Enhanced Physical Layer Security for Ultra-Dense D2D Communications Underlaying Cellular Networks with Full-Duplex Users

In this paper, we investigate the security issues for ultra-dense Device-to-Device (D2D) communications underlaying cellular networks with eavesdroppers (Eves) overhearing D2D communications. As D2D links are vulnerable to security threats, we try to enhance the D2D security performance by introducing full-duplex cellular users (FD-CUEs), and the FD-CUEs intend to jam Eves by transmitting artificial noise while simultaneously receiving useful signal from its serving base station. Using stochastic geometry, the D2D connection probability, which refers to D2D users transmit signal successfully, the D2D secrecy probability, which refers to the probability that the transmitted secrecy information cannot be decoded by any Eve, and the FD-CUE connection probability are analyzed. Moreover, we propose an effective algorithm to improve the D2D secrecy probability subject to the security constraints. Our analytical results match well with the simulations. From the simulation results, it is clear that the D2D ergodic secrecy rate of the proposed scheme outperforms that of the traditional D2D underlaying cellular networks without FD-CUEs.