On the Performance and Optimization of HAPS Assisted Dual-Hop Hybrid RF/FSO System

In this paper, we derive accurate outage probability and bit error rate expressions for a high altitude platform station (HAPS) assisted terrestrial communication system. In particular, HAPS is deployed as a relay node to assist two ground stations for data transmission. Each ground station-to-HAPS communication link works on a hybrid radio frequency (RF) and free space optics (FSO) mode. Selection combining is performed at the HAPS and the destination ground station to select either RF or FSO link based on the instantaneous channel signal-to-noise ratio (SNR). The accuracy of the derived outage probability and bit error rate expressions are validated with extensive computer simulations. We further develop an optimal power allocation scheme that optimizes the transmit power of source-ground-station and HAPS while satisfying practical energy consumption constraints. The derived expressions provide more insights on system design and assist analyzing HAPS-terrestrial integrated network supported by hybrid RF/FSO system.