1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T J.188TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2002) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Miscellaneous A framework for an efficient parallel video transmission system including co
2、decs with functions of failure detection and picture quality evaluation ITU-T Recommendation J.188 ITU-T J-SERIES RECOMMENDATIONS CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS General Recommendations J.1J.9 General specifications for analogue sound-progr
3、amme transmission J.10J.19 Performance characteristics of analogue sound-programme circuits J.20J.29 Equipment and lines used for analogue sound-programme circuits J.30J.39 Digital encoders for analogue sound-programme signals J.40J.49 Digital transmission of sound-programme signals J.50J.59 Circuit
4、s for analogue television transmission J.60J.69 Analogue television transmission over metallic lines and interconnection with radio-relay links J.70J.79 Digital transmission of television signals J.80J.89 Ancillary digital services for television transmission J.90J.99 Operational requirements and me
5、thods for television transmission J.100J.109 Interactive systems for digital television distribution J.110J.129 Transport of MPEG-2 signals on packetised networks J.130J.139 Measurement of the quality of service J.140J.149 Digital television distribution through local subscriber networks J.150J.159
6、IPCablecom J.160J.179 Miscellaneous J.180J.199 Application for Interactive Digital Television J.200J.209 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. J.188 (07/2002) i ITU-T Recommendation J.188 A framework for an efficient parallel video transmission system inc
7、luding codecs with functions of failure detection and picture quality evaluation Summary Parallel transmission links including codecs are often set up to realize a highly reliable contribution and primary distribution of television programs, in particular of big events such as Olympics and World Cup
8、 Soccer. This configuration, however, has the following issues: 1) The reserve link is totally wasted during normal periods. 2) Switching to the reserve link should be perfect to avoid a disrupted television program, when a failure occurs in a transmission link. 3) In addition, objective assessment
9、of received video quality has been strongly demanded in an actual operation of digital television program transmission. This Recommendation, therefore, recommends a framework for methods that support solutions for these issues. This framework mainly consists of the following three elements: 1) It re
10、duces coding noise and improves picture quality compared to only one link by outputting the average signal of two links, when both links are normal (Efficiency). 2) It detects a failure that occurs in one of the two links by monitoring the two links by comparing them (Support of failure detection).
11、3) It evaluates the quality of the two decoded pictures by comparing them (Automatic picture quality assessment). Appendices show examples of methods in this framework. Such methods improve the operational efficiency and reliability of parallel video transmission links. Source ITU-T Recommendation J
12、.188 was prepared by ITU-T Study Group 9 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 July 2002. ii ITU-T Rec. J.188 (07/2002) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecom
13、munication 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 worldwide basis. The World Telecommunication Standardization Ass
14、embly (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 ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology wh
15、ich fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PRO
16、PERTY 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. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asser
17、ted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that
18、this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2002 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. J.188 (07/2002) iii CONTENT
19、S Page 1 Scope 1 2 References. 1 2.1 Normative references 1 2.2 Informative references 1 3 Terms, definitions and acronyms 1 4 User requirements. 1 4.1 Improvement in efficiency of transmission link usage. 2 4.2 Improvement in reliability by real-time failure detection 2 4.3 Improvement in efficienc
20、y of operation and maintenance by objective picture quality assessment by use of only received pictures 2 5 Recommended framework 2 5.1 General configuration. 2 5.2 Description of each element . 3 5.2.1 Adjustment of delay difference 3 5.2.2 Averaging . 3 5.2.3 Failure detection . 3 5.2.4 Objective
21、picture quality assessment 3 Appendix I Averaging 3 I.1 Theoretical background 3 I.2 Picture shifting method. 4 I.2.1 Spatial shifting method. 4 I.2.2 Temporal shifting method 5 Appendix II Failure detection and identification 6 II.1 Detection of failure. 6 II.2 Identification of disrupted link . 6
22、Appendix III Coding noise assessment. 8 III.1 Theoretical background 8 III.2 Method for SNR estimation 9 ITU-T Rec. J.188 (07/2002) 1 ITU-T Recommendation J.188 A framework for an efficient parallel video transmission system including codecs with functions of failure detection and picture quality ev
23、aluation 1 Scope This Recommendation considers the parallel transmission link that is often used for contribution and primary distribution of television. Particularly, it considers the case where the parallel link includes compression encoders and decoders such as MPEG-2. Signal-to-noise ratio is im
24、proved by reducing the compression coding noise through averaging of the two links, i.e. the utilization efficiency of the links is improved. In addition, automatic detection of transmission failure is supported through monitoring based on a comparison of videos over the two links. Further, the asse
25、ssment of picture quality such as estimation of signal-to-noise ratio is made possible by utilizing the difference of coding noise in two links. This Recommendation recommends that framework. The appendices describe examples of specific methods. Such systems are for use by organizations such as comm
26、unication companies or cable operators. 2 References The following ITU-T 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
27、 other references are subject to revision; users of this Recommendation 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-T Recommendations is regularly published. Th
28、e reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 2.1 Normative reference ITU-T Recommendation J.143 (2000), User requirements for objective perceptual video quality measurements in digital cable television. 2.2 Informat
29、ive references ITU-T Recommendation J.144 (2001), Objective perceptual video quality measurement techniques for digital cable television in the presence of a full reference. ITU-T Recommendation H.262 (2000), Information technology Generic coding of moving pictures and associated audio information:
30、Video. ITU-R Recommendation BT.800-2 (1995), User requirements for the transmission through contribution and primary distribution networks of digital television signals defined according to the 4:2:2 standard of Recommendation ITU-R BT.601 (Part A). 3 Terms, definitions and acronyms This Recommendat
31、ion does not use any unusual terms or abbreviations. 4 User requirements The user requirements for parallel transmission links that the framework described in this Recommendation should fulfil are the following. 2 ITU-T Rec. J.188 (07/2002) 4.1 Improvement in efficiency of transmission link usage Th
32、e reserve link is totally wasted in parallel transmission links during normal periods that occupy most of the time. The efficiency of transmission link usage should be improved by somehow utilizing also the reserve link during normal periods. 4.2 Improvement in reliability by real-time failure detec
33、tion It is important, when failure occurs, to switch to the reserve link as soon as possible to reduce the time during which disrupted pictures are output. Usually, operators monitor the link and switch to the reserve link when failure occurs. It is required to reduce the burden on operators and the
34、 time during which disrupted video is output, by automating this monitoring. 4.3 Improvement in efficiency of operation and maintenance by objective picture quality assessment by use of only received pictures The degradation due to compression coding changes according to picture content even when th
35、ere is no transmission error. The quality of received pictures should be automatically monitored. See ITU-T Rec. J.143. 5 Recommended framework This Recommendation recommends a scheme for efficient parallel transmission of television. 5.1 General configuration Figure 1 shows the framework recommende
36、d in this Recommendation to fulfil the requirements. J.188_F01EncoderEncoderInputvideoDecoderDecoderOutputvideoTransmissionAveragingQualitySwitchDelayadjustmentFailuredetectionQualityassessmentFigure 1/J.188 Recommended framework This Recommendation assumes that codecs are included in each of the tw
37、o links. First, one of the two received videos is, if necessary, delayed appropriately so that the transmission delays of both links would be the same. After that, averaging of two decoded pictures is performed to reduce noise, which leads to efficient usage of links, while failures are detected by
38、comparing the two decoded pictures. Appropriate switching is performed according to this failure detection information. In addition, when there is no transmission error, objective quality assessment of the decoded pictures is performed by comparing the decoded pictures in the two links. ITU-T Rec. J
39、.188 (07/2002) 3 5.2 Description of each element 5.2.1 Adjustment of delay difference This framework requires that the delay of two videos should be the same for the following averaging and quality assessment processing. It is recommended, therefore, that a delay adjustment unit should be inserted (
40、Figure 1). Specific methods may be reading time codes or matching of pictures. 5.2.2 Averaging The improvement in the efficiency of parallel link usage assumes that each of the links includes a compression encoder and a decoder (Figure 2). It is recommended that the two decoded video signals be aver
41、aged to cancel coding noise so that an improvement in signal-to-noise ratio could be realized. For this, it is important to reduce the correlation between the two noise signals due to the compression coding. Such methods include shifting video signals spatially and/or temporally, which is described
42、specifically in Appendix I. J.188_F02EncoderEncoderInputvideoDecoderDecoderOutputvideoTransmissionSwitchingNormallinkReservedlinkFigure 2/J.188 Method for improvement in transmission efficiency 5.2.3 Failure detection The parallel links considered in this Recommendation provide two received pictures
43、. The recommended framework takes advantage of this characteristic to perform precise failure detection comparing to the case where only one received signal is available, i.e. the occurrence of failures is detected by comparison of two received pictures. Appendix II describes the specific methods. 5
44、.2.4 Objective picture quality assessment Picture quality assessment, as in 5.2.2, assumes a compression encoder and a decoder in each of the two links in a parallel system. It is recommended that the degradation of picture quality due to compression coding be estimated by utilizing the difference o
45、f two coding noise signals. Appendix III describes the theoretical background and a specific estimation method. Appendix I Averaging I.1 Theoretical background For improvement of efficiency of parallel links usage, we can reduce the correlation between the coding noise signals of two decoded videos
46、to increase the improvement of the SN ratio by averaging. Let x be the original signal, x1, x2the two decoded signals, and d1, d2their coding noise, respectively, where x1= x + d1, x2= x + d2(Figure I.1). The noise power is supposed to be the same 4 ITU-T Rec. J.188 (07/2002) in the two channels and
47、 is represented by n. 21dd represents the correlation coefficient of d1and d2. J.188_FI.1xAveragingEncoder + DecoderEncoder + Decoder2xx21+11dxx +=22dxx +=Figure I.1/J.188 Averaging of two received signals The coding noise dmof the average signal of x1, x2is: 222121ddxxxdm+=+= and its power nmis: ()
48、21221212 ddmnddn+=+= When the noises of the two channels are independent, therefore, the averaging improves SNR by 3 dB. Conversely, as their correlation becomes larger, the improvement becomes smaller. From experimental results, it has been found that an improvement of PSNR by 1 to 2 dB is realized
49、. I.2 Picture shifting method In compression codecs, pictures are usually separated into many blocks and compression is performed block by block by utilizing spatial and temporal correlation. In order to reduce the correlation between the coding noise of two links, therefore, it can be considered that the picture is relatively shifted in at least one of the links. The shifting methods include a spatial method and a temporal method. I.2.1 Spatial shifting method Major picture coding schemes such as MPEG-2 (ITU-T Rec. H.262) perform an orthogo
