Satellite mobile communication systems can be divided into geostationary orbit (GEO), medium orbit (MEO) and low orbit (LEO) satellite mobile communication systems according to the orbits used.
Chinese name
Satellite mobile communication system
Foreign name
Satellite Mobile Communication System
Classification by track
GEO、MEO、LEO
Features
Multiple access transmission using satellite communication, etc
Its biggest feature is the use of satellite communicationsMultiple access transmission mode, providing global users with large span, large range, long-distance roaming and mobile, flexible mobile communication servicesCellular mobile communication systemIt has more unique advantages in remote areas, mountainous areas, islands, disaster areas, ocean going ships, ocean going aircraft and other communications.Satellite mobile communication systems can be divided into geostationary orbit (GEO), medium orbit (MEO) and low orbit (LEO) satellite mobile communication systems according to the orbits used.GEO system has mature technology and relatively low cost. The GEO systems that can provide services include INMARSAT system, North American satellite mobile system MSAT, and Australian satellite mobile communication system Mobilesat system;LEO system has the advantages of short transmission delay, low path loss, easy global coverage and avoiding the congestion of geostationary orbit. Typical systems include Iridium, Globalstar, Teldest, etc;MEO has both the advantages and disadvantages of GEO and LEO systems. Typical systems include Odyssey, AMSC, INMARSMT-P systems, etc.In addition, there are regional satellite mobile systems, such as AMPT in Asia, N-STAR in Japan, ECO-8 in Brazil, etc.
Connection technology
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The satellite mobile communication mainly adopts TDMA and CDMA multiple access connection technology, but CDMA technology is considered to be a more promising technology, which is still in the experimental development stage.WARC-92 divides frequencies for satellite mobile services, including 84.2MHz bandwidth for space to ground links (1525-1530MHz, 2170-2200MHz, 2483.5-2500MHz, 2500-2520MHz, 1613.8-1626.5MHz), and 66.5MHz bandwidth for ground to air links (1610-1626.5MHz, 1980-2010MHz, 2670-2690MHz).Due to the variety of satellite mobile communication systems and the fierce competition between them, many systems will not be commercially available until the 21st century. Moreover, the regions that most need satellite mobile communication in China are often underdeveloped regions. As the land cellular mobile communication market has huge potential, but many issues involving China's frequency use rights, communication sovereignty, business management and other aspects cannot be rushed.The State Radio Commission has revised China's "Radio Frequency Division Table" and believes that the planning and allocation of frequencies used in satellite mobile services will be considered.The use of non geostationary satellites has increased the difficulty of inter satellite coordination. Frequency coordination is not only required between non geostationary satellites, but also between non geostationary satellites and geostationary satellites, as well as between terrestrial radio services.
Coverage mode
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The satellite has a huge coverage areaSynchronous communication satelliteIt can cover 1/3 of the earth's area. As long as there are three geostationary satellites, communication can be realized in all regions except the South and North Poles.This has become an important means of intercontinental and long-distance communication in the world, and also has a market share in the mobile communications of vehicles, ships and aircraft in the land, sea and air fields in some regions.However, synchronous communication satellites cannot realize mobile communication of personal mobile phones.To solve this problem, communication satellites in low and medium orbits can be used.The middle and low orbit satellites are only hundreds or thousands of kilometers away from the ground. They orbit the earth quickly over the earth, so they are called non synchronous earth satellites, orMobile communication satelliteThis satellite system is designed for personal mobile phone communication.Typical systems include "Yixing" system“Global Star System”Etc.These systems cover the whole earth's surface with dozens of small satellites in medium and low orbit, just like setting a cellular mobile communication system covering the whole world "upside down" in the sky.Each satellite can cover an area of several hundred kilometers in diameter, which is much larger than that of the ground cellular base station.
The coverage station area formed by satellites moves rapidly on the earth's surface, and it will circle the earth in about two hours. Therefore, there is also a problem of "handoff" for users' mobile phones.The difference between the terrestrial cellular system and the terrestrial cellular system is that in the terrestrial cellular system, the user moves through the cell, while in the satellite mobile communication system, the cell moves through the user. This difference makes it easier for the satellite mobile communication system to solve the "handover" problem than in the terrestrial cellular system.
feasibility
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The satellite mobile communication system covers the world, can solve the mobile communication services in the sparsely populated and underdeveloped areas, and is an important part of global personal communication.But its service cost is high, and it can not replace the terrestrial cellular mobile communication system.Mobile communication technology of satellite mobile communication system
