Adaptive Beam Divergence for Different HAPS Altitudes in Satellite‐HAPS FSO Communication

ABSTRACT Satellite communication fulfills the demand of global connectivity for next‐generation networks. Free space optical (FSO) communication connects these high‐bandwidth global links for seamless transmission. High altitude platform station (HAPS) improves the outage probability by relaying the signal when transmission to the long distances in one hop is not reliable. In this work, we consider adaptive beam divergence (ABD) technique for a low earth orbit (LEO) satellite, which transmits the FSO signal to the HAPS, where the divergence angle of the signal is selected based on the altitude of the HAPS. We considered the effects of threshold signal‐to‐noise ratio (SNR), receiver aperture diameter, jitter standard deviation, optical‐to‐electrical conversion efficiency and the horizontal distance between satellite and HAPS on the link outage probability. The results show that by using an appropriate beam divergence angle according to the height of the HAPS, the performance of the system improves. Additionally, it is observed that for a fixed outage probability, ABD achieves communication for longer transmission range with the HAPS located at an altitude, which is lower in comparison with the altitudes at lower and upper fixed divergence angles by 1.610 and 2.169 km, respectively.