A TECHNICAL COMPARISON OF SEVERAL GLOBAL MOBILE SATELLITE-COMMUNICATIONS SYSTEMS

The era of satellite-based Mobile Satellite Communications (MSG) systems started with the first MARISAT satellite which was launched into a geostationary orbit over the Pacific Ocean in 1976 to provide communications between ships and shore stations. The combination of high cost and unacceptably large equipment has kept the space-based MSC systems from appealing to the wider market of personal mobile communications. The progress made over the last ten years, however, in digital voice processing, satellite technology, and component miniaturization has resulted in the viability of satellite-based mobile satellite communications systems to meet the growing market in personal mobile communications using handsets similar to those currently in use with land-based cellular systems. Three of the more mature LEO/MEO satellite systems are addressed in this paper including GLOBALSTAR, Iridium, and Odyssey. The system architectures of each system are presented along with a description of the satellite and user handset designs and the multi-access techniques employed. It will be shown that, although a number of similarities exist amongst the system addressed in this paper, each system is unique in a variety of significant design areas. It is concluded in this paper that the technical feasibility of satellite-based mobile satellite communications systems seems to be secure. It will be challenging; however, for the vendors to actually develop and deploy these systems in a cost effective, timely, and reliable way that meets a continually evolving set of requirements based upon a rapidly changing technology base.