1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU J.87 (03/2001) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Digital transmission of television signals Use of hybrid cable television links for the sec
2、ondary distribution of television into the users premises ITU-T Recommendation J.87 (Formerly CCITT Recommendation) ITU-T J-SEMES RECOMMENDATIONS CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS I General Recommendations General specifications for analogue
3、sound-programme transmission Performance characteristics of analogue sound-programme circuits Equipment and lines used for analogue sound-programme circuits Digital encoders for analogue sound-programme signals Digital transmission of sound-programme signals Circuits for analogue television transmis
4、sion Analogue television transmission over metallic lines and interconnection with radio-relay links Digital transmission of television signals Ancillary digital services for television transmission Operational requirements and methods for television transmission Interactive systems for digital tele
5、vision distribution Transport of MPEG-2 signals on packetised networks Measurement of the qualiy of service Digital television distribution through local subscriber networks IPCablecom , Miscellaneous Application for Interactive Digital Television J.1-J.9 J. 1 0-J. 1 9 5.20-5.29 5.30-5.39 5.40-3.49
6、J.50-J.59 3.60-3.69 J.70-J.79 J.8oJ.89 J.90-J.99 J. 100-J. 109 J.110-5.129 J. 130-5.139 J. 140-J. 149 J. 150-J. 159 J. 160-5.179 J. 180-J. 199 5.200-J.209 II For further details, please refer to the list of ITU-T Recommendations. ITU-T Recommendation 5.87 Use of hybrid cable television links for the
7、 secondary distribution of television into the users premises Summary This Recommendation is limited to rules which facilitate the carriage of both analogue and digital television signals of satisfactory quality on a hybrid link into the users premises. Digital television signals are referred to in
8、ITU-T J.83,5.84 and ITU-R BT.1306-1. Source ITU-T Recommendation 5.87 was prepared by ITU-T Study Group9 (2001-2004) and approved under the WTSA Resolution 1 procedure on 9 March 2001. ITU-T 5.87 (03/2001) 1 FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized a
9、gency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwi
10、de basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of IT-T Recommendations is covered by the procedure laid down in WTSA
11、Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administra
12、tion and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. TTU takes no position concerning the evidence, validity or applicabilit
13、y of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement th
14、is Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. o ITU 2001 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electr
15、onic or mechanical, including photocopying and microfilm, without permission in writing from ITU. 11 ITU-T 5.87 (03/2001) CONTENTS 1 Background . 2 Scope 3 Normative references 4 Terms and definitions . 5 Abbreviations . 6 Architecture for hybrid links into the users premises 7 8 Annex A - Technical
16、 parameters of the hybrid analogue/digital system Appendix I - Constraints on frequency allocation Appendix II - Technical parameters under study Technical requirement and constraints for hybrid links . Reference model for the hybrid analogue/digital links ITU-T 5.87 (03/2001) Page 1 1 1 2 3 4 7 8 i
17、ii ITU-T Recommendation 5.87 Use of hybrid cable television links for the secondary distribution of television into the users premises 1 Background Converging technologies on multimedia and interactive services associated with the secondary distribution of television services are making it possible
18、for a great deal of information to be accessed through the use of hybrid links into the users premises. For an undetermined period during the analogue to digital transition, it will be necessary to co-carry both formats using a coaxial cable delivery system into the users premises. 2 Scope This Reco
19、mmendation is limited to rules which facilitate the carriage of both analogue and digital television signals of satisfactory quality on a hybrid link into the users premises. Digital television signals are referred to in ITU-T 5.83,5.84 and ITU-R BT.1306-1. 3 Normative references The following ITU-T
20、 Recommendations, and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommenda
21、tion are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU Recommendations is regularly published. - ITU-T 5.83 (1 997), Digital multi-programme systems for television, s
22、ound and data services for cable distribution. ITU-T 5.84 (1 997), Distribution of digital multi-programme signals for television, sound and data services through SMA TV networks. - ITU-R BT. 1306-1 (1 997), Error-correction, data framing, modulation and emission methods for digital terrestrial tele
23、vision broadcasting. - 4 Terms and definitions This Recommendation defines the following term: 4.1 single super heterodyne receiver which is tuned to an analogue channel. taboo channel: A channel which coincides with the frequency of the local oscillator in the 5 Abbreviations This Recommendation us
24、es the following abbreviations. C/N Carrier-to-Noise Ratio CIN Composite Intermodulation Noise cso Composite Second Order CTB Composite Triple Beat ITU-T 5.87 (03/2001) FDM Frequency Division Multiplexing IF Intermediate Frequency OFDM Orthogonal Frequency Division Multiplexing QAM Quadrature Amplit
25、ude Modulation SMATV Satellite Master Antenna Television VSB Vestigial Side Band 6 Digital signals should be assembled in Frequency Division Multiplexing (FDM) as well as analogue signals in order to assure the gradual transition from analogue to digital signals. Multimedia applications demand bidir
26、ectionality for hybrid links. Activation of the upstream facility is recommended on hybrid systems, where appropriate, for the implementation of user requirement for upstream signals, e.g. control functionality and data return. Architecture for hybrid links into the users premises 7 The spectrum for
27、 residual analogue television should be located where incumbent reception equipment will operate without additional adaptation. This will generally mean that the digital signals are carried on the higher frequency channels. However, digital signals can be transmitted between analogue channels. In th
28、is case, especially when digital channels are allocated adjacent to residual analogue channels, the receiving quality of the analogue channels should be maintained. In general, digital signals have a noise-like spectral energy distribution. When digital signals are impressed upon the analogue signal
29、s present, they do not add new Composite Second Order (CSO) or Composite Triple Beat (CTB) products as they would if they were analogue television signals. They add a new form of impairment called Composite Intermodulation Noise (CIN) instead, which is manifested as a reduction in the video signal-t
30、o-noise ratio on the analogue channels. To minimize the effects of CIN on the Co-carried analogue signals, it is desirable to carry QAM, VSB, and OFDM digital signals at an appropriately lower level than the analogue signals, but not so low as to affect the reliability of the digital signal transmis
31、sions. It is recommended that QAM, VSB, and OFDM digital video carriers generally be run at levels of eight to ten dB below the Co-carried analogue signals and retain adequate operational margins for both analogue and digital signals on the system. In order to retain adequate operational margins for
32、 both types of signals assembled in FDM on the system, Carrier-to-Noise Ratio, Distortion, Mutual Interference along with CIN should be considered. In the case of introducing supplementary digital channels in the cable networks, it is desired that: - - Conditions for hybrid digitaknalogue transmissi
33、on should be bounded by: - - - An example for constraints on frequency allocation is provided in Appendix I. In each case, the boundary conditions are related to the type of receiver used in the cable system. The type of receiver means either a general receiver available on the market or a special r
34、eceiver for the system. In the case of using single super heterodyne receiver, the digital channel which suffers interference from Technical requirement and constraints for hybrid links a low bit error rate should be kept for the digital channels; disturbances of the conventional analogue channels s
35、hould be avoided. the interference fi-om intermodulation distortion; the transmission level for digital channels adjacent to an analogue channel; the transmission level for digital channels in taboo channels. 2 ITU-T 5.87 (03/2001) the local oscillator should have a signal level sufficiently high to
36、 maintain signal quality. At the same time, in case of possible interference by the leakage of a local oscillator from a digital receiver, the leakage level of the local oscillator needs to be sufficiently low so as not to disturb the transmitted signals. If these conditions are not met, a double su
37、per heterodyne receiver is recommended for use in order to avoid local oscillator interference with the transmission frequencies of the signals. Technical parameters are described in Appendix II for considering the performance of receivers of digital channels. Annex A shows the technical parameters
38、of the hybrid analogue/digital system related to Annex UJ.83 and system CBT. 1306-1. 1 8 A three-stage reference model for the evolution of hybrid analogue/digital links is shown in Figure 1. In the first stage, analogue signals are dominant. In the second stage, analogue and digital signals are com
39、parable. In the third stage, digital signals are dominant. Reference model for the hybrid analogue/digital links I 1 VSB-AM VSB-AM VSB-AM Digital VSB-AM VSB-AM a) First stage (a few digital signals among many analogue signals) I b) Second stage (comparable number of analogue and digital signals) c)
40、Third stage (a few analogue signals among many digital signals) Figure 1/5.87 - Reference model for evolution of hybrid analogue/digital links ITU-T 5.87 (03/2001) 3 ANNEX A a) Signai level at subscribers tapoff Technical parameters of the hybrid analogue/digital system (This Annex relates to Annex
41、C/J.83 and system CBT. 1306-1) 53-85 dBpV (75 fi terminated) (maximum envelope level of modulated signai) Table A.l shows a number of technical parameters which may affect the detailed specification for the use of hybrid analogue/digital cable television links for the secondary distribution of telev
42、ision into the users premises. cl) c2) d) e) CTB from many NTSC TV channels CSO from many NTSC TV channels CIN from many QAM channels Adjacent interference between a NTSC TV channel and a QAM channel Table A.l/J.87 - Technical parameters for digital signal on hybrid analogue/digital cable television
43、 links for the secondary distribution of television into the users premises Below -43 dB Under study Under study See Figure A. 1 Parameters I Specifications I b) RequiredCN I 31dB NOTE - Parameters a) to e) are required to attain total system performance. Each parameter should be considered a perfor
44、mance measure of existing cable television systems for analogue service using NTSC system M (video carrier to audio carrier level ratio is 1 O dB). The range of signal level for adjacent NTSC/QAM signals at subscribers tapoff is shown in Figure A. 1. LNTSC and LQ are lower bounds for NTSC and QAM si
45、gnals respectively, determined by required C/N for each signal and system noise. UNTSC and UQAM are upper bounds for NTSC and QAM signals respectively, determined by interference to other telecommunication systems. Lines A and B are upper bounds for QAM signal determined by interference to lower and
46、 upper adjacent NTSC signals respectively. Lines C and D are lower bounds for QAM signal determined by interference from lower and upper adjacent NTSC signals respectively. In the cable system using VSB-AM NTSC for analogue signals and system C of ITU-T 5.83 for digital signals, line A: EQAM (ENTSC-
47、 - 18) dB line D: EQAM (ENTSC+ - 20) dB O Where QAM signal level EQ is defined by maximum envelope level of modulated signal, and its upper and lower adjacent NTSC signal levels ENTSC+ and ENTSC- are defined by unmodulated video carrier levels. 4 ITU-T 5.87 (03/2001) ums, LNTSC NTSC signal level Par
48、ameters a) b) Required Chi ci) CTB from many NTSC TV channels c2) CSO from many NTSC TV channels d) CIN from many OFDM channels e) Adjacent interference between a NTSC TV channel and a OFDM channel Signai level at subscribers tapoff T09055w-97 Specifications 47-81 dBpV (75 R terminated) (average lev
49、el of modulated signal) 24 dB Below -45 dB Under study Under study See Figure A.2 Figure A.VJ.87 - Range of signal level for adjacent NTSUQAM signals at subscribers tapoff The range of signal level for adjacent NTSC/OFDM signals at subscribers tapoff is shown in FigureA.2. LNTSC andL0FDM are lower bounds for NTSC and OFDM signals respectively, determined by required C/N for each signal and system noise. UNTSC and UOFDM are upper bounds for NTSC and OFDM signals respectively, determined by interference to other telecommunication systems. Lines A and B are upper bounds for O
