Multi-HAPS THz Satellite Communication: Error and Capacity Analyses under I/Q Imbalance

Satellite communication (SatCom) has become an important field of research to accomplish the requirements of next-generation wireless communication systems such as high data rates and capacity while providing global coverage. Besides traditional communication applications, SatCom is gathering more and more attention as it enhances the performance of sensing applications, such as environmental monitoring, atmospheric pollution monitoring, etc. In order to deliver worldwide service and improve accurate data collection in sensor networks, high-altitude platform station (HAPS) systems can be employed in SatCom. Moreover, utilizing terahertz (THz) frequencies in HAPS-assisted SatCom systems offers incredibly high bandwidths, enabling extreme data rates and higher resolution in sensing applications. In this paper, a THz SatCom system model is considered where K number of HAPS systems are deployed to assist the transmission between a low Earth orbit satellite and a ground station by utilizing variable-gain amplify-and-forward relaying. Symbol error rate and ergodic capacity analyses are performed in the presence of attenuation depending on the atmospheric conditions, fading, pointing error, and in-phase and quadrature imbalance. Theoretical findings are validated through Monte-Carlo simulations.