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Mobile Satellite Communications
By Editor | January 31, 2008
Mobile satellite communications or mobile satellite services (MSS) as they are more commonly referred to are satellite communication systems which use portable terrestrial terminals as opposed to fixed satellite services (FSS) which uses fixed terrestrial terminals where the location of the ground stations are not changed frequently. Consumer satellite television uses FSS. MSS terminals can be placed in ships, planes and vehicles or can be carried by individuals. Satellite telephones make use of MSS. There are three major kinds of MSS: aeronautical MSS (AMSS), land MSS (LMSS) and maritime MSS (MMSS).
Satellite telephones form the bulk of mobile satellite communications. Satellite phones use geostationary satellites or low (non-polar and polar) Earth orbits. Mobile satellite communications can be described as radiocommunication between mobile earth stations and one or more space stations, or between mobile earth stations by using one or more space stations, or between space stations.
Mobile satellite service helps primarily for connecting stations which are not otherwise reachable through either submarine communication cables or other forms of land communication services. Thus mobile satellite services help in communication from places like ships (MMSS), planes (AMSS) and even in cars if one is travelling in remote areas (LMSS). 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. By their very nature, satellite phones have a global connectivity. The link is not dependent on terrestrial location. Since some mobile satellite services do not have geostationary satellites (as the cost of geostationary satellites are high), they opt for several low earth orbit (LEO) satellites. The group of such LEO satellites for a particular purpose are termed as a satellite constellation. The Global Positioning System (GPS), the European Galileo positioning system, the Chinese COMPASS navigation system and the Indian IRNSS are all Global Navigation Satellite Systems (GNSS) that use mobile satellite communications.
Highly elliptic and medium earth orbit satellite systems can also be used for mobile satellite services instead of low earth orbits. As one goes farther away from earth, the coverage of the satellites increases and thus lesser satellites are required. For instance, four HEO satellites can cover the earth whereas about ten MEO satellites would be required and about 24 LEO satellites though Iridium has 66 satellites. HEO and MEO satellites are still in a developmental stage. Iridium, Globastar and Inmarsat use LEO satellites for mobile satellite communications.
Canada’s CASCADE system based CASSIOPE communications satellite will offer discontinuous coverage where LEO satellites will receive data will travelling over one part of the world and transmit it when it passes over the destination. Orbcomm will also use this store and forward method of mobile satellite service.
Mobile satellite communications will help to connect remote islands which are not connected to the rest of the world through fibre optic submarine communication cables like Saint Helena, the Pacific Islands and Ascension Island.
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