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Satellite Communications Systems
By Editor | September 10, 2008
Satellite communication systems are referred to as satcoms in short. Satellite communication is carried out through artificial satellites positioned in space in different kinds of orbits. There are five different kinds of orbits – low (non-polar and polar) Earth (LEO) orbits, medium earth orbits (MEO), highly elliptical orbits (HEO) and geostationary orbits.
Satellite communication systems are largely used for communication through satellite phones. Satellite phones use geostationary satellites or low (non-polar and polar) Earth orbits. There are two kinds of satellite communication systems. One, fixed point-to-point. This is similar to someone calling up from a landline number to another landline number. In fixed point to point services, as the name implies, both the points of telecommunication are fixed or stationary. In such cases, satellite communication provides a parallel to fibre optic submarine communication cables and though the latter is cheaper, the former continues to be used in places where it is impractical or impossible to lay fibre optic submarine communication cables. Some islands like Ascension Island, St. Helena and the Pacific islands depend on satellite communication systems as fibre optic submarine communication cables have not been laid over there. Also, the polar caps are other instances of places which depend on satellite communication systems. For fixed (point-to-point) services, communications satellites (or comsats as they are referred to in short) provide a microwave radio relay technology complementary to that of fibre optic submarine communication cables. Two, mobile satellite communications (MSS or Mobile Satellite Services) where one or both the points is/are mobile. For instance, the mobile point(s) may be a ship (Marine MSS), (Air MSS) and even in cars if one is travelling in remote areas (Land MSS). Similarly, places like remote mountains or the countryside where there are no towers of cellular phone operators or any other form of telecommunication, satellite phones prove useful as they depend on space satellites for communication. Iridium, Globastar and Inmarsat are popular providers of mobile satellite services.
Satellite communication systems have a constellation or a system of interlinked satellites. The least number of satellites is required if one uses geostationary satellites (called so because they appear to be in a fixed position to an observer on earth as they revolve around the earth at a constant speed and thus they help in simplifying technology on earth as there is no need to enable the gadget on earth to revolve to track and maintain a link with the satellite) – four to six satellites are enough to cover the whole surface of the earth. For highly elliptic and medium earth orbit satellite systems, more number of satellites is used. For low earth orbit satellite constellations, about 24 would be required at least. The global satellite company Iridium has 66 satellites in its constellation.
Satellite communication systems are used for satellite television and also for worldwide radio stations. Fixed Service Satellite (FSS) is slowly being replaced by Direct Broadcast Satellite (DBS) in a lot of countries for satellite television. Satellite communication is also used for internet access where wireline broadband or dial-up internet connections are not possible.
Topics: Satellite Communications |