Best beam selection and PHY switching policy for hybrid FSO/RF inter-satellite communication link

Abstract

Free space optical (FSO) inter-satellite links could often be non-reliable due to the imperfect line of sight (LOS) links. To achieve more reliable communication, the authors propose hybrid inter-satellite links. However, this leads to new challenges like switching physical (PHY) layers at the satellite's transmitter. In this work, they propose a novel hybrid radio frequency-FSO (RF/FSO) satellite system. For it, they develop a novel best beam selection policy (BBSP) and switching of FSO and RF to improve the reliability of the inter-satellite links. To obtain more insights, they investigate the performance of BBSP by deriving expressions for the outage probability, average spectral efficiency, and average bit error rate of the BBSP. For the PHY switching, they compare the instantaneous error probabilities of RF and FSO links and find the signal-to-noise ratio threshold at which it is more efficient to switch to RF. They further improve this threshold by considering a satellite transmitting multiple beams and choosing the best source beam. To validate the analytical findings, they simulate the proposed model with CubeSat level parameters. They and that the BBSP delivers superior performance in terms of various performance measures, which shows its applicability in next-generation satellite systems.