Improving the Security and Reliability of Energy-Constrained Two-Way Relay Systems With Nonlinear Energy Harvesting

This paper presents a novel three-time slot transmission protocol designed for energy-constrained two-way relay systems. In a departure from traditional energy sources, our approach serves a dual purpose by not only providing power to the system but also significantly enhancing its security. We leverage both physical-layer network coding (PNC) and bit-level Exclusive OR (XOR) technology to amplify system capacity and bolster security. Given the unavailability of exact closed-form solutions, we utilize tight upper bounds for the signal-to-noise ratio (SNR) to derive approximate closed-form results, specifically focusing on outage and intercept performance under Rayleigh channel conditions. We also provide performance bounds for outage and intercept probabilities in the high SNR regime. Our simulation results validate the accuracy of our derived probabilities, demonstrating consistency with Monte Carlo simulations. Furthermore, our investigation reveals that the time allocation factor has minimal impact on the security and reliability of the proposed protocol, particularly under high SNR conditions. In addition, we conduct a comparative analysis between the XOR scheme introduced in this article and non-XOR (NXOR) systems. This analysis underscores the superior security-reliability tradeoff of our approach, particularly in scenarios characterized by poor channel conditions between the energy source user and potential eavesdroppers.