Secure Transmission in Underlay D2D Communications Using Optimal Relay Selection

This paper investigates the physical layer security of inband underlay Device-to-Device (D2D) communication, where there is no direct link between D2D users. In this respect, optimal relay selection is utilized to secure the D2D transmission. The eavesdropper uses either maximal-ratio combining or selection combining to improve the wiretapped signals. The D2D secrecy performance analysis is performed regarding the secrecy out-age probability (SOP) and the probability of non-zero secrecy capacity, and closed-form expressions are provided. To validate the correctness of our analysis, numerical and simulation results are presented. Furthermore, the asymptotic analysis of the SOP is provided, where new insights into the system parameters are revealed.