C( state) medians( g (-1), . . . , g (-S), (-I), . . . , g (-n) = LTP gains used for the last n subframes, g (-1) I medians( g (- 1), . . . , g (-5) g( -1) medians( g( -l), . . . , g (-5) (4) whe
48、re g= current decoded fixed codebook gain, g(-l), . . . , g(-n) = fixed codebook gains used for the last n subframes, median50 = 5-point median operation, C(state) = attenuation factor (C(1) = 0.98, C(2) = 0.98, C(3) = 0.98, C(4) = 0.98, C(5) = 0.98, C(6) = 0.7), and state = state number. The higher
49、 the state value is, the more the gains are attenuated. Also the memory of the predictive fixed codebook gain is updated by using the average value of the past four values in the memory: l4 ener(0) = -E ener(-i) 4 i=l The past LSFs are shifted towards their mean: (6) Zsf - qi( i) = Zsf - q2( i) = a past- Zsf - q( i) + (i - a)mean- Zsf (i), i = O .9 where a = 0.95, lsf-ql and lsf-q2 are two sets of LSF-vectors for current frame, past-lsf-q is lsf-q2 from the previous frame, and mean-lsf is the average LSF-vector. Note that two sets of
