Digital TV in the Convergent Environment

Transcription

1 Digital TV in the Convergent Environment The growth of digital TV in UK homes has been much more rapid than the penetration of the Internet, which has itself grown at a phenomenal rate. The digital TV services started on 1 October 1998 with satellite broadcasting followed by terrestrial broadcasting on 15 November 1998 and more recently by cable services. By mid-2000, about one-and-a-half years after the The growth of digital TV start of digital services, 5 million (or about 20 percent) UK homes had digital TV. Of these 5 million homes, 4 heralds a seamless million had satellite services, convergence of media, 750,000 had terrestrial services, and the rest had cable services. This figure of 5 million homes with digital telecommunications, and TV approaches the 25 percent of information technology, homes that now have Internet access (of course it took the Internet more offering viewers increasingly than two years to grow to that level of penetration into homes). exciting, informative The main incentives for installing digital TV are additional programs interactive programming. (both those available free to viewers and those available by subscription only) delivered with high quality in wide-screen aspect ratio. However, the enhanced possibilities of interactivity are likely to make the technology increasingly attractive. After all, UK audiences can be said to have had a form of interactive digital broadcast services for more than 20 years with Teletext. This provides hundreds of 1 Example of the BBC Web page. Charles P. Sandbank UK Department of Trade and Industry screen pages of news, weather, sport, games, programe guides, and so on, delivered by a digital signal transmitted by modulating the spare lines in the vertical blanking interval. Teletext is now virtually universally available in most European homes and in many countries throughout the world. People are used to accessing the text with their TV remote control and the further steps towards interactive media offered by digital TV should come naturally to those familiar with Teletext. UK broadcasters have recognized that the Internet can be an opportunity rather than competition or a threat. Even before the start of digital TV services, they provided material available on the Internet that viewers of their analog programs would find relevant and interesting. They have given the availability of this material prominent publicity in their programming. They have also used their infrastructure (such as the support base for news and sport services) to offer an extensive set of interactive Web pages, an example of which is shown in Figure 1. Many of these Web pages have been freely available as a public service. In fact, the Web site of the British ing Corporation (BBC) is reported to have had the highest number of hits of any European content page site. In countries such as the UK where digital TV services have become extensively available, the ground is prepared for a seamless convergence of media, telecommunications, and information technology. Interactivity is provided mainly by a combination of local storage (which is now becoming vast) and the Public Switched Telephone Network (PSTN), including mobile access. The industry is also investigating other return channels, such as those using satellites or the terrestrial TV antenna systems. Thus digital TV is a key element in the communications revolution. Where there is rapid growth in the number of homes with digital TV, there is likely to be a more favorable climate for the development of electronic commerce. Standards Digital TV standards have emerged primarily from three sources, Digital Video ing Group (DVB) in Europe, Advanced Television Systems Committee (ATSC) in North America, and the Association of Radio Industries and Businesses (ARIB) in Japan. All are based 32 January/February /01/$ IEEE

2 service provider service provider A 9 A 4 A y Transmission network independent network A x network Forward interaction path ing delivery media: Integrated Services Digital Network/ Broadband ISDN Satellite Cable TV Satellite master antenna TV Terrestrial Multichannel Mulitipoint Distribution System (MMDS) /Local Multipoint Distribution System (LMDS) Return interaction path Interaction channel Interaction media: PSTN/ISDN/B-ISDN Coax + fibre Satellite (very small aperture terminal) Terrestrial Global system for mobile communications (GSM) MMDS/LMDS Internet channel A b A 1 interface module interface module (can be external to STB) Network interface unit A 0 A a Set-top box (STB) Transmission network independent Settop unit 2 Functional reference model for interactive TV services. Transmission network physical link on the Moving Pictures Expert Group s MPEG-2 video coding standard. There are strong similarities between the DVB and the more recent ARIB standard. The ATSC standard has been tailored to deliver high-definition television (HDTV) services for terrestrial fixed-antenna reception using vestigial sideband (VSB) modulation. In addition to the terrestrial digital transmission standard, separate standards for satellite and for cable transmission have been specified in North America. The European Telecommunications Standards Institute (ETSI) is the official body responsible for approval and publication of European telecommunications standards. ETSI standards carry much weight with industry and can be incorporated in European legislation. From the outset, ETSI requested a set of digital TV standards for satellite, terrestrial, and cable delivery under a common umbrella. DVB therefore concentrated on specifying what is essentially a data channel for the maximum commonality among the various transmission media. Furthermore, for terrestrial transmission, DVB selected coded orthogonal frequency division modulation (COFDM) because it is much more rugged in a multipath environment. COFDM protects the integrity of the data to such an extent that even mobile television reception is possible under adverse city center conditions where multipath can be very severe. The DVB standard is ideally suited for its place in the convergent environment because of its wide common base for different delivery media and its ruggedness in terrestrial transmission. As specifications are developed, they are submitted by DVB for publication to ETSI. The DVB standards have now also been adopted in many countries outside Europe and are under consideration in other countries that have not yet established digital TV services. DVB standards have also therefore been submitted to the International Telecommunications Union (ITU) where they have been published essentially in the form of the parent ETSI standard. In some cases where different standards have been submitted from North America and Japan, two or three versions have been included in the same ITU recommendation as regional alternatives. Of course, the objective of the ITU is to make universally acceptable recommendations without regional differences or alternative options for equivalent functions. This is to some extent now starting to happen in the digital TV field for both recommendations of general principle and those dealing with specific applications. One important example is ITU-T Rec. J110 (also published as ITU-R Rec. BT 1369), Basic Principles for a Worldwide Common Family of Systems for the Provision of TV Services. Its objective is to encourage open standards and limit the proliferation of proprietary interfaces. It recommends a very disciplined separation of network-dependent and network-independent interfaces. Figure 2 illustrates this approach. IEEE Computer Graphics and Applications 33

3 Enhanced broadcast 2 broadcast 2 Internet access 2 3 Application areas and profiles of the DVB Multimedia Home Platform. Enhanced broadcast 1 Java virtual machine DVB Java APIs transport protocols: DVB OC HTML subset* plug-in broadcast 1 DVB Java API extensions for interactivity transport protocols Internet access 1 Java APIs for Internet access transport protocols: IP HTML 4.0, ECMA script, DOM, CSS, *optional element The network-independent interfaces are: A a A 0 A y A9 Set-top unit to interactive interface module Set-top unit to network interface unit network to service provider s system and broadcast network s The network-dependent interfaces are: A b A 1 A x A 4 interface module to interaction media Network interface unit to broadcast interaction media Interaction media to interactive network Interaction and broadcast media to network s The ETSI and ITU have published a series of recommendations dealing with the network-dependent aspects for PSTN, cable television (CATV), Digital European Cordless Communications (DECT), Global System for Mobile Communications (GSM), Local Multipoint Distribution System (LMDS), as well as the networkindependent protocols. The media, telecommunications, and computing industries are now focusing on an applications programming interface (API), where there is a real prospect for a substantial world-wide common platform. A number of proprietary APIs are in use, developed largely by pay TV service providers. There is also one open API, Multimedia and Hypermedia Experts Group MHEG-5, developed for interactive broadcast applications by the international Digital Audio-Visual Council (Davic), which completed its work in MHEG-5 has been used for terrestrial digital TV broadcasts in the UK. The DVB Project has been developing a more extensive API named the MHP, Multimedia Home Platform. Figure 3 shows the three overlapping areas of application. A fourth profile for broadband access is under consideration. Provision is made for accommodating legacy systems like the proprietary APIs and MHEG- 5, whose users in Europe are developing strategies for migrating to MHP as it becomes commercially available. Software capable of interpreting the legacy applications would reside above the MHP applications. Such software could be incorporated in the receiver during manufacture or by downloading as data in the broadcast system. The enhanced broadcast profile broadly covers the applications that can be executed with local storage in the receiver. The interactive broadcast profile applications require a modem, which provides one of the return channel options. The third profile covers full Internet access. Specifications defining the first two profiles have been submitted by DVB to ETSI and the ITU, which also has had contributions on the subject of the API from Japan and North America. There are differences in the approach to the API from Europe, North America, and Japan. For example, ARIB has profiles that define more precisely the way the information is presented to the viewer while DVB s profiles are associated with mandatory evolution of using Java to manage and control the application. ATSC uses the object carousel (the repetitive transmission of files) and DVB uses the data carousel (the repetitive transmission of data). However, a very substantial area of common ground exists and many possibilities of further worldwide commonality in areas such as the profiles have yet to be defined. An ITU recommendation for digital TV broadcasting APIs with a common core and relatively minor regional differences is now a real possibility. 34 January/February 2001

4 Convergent services UK digital TV services are now offering extensive interactive additional up-to-the-minute material providing background to the programs being broadcast. Figure 4 shows an example. The viewer can also access less immediate but fuller background information such as the past performance of sports competitors and so on. Additionally, the viewer can select different camera angles if the service provider has allocated sufficient data capacity for this facility. TV Anytime is a consortium formed to continue and implement one of the proposals started by Davic channels before it disbanded. This proposal examined the possibilities opened up by the prospect of hundreds of hours of media storage in future settop boxes. Figure 5 illustrates one of the ways this storage could be used to rearrange the material from a number of sources to create local channels dedicated to specific themes. This would enable programs to be located where they could be found more readily and viewed at more convenient times. Figures 5 and 6 illustrate applications that do not require a direct return interaction path. Figure 6 shows the first step in linking the locally stored material delivered by the data carousel to more extensive information accessible on demand from the broadcaster s Web site through the PSTN. In order to execute this application without a separate PC, one needs the type of receiving equipment illustrated in Figure 7, which is now available in the UK. This Bush receiver incorporates a PACE Microtechnology PLC Internet subsystem to provide the combined function of digital broadcast 1 2 C TV service receiver and the Internet terminal. Of course the companion Internet material has to be authored in a way that it can be displayed to be compatible with the resolution of the TV screen. Current TV screens have a resolution that is far less than that of the displays used with PCs. If (or when) HDTV becomes widely established, the resolution of TV receivers would no longer be less than that of PCs and special authoring would not be necessary. Thus perhaps the market for HDTV receivers might be driven by the aspect of convergence illustrated in Figure 7, where high levels of resolution are demanded if the TV set is to be used for displaying the Internet without reauthoring. This is a rather different perspective on the perception that the market for HDTV receivers will be driven Set-top box with storage - TiVo Kids Lifestyle Sport Factual Youth Multimedia content 4 Multimedia service supporting a digital TV program of the 1999 Wimbledon tournament. 5 Local storage used to create common channels according to content. 6 Linking broadcast multimedia with the Internet. 7 TV receiver capable of Internet access. IEEE Computer Graphics and Applications 35

5 Analog Ceefax = Digital text Headline to SMS Full story to WAP 8 Common authoring for analog TV, digital TV, and mobile telephone terminals. by the prospect of displaying sports or drama programs at high resolution. Finally, another aspect of common authoring is to achieve convergence with an increasingly important area of telecommunications (shown in Figure 8). This shows the link between traditional Teletext with the improved digital TV text and the limited display capabilities of the mobile terminals using the GSM message system or wireless access protocol (WAP). The task of common authoring for such a wide range of media is an example of some of the combined content creation and technological challenges that lie ahead. Digital TV in the convergent environment will transform the media industry by creating a wide spectrum of opportunities. At the top end there will still be the oneway broadcast simultaneously received by millions of viewers, but then there will be many new possibilities ranging down to the intimate exchange of material in small groups at the other end of the spectrum. As this communications revolution develops, it will substantially influence our civilization. Acknowledgments The author takes pleasure in acknowledging helpful discussions with colleagues from the Department of Trade and Industry (DTI), DVB, ITU, University of Bradford, and Henry Price of the BBC who also provided the illustrations of interactive services. Charles Sandbank is ing Technology Adviser to the UK Department of Trade and Industry and the Royal Academy of Engineering visiting professor in information systems at the University of Bradford. He studied physics and electrical engineering at London University. While at Standard Telephones and Cables he developed the first silicon chip integrated circuits in Europe. At Standard Telecommunications Laboratories (now Nortel) UK Research Laboratories he was responsible for the team that pioneered the use of optical fibers for communication. As head of the BBC Research Laboratory and later the BBC s Deputy Director of Engineering he played a significant part in the establishment of digital sound and vision broadcasting. He is a fellow of the Royal Academy of Engineering, the Institution of Electrical Engineering, the Society of Motion Picture and Television Engineers, the British Kinematograph Sound and Television Society, and the Royal Television Society. Readers may contact Sandbank at the Department of Trade and Industry, 151 Buckingham Palace Rd., London 5W1 W 9SS. 36 January/February 2001