A LINK STUDY OF A LOW-EARTH-ORBIT SATELLITE-COMMUNICATIONS SYSTEM USING OPTICAL INTERSATELLITE LINKS

Link conditions of a low-earth orbit (LEO) satellite communications sy stem were evaluated, to provide the information necessary for designin g a broadband LEO-SAT communications system. The study was made both f or optical intersatellite and user/satellite links. For the optical in tersatellite link (ISL), we examined several ISL configurations in a c ircular polar orbit, and found that when the satellites are in the sam e orbital plane, the link parameters are quite stable, that is, the li nk between adjacent satellites can be regarded as fixed and, therefore , suitable for broadband transmission via an optical link. However, th e link conditions between adjacent orbits change very quickly and over a wide range. To overcome this and extend the network path between sa tellites in adjacent orbital planes, we proposed intermittent use of t he link between satellites in co-rotating adjacent orbital planes at t he low latitude region, i.e., only during the period of stable conditi ons. The optical intersatellite link budget also sets link parameters that are realistic, given present optoelectronic technologies. From qu antitative evaluations of the user/satellite link, we believe that bot h the satellite altitude and minimum elevation angle are critical, bot h in defining the quality of the service of the LEO-SAT system and in their impact on the other transmission parameters. The link loss, the visible period and the required number of satellites vs. satellite alt itude and elevation angle are also indicated. These are important cons iderations for future system design.