1.1 Birth of Satellite Communications
Satellite communications are the outcome of research in the area of communications and space technologies whose objective is to achieve everâincreasing ranges and capacities with the lowest possible costs.
The World War II stimulated the expansion of two very distinct technologies â missiles and microwaves. The expertise eventually gained in the combined use of these two techniques opened up the era of satellite communications. The service provided in this way usefully complements that previously provided exclusively by terrestrial networks using radio and cables.
The space era started in 1957 with the launching of the first artificial satellite (Sputnik). Subsequent years have been marked by various experiments including the following: Christmas greetings from President Eisenhower broadcast by Score (1958), the reflecting satellite ECHO (1960), storeâandâforward transmission by the Courier satellite (1960), powered relay satellites (Telstar and Relay in 1962), and the first geostationary satellite Syncom (1963).
In 1965, the first commercial geostationary satellite Intelsat I (or Early Bird) inaugurated the long series of Intelsats; in the same year, the first Soviet communications satellite of the Molniya series was launched.
1.2 Development of Satellite Communications
The first satellites provided a low capacity at a relatively high cost; for example, Intelsat I weighed 68 kg at launch for a capacity of 480 telephone channels and an annual cost of $32 500 per channel at the time. This cost resulted from a combination of the cost of the launcher, that of the satellite, the short lifetime of the satellite (1.5 years), and its low capacity. The reduction in cost is the result of much effort, which has led to the production of reliable launchers that can put heavier and heavier satellites into orbit (typically 5900 kg at launch in 1975, reaching 10 500 kg by Ariane 5 ECA and 13 000 kg by Delta IV in 2008). Today, Delta IV Heavy is capable of sending a payload of 28 790 kg to low earth orbit (LEO) and 14 220 kg to geostationary transfer orbit (GTO); SpaceX Falcon Heavy can send payload of 63 700 kg to LEO, 26 700 kg to GTO, and 3500 kg to Mars.
In addition, increasing expertise in microwave techniques has enabled realisation of contoured multibeam antennas whose beams adapt to the shape of continents, frequency reuse from one beam to the other, and incorporation of higherâpower transmission amplifiers. Increased satellite capacity has led to a reduced cost per telephone channel in recent history and now is calculated as reduction of the cost per bit in the digital age.
In addition to the reduction in the cost of communication, the most outstanding feature is the variety of services offered by satellite communications systems. Originally these were designed to carry communications from one point to another, as with cables, and the extended coverage of the satellite was used to set up longâdistance links; hence Early Bird enabled stations on opposite sides of the Atlantic Ocean to be connected. However, as a consequence of the limited performance of the satellite, it was necessary to use earth stations equipped with large antennas and therefore of high cost (around $10 million for a station equipped with a 30 m diameter antenna).
The increasing size and power of satellites has permitted a consequent reduction in the size of earth stations, and hence their cost, leading to an increase in number from thousands to millions. In this way it has been possible to exploit another feature of the satellite: its ability to collect or broadcast signals from or to several locations. Instead of transmitting signals from one point to another, transmission can be from a single transmitter to a large number of receivers distributed over a wide area; or, conversely, transmission can be from a large number of stations to a single central station, often called a hub. In this way, multipoint dataâtransmission networks and dataâcollection networks have been developed under the name very small aperture terminal networks (VSATs) MAR-95. Over 1 000 000 VSATs had been installed up to 2008 and about 6 000 000 in 2018.
For TV services, satellites are of paramount importance for satellite news gathering (SNG), for the exchange of programmes between broadcasters, and for distributing programmes to terrestrial broadcasting stations and cable heads, or directly to the individual consumer. The latter are commonly called direct broadcasting by satellite (DBS) systems, or directâtoâhome (DTH) systems. A rapidly growing service is digital video broadcasting by satellite (DVBâS), developed in early 1991; the second generation (DVBâS2) has been standardised by the European Telecommunication Standard Institute (ETSI); and DVBâS2X as an extension of DVBâS2 was completed in 2014. These DBS systems operate with small earth stations having antennas with a diameter from 0.5 to 1 m.
In the past, customer stations were receive only (RCVO) stations. With the introduction of twoâway communication...
