ETSI TS 126 226-2017 Digital cellular telecommunications system (Phase 2+) (GSM) Universal Mobile Telecommunications System (UMTS) Cellular text telephone modem General description.pdf

1、 ETSI TS 126 226 V14.0.0 (2017-04) Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); Cellular text telephone modem; General description (3GPP TS 26.226 version 14.0.0 Release 14) TECHNICAL SPECIFICATION GLOBAL SYSTEM FOR MOBILE COMMUNICAT

2、IONSRETSI ETSI TS 126 226 V14.0.0 (2017-04)13GPP TS 26.226 version 14.0.0 Release 14Reference RTS/TSGS-0426226ve00 Keywords GSM,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 348 623 562 00017 - NAF 742 C Association bu

3、t 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 content of any electronic and/or print version

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7、m except as authorized by written permission of ETSI. The content of the PDF version shall not be modified without the written authorization of ETSI. The copyright and the foregoing restriction extend to reproduction in all media. European Telecommunications Standards Institute 2017. All rights rese

8、rved. DECTTM, PLUGTESTSTM, UMTSTMand the ETSI logo are Trade Marks of ETSI registered for the benefit of its Members. 3GPPTM and LTE are Trade Marks of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners. GSM and the GSM logo are Trade Marks registered and owned by

9、 the GSM Association. ETSI ETSI TS 126 226 V14.0.0 (2017-04)23GPP TS 26.226 version 14.0.0 Release 14Contents 1 Scope 4g32 References 4g33 Definitions and Abbreviations 4g33.1 Definitions 4g33.2 Abbreviations . 4g34 General . 5g35 The problem . 5g35.1 US regulatory issues . 5g36 The goals and object

10、ives 6g37 Text Telephony architecture based upon CTM 6g37.1 Text Telephone devices 8g37.2 Error resilient transmission in the speech path . 8g37.3 Interworking with traditional Text Telephone devices . 8g38 Technical description of CTM . 9g38.1 Overview 9g38.2 CTM transmitter . 9g38.2.1 Character se

11、t . 9g38.2.2 FEC error protection . 9g38.2.3 CTM burst structure 10g38.2.4 Periodic muting and insertion of resynchronization sequence 11g38.2.5 Interleaver and synchronization preamble 14g38.2.6 CTM modulator 15g38.2.7 Switching between speech and data 16g38.3 CTM receiver . 16g39 CTM negotiation a

12、nd inband signaling 16g39.1 Definition of control characters 17g39.2 CTM availability negotiation . 17g310 Functions in the CTM environment . 17g310.1 CTM to CTM communication 17g310.2 CTM between the mobile side and a gateway 18g310.3 CTM within the transcoding equipment . 18g310.4 Cascading of CTM

13、 adapters in the speech path 18g310.5 Rerouting of a call from a CTM supported environment to a non-supported environment 18g3Annex A (Informative): CTM Receiver 20g3A.1 Demodulator . 20g3A.2 Synchronization and de-interleaver 20g3A.3 Puncture and resynchronization . 21g3A.4 FEC error correction . 2

14、1g3Annex B (informative): Change history . 22g3History 23g3ETSI ETSI TS 126 226 V14.0.0 (2017-04)33GPP TS 26.226 version 14.0.0 Release 14Foreword This technical description has been produced by T1P1. The present document is a description of the Cellular Text Telephone Modem solution for reliable tr

15、ansmission of a text telephone conversation via the speech channel of cellular or PSTN networks The contents of the present document are subject to continuing work within 3GPP and may change following formal 3GPP approval. Should the 3GPP TSG modify the contents of this TD, it will be re-released by

16、 the 3GPP TSG with an identifying change of release date and an increase in version number as follows: Version x.y.z where: x the first digit: 1 presented to 3GPP for information; 2 presented to 3GPP for approval; 3 Indicates 3GPP approved document under change control. y the second digit is increme

17、nted for all changes of substance, i.e. technical enhancements, corrections, updates, etc. z the third digit is incremented when editorial only changes have been incorporated in the specification; ETSI ETSI TS 126 226 V14.0.0 (2017-04)43GPP TS 26.226 version 14.0.0 Release 141 Scope This Technical S

18、pecification (TS) concerns the Cellular Text Telephone Modem (CTM). CTM allows reliable transmission of a text telephone conversation alternating with a speech conversation through the existing speech communication paths in cellular mobile phone systems. This reliability is achieved by an improved m

19、odulation technique, including error protection, interleaving and synchronization. Together with recommendations ITU-T V.18 and T.140, CTM may serve for worldwide applications in text telephony. A general overview and explanations of possible implementation architectures is provided. CTM is intended

20、 for use in end terminals (on the mobile or fixed side) and within the network for the adaptation between CTM and existing traditional text telephone standards. The CTM transmitter is fully specified and a bit exact C-code reference is provided. An implementation of an example CTM receiver is also d

21、escribed. 2 References This TS incorporates by dated and undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of

22、these publications apply to this TS only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication referred to applies. 1 3GPP TS 26.231: “Cellular text telephone modem; Minimum performance requirements“. 2 ITU-T Recommendation V.18 (2000-11): “O

23、perational and interworking requirements for DCEs operating in the text telephone mode“. 3 3GPP TS 26.230: “Cellular text telephone modem; Transmitter bit exact C-code“. 4 ANSI TIA/EIA-825 (2000-03): “A Frequency Shift Keyed Modem for use of the Public Switched Telephone Network“. 5 ITU-T Recommenda

24、tion T.140 (1998-02): “Protocol for multimedia application text conversation, Feb. 1998“. 6 ISO/IEC 10646-1: “Information technology Universal Multiple-Octet Coded Character Set (UCS) Part1: Architecture and Basic Multilingual Plane“. 7 ITU-T Recommendation H.248 (2000-11), Annex F: “Text Telephony,

25、 Text Conversation, Fax and Call discrimination packages“. 3 Definitions and Abbreviations 3.1 Definitions Cellular Text Telephone Modem: modem (consisting of transmitter and receiver) that allows the reliable transmission of text via the speech channel of cellular phone systems or PSTN networks Bau

26、dot Code: modem signal and character coding scheme of the North American Text Telephone, as specified in ITU-T V.18 2, Annex A.1 (“5-bit operational code“) and in ANSI TIA/EIA-825 4 Text Telephone Code: modem signal and character coding scheme of any of the PSTN Text Telephone types supported by the

27、 harmonizing ITU-T Recommendation V.18 2 3.2 Abbreviations For the purposes of this TS, the following abbreviations apply: ETSI ETSI TS 126 226 V14.0.0 (2017-04)53GPP TS 26.226 version 14.0.0 Release 14BP Band Pass CER Character Error Rate CTM Cellular Text Telephone Modem FCC Federal Communications

28、 Commission FEC Forward Error Correction GSM Global System for Mobile communications HCO Hearing Carry Over Alternating transmission of speech and text. ITU-T International Telecommunication Union Telecommunication standardization sector (former CCITT) LP Low PassPCM Pulse Code Modulation PSTN Publi

29、c Switched Telephone Network TTY Text Telephone UCS Universal Multiple-Octet Coded Character Set UMTS Universal Mobile Telecommunications Systems VAD Voice Activity Detection VCO Voice Carry Over alternating transmission of speech and text 4 General Deaf, hard of hearing, and speech-impaired persons

30、 have been using specific Text Telephone (referred to as TTY in North America) equipment in the fixed network for many years to transmit text and speech through ordinary speech traffic channels. Modern digital cellular systems, however, do not provide satisfactory character error rates for text tran

31、smitted in the speech channel with the traditional modulation developed for the fixed network. The FCC under the US Government has required an urgent solution for all emergency (911) calls for one specific text telephone protocol called Baudot Code. This TS addresses these FCC requirements, and spec

32、ifies a solution for the GSM and UMTS and potentially other cellular technologies. The goal is to provide a solution that can support all traditional text telephony systems worldwide. Internationally, PSTN text telephony is standardized in ITU-T V.18 2 and ITU-T T.140 5. 5 The problem Due to the fac

33、t that digital cellular phone systems are optimized for speech signals and the radio transmission may be subject to relatively high error rates, the transmission of text telephone modem signals via the speech path in cellular networks is in some cases unsatisfactory: i.e. received messages show an u

34、nacceptably high character error rate (CER). One reason for this is that the digital cellular phones use speech coding in order to compress the signal. Since this coding is optimized for speech-like signals, modem signals are more or less distorted. A further problem is in the transmission errors an

35、d the applied error concealment in digital cellular phone systems in case of poor channel conditions. The repetition of speech frames results in character errors or even in error propagation. The traditional text telephone modulation technique, designed years ago for PSTN lines, was not developed fo

36、r these sophisticated, speech-optimized transmission channels. Data transmission methods exist in the wireless services, but for various reasons, a text telephone transmission method for the speech path is desired. Two reasons are: 1: text telephony is acknowledged as a way to contact the emergency

37、services, and emergency services in wireless networks are so far only defined for speech calls. 2: Alternating speech and text in a call is desired, and one simple way to accomplish that without special service support (like multimedia) is by alternating the use of the speech channel. 5.1 US regulat

38、ory issues The FCC under the US Government has required an urgent solution for all emergency (911) calls for one specific text telephone protocol of the ITU-T V.18 standard, called “Baudot Code“. This TS addresses these FCC requirements and this section points out specific US regulatory issues. The

39、minimum performance requirements for the CTM transmission are included in 1. That specification shall be applied for verifying performance. ETSI ETSI TS 126 226 V14.0.0 (2017-04)63GPP TS 26.226 version 14.0.0 Release 14The FCC requires that the solution for cellular systems is fully compatible to tr

40、aditional text telephone standards, at least it shall support Baudot modulation at 45.45 baud in the landline end. 6 The goals and objectives CTM is developed to provide a solution that: - meets the FCC Emergency Call (911) requirements for Text Telephony; - meets the requirements for a Global solut

41、ion for Text Telephony; - works with GSM AMR, EFR, and FR codecs, as well as future codecs; - is applicable for existing and future speech traffic channels in GSM and UMTS; - minimizes the impact to existing or future cellular networks; - allows roaming between networks of different operators; - pro

42、vides a transmission rate of 10 characters per second according to a net bit rate of 80 bit/s; - does not introduce an additional delay of more than 800 ms for text transmission; - does not have any impact for voice transmission, i.e. speech signals must not be distorted or delayed. 7 Text Telephony

43、 architecture based upon CTM An overall architecture for supporting traditional text telephone communication via cellular telephone systems is depicted in figure 1. This Technical Specification covers the gray shaded transmission and receiving parts of the Cellular Text Telephone Modem (CTM). The te

44、xt telephone detector may act as specified in V.18 2. This section provides an overview of the CTM transmitter and the CTM receiver. The Cellular Text Telephone Modem is fully specified in the following sections. The ANSI C-Code for a bit-exact implementation is provided in 3. ETSI ETSI TS 126 226 V

45、14.0.0 (2017-04)73GPP TS 26.226 version 14.0.0 Release 14Figure 1 One Text Telephony architecture using CTM (a) traditional text telephone on both subscribers sides, CTM acts as a signal adaptation device between text telephone code and CTM signals (b) alternative solution for the mobile subscribers

46、 part TextTelephonespeechinputspeechencoderspeechdecoderspeechoutputTextTelephonespeechinputspeechencoderspeechdecoderspeechoutputradiointerfacePSTN, otherPLMN,orothernetworkwith texttelephone supporttexttelephonedetectorCTMtransmittertextspeechCTMspeechencoderspeechdecoderradiointerfacetext convers

47、ationuser interfacespeechoutputspeechinput(a)(b)+CTMreceivertextspeech+CTMtransmittertextspeechCTM+CTMreceivertextspeech+CTMtransmitterspeechCTM+CTMreceivertexttextmobile subscribers partnetwork partmobile subscribers part alternative solutionS1S2S3S4S1S2S3S4S1S2texttelephoneregeneratortexttelephone

48、regeneratortexttelephonedetectorsubscriber inPSTN or othernetworktexttelephonesignalanalogue orPCM codedanalogue orPCM codedPCM codedPCM codedanalogue orPCM codedanalogue orPCM codedanalogue orPCM codeddigitalCTMsignalCTMsignalCTM AdaptorCTM Adaptor* Potential VCO Switch. Outside the scope of this s

49、tandard.ETSI ETSI TS 126 226 V14.0.0 (2017-04)83GPP TS 26.226 version 14.0.0 Release 147.1 Text Telephone devices Text telephone devices are text-based terminals that allow the users to communicate by text, character by character via telephone networks. A text telephone device for PSTN consists of a keyboard, a text-oriented display and a modem, which transforms the text telephone characters into audio signals that can be transmitted via the telephone network. The protocols used by text telephone devices vary regionally. The major f