Điện thoại di động mạng lưới Radio P14

Mobile Satellite Communication∗In principle communications satellites provide the same connectivity as terrestrial (wireless and wireline) networks. The advantages of satellites, such as fast wide-area coverage, flexible transmission parameters and cost independence due to distance, are compared with the disadvantages, such as restricted channel capacity because of the frequencies available, orbital positions, need for line-of-sight connectivity and high initial investment besides relatively long signal propagation times. As a result, only certain application areas have been developed for satellites in the past....
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Điện thoại di động mạng lưới Radio P14 Mobile Radio Networks: Networking and Protocols. Bernhard H. Walke Copyright©1999 John Wiley & Sons Ltd ISBNs: 0-471-97595-8 (Hardback); 0-470-84193-1 (Electronic)14Mobile Satellite Communication∗14.1 FundamentalsIn principle communications satellites provide the same connectivity as ter-restrial (wireless and wireline) networks. The advantages of satellites, suchas fast wide-area coverage, flexible transmission parameters and cost indepen-dence due to distance, are compared with the disadvantages, such as restrictedchannel capacity because of the frequencies available, orbital positions, needfor line-of-sight connectivity and high initial investment besides relatively longsignal propagation times. As a result, only certain application areas have beendeveloped for satellites in the past.14.1.1 Application AreasSatellites are being widely used for distribution functions, e.g., for transmit-ting television and radio programmes as well as for data. Existing communi-cations networks can be totally bridged through the use of satellite systems.Satellite communication, which until recently was almost only exclusively usedfor navigation and aviation as well as in land vehicles, is a branch that opens upa totally new world of applications. Satellite paging along with GPS (GlobalPositioning System) and GLONAS have recently been introduced for civil use.The interest in global personal communications is leading to big efforts in thedevelopment of new satellite systems that operate at the low orbital heights. Currently mobile satellite systems are being used mainly in areas whereno other terrestrial communications systems are available (on the open seas,in the desert, in rural regions, etc.). These systems are also attractive tousers who operate internationally and otherwise use different kinds of terres-trial mobile radio systems, requiring them to carry terminals with differentstandards. A differentiation is made between worldwide, regional and national systems,depending on the coverage area of a satellite system. In terms of institutionaland organizational structure, a distinction is made between international, na-tional and private operators of satellite systems. Tables 14.1–14.5 present acompilation of the known parameters of all systems currently in development. ∗ With the collaboration of Branko Bjelajac and Alexander Guntsch Table 14.1: Narrowband satellite systems concentrating on telephony applications—Part 1 716System Globalstar ICO IRIDIUM Odyssey Ellipso ECCO (later: Aries)Company Loral, Qual- ICO Global Motorola TRW, Teleglobe Mobile Constellation comm, Alcatel Communications Canada Communications Inc., Telebras Espace HoldingsOrbit LEO (circular) MEO (circular) LEO (circular) MEO (circular) MEO LEO (circular) (circ. + ell.)Path altitude [km] 1414 10 355 780 10 354 520–7846 (ell.) 2000 8040 (circ.)No. of sats. + spare 48 + 8 10 + 2 66 + 12 12 + 2 on the 14 + 3 11 + 1 (latersats. Ground add’l 35 + 7)No. of orbits 8 2 11 3 3 (2 ellipt. + 1 1 equat. (later circular) add’l 7)No. of ground 100 12 21 7 ≥ 20 11 (more later)stations 14Inclination [°] 52 45 86 50 116.5 (ellipt.)/ 0 0 (later 62) ...