Secure transmission in multi-antenna hybrid satellite-terrestrial relay networks in the presence of eavesdropper

This paper investigates the secrecy capacity of a multi-antenna amplify-and-forward (AF) hybrid satellite-terrestrial relay netwrok (HSTRN), which consists of a satellite, a relay, a terrestrial destination and a terrestrial eavesdropper. Specifically, by employing a two-stage beamforming (BF) scheme, where the relay first adopts the maximal ratio combining (MRC) to receive the signal from satellite and then performs zero-forcing (ZF) to completely null the eavesdropper´s signal, the achievable secrecy capacity of the considered hybrid network is derived in closed-from. Eventually, simulation results are provided to demonstrate the superiority of the proposed BF scheme as well as the validity of the theoretical results, and show the effect of various channel parameters on the system performance.