Physical layer security in hybrid satellite-terrestrial relay networks

Featured by broad coverage and seamless connectivity in remote areas, hybrid satellite-terrestrial relay networks (HSTRNs) have gained growing attention in fifth- and next-generation communications. However, security issues in such networks have been rapidly increasing due to the inherent openness of wireless medium. Recently, an information-theoretic approach based physical layer security (PLS) emerges as a promising technique to ensure overall security in wireless communications. Unlike conventional cryptographic methods, PLS techniques exploit physical characteristics of wireless fading channels and provide confidentiality to radio transmissions. In this chapter, we introduce the HSTRN architecture and present practical challenges to PLS in HSTRNs. Specifically, by adopting pertinent channel models for satellite and terrestrial links, we examine the secrecy outage probability (SOP) performance of a basic HSTRN in the presence of a single eavesdropper and generalized HSTRN configuration with multiple eavesdroppers. For multiple eavesdroppers, we consider two different scenarios of colluding and non-colluding eavesdroppers. Moreover, at a high signal-to-noise ratio regime, we analyze the asymptotic behavior of SOP performance and reveal the achievable diversity order of the considered HSTRNs. We further demonstrate numerical and simulation results to justify our hypothesis and illustrate the impact of various channel/system parameters on the secrecy performance of HSTRN communications.