Call by call basis GES assignment method for ICO systems adopting time-dependent service areas

This paper describes a gateway earth station (GES) assignment method, which is one of important networking issues associated with personal communications systems using non-geostationary satellites, known as ICO (intermediate circular orbit) and LEO (low Earth orbit) satellites. First, two types of service areas are defined for GES´s. One is the “time-independent service area”, and the other is the “time-dependent service area”. Both are defined as the area which is continuously covered by a GES, and differ in duration in which the GES continuously covers. The time-independent service area of a GES is defined as the area which the GES continuously covers for infinitely long duration. The time-dependent service area of a GES is defined as the area which the GES continuously covers for a predetermined finite duration. Hence, the time-dependent service area of a GES changes its shape time-by-time. The composite time-dependent service area of multiple GES´s, obtained by superimposing time-dependent service areas of each GES time-by-time, is introduced. It is shown that the composite time-dependent service area is wider than the simple summation of time-independent service areas of multiple GES´s. For handheld terminals currently located within the composite time-dependent service area, appropriate GES assignment is required so that the subscribers can initiate and continue calls, due to time-dependency of the GES service areas. This paper proposes a GES assignment method making use of advantageous features obtained by adopting the time-dependent service areas