LEO MEO SYSTEMS - GLOBAL MOBILE COMMUNICATION-SYSTEMS/

LEO/MEO systems are moving from a dream to a reality, their global rea ch is becoming apparent with the launch of the first LEO satellites. T he global mobility offered by these systems is expected to have a prof ound effect on the way that organizations and individuals operate. Bil lions of dollars are invested in the research and development of LEO/M EO based communication systems, and larger amounts will be needed for their ongoing operation and use. Many global satellite based systems h ave been announced over the last decade, Ellipsat, Globalstar, ICO, Ir idium, M-Star, Odyssey, Orbcomm, and Teledesic, are just a few of the many systems in deployment or under development. Being such a risky ve nture, limited experience exists in developing and managing large scal e civilian satellite based mobile communication systems. Many interest ing and challenging research issues are faced by the designers and ope rators of such systems. This paper presents the different approaches t o the configuration of the various LEO and MEO based communication sys tems. It compares their advantages and disadvantages, and analyzes the ir economic viability. Based on the analysis, it is possible to identi fy the specific roles that each type will play in the global communica tion market. The paper presents and discusses some of the important re search areas involved in their development, configuration, maintenance , operation and management. In particular, it introduces the problem o f gateway placement in LEO/MEO systems and presents a mathematical for mulation of the problem.