Secrecy Outage Analysis of Hybrid Satellite-Terrestrial Relay Networks with Opportunistic Relaying Schemes

In this paper, we investigate the secrecy performance of a hybrid satellite-terrestrial relay network, where a satellite communicates with a terrestrial destination via multiple relays in the presence of eavesdropper. Particularly, to strengthen the system security against wiretapping attack, we present amplify-and-forward (AF) based optimal and partial relay selection schemes to minimize the secrecy outage probability (SOP). Hereby, the optimal scheme depends on both main and wiretapper links, while the partial scheme relies only on the legitimate terrestrial links. We derive the SOP expressions for both schemes by considering Shadowed-Rician fading for satellite channels and Nakagami-m fading for terrestrial channels. We further simplify these expressions at asymptotic high signal-to-noise ratio (SNR) and main-to-eavesdropper ratio (MER) regime to reveal useful insights on achievable diversity gains. Finally, the theoretical analysis is validated through Monte-Carlo simulations.