Secrecy Performance Analysis of Two-Way Relay Non-Orthogonal Multiple Access Systems

Abstract

This paper studies physical layer security for two-way relay non-orthogonal multiple access systems. Specifically, by employing a decode-and-forward relay and considering both the maximum-ratio combining and selection combining schemes at the eavesdropper, instantaneous end-to-end signal-to-interference-plus-noise ratios are first formulated and approximated for the interference-limited scenario. Then analytical expressions for the secrecy outage probability and the intercept probability are obtained. Moreover, we analyze the effective secrecy diversity order and demonstrate that the eavesdropper severely degrades the secrecy performance, and even reduces the diversity order to zero. Numerical and simulation results verify our derivations and reveal that, due to information leakage in the first time phase, there exists a secrecy performance floor. It is also demonstrated that the secrecy outage probability performance degrades when the eavesdropper is closer to either of the users. Between the two combining schemes, the results demonstrate that the secrecy outage probability performance is better when the selection combining scheme is employed by the eavesdropper.

Keywords

• Physical layer security
• non-orthogonal multiple access (NOMA)
• two-way relay networks
• secrecy outage probability
• intercept probability
• decode-and-forward (DF)