1、 ETSI TS 126 091 V15.0.0 (2018-07) Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); LTE; Mandatory Speech Codec speech processing functions; Adaptive Multi-Rate (AMR) speech codec; Error concealment of lost frames (3GPP TS 26.091 version
2、 15.0.0 Release 15) TECHNICAL SPECIFICATION ETSI ETSI TS 126 091 V15.0.0 (2018-07)13GPP TS 26.091 version 15.0.0 Release 15Reference RTS/TSGS-0426091vf00 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 65 47 16 Siret N 3
3、48 623 562 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 in print. The con
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9、nd the GSM logo are trademarks registered and owned by the GSM Association. ETSI ETSI TS 126 091 V15.0.0 (2018-07)23GPP TS 26.091 version 15.0.0 Release 15Intellectual Property Rights Essential patents IPRs essential or potentially essential to normative deliverables may have been declared to ETSI.
10、The information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found in ETSI SR 000 314: “Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards“, which is available
11、from the ETSI Secretariat. Latest updates are available on the ETSI Web server (https:/ipr.etsi.org/). 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 ETSI SR 000 31
12、4 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Trademarks The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners. ETSI claims no ownership of these except for any which are
13、indicated as being the property of ETSI, and conveys no right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks. Foreword This Tech
14、nical 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 corresponding ETS
15、I 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 “cannot“ are to b
16、e 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 126 091 V15.0.0 (2018-07)33GPP TS 26.091 version 15.0.0 Release 15Contents
17、 Intellectual Property Rights 2g3Foreword . 2g3Modal verbs terminology 2g3Foreword . 4g31 Scope 5g32 References 5g33 Definitions and abbreviations . 5g33.1 Definitions 5g33.2 Abbreviations . 5g34 General . 6g35 Requirements 6g35.1 Error detection 6g35.2 Lost speech frames . 6g35.3 First lost SID fra
18、me 6g35.4 Subsequent lost SID frames 6g36 Example ECU/BFH Solution 1 6g36.1 State Machine . 6g36.2 Assumed Active Speech Frame Error Concealment Unit Actions . 8g36.2.1 BFI = 0, prevBFI = 0, State = 0 8g36.2.2 BFI = 0, prevBFI = 1, State = 0 or 5 . 8g36.2.3 BFI = 1, prevBFI = 0 or 1, State = 1.6 9g3
19、6.2.3.1 LTP-lag update 9g36.2.3.2 Innovation sequence 9g36.3 Assumed Non-Active Speech Signal Error Concealment Unit Actions . 10g36.3.1 General 10g36.3.2 Detectors. 10g36.3.2.1 Background detector . 10g36.3.2.2 Voicing detector 10g36.3.3 Background ECU Actions 10g36.4 Substitution and muting of los
20、t SID frames . 10g37 Example ECU/BFH Solution 2 10g37.1 State Machine . 10g37.2 Substitution and muting of lost speech frames . 11g37.2.1 BFI = 0, prevBFI = 0, State = 0 11g37.2.2 BFI = 0, prevBFI = 1, State = 0 or 5 . 11g37.2.3 BFI = 1, prevBFI = 0 or 1, State = 1.6 11g37.2.3.1 LTP-lag update 12g37
21、.2.4 Innovation sequence . 12g37.3 Substitution and muting of lost SID frames . 12g3Annex A (informative): Change history . 13g3History 14g3ETSI ETSI TS 126 091 V15.0.0 (2018-07)43GPP TS 26.091 version 15.0.0 Release 15Foreword This Technical Specification has been produced by the 3rdGeneration Part
22、nership Project (3GPP). The contents of the present document are subject to continuing work within the TSG and may change following formal TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an identifying change of release date and an inc
23、rease in version number as follows: Version x.y.z where: x the first digit: 1 presented to TSG for information; 2 presented to TSG for approval; 3 or greater indicates TSG approved document under change control. y the second digit is incremented for all changes of substance, i.e. technical enhanceme
24、nts, corrections, updates, etc. z the third digit is incremented when editorial only changes have been incorporated in the document. ETSI ETSI TS 126 091 V15.0.0 (2018-07)53GPP TS 26.091 version 15.0.0 Release 151 Scope The present document defines an error concealment procedure, also termed frame s
25、ubstitution and muting procedure, which shall be used by the AMR speech codec receiving end when one or more lost speech or lost Silence Descriptor (SID) frames are received. The requirements of the present document are mandatory for implementation in all networks and User Equipment (UE)s capable of
26、 supporting the AMR speech codec. 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 docum
27、ent. - References are either specific (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. In the case of a reference to a 3GPP document (i
28、ncluding a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document. 1 3GPP TS 26.102: “AMR Speech Codec; Interface to Iu snd Uu“. 2 3GPP TS 26.090: “Transcoding functions“. 3 3GPP TS 26.093: “Source Controlled Rate
29、operation“. 4 3GPP TS 26.101: “Frame Structure“. 3 Definitions and abbreviations 3.1 Definitions For the purposes 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
30、 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 the present document can be found in the references. 3.2 Abbreviations For the purposes of the present documen
31、t, the following abbreviations apply: AN Access Network BFH Bad Frame Handling BFI Bad Frame Indication from AN BSI_netw Bad Sub-block Indication obtained from AN interface CRC checks CRC Cyclic Redundancy Check ECU Error Concealment Unit medianN N-point median operation PDFI Potentially Degraded Fr
32、ame Indication prevBFI Bad Frame Indication of previous frame RX Receive SCR Source Controlled Rate (operation) SID Silence Descriptor frame (Background descriptor) ETSI ETSI TS 126 091 V15.0.0 (2018-07)63GPP TS 26.091 version 15.0.0 Release 154 General The purpose of the error concealment procedure
33、 is to conceal the effect of lost AMR speech 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 error concealment procedure. The network shall indica
34、te lost speech or lost SID frames by setting the RX_TYPE values 3 to SPEECH_BAD or SID_BAD. If these flags are set, the speech decoder shall perform parameter substitution to conceal errors. The network should also indicate potentially degraded frames using the flag RX_TYPE value SPEECH_PROBABLY_DEG
35、RADED. This flag may be derived from channel quality indicators. It may be used by the speech decoder selectively depending on the estimated signal type. The example solutions provided in paragraphs 6 and 7 apply only to bad frame handling on a complete speech frame basis. Sub-frame based error conc
36、ealment may be derived using similar methods. 5 Requirements 5.1 Error detection If the most sensitive bits of the AMR speech data (class A in 4) are received in error, the network shall indicate RX_TYPE = SPEECH_BAD in which case the BFI flag is set. If a SID frame is received in error, the network
37、 shall indicate RX_TYPE = SID_BAD in which case the BFI flag is also set. The RX_TYPE = SPEECH_PROBABLY_DEGRADED flag should be set appropriately using quality information from the channel decoder, in which case the PDFI flag is set. 5.2 Lost speech frames Normal decoding of lost speech frames would
38、 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 extrapolation of the previous good speech frame(s). This substitution is done so that it gradually will decrease the output level, resulting in
39、 silence at the output. Clauses 6, and 7 provide example solutions. 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 Subsequent lost SID frames F
40、or 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. Clauses 6 and 7 provide example solutions. 6 Example ECU/BFH Solution 1 The C code
41、 of the following example is embedded in the bit exact software of the 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 mac
42、hine 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 frame is detected, the state counter is reset to zero, except when we are in state 6, where we set t
43、he state counter to 5. 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 = state variable): ETSI ETSI TS 126 091
44、 V15.0.0 (2018-07)73GPP TS 26.091 version 15.0.0 Release 15if(BFI != 0 ) State = State + 1; else if(State = 6) State = 5; else State = 0; if(State 6 ) State = 6; In addition to this state machine, the Bad Frame Flag from the previous frame is checked (prevBFI). The processing depends on the value of
45、 the State-variable. In states 0 and 5, the processing depends also on the two flags BFI and prevBFI. ETSI ETSI TS 126 091 V15.0.0 (2018-07)83GPP TS 26.091 version 15.0.0 Release 15The procedure can be described as follows: Figure 1: State machine for controlling the bad frame substitution 6.2 Assum
46、ed Active Speech Frame Error Concealment Unit Actions 6.2.1 BFI = 0, prevBFI = 0, State = 0 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 save
47、d. 6.2.2 BFI = 0, prevBFI = 1, State = 0 or 5 No error is detected in the 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: (1) where = current decoded LTP gain, = LTP gai
48、n used for the last good subframe (BFI = 0), and STATE = 0BFI = 0PrevBFI = 0 or 1STATE = 1BFI = 1PrevBFI = 0STATE = 2BFI = 1PrevBFI = 1STATE = 3BFI = 1PrevBFI = 1STATE = 5BFI = 0 or 1PrevBFI = 1STATE = 6BFI = 1PrevBFI = 0 or 1Good frame (BFI=0) Bad frame (BFI=1) STATE = 4BFI = 1PrevBFI = 1()() ()ggg
49、ggggppppppp=,111gp()gp1ETSI ETSI TS 126 091 V15.0.0 (2018-07)93GPP TS 26.091 version 15.0.0 Release 15(2) where = current decoded fixed codebook gain and = fixed codebook gain used for the last good subframe (BFI = 0). The rest of the received speech parameters are used normally in the 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. The LTP gain and fixed codebook gain are replac
