Physical Layer Security of Multiuser Multirelay Hybrid Satellite-Terrestrial Relay Networks

In this paper, we study the physical layer security of a downlink hybrid satellite-terrestrial relay network (HSTRN), where a multi-antenna satellite communicates with multiple terrestrial destinations via multiple cooperative relays in the presence of multiple eavesdroppers. We investigate the secrecy performance of the considered HSTRN by employing two classic cooperative protocols, namely, amplify-and-forward and decode-and-forward for two intercepting scenarios at eavesdroppers, i.e., non-colluding and colluding eavesdroppers. For both these cooperative protocols, we present opportunistic user-relay selection criteria and then derive novel and accurate expressions of the secrecy outage probability (SOP) by adopting Shadowed-Rician fading for satellite links and Nakagami-m fading for terrestrial links. Furthermore, in order to extract useful insights on the system design, we obtain the tractable asymptotic SOP expressions at high signal-to-noise ratio regime. Finally, we provide the numerical and simulation results to validate our analysis and highlight the impact of various channel/system parameters on the secrecy performance of the considered HSTRN.