Toward Seamless Connectivity: HAPS-Assisted Hybrid THz/FSO Bidirectional Communication for Multi-Satellite Multi-Ground Station Network

In the next generation wireless communication paradigm, hybrid communication strategies and vertical network integration are critical to ensure high-capacity and resilient connectivity. In this manner, we consider a high-altitude platform station (HAPS)-assisted bidirectional relaying system operating with hybrid terahertz (THz)/free-space optical (FSO) links in a multi-satellite and multi-ground station communication scenario. Unlike conventional setups, both the satellite and ground station nodes are dynamically selected, and bidirectional relaying is employed to enhance spectral efficiency. Realistic physical impairments, such as beam divergence and misalignment are incorporated into the system model, and system outage probability expression is derived to evaluate the overall performance under various configurations. The results show that the hybrid THz/FSO approach not only enhances reliability against pointing errors but also benefits significantly from multi-node diversity, making it a strong candidate for future reliable and high-capacity integrated non-terrestrial network architectures.