1、 ETSI TS 126 191 V15.0.0 (2018-07) Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); LTE; Speech codec speech processing functions; Adaptive Multi-Rate - Wideband (AMR-WB) speech codec; Error concealment of erroneous or lost frames (3GPP
2、TS 26.191 version 15.0.0 Release 15) TECHNICAL SPECIFICATION ETSI ETSI TS 126 191 V15.0.0 (2018-07)13GPP TS 26.191 version 15.0.0 Release 15Reference RTS/TSGS-0426191vf00 Keywords GSM,LTE,UMTS ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE Tel.: +33 4 92 94 42 00 Fax: +33 4 93 6
3、5 47 16 Siret N 348 623 562 00017 - NAF 742 C Association but non lucratif enregistre la Sous-Prfecture de Grasse (06) N 7803/88 Important notice The present document can be downloaded from: http:/www.etsi.org/standards-search The present document may be made available in electronic versions and/or
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9、its Members. GSMand the GSM logo are trademarks registered and owned by the GSM Association. ETSI ETSI TS 126 191 V15.0.0 (2018-07)23GPP TS 26.191 version 15.0.0 Release 15Intellectual Property Rights Essential patents IPRs essential or potentially essential to normative deliverables may have been d
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14、oreword This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP). The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or GSM identities. These should be interpreted as being references to the
15、corresponding ETSI deliverables. The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under http:/webapp.etsi.org/key/queryform.asp. Modal verbs terminology In the present document “shall“, “shall not“, “should“, “should not“, “may“, “need not“, “will“, “will not“, “can“ and
16、“cannot“ are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions). “must“ and “must not“ are NOT allowed in ETSI deliverables except when used in direct citation. ETSI ETSI TS 126 191 V15.0.0 (2018-07)33GPP TS 26.191 version 15.0.0 R
17、elease 15Contents Intellectual Property Rights 2g3Foreword . 2g3Modal verbs terminology 2g3Foreword . 4g31 Scope 5g32 Normative references . 5g33 Definitions and abbreviations . 5g33.1 Definitions 5g33.2 Abbreviations . 5g34 General . 6g35 Requirements 6g35.1 Error detection 6g35.2 Erroneous or lost
18、 speech frames . 6g35.3 First lost SID frame 6g35.4 Subsequent lost SID frames 6g36 Example ECU/BFH Solution . 6g36.1 State Machine . 6g36.2 Substitution and muting of erroneous/lost speech frames 8g36.2.1 BFI = 0, prevBFI = 0, State = 0 or 1 . 8g36.2.2 BFI = 0, prevBFI = 1, State = 0 to3 8g36.2.3 B
19、FI = 1, prevBFI = 0 or 1, State = 1.6 8g36.2.3.1 LTP gain 2 presented to TSG for approval; 3 Indicates TSG approved document under change control. y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates, etc. z the third digit is incremented
20、when editorial only changes have been incorporated in the specification; ETSI ETSI TS 126 191 V15.0.0 (2018-07)53GPP TS 26.191 version 15.0.0 Release 151 Scope This specification defines an error concealment procedure, also termed frame substitution and muting procedure, which shall be used by the A
21、MR-WB speech codec receiving end when one or more erroneous/lost speech or lost Silence Descriptor (SID) frames are received. The requirements of this document are mandatory for implementation in all networks and User Equipment (UE)s capable of supporting the AMR-WB speech codec. It is not mandatory
22、 to follow the bit exact implementation outlined in this document and the corresponding C source code. 2 Normative references The following documents contain provisions which, through reference in this text, constitute provisions of the present document. - References are either specific (identified
23、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. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference
24、 implicitly refers to the latest version of that document in the same Release as the present document. 1 3GPP TS 26.202“AMR Wideband Speech Codec; Interface to RAN“. 2 3GPP TS 26.190“AMR Wideband Speech Codec; Transcoding functions“. 3 3GPP TS 26.193“AMR Wideband Speech Codec; Source Controlled Rate
25、 operation“. 4 3GPP TS 26.201“AMR Wideband Speech Codec; Frame structure“. 3 Definitions and abbreviations 3.1 Definitions For the purposes of this document, the following definition applies: N-point median operation: Consists of sorting the N elements belonging to the set for which the median opera
26、tion is to be performed in an ascending order according to their values, and selecting the (int (N/2) + 1) -th largest value of the sorted set as the median value. Further definitions of terms used in this document can be found in the references. 3.2 Abbreviations For the purposes of this document,
27、the following abbreviations apply: AMR-WB Adaptive Multi Rate - WideBand AN Access Network BFI Bad Frame Indication from AN BSI_netw Bad Sub-block Indication obtained from AN interface CRC checks prevBFI Bad Frame Indication of previous frame RX Receive SCR Source Controlled Rate (operation) SID Sil
28、ence Descriptor frame (Background noise) CRC Cyclic Redundancy Check ECU Error Concealment Unit BFH Bad Frame Handling medianN N-point median operation ETSI ETSI TS 126 191 V15.0.0 (2018-07)63GPP TS 26.191 version 15.0.0 Release 154 General The purpose of the error concealment procedure is to concea
29、l the effect of erroneous/lost AMR-WB speech frames. The purpose of muting the output in the case of several erroneous/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 error concealment procedure. The network sh
30、all indicate erroneous/lost speech or lost SID frames by setting the RX_TYPE values 3 to SPEECH_BAD, SID_BAD or SPEECH_LOST. If these flags are set, the speech decoder shall perform parameter substitution to conceal errors. The example solution provided in paragraph 6 apply only to bad frame handlin
31、g on a complete speech frame basis. Sub-frame based error concealment may be derived using similar methods. 5 Requirements 5.1 Error detection If the most sensitive bits of the AMR-WB speech data (class A in 4) are received in error, the network shall indicate RX_TYPE = SPEECH_BAD in which case the
32、BFI flag is set. When the frame is not received, the network shall indicate RX_TYPE = RX_SPEECH_LOST in which case the BFI flag is set as well. If a SID frame is received in error, the network shall indicate RX_TYPE = SID_BAD 5.2 Erroneous or lost speech frames Normal decoding of erroneous/lost spee
33、ch frames would result in very unpleasant noise effects. In order to improve the subjective quality, erroneous/lost speech frames shall be substituted with either a repetition or an extrapolation of the previous good speech frame(s). This substitution is done so that it gradually will decrease the o
34、utput level, resulting in silence at the output. Subclause 6 provides example solution. 5.3 First lost SID frame A lost SID frame shall be substituted by using the SID information from earlier received valid SID frames and the procedure for valid SID frames be applied as described in 3. 5.4 Subseque
35、nt lost SID frames For many subsequent lost SID frames, a muting technique shall be applied to the comfort noise that will gradually decrease the output level. For subsequent lost SID frames, the muting of the output shall be maintained. Subclause 6 provides example solutions. 6 Example ECU/BFH Solu
36、tion 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 0. Each time a bad frame is detected, the state counter is incremented by one and is saturated when it reaches 6. Each time a good speech fram
37、e is detected, the state counter is right-shifted by one. The state indicates the quality of the channel: 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 (BFI = bad frame indicator, State = st
38、ate variable): if(BFI != 0 ) State = State + 1; if(State 6) State = 6; else State = State 1; ETSI ETSI TS 126 191 V15.0.0 (2018-07)73GPP TS 26.191 version 15.0.0 Release 15In addition to this state machine, the Bad Frame Flag from the previous frame is checked (prevBFI). The processing depends on th
39、e value of the State-variable. In states 0 and 6, the processing depends on the BFI flag. The procedure can be described as follows: Figure 1: State machine for controlling the bad frame substitution STATE = 0BFI = 0PrevBFI = 0 or 1Good frame (BFI=0)Bad frame (BFI=1)STATE = 1(BFI, prevBFI) =(1,0) or
40、 (0,1) or(0,0)STATE = 2(BFI, prevBFI) =(1,1) or (1,0) or(0,1)STATE = 3(BFI, prevBFI) =(1,1) or (1,0) or(0,1)STATE = 4BFI = 1prevBFI = 0 or 1STATE = 5BFI = 1prevBFI = 1STATE = 6BFI = 1prevBFI = 1ETSI ETSI TS 126 191 V15.0.0 (2018-07)83GPP TS 26.191 version 15.0.0 Release 156.2 Substitution and muting
41、 of erroneous/lost speech frames 6.2.1 BFI = 0, prevBFI = 0, State = 0 or 1 No error is detected in the received or in the previous received speech frame. The received speech parameters are used normally in the speech synthesis. The current frame of speech parameters is saved. 6.2.2 BFI = 0, prevBFI
42、 = 1, State = 0 to3 No error is detected in the received speech frame but the previous received speech frame was bad. The LTP gain is used normally in the speech synthesis and fixed codebook gain are limited below the values used for the last received good subframe: =otherwisengnggorggngcccreceivedc
43、receivedcreceivedc,)1(*25.125.1)1( 100,)( (1) where creceivedg= current decoded fixed codebook-gain )1( ngc= fixed codebook gain used for the last good subframe (BFI = 0) )(ngc= fixed codebook gain to be used for the current frame. The rest of the received speech parameters are used normally in the
44、speech synthesis. The current frame of speech parameters is saved. 6.2.3 BFI = 1, prevBFI = 0 or 1, State = 1.6 An error is detected in the received speech frame and the substitution and muting procedure is started. 6.2.3.1 LTP gain & fixed codebook gain concealment when RX_FRAMETYPE = SPEECH_BAD Th
45、e LTP gain pg and fixed codebook gain cg are replaced by attenuated values from the previous subframes: )5(),.,1(5)( = ngngmedianstatePgpppp(2)=2VAD_HIST ,)5(),.,1(52VAD_HIST,)5(),.,1(5)(ngngmedianngngmedianstatePgcccccc(3) where: gp= current decoded LTP gain, cg = current decoded fixed codebook gai
46、n, )5(),.,1( ngngpp= LTP gains used for the last 5 subframes, )5(),.,1( ngngcc= fixed codebook gains used for the last 5 subframes, median5() = 5-point median operation, )(statePp= attenuation factor (Pp(1) = 0.98, Pp(2) = 0.96, Pp(3) = 0.75, Pp(4) = 0.23, Pp(5) = 0.05, Pp(6) = 0.01), )(statePc= att
47、enuation factor (Pc(1) = 0.98, Pc(2) = 0.98, Pc(3) = 0.98, Pc(4) = 0.98, Pc(5) = 0.98, Pc(6) = 0.70), state = state number 06, VAD_HIST is number of consecutive VAD=0 decisions. ETSI ETSI TS 126 191 V15.0.0 (2018-07)93GPP TS 26.191 version 15.0.0 Release 15The higher the state value is, the more the
48、 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: () ()341041=iinenerener (4) 6.2.3.2 LTP gain & fixed codebook gain concealment when RX_FRAMETYPE = SPEECH_LOST The LTP gain pg and fixed codebook
49、gain cg are replaced by attenuated values from the previous subframes: )5(),.,1(5)( = ngngmedianstatePgpppp(5)=2VAD_HIST ,)5(),.,1(52VAD_HIST,)5(),.,1(5)(ngngmedianngngmedianstatePgcccccc(6) where: gp= current decoded LTP gain, cg = current decoded fixed codebook gain, )5(),.,1( ngngpp= LTP gains used for the last 5 subframes, )5(),.,1( ngngcc= fixed codebook gains used for the last 5 subframes, median5() = 5-point median operation, )(statePp= attenuation factor (Pp(1) = 0.95, Pp(2) = 0.90
