To address the reliability threat of LEO satellite (LEO-Sat) to terrestrial communications, this paper proposes a novel network using mobile multi-UAV as decoded-and-forward (DF) relays under the orthogonal time frequency space (OTFS) scheme. In particular, OTFS is used to cope with the severe Doppler frequency shift of the LEO-Sat communication (LEO-Satcom) system with higher carrier frequency tendency and relatively high-speed mobility. The addition of mobile multi-UAV not only improves the coverage performance but also compensates for the severe path loss. Stochastic geometry theory is utilized to characterize the mobile model of UAVs and thus assist in the reliability performance analysis. Simulation results demonstrate that the proposed OTFS-based LEO-Satcom network has improved system reliability compared to the conventional time-frequency domain modulation scheme. The impact of UAVs' deployment properties on reliable transmission is further illustrated.

LEO satellite, OTFS, stochastic geometry