Physical Layer Security Improvement of Dual-Hop Dual-Relay Network Using Signal Space Diversity

We examine the physical-layer security performance of a conventional dual-hop dual-relay (DH-DR) network, where two decode-and-forward relays are used to facilitate the communication from the source to the destination without a direct link between the source and the destination. The conventional DH-DR system employs an ordinary modulation scheme such as a 4-QAM modulation. Thus, we propose a signal-space technique to incorporate into the conventional DH-DR system that significantly improves the security performance of the conventional system. Note that both DF relays do not duplicate the data and instead forward different symbols to the destination because of the signal space technique. We analyze the proposed system for the secrecy outage probability and the intercept probability. The results confirm the 4 dB improvement in secrecy outage probability. Moreover, we assess the secrecy performance of the proposed system and compare it with the conventional system to show the superiority of the proposed system over the conventional one. Furthermore, we use Monte Carlo simulations to evaluate the proposed system's performance.