COVERAGE CONCEPTS FOR SATELLITE CONSTELLATIONS PROVIDING COMMUNICATIONS SERVICES TO FIXED AND MOBILE USERS

This article recalls some important limitations of geostationary (GEO) satellite systems when used for personal mobile communications, It sh ows how such limitations can be overcome by considering non-GEO conste llations of satellites, either in low earth orbit (LEG) or in intermed iate circular orbits (ICO). Those systems, which are now planned for t he end of the century, can provide communications services to both fix ed and mobile users. Two concepts of coverage can be considered and ar e compared: the 'satellite-fixed' and the 'earth-fixed' cell coverage. The latter offers significant advantages in terms of low handover fai lure probability, which makes the concept appealing for fixed users-or iented services.