Study on ISL network structure in LEO satellite communication systems

Many parameters have to be taken into account in designing an LEO satellite constellation including transmission delay, service coverage, minimum elevation angle, and the effects of space radiation. We selected the 2ππ constellation for the NeLS ISL study to maintain continuous ISL connections, which is expressed by using a Walker notation of 120/10/1 with 55° of inclination. The satellite orbit parameters were examined under conditions where at least two satellites were always visible from the user terminal to enable satellite diversity. The optimum inclination angle for the 2ππ constellation was directly derived from the spherical triangle formed by three adjacent satellites. To evaluate the NeLS's ISL performance, the structure for ISL connections was simplified by using constellation parameters of 121/11/0 instead of 120/10/1. The ISL network had a bi-directional MSN structure with these parameters. The inter-orbital ISL, especially, achieved a ring network shaped like a figure-of-eight using nn to n-1n-1 connections. The bi-directional MSN topology of ISL connections is also discussed. A combination of constellation parameters PP, SS, and FF were found to have simple relations in the n   to n-1n-1 connections of inter-orbital ISLs. Finally, optimum parameters for the NeLS constellation are discussed, and a candidate parameter (T/P/F=132/11/-1T/P/F=132/11/-1, h=1100km, and I=57.92∘I=57.92∘) is proposed.