Digital Multi–Programme TV/HDTV by Satellite
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Digital multi–programme TV/HDTV by satellite M. Cominetti (RAI) A. Morello (RAI) M. Visintin (RAI) The progress of digital technology 1. Introduction since the WARC’77 is considered and the perspectives of future The significant progress of digital techniques in applications via satellite channels production, transmission and emission of radio are identified. Among these, digital and television programmes is rapidly changing the established concepts of broadcasting. multi–programme television systems, with different quality levels (EDTV, SDTV) and possible The latest developments in VLSI (very–large scale evolution to HDTV, are evaluated in integration) technology have significantly contrib- uted to the rapid emergence of digital image/video terms of picture quality and service compression techniques in broadcast and informa- availability on the satellite channels tion–oriented applications; optical fibre technolo- of the BSS bands (12 GHz and gy allows broadband end–to–end connectivity at 22 GHz) and of the FSS band (11 very high bit–rates including digital video capabil- GHz) in Europe. A usable channel ities; even the narrow–band terrestrial broadcast capacity of 45 Mbit/s is assumed, as channels in the VHF/UHF bands (6–7 MHz and 8 well as the adoption of advanced MHz) are under investigation, in the USA [1] and channel coding techniques with in Europe [2], for the future introduction of digital QPSK and 8PSK modulations. For television services. high and medium–power satellites, in operation or planned, the The interest for digital television in broadcasting receiving antenna diameters and multimedia communications is a clear exam- required for correct reception are ple of the current evolution from the analogue to reported. High–level modulations the digital world. (16QAM, 32QAM, 64QAM) are considered for distribution of the The satellite channels, either in the BSS bands satellite signal in cable networks. (broadcast satellite service) at 12 GHz or in the FSS bands (fixed satellite service), offer an impor- tant opportunity for a short time–scale introduc- tion of digital multi–programme television ser- In a longer term perspective, the new frequency vices, with possible evolution to high–definition band (21.4 to 22 GHz) allocated by the WARC’92 Original language: English. Manuscript received 3/6/1993. television (HDTV). to wide RF–band HDTV (W–HDTV) services in 30 EBU Technical Review Summer 1993 Cominetti et al. Regions 1 and 3 will also offer important opportu- C/N values of 19 dB and 16.9 dB are then achiev- nities for new services. able in Italy (climatic zone K) for 99% and 99.7% of the worst month, respectively. Further improve- ments are expected with the next generation of re- 2. Technology trends and the ceivers (NF = 0.8 dB), soon to be available on the evolution of satellite market. television Technology progress in receiving antennas is also Satellite television is developing rapidly in Europe very promising. For example, modern 50–60 cm in response to the emergence of new technologies receiving antennas show an improved radiation and the creation of a favourable commercial envi- pattern, providing the same protection against in- ronment through the deregulation of the commu- terference as was assumed by the WARC’77 Plan nications sector. The success of satellite broadcast- for 90–cm dishes. ing depends on the programmes provided and, increasingly, on the way programme–providers Significant improvements have also been made in can offer an attractive package for the various au- satellite technology. Today, improved power sup- diences. The set of parameters characterising the ply performance permits continuous operation un- satellite are then important strategic factors con- der eclipse conditions, allowing exploitation of a tributing towards penetration of a dedicated mar- wider arc of orbital positions. Shaped–beam ket. Parameters to be considered are: orbital posi- technology can be employed to cover the service tion, type of polarization (circular or linear), area efficiently, with perhaps only 1 dB variation frequency band, satellite power, coverage, avail- in eirp, and to provide a geographical isolation ca- ability of backup capacity. Equally important are: pability not feasible with a simple beam. technical quality and number of programmes de- livered to the users, availability of reliable trans- Finally, the progress of receiving systems and sat- mission systems and low–cost receivers. ellite technology allows a significant relaxation of the satellite power with respect to the WARC’77 assumptions. This is the key of the success of DTH 2.1. The need for modernisation of (direct–to–home) television services via medium– the WARC’77 Plan power pan–European telecommunications satel- lites (e.g. Eutelsat II, Astra) in the FSS band, which The WARC’77 Plan was established for the use of are no longer penalised by their relatively low BSS in the band 11.7–12.5 GHz, for Regions 1 and eirps. A large number of television programmes 3. The Plan assigned five channels to each country, are now available in Europe from these satellites, with a channel spacing of 19.18 MHz. It was based either directly or through cable distribution net- on FM/TV systems (PAL, SECAM, NTSC) with works. 13.5 MHz/V frequency deviation and 27 MHz re- ceiver bandwidth. The protection ratios are 31 dB This new scenario has stimulated the need for a (co–channel, CCI) and 15 dB (adjacent channel, modernisation of the WARC’77 Plan in order to ACI). fulfil the increasing demand for new programmes with supranational and pan–European coverages For the case of Italy, a satellite eirp (effective iso- and offers the prospects of more efficient utilisa- tropic radiated power) of about 64 dBW at the tion of the spectrum and orbit resources (Resolu- beam centre was assigned in order to guarantee a tion 524 of WARC’92). carrier–to–noise ratio (C/N) of 14 dB (in 27 MHz) at the –3 dB area contour for 99% of the worst The adoption of digital techniques allows im- month, assuming a receiving system with a 90–cm provements in the capacity without changing the antenna and a figure–of–merit (G/T) of 6 dB/°K. Plan [3, 4], whilst complying with the required This C/N value is necessary to achieve adequate protection ratios for analogue TV/FM systems and service quality with analogue FM/TV systems. allowing a significant eirp reduction. In fact (Sec- The 64 dBW eirp requires the use of a high–power tion 5), each one of the five WARC’77 channels as- travelling–wave tube amplifier TWTA (at least signed to a service area could provide up to four 230 W for Italy) on the satellite. EDTV programmes (enhanced–definition televi- sion) or even eight SDTV programmes (standard Receiving systems currently available on the mar- definition television), time–multiplexed on a ket having a noise figure (NF) = 1.5 to 1.2 dB and single digital carrier, as an alternative to one 60–cm antenna with 70% efficiency, offer signifi- HDTV programme. The flexibility of the Plan, cantly better performance; they allow for a G/T of such as the use of supranational service areas or the 13.5 dB/°K in clear sky. With WARC’77 eirps, reduction of the satellite spacing in orbit, could be EBU Technical Review Summer 1993 31 Cominetti et al. n 2 1 Services Video coder Inner code Modulator Outer code Convolutional3/4 QPSK RS(255,239) Audio Service or TCM 2/3 or 8PSK Output to coder multiplex Transport multiplex RF channel Data Service components coder Source coding Channel and multiplexing adaptation Figure 1 Block diagram of a significantly facilitated by the adoption of digital on GaAs HEMTs. A noise figure of 1.6–1.7 dB is digital television systems, requiring lower protection ratios than achievable, with a conversion gain higher than transmission system. analogue FM systems. 60 dB. These technological improvements in- crease the perspectives for the future utilisation of In the case of a radical re–planning of the 12 GHz this new frequency band for W–HDTV BSS. BSS band for digital services, with the introduc- tion of the concept of a “single frequency plan” al- ready proposed for the 22 GHz band, the full 3. Satellite digital television: 800–MHz band could be allocated to each service technical factors area, on both polarizations, simply by exploiting The adoption of a digital solution offers significant the orbital separation of the satellites and the geo- advantages: graphical separation of service areas. In this case, a total of 40 RF channels, each 40 MHz wide, – high and constant quality and service reliabil- would be available per service area on each of the ity; two polarizations. – ruggedness against noise and interference; 2.2. Perspectives of W–HDTV BSS – spectrum efficiency (e.g. by frequency re–use) at 21.4–22 GHz and planning flexibility; – reduction of the satellite power; The WARC’92 allocated the frequency band 21.4–22 GHz to the broadcasting satellite service – flexibility of the multiplex for different service configurations (e.g. multi–programme televi- for W–HDTV in Regions 1 and 3. These results sion or HDTV). have stimulated several European organizations to join in a project, called HD–SAT, as part of the Eu- The overall service quality depends jointly on the ropean Communities RACE II programme (Re- intrinsic performance of the picture coding algo- search and Development in Advanced Commu- rithm and on the service availability. The optimisa- nication Technologies in Europe). HD–SAT began tion of the system then requires a trade–off in the in 1992, for a duration of 3 to 4 years, and intends bit–rate allocation between source coding and to prove the technical feasibility of bandwidth–ef- channel coding, to achieve the highest picture ficient coding and modulation digital systems for quality and service continuity on the satellite chan- W–HDTV satellite broadcasting in the “Ka” band nel.