Therefore, when we start thinking in terms of non-geostationary earth orbit satellites, the issues that one must look into are, orbital considerations, where the satellites are, what is the position, because that will also give us the time-delay, etc., channel modelling and capacity issues, because even though the satellite is in the free space, if mobile receives the satellite signal through various parts, some of the signals will have multipath reception, some of them would have multipath reception, as well as direct reception, and so on. So, one must consider how one would like to do the channel modelling and what is the type of capacity that you will get, one should also study the propagation environment and interference, what kind of modulation techniques one would like to have for the satellite communication and associated performance issues. And then how you would like to interconnect or accessing and networking issues. And one of the major themes in satellite mobile communication is hand over, as I have already mentioned, the satellites move at much faster rate and therefore the number of hand-over is much larger that in the case of terrestrial system.

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