Relay Selection Strategies for Physical-Layer Security in D2D-Assisted Cellular Networks

Two sequential relay selection strategies are investigated for a cooperative relay-assisted device-to-device (D2D) communication underlaying cellular network over mixed fading channels. The relay selection schemes aim to improve the D2D communication performance and the wireless physical layer security of the cellular network. In this paper, the study is conducted analytically by obtaining an expression for the secrecy outage probability (SOP) of the cellular network. Moreover, in an effort to assess the usefulness of the cooperation between the two networks, an expression for the mutual outage probability (MOP)â€"which represents the true outage probability across both the D2D and cellular networksâ€"is derived. Also, an asymptotic analysis of the MOP in the high signal-to-noise ratio regime is obtained and the diversity order is evaluated. Monte-Carlo simulations are provided to validate the accuracy of our proposed analytical framework.