A GLOBAL MESSAGE NETWORK EMPLOYING LOW EARTH-ORBITING SATELLITES

A global message communication network for low density traffic, employing satellites at low altitudes, is the subject of this paper. This network affords round the clock service to any part of the globe, including the polar regions. Such a network can accommodate static and mobile user terminals simultaneously. The oblate globe is modeled as a regular polyhedron with 12 facets for setting up the orbits. Satellites are positioned uniformly in low-altitude symmetrical orbits. The symmetrical orbits are those whose axes are symmetrical in the three-dimensional space. We study the coverage aspects of the 6-orbit scheme and the 10-orbit scheme, each with satellites deployed at an altitude of 5000 km. At this altitude, the terrestrial user terminals can access satellites at a grazing angle of 45-degrees. The method of access over the cross-links is considered to be the slotted ALOHA scheme. For low density traffic, the down-link and up-link throughput rates are estimated. Simulation results agree with these analytical estimates for low values of network offered load.