Physical Layer Security for Hybrid Satellite Terrestrial Relay Networks With Joint Relay Selection and User Scheduling

In this paper, we investigate the impacts of joint relay selection and user scheduling scheme on the physical layer security for hybrid satellite-terrestrial relay systems, where multiple terrestrial relays, multiple terrestrial users, and multiple illegitimate eavesdroppers are considered in the network. To strengthen the system security against wiretapping attack, we present a joint opportunistic relay selection and the threshold based user scheduling scheme to balance the system performance and implementation complexity. Furthermore, two representative eavesdropping cases are considered, i.e., the Case I, colluding case: the eavesdroppers cooperate with each other and wiretap the information together, and the Case II, non-colluding case: the best eavesdropper will be chosen to wiretap the information channel. Besides, we derive the closed-form expressions for the average secrecy capacity based on the proposed relay selection and user scheduling scheme in the presence of two eavesdropping cases. To get more insights at high signal-to-noise ratios, the asymptotic expressions for the average secrecy capacity are also derived under two cases, from which we can get the effect of different parameters on the system performance conveniently. At last, analytical results are validated through comparison with the Monte Carlo simulations.