Complexity-Aware Relay Selection for 5G Large-Scale Secure Two-Way Relay Systems

This paper focuses on the complexity issue of relay selection for fifth-generation (5G) large-scale secure two-way amplify-and-forward (TWR-AF) relay systems with massive relays and eavesdroppers. A novel and distributed relay selection criterion [i.e., low-complexity relay selection criterion (LRSC)] is proposed to maximize the overall secrecy performance. Utilizing LRSC, the calculations of sources' received signal-to-noise ratios (SNRs), the channel estimation, and the knowledge of the relay-eavesdropper links are not required. Particularly, a relay is selected based on the received power of relays and the average knowledge of the source-eavesdropper links. These low-complexity properties make LRSC more attractive for 5G large-scale networks. Moreover, the secrecy outage probability and the impact of the eavesdropper density on the secrecy performance are presented, and some useful insights are obtained. Simulation results highlight the effectiveness of our relay selection design.