1、REPORT ITU-R B0.2008-1 DIGITAL MULTIPROGRAMME BROADCASTING BY SATELLITE (Question ITU-R 21711 i) ( 1995- 1998) 1 Introduction In response to Question ITU-R 21711 1, this Report provides background information collected during the preparation of Recommendations ITU-R B0.1211 and ITU-R B0.1294. These
2、Recommendations are for broadcast of television direct from satellite to small antennas, such as used by a direct-to-home (DTH) system, a satellite master antenna television (SMATV) or a direct-to-cable-head system. However, considerations have been given to related Questions, such as compatibility
3、with the bit rates, channel coding and modulation techniques used by terrestrial, SMATV and cable distribution systems. The way studies have been organized is summarized in Fig. 1, A list of acronyms used in this report may be found in 0 9. 2 Source coding and multiplexing It is expected that satell
4、ite digital video broadcasting (DVB) systems will draw upon evolving standards, such as: 1) 2) 3) Suppliers of digital multiprogramme television services that are also to be received by SMATV installations should be aware of the bit rate compatibilities required by SMATV systems (Doc. 10-1 1S/68). i
5、mage coding: International Standard ISOAEC 13818-2; audio coding: Recommendation ITU-R BS.1196; multiplexing: International Standard ISO/IEC 13818-1. 2.1 MPEG-2 video compression architecture The MPEG-2 video compression standard, ISODEC 13818-2, defines a syntax or language which is to be understoo
6、d by an MPEG-2 compatible decoder. An MPEG-2 data stream describes exactly what actions an MPEG-2 compatible decoder must take to reconstruct the original video sequence. The overall MPEG-2 architecture and syntax were designed such that an MPEG-2 decoder is a much simpler device than an MPEG-2 enco
7、der. This is very important in broadcast applications where there is typically one encoder for many thousands or millions of decoders. This type of architecture greatly reduces the overall system cost. For a given application, certain fundamental MPEG-2 parameters can be selected which set static re
8、solution, acquisition time, use of B-frames and other basic characteristics. The range of parameters used in a given system will determine the fundamental compliance requirements for the systems decoders. Any given video sequence can be encoded in different ways using different compression algorithm
9、s into MPEG-2 syntax compliant data streams. Each of these MPEG-2 syntax compliant data streams will be different from each other, and yet when presented to an MPEG-2 compliant decoder they can all result in video output sequences similar to the original encoder input sequence. STD*ITU-R RECMN BO-ZO
10、OB-L-ENGL 1798 = 4855212 053b455 027 Rep. ITU-R B0.2008-1 58 FIGURE 1 Organization of work Question ITU-R 217/11 “Digital multi-programme television emissions within a satellite transponder” what are : the minimum bit-rate per programme, the performance requirements, the modulation and coding techni
11、ques, the multiplexing structure, the link overhead capacity, the interference sensitivity . J, Report ITU-R B0.2008 “Digital multiprogramme broadcasting by satellite” Contains information on - Source coding and multiplexing - Channel coding - Modulation - Satellite channel access - Commonalities wi
12、th other media - Example of digital multiprogramme satellite - Feasibility of common functional requirements for broadcasting systems satellite multiprogramme TV reception Y Annex 1 to Report ITU-R BO. 2008 “Feasibility of common functional requirements for satellite multiprogramme TV reception. Arc
13、hitecture and cost estimations” - Generic reference model for the common functional requirements of a satellite IRD - Universal elements of a satellite IRD - Cost estimations - Summary characteristics of digital multiprogramme TV systems by satellite J, Recommendation ITU-R B0.1211 “Digital multipro
14、gramme emission systems for television, sound and data services for satellites operating in the 11/12 GHz frequency range” Recommends that the DVB-S framing structure, channel coding and modulation methods as specified should be considered in converging to a world-wide standard for the introduction
15、of digital multi-programme television services from satellites operating in the 11/12 GHz down-link frequency range. 1 Special Rapporteur I - analyse the commonalities between existing systems - define and describe the functions of a generic system model - identify the processes and the minimum set
16、of parameters of the various sub-systems - define the internal interfaces between the modules of the generic system and the external system interfaces * Recommendation ITU-R B0.1294 “Common functional requirements for the reception of digital multiprogramme television emissions by satellites operati
17、ng in the 11/12 GHz frequency range” recommends : - that one of the transmission systems described be selected when implementing digital multiprogramme television services via satellite; - that the universal elements of the common functional requirements of a satellite integrated receiver-decoder (I
18、RD) serve as a basis for implementation of the services in those areas where more than one system coexists or may coexist in the future; - that further studies be carried out to address the benefits of including other essential satellite IRD functions that are not specified in this Recommendation. S
19、TD-ITU-R RECMN BO-ZO08-1-ENGL 1998 m 4855232 053b45b Tb3 W Rep. ITU-R B0.2008-1 59 Movies An important point is that the more efficient encoding algorithms can provide better output video quality using fewer bits per sequence than less efficient algorithms. That is, any given video sequence can be c
20、ompressed to an MPEG-2 syntax compliant bitstream in a variety of ways, some more efficient than others. 2.5 to 4 MbiVs MPEG-2 encoders are quite complex devices, and the encoding algorithms used in them are constantly being refined and improved. It is expected that these improvements will continue
21、for some time to come. Educational material General material MPEG-2 decoders currently deployed in many operational digital multiprogramme systems are designed to be able to properly decode any MPEG-2 syntax compliant data stream. Thus these decoders do not become obsolete as encoders are routinely
22、upgraded with new more efficient encoding algorithms. 2.0 to 4 Mbit/s 3 to 7 Mbit/s Thus MPEG-2 video encoders can be improved and upgraded over time without requiring hardware or software upgrades at the decoder. This is a very valuable characteristic of the MPEG-2 video architecture in that it all
23、ows for future technical improvements in MPEG-2 video compression efficiency without requiring changes in the MPEG-2 decoders. sports Associated audio (two channel stereo)() 2.2 Statistical multiplexing methods 5 to Il Mbit/s 64 to 256 kbit/s Techniques have been developed in the broadcast equipment
24、 industry to provide for variable bit rate operation of MPEG-2 encoders. This technique takes advantage of the statistical nature of video sequences, allocating more channel capacity to difficult sequences and less channel capacity to easier sequences. Statistical multiplex algorithms are operationa
25、l on many systems, but it is believed that significant technical advances are still possible in this field. 2.3 Number of programmes per transponder The number of programmes that can be carried in a transponder is a function of a number of parameters. These parameters include the available informati
26、on rate, the type of video source format being used (component or composite), the overall quality of the video source material, the video resolution, the criticality of the video material as it relates to the compression algorithm (Le., type of programme material), and the desired video quality. Giv
27、en the current state of video compression technology, Table 1 provides ranges of information bit rates per programme suitable for providing standard definition TV (SDTV) quality. TABLE 1 Examples of bit rates per programme for SDTV (1 Significant higher bit rates would be required for multi-channel
28、surround sound. The number of programmes which can be carried in a transponder can be estimated by allocating the total transponder information bit rate among the video and audio services of choice. Capacity must also be reserved for programme information and conditional access data channels. It is
29、expected that future advances in compression technology, statistical multiplexing methods and transmission coding could significantly increase the number of programmes currently carried in a given transponder. STD-ITU-R RECMN BO=ZOOB-L-ENGL I998 M 4855232 053b457 9TT W 60 Rep. ITU-R B0.2008-1 2.4 Id
30、entification of a strategy to distinguish MPEG-2 transport streams (TS) among applications In MPEG-2 systems, the private sections can be defined individually according to each application. The framework of the recommendation on service and programme information data for digital broadcasting systems
31、 which use the private sections was issued by Working Party 11D in 1994. But different private sections are incorporated into DVB or other systems. In Telecommunication Standardization Study Group 9, studies on programme guides and navigation tools were also started by a Special Rapporteur. If no un
32、ified consideration is carried out, mutual interference among privately defined sections will occur in the receiver This problem will be avoided if the identification of specific systems is provided in the context of the TS. This point is thought to be essential for realizing the inter-operability o
33、f digital broadcasting systems. Therefore, studies should be carried out in Radiocommunication Study Group 11 in cooperation with related Study Groups, Working Parties and Task Groups within the ITU-R and ITU-T and ISOEC, for the realization of a unified strategy. 3 Channel coding Channel coding inc
34、ludes energy dispersal, outer coding, interleaving, inner coding and baseband shaping. It is desirable to converge to a common channel coding scheme to enable greater compatibility among different systems as explained in Annex 1, 4 Modulation Several types of channel modulation techniques are suitab
35、le for use on a satellite. The technique used by most systems currently being planned or implemented is QPSK modulation. QPSK modulation provides a reasonable trade-off of power/bandwidth on the satellite, ability to work with non-linearities associated with satellite transponders, and simplicity in
36、 implementation of the integrated receiveddecoder (IRD). Work has also examined compatibility of a satellite modulation technique with modulation techniques used for cable and terrestrial broadcasting systems. Use of the same modulation technique from satellite could provide a means of achieving max
37、imum compatibility for digital emissions. Orthogonal frequency division multiplexing (OFDM) and single carrier (QAM) or vestigial sideband (VSB) are also currently being investigated for terrestrial broadcasting of digital video. Other investigations Cominetti et al., 19931 and Doc. lO-llS/136 show
38、that OFDM does not provide the best exploitation of the satellite power resources. Also, these modulation techniques require more power from the transponder and has a high sensitivity to travelling wave tube amplifier (TWTA) non-linear distortions. It should be noted that these preliminary conclusio
39、ns for OFDM apply to fixed reception only, with direct antennas, for which multipath propagation and selected fadings are not expected. In the case of portable or mobile reception for television, the advantages of OFDM in terms of selective fading margins might compensate for the losses due to the e
40、xtra power requirements and non-linear TWTA distortions. However, equalization techniques are also being investigated for QPSK modulation to compensate for multipath signals. If mobile television from satellite is to be investigated, both OFDM and QPSK using equalization need further investigation.
41、5 Satellite channel access Two techniques for accommodating multiple television programmes within a single satellite transponder are time division multiplexing access (TDMA) and frequency division multiplexing access (FDMA). STD-ITU-R RECMN B0.2008-1-ENGL 1998 9 4855212 053b458 83b 9 61 Rep. ITU-R B
42、0.2008-1 In the case of TDMA, the digitized TV programmes are time multiplexed onto a single carrier, while in the case of FDMA the TV programmes are carried by N different independent carriers, sharing the transponder bandwidth. Doc. 10-1 1S/135 discusses a comparison of these two techniques. QPSK
43、modulation with convolutional code rate 3/4 is assumed in the study, with total useful bit rates between 34 and 45 Mbit/s in a 36 MHz transponder. Similar bit rates could also be accommodated in transponder bandwidths in the range 24 to 33 MHz, modifying the coding rate accordingly. The results show
44、 that the CIN penalty of the FDMA approach is relevant. For example, the FDMA approach requires 2.3 dB (two carriers per transponder) and 5.8 dB (four carriers) additional CIN with respect to a single TDMA, for an equal total bit rate of 34 Mbit/s. 6 Commonalties with other media Maximum commonality
45、 of digital multiprogramme television broadcasting amongst different delivery media should be pursued; even where transmission environments are quite different, at least the most essential elements can be the same, However, some differences among them are required because of the best optimization of
46、 the capabilities of each transmission media. The media considered are: satellite, cable, SMATV, terrestrial and microwave multipoint distribution system. The Recommendation ITU-R BO. 121 1 recommends that the DVB-S framing structure, channel coding and modulation methods should be considered in con
47、verging to a worldwide standard for satellite multiprogramme broadcasting services. A draft new Recommendation on digital multiprogramme system for television, sound and data services for cable distribution, which recommends the use of the DVB-C system for distribution on cable, has been submitted t
48、o ITU-T. Similarly, a draft new Recommendation on digital multiprogramme, system for television, sound and data services for SMATV distribution, which recommends the use of the DVB-CS system for distribution on satellite master antenna systems has been submitted to ITU-T. It is expected that whateve
49、r the media is, the characteristics of video source coding, audio source coding and transport multiplex may be common ensuring the maximum flexibility of the transport multiplex to be interconnected between different media. The basis could be the MPEG-2 multiplex (the Transport Stream) structure, which is a fixed length packet structure which has 188 bytes of data. Also the MPEG-2 TS has some service information (SI) elements and makes adequate provision for more developed SI systems to be added. The framing, synchronization and randomization can be common. When outer coding is needed
