Background. Communication satellites and systems

Communication satellites and systems

Part I 51.1-51.3.2 (Background)

Background

In 1883, Konstantin E Tsiolkovsky, a Russian schoolmaster ex­plained the principles of rocket flight in space. Twelve years later, he mentioned the possibilities of artificial satellites circling the earth outside its atmosphere. Half a century later, Arthur C Clarke wrote of orbiting radio relay stations (Clarke, 1945) and identified many of the advantages which satellite communication would have over terrestrial systems for long distance communication and broad­casting. Above all he pointed to the unique value of geostationary satellites.

Sputnik 1, the first man-made satellite, was put into low orbit (227km x 941km x 65.1°) in October 1957 and stimulated many other tests and demonstrations of practical applications for artificial satellites in the following years, above all for telecommunications. By 1962 the Telstar 1 (Dickieson, 1963) and Relay 1 (NASA, 1968) satellites had demonstrated long distance telephone links between fixed earth stations. By 1964 an experimental satellite, Syncom III, had been placed in an accurate geostationary orbit. In the same year INTELSAT, an international consortium having the objective of setting up a global satellite network for fixed telecommunications, came into being. By July 1965 the 'Early Bird' satellite, taken over by INTELSAT and later to be renamed INTELSAT I Fl, was in operation, relaying telephone calls between Europe and North America.

Much has happened since 1965. Satellites provide a major me­dium for linking together terrestrial telecommunications networks, province by province and country by country, using earth stations at fixed locations, typically with high gain antennas. INTELSAT has developed very extensively (Hall and Moss, 1978; Sachdev, 1990). INTERSPUTNIK became a second global system. Several regional systems, such as EUTELSAT, PALAPA and ARABSAT and many national networks are now in operation.

These systems have also become an important medium for the distribution of television programme material, to terrestrial broad­casting stations and more recently direct to home. In direct to the home television these satellites are competing, not only with terre­strial radio and cable broadcasting but also with newly emerging high power broadcasting satellites. And a substantial market has developed in the supply of satellite relay facilities for linking together networks of small, low cost earth stations on the users' premises.

There were early experiments with mobile earth stations as part of the NASA Applications Technology Satellite programme in the second half of the 1960s. The MARISAT system was set up by the Communications Satellite Corporation, starting in 1976, to provide telephone and data services by satellite to merchant ships. The internationally owned INMARSAT consortium took over that func­tion in 1982. More recently there has been widespread interest in satellite communication for airliners and for various kinds of mobile station on land; INMARSAT and a number of national systems are developing new facilities to meet these needs, often coupled with position finding aids.

51.2 International regulations
51.2.1 Frequency bands

Of the bands allocated for satellite links between fixed earth stations (ITU, 1990a), the fixed-satellite service, those given in Table 51.1 are the ones which are already used, or are likely to be used soon, for commercial systems on a substantial scale. The following notes apply to this table:

a. These bands are to be used in accordance with a frequency and orbital slot allotment plan agreed in 1987.

b. ITU Region 2 only (North and South America). In Canada, Mexico and USA, the fixed satellite service has higher alloca­tion status than any of the other services with which the band is
shared. (ITU, 1990c.)

c. Not in ITU Region 2. This band is allocated exclusively for the fixed satellite service in many countries in ITU Regions 1 and 3.

d. These bands are allocated exclusively for the fixed satellite and mobile satellite services in most countries.

Table 51.1 Frequency allocations for the fixed satellite service

These bands are also allocated for terrestrial radio systems except where otherwise indicated, and some bands are also allocated, partly or wholly, for other kinds of space system.

There are certain other bands, relatively narrow in bandwidth, also allocated for the fixed satellite service, in particular around 2.6GHz, 3.6GHz and 6.6GHz, and there are wide bands above 30GHz, but none of these bands is used much at present.

The frequency bands allocated for links between satellites (ITU, 1990a) and mobile stations (the mobile-satellite services) on land, by sea or in the air and already used for commercial systems, are shown in Table 51.2. The following notes apply to this table:

a. Not in ITU Region 1 (Europe, Africa, Asia west of the Persian Gulf and the whole of the USSR). Use for mobile satellite systems is subject to protection of terrestrial systems for which
the band is also allocated. (ITU, 1990d,e.)

b. ITU Region 3 only (Australasia and Asia, excluding USSR and countries west of the Persian Gulf). Otherwise as note a.

c. Land vehicles may use these bands for low bit rate data systems provided that they do not interfere with use by ships. (ITU, 1990f.)

The links, called feeder links, between these satellites and stations at fixed locations on the ground are operated in bands allocated to the fixed-satellite service (Table 51.1). It is already evident that the bandwidth allocated for satellite to mobile station links will not be sufficient for rapidly growing systems and prospective new sys­tems, particularly for service to land vehicles, and the allocation of additional spectrum will be considered at an ITU conference in 1992.

Table 51.2 Frequency allocations for mobile satellite services

The frequency bands allocated for down-links from broadcasting satellites (the broadcasting satellite service) and currently being taken into use, albeit slowly, for television are as in Table 51.3

Table 51.3 Frequency bands allocated for down-links from broadcasting satellites

Frequency and orbital slot assignment plans have been drawn up for these bands (ITU, 1990g). The feeder links which carry pro­gramme signals up to these satellites may be assigned frequencies in bands allocated to the fixed satellite service for up-links. How­ever, other frequency bands, not to be used for fixed satellite systems, have been set aside especially for these feeder links and assignment plans have been drawn up. The plans are in the bands given in Table 51.4 (ITU, 1990h).

Various other bands have been allocated for satellite broadcasting (down-links), in particular around 42GHz and 85GHz, but there is little sign at present of these allocations being taken into use.

Finally, frequency bands have been allocated (ITU, 1990a) for assignments to inter-satellite links, used for any kind of satellite system. The main bands below lOOGHz are:22.55GHz-23.55GHz; 32.0GHz-33.OGHz; 54.25GHz-58.2GHz; 59GHz-64GHz.

Table 51.4 Frequency bands allocated for feeder links used in broadcast satellite services

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