Closed-Form Outage Probability Analysis for OTFS-Based Multi-Beam LEO Satellites

This paper considers a challenging communication scenario wherein a multi-beam low earth orbit satellite caters to high traffic demands from massive high-mobility terminals. To mitigate the Doppler frequency shift induced by relative motion, we consider orthogonal time frequency space modulation to obtain full time-frequency diversity gain. In addition, non-orthogonal multiple access is used to serve the massive terminals and their traffic requirements. Specifically, each active beam utilizes maximum ratio transmission to exploit diversity gain. Within each beam, the power domain is overlaid onto the delayDoppler domain, enabling multi-user information sharing across the resources of the delay-Doppler grid. Then, we present a novel probability density function for the sum of inter-beam interference with varying beam gains, and derive a closed-form expression of the outage probability. Finally, theoretical analysis and simulation results corroborate the accuracy and superiority of the proposed scheme.