Television transmission directly to home receivers has been one of the more successful commercial applications of satellite communications. The transmissions have not been at the power levels originally planned in every case nor has the re ception been always on small size antennas. But throughout the world, there has developed a market for direct broadcast satellite television (DBS-TV). The development of direct broadcast satellite radio (DBS-R) is lagging behind that of DBS-TV.
The planning for DBS-TV in Europe and Asia at 12 GHz took place in 1977 at the World Administrative Radio Conference. And in 1983, the formal plan was made for the western hemisphere, also at 12 GHz. T hese plans required high powers (63 dBW EIRP for Europe and Asia and 57 dBW EIRP for the western hemisphere). The actual implementation of satellite broadcast television and radio began at lower power levels using satellites and frequencies intended for FSS. Recent developments have been implementations in accord with the formal plans, using specified power levels, frequencies, and receiver antenna sizes. The development and future plans for DBS-TV in Europe are shown in Table3.8.
The early (and many current) operations of "broadcast" TV from satellites used FSS transponders at relatively low power levels and required fairly large TVRO antennas. The launch of OLYMPUS in 1989 with 180 W RF power provided experimentally high power DBS-TV. The U.S. and Canada had flown the Communications Technology Satellite (CTS) in 1976 with 235 W, 57 dBW EIRP at Ku-band. Japan had flown 100 W transmitters on BSE in 1978. In evaluating OLYMPUS results, ESTEC reported that "the need for high power DBS-TV had evaporated."
The TV SAT satellites developed by France and Germany were high power operational DBS-TV satellites for Europe, with 260 W per channel. This implementation of DBS-TV had power levels and geographical coverage that matched the WARC-77 DBS plan. The operational experience seems to demonstrate that currently there is no need for high power DBS. Additionally, the target coverage areas are thought to be more economically viable if the coverage is a commo n language area rather than limited to a single country size. (More potential customers are reachable.)
Development and Future Plans for DBS-TV in Europe
HISPASAT, launched in september 1992, has three Ku-band channels with 110 W of power for DBS-TV. ANT, the manufacturer of the transmitters for TV SAT at 230 to 260 W and for HISPASAT at 110 W, does not see a return to the 250 W level for some years.
EUTELSAT has planned for DBS-TV, using the EUROPESAT series of satellites. The operational system is awaiting approval, but a decision is expected soon. A "gapsat" will be procured to initiate service within 24 months while the operational EUROPESAT is being devel oped. Four spacecraft (including the pre-EUROPESAT) are to be co-located at 19 degrees W. Antennas will provide coverages that match the geographic regions corresponding to languages. For spectrum, EUTELSAT is making use of a WARC-1977 provision of fiv e channels per country. Eight countries provide a total of 40 channels which may be redistributed. The final configuration will have three satellites of 14 channels each; 40 are considered operational and two are spare channels. Thus, each of the 10 pa rticipating countries will have four channels, compared with the five allocated by WARC-1977. The "gapsat," or pre-EUROPESAT, will use 33 MHz transponder bandwidths. For digital HDTV, a 108 MHz bandwidth transponder is being considered. Modem s that support 140 to 155 Mbits/sec operation may be used. EIRP varies from 55 dBW minimum to 60 dBW (part of Italy) and 57 dBW (France).
EUREKA 95 is a large pan-European program to carry out research and development, future system evaluation, pilo t production of equipment for HDTV service (for major events), and to prepare for a market introduction by 1995 of satellite transmission of HD-MAC, "studio to home." (The goal of satellite delivery relates EUREKA to satellite television broadc asting.) The project also embraces cable delivery of HD-MAC, development and maintenance of specifications, and transmission test and evaluation. Coding for bit rate reduction will produce a system for distribution of HD-MAC at 140 Mbits/sec.
FLASH TV research and development activity had been sponsored by the Commission of European Communities. It is aimed at broadcast of digital HDTV for redistribution ("contribution links") rather than DBS-TV. An application might be to theaters for projection of a movie. FLASH TV will use less than 70 Mbits/sec, whereas HD-MAC will be transmitted at 140 Mbits/sec.
HDTV demands high data rates, in turn leading to large TVRO stations and concern for link margins, interference and propagation. T he trade-off of data rate versus video quality and use of coding (compression) is being investigated by many. In flash TV, a novel approach is being investigated. The transmission data rate will be adapted to the available margin by a low rate feedback link from the receiver (in essence, bit error rate monitoring at the receiver). The scheme also envisions use of video compression, probably 34 Mbits/sec to 70 Mbits/sec transmission rates, and reception with antennas of less than 4 m size. To be implem ented at Ku-band, it is also thought that the flexible bit rate technology might be transferred to Ka-band (30/20 GHz), should that become desirable. The flexible rates will also be interfaced to terrestrial networks. A graceful degradation characterist ic is expected in video quality. The original video input is considered to have high and low priority units (components). In case of node congestion, the ATM network can drop the low-priority video data without resulting in unacceptable video quality.
The video in flash TV is not HDTV or HD-MAC, but it is high quality. The difference may be better understood by comparing the encoding schemes. First, the HD-MAC standard is 1,250 lines, refreshed at 50 Hz, with a 16:9 picture aspect ratio. The sam e camera would be used in this case. The camera output is about 1.6 gbits/sec when converted to a digital bit stream. A conventional approach would take this output and apply discrete cosine transforms to reduce the data rate. In flash TV, other proces sing is performed with the objective of reducing the data rate to 70 Mbits/sec. Using a 36 MHz transponder, and 74 dBW uplink EIRP, reception of high quality is anticipated using a 2 m to 4 m antenna, with a target of 3 m. This system is expected to del iver a professional quality picture appropriate for consumer display by 1994. By comparison, it is expected that analog HD-MAC can be received by EUROPESAT with an 0.8 m antenna. However, due to bandwidth and EIRP requirements, there will be relatively few direct broadcast TV channels. The flash TV concept, compatible with a 36 MHz transponder and terrestrial transmission, would have much broader applicability in business, government, news gathering, and entertainment.
In summary, the plans in eur ope for DBS-TV include the introduction of additional transponders for conventional analog television. Hd-mac over satellite under the EUREKA '95 program makes available analog, improved format television. And the EUROPESAT program in the mid to late 90 s would provide compressed digital HDTV. To successfully implement these programs, continued technology developments and improvements are needed.
ESA views video satellite applications as opportunities for industrial growth. The ESA Advanced System s And Technology Program (ASTP) has been funded since 1978. In the current phase (1990-1994) 36% of the 200 MAU (roughly $200 million) program supports broadcasting and fixed services. Broadcasting technologies supported include digital television, HDTV , and sound broadcasting. The objectives of the ASTP include "maintaining and improving the competitiveness of European industry in the world-market for equipment required in space and on earth for satellite communications."
The European C ommission is carrying out r&d programs in communications and information which total about $6 billion over five years, but with only about one percent devoted to satellite communications. Within the FLASH TV program, there are efforts to develop vide o compression techniques that would permit high quality television transmission at 34 to 70 Mbits/sec rates.
Telespazio is conducting Ka-band experiments using olympus to evaluate use of the 23 GHz DBS-TV band for digital HDTV broadcast. A 34 Mbits/ sec video-codec based on the discrete cosine transform is used to generate compressed, digital, television signals that are transmitted through the satellite. Another phase of the experiments will use a 70 Mbits/sec signal to evaluate bit error rates ove r the link. This work supports international satellite broadcast of HDTV.
In Japan, DBS-TV was developed early and under government sponsorship. NHK is Japan's public broadcaster and provided continuity of planning and fund ing to result in Japan being the first country to implement high power broadcast satellite service. Development of DBS-TV in Japan is shown in Table 3.9.
NHK is supported by monthly receiver fees of 1370 yen for terrestrial broad casts and an additional 930 yen for satellite broadcasts. In 1992, the NHK budget was 513 billion yen. There are more than six million satellite receivers, and in 1991, two 24-hour satellite channels were being broadcast by NHK. NHK shares the broadcas t satellites with JSB (Japan Satellite Broadcasting Corporation, a commercial broadcaster) and TAO (Telecommunication Advancement Organization), which performs satellite control. Currently, Hi-Vision HDTV is being satellite broadcast (using the analog MU SE transmission system) to more than 300 public sites and 10,000 individual receivers.
MELCO has developed a flat-plate, broadcast satellite, ground receive antenna (12 GHz, 1 m square, 47 dB gain) with built-in LNA, G/T>16 dB, linearly polarized. An other development by MELCO is a multibeam, BSS or FSS TV receive antenna using three separate feeds to receive from three differently located satellites without repointing.
NHK has developed mobile receivers for satellite broadcasts, for use by trains , buses, and automobiles. The smallest receivers are 0.32 x 0.12 m high, consist of patch array antennas with 27 dBi gain, and consume 40 W of power.
A potential new service being investigated by NHK is ISDB (Integrated Services Digital Broadcasting) which combines high definition, still images with high quality digital sound and with digital data (as with ISDN, a combination of video, sound and data). One coding approach could provide four video channels with multiple sound channels accompanying ea ch, at a transmitted bit rate of 40 Mbits/sec.
Development and Future Plans for DBS-TV in Japan
The development of DBS-TV in Japan, shown in Table 3.9, indi cates that DBS-TV is a mature technology. Small antennas, approximately 0.5 m diameter, were observed on many apartments and homes. With this maturity of service, the next technology hurdles are television compression and HDTV broadcast by satellite.
NHK has developed a 135 Mbits/sec codec for HDTV using the techniques of discrete cosine transform and motion compensation. For international transmissions, KDD and CANON have developed a HDTV codec operating at 120 Mbits/sec with transmission through a 72 MHz transponder.
For the COMETS experimental satellite, CRL is developing a 22 GHz, 200 W transponder to be used for HDTV broadcast experiments.
Russia is planning to update its current DBS-TV system, EKRAN, with a sy stem designated as GELIKON, which will have a greater number of channels at frequencies higher than those presently used. GELIKON will use 4 and 11 GHz for satellite-earth transmissions. GELIKON will be followed by a system designated as GALS. Technica l details and schedules for these systems were not provided.
The DBS plan developed for Europe at WARC-77 allows for high quality sound transmissions. And some multi-channel sound broadcasts are occurring using existing transp onders. But the major thrust of new activity is focussed on satellite transmissions to portable and mobile receivers (as in automobiles). WARC-77 provided a world-wide allocation for the broadcast satellite service-sound (BSS-Sound) at 1452-1492 MHz and called for a world-wide planning conference on BSS-Sound not later than 1998.
Currently, there is work underway to establish digital audio broadcasting (DAB) as a terrestrial broadcast service, so there is much activity to develop equipments and stan dards, and there is some competition between the satellite and terrestrial service providers.
Alcatel, in a study performed with CNES (the French space agency), concluded that DBS-R from GEO is not economical. ESA's ARCHIMEDES satellite program, plan ned for a 1998 launch into a highly inclined and highly elliptical orbit, is considering a sound broadcasting payload. The orbital inclination provides better coverage at high latitudes, to better reach the population of Europe, and the elliptical orbit provides longer view times from lower orbits. The ARCHIMEDES planning effort is supported by market studies that have determined that a market exists if the costs are competitive with terrestrial alternatives.
ESA has included funding for satellite s ound and broadcasting developments in its ASTP program. DLR (in cooperation with Bosch and CCETT) is developing channel coding for DAB for both satellite and terrestrial transmissions. EUTELSAT is studying digital audio broadcasting at Ku-band (in the 4 0 MHz allocated at WARC-1992).
For DAB, NHK is currently using three transponders. The DAB receivers sell for 20,000 yen and a monthly fee of 300-600 yen/channel/month is paid. Six programs are provided per transponder. A 0.5 m diameter antenna is needed for reception in Tokyo.
Japan is just starting to address DBS-R as allowed by the WARC-92. The next generation COMETS experimental satellite may include a DBS-R experiment at 2.6 GHz.