Enhancing the secrecy performance of two-way relay systems with eavesdropping user

Abstract

For the security challenges generated by the eavesdroppers existing in wireless communication systems, we propose a model for securely exchanging data between two users with a two-way relay, where two users and the relay encrypt the exchanged data using data from the other two users. In the process of relay forwarding data, we adopt two encoding schemes: In Scheme 1, traditional physical-layer network coding (PNC) technology is used to perform bit-level exclusive-or (XOR) processing on data exchanged between two users; In Scheme 2, PNC and non-orthogonal multiple access technologies are employed, where bit-level XOR processing on these two exchanged data with other corresponding user’s data is performed first, and then the modulated signals are superimposed in the power domain and transmitted. Closed-form results in terms of the exact and asymptotic outage probability (OP) and intercept probability (IP) are derived. Compared with the benchmark scheme, the results reveal that the proposed schemes improve the secrecy performance without degrading outage performance. The optimal balance between OP and IP can be obtained by selecting an appropriate power allocation coefficient in Scheme 2. Finally, as long as the interception in the first slot fails, both forwarding schemes accomplish a secure transmission.