By Satpert
Introduction
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 reception 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.
A DBS subscriber installation consists of a dish antenna two to three feet (60 to 90 centimeters) in diameter, a conventional TV set, a signal converter placed next to the TV set, and a length of coaxial cable between the dish and the converter. The dish intercepts microwave signals directly from the satellite. The converter produces output that can be viewed on the TV receiver.
NEW SERVICES AND APPLICATIONS
The current revolution in telecommunications encompasses a number of major trends. These include the following:
- The merging of telecommunications and information sciences in the context of digital processing and intelligent networks.
- The shift from telecommunications systems that were previously driven by telephone services to systems that are driven by data and imaging services. (This implies that the cost of service per Hz will drop and the average bit rate of services will increase, perhaps dramatically.)
- The shift from telecommunications systems that are locally and nationally defined to those that are shaped by global markets.
- The shift from telecommunications systems that are shaped by human communications needs to those that are machine-driven.
- A change from communications systems that are overwhelmingly fixed to those that is increasingly mobile.
- The evolution of global digital standards that allow voice, data, video, imaging, and other services to be intermixed and for public switched and private network services to interconnect on demand.
- A redefinition of the optimal transmission technologies in terms of fiber optics, terrestrial wireless and satellite services as economics, standards, service demand, broadcasting and mobility requirements change.
These general trends in telecommunications can be seen throughout the countries of the OECD and certainly in Europe. The areas where there seems to be active European research and development of new telecommunications services and applications with special emphasis on satellite communications are highlighted below.
Broadcast TV, Television Distribution and HDTV
Currently Europe is well served by communications satellites that can provide many of these services. There are: TV Sat (DBS) and KOPERNICUS (TV Distribution) in Germany, TDF (DBS) and Telecom (TV Distribution) in France, BSB (DBS) in the United Kingdom, and the complete family of EUTELSAT satellites and the RTL/STS consortium satellite for television distribution throughout Europe. The RAI broadcasting group will be experimenting with the ITALSAT project, and experiments with DBS services were carried out on the TELE-X satellite in Sweden and other parts of Scandinavia. The HISPASAT project will cover Spain and South America. These various satellite projects place Europe at the forefront of satellite television distribution and broadcasting. MAC standards developed by the IBA of the United Kingdom (most notably MAC-D2) have been adopted in various parts of Europe.
This strong interest is reflected in ongoing satellite R&D in this area. The ESA OLYMPUS satellite, which evolved from the precursor H-SAT and L-Sat projects, is the most notable experiment with DBS channels, HDTV, and even audio broadcasting. This project is considered in many ways as a precursor to the EUTELSAT operational system known as EUROPESAT. The technical feasibility of DBS service has been clearly established, despite technical difficulties that OLYMPUS has experienced. Current OLYMPUS tests and demonstrations have been oriented largely toward determining market interest. The feasibility of using this technology for educational, health and other tele-services (beyond entertainment and business-oriented teletext services) is one of the key market issues under investigation.
The European Broadcasting Union (EBU) has expressed some interest in the feasibility of DBS-Radio services in order to provide high quality CD-like audio services throughout Europe. For the most part, European telecommunications officials seem more interested in terrestrial technologies for mobile communications services and radio broadcasting than they are than satellite transmission.
Scientific Visualization
The European scientific community is reasonably well networked through Network Diane, public switched networks, and scientific networks of various national and international research agencies. These networks operate primarily at the level of e-mail and often use commercial or proprietary systems to achieve intercommunication. To date, scientific visualization in networked environments for remote database access, burst and browse file review, and interactive research projects is more limited in Europe than in the U.S. Full color, 3-D scientific visualizations operating at speeds of 45 to 90 Mbits/sec have been limited. OLYMPUS experiments, for instance, have focused primarily on broadcast television, with limited tests of interactive scientific visualization. Although ESA, the EC, national telecommunications organizations and scientific agencies throughout Europe have experience in this area and are conducting active research, it appears that the U.S. may have a three to five year lead. ACTS experiments scheduled for 1993-94 should help sustain this lead.
Virtual Reality and Other Advanced Imaging Services
In this area, too, the U.S. appears to hold a slight lead, but this technical advantage has no particular relationship to satellite communications. Developments in frame relay, cell relay, ATM in the context of B-ISDN, and the Bellcore-developed standard for switched megabit digital services (SMDS) are the primary enabling technologies for advanced imaging services, and these are being almost exclusively implemented as terrestrial telecommunications technologies in the form of fiber optic networks. Both in Europe and in the United States, advanced imaging services, except possibly for scientific visualization, are seen as being delivered by fiber optics except possibly in rural and remote areas. The choice of fiber over satellites is driven by cost considerations, quality or bit error rate performance, and concerns about transmission delay and its compatibility with ATM/cell relay. Clearly, enhanced U.S. and European research is needed to address these issues and also to ensure that advances in digital compression techniques are applied to satellites as effectively as to terrestrial technologies.
Mobile Services
Similar observations also can be made in comparing terrestrial wireless mobile technologies (e.g., digital cellular, GSM, and PCS or microcellular service) with MMS now under development. Both in the U.S. and Japan R&D, trial implementation and actual investment in operational systems focus on terrestrial systems. Europe even resisted new allocations for LEO satellite systems for mobile services at WARC-1992 because of the strong preference for terrestrial wireless technology. In Europe, the Inmarsat system has the potential to be used for MSS to land areas. However, Inmarsat is precluded by agreement from providing services to land areas of the United States. To provide worldwide MSS, both the “little LEOs” (for paging and text messages) and the “big LEOs” (for voice traffic) are being developed more aggressively in the United States than in Europe.
NASA has contributed little R&D in this area, with the exception of the ACTS OBP serving as a prototype for a similar system on the Motorola IRIDIUM system. There appears to be great potential in low-orbit mobile communications satellite and navigational systems, but to date neither Europe nor the U.S. has devoted significant R&D to this area, in terms of either national or regionally-funded research.
Digital Compression Techniques/Advanced Processing and Encoding/Error Control
These are three areas of telecommunications research which relate to the overall progress of the field but are not uniquely related to satellites. Nevertheless, there are often unique aspects of these areas of research that can provide unique advantages to satellites, or place satellites at a special disadvantage. The ability to use bit-by-bit processing on-board the satellite can provide up to a 9 dB advantage in a way that cannot be easily provided in a terrestrial system. Current techniques of forward error correction (FEC) used on satellites may be eliminated on fiber optic cable systems that deliver quality performance of 10(superscript -11). This could place satellites at a major disadvantage. The most efficient protocols to send data faster with the lowest amount of overhead and delay, such as cell relay or ATM, are extremely intolerant of transmission delay. Most research on multi-gigabit transmission systems, such as soliton pulse communications systems which need non-linear transmission media, assumes that satellite transmission will not operate at such high speeds. Again, these critical areas seem to be overlooked, and are very modestly funded in both the United States and Europe.
In general, the U.S. seems to be ahead or even with Europe in terms of research related to advanced applications and services for communications satellites. There are certain areas (e.g., advanced imaging, mobile services and advanced digital techniques) where neither is making significant advances.
References
1. http://www.arianespace.com/images/launch-kits/launch-kit-pdf-eng/NSS12_THOR6_GB.pdf
2. http://www.econ.umn.edu/~bajari/undergradiosp10/ectagoolsbeepetrin.pdf
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