Physical Layer Security in an Untrusted Energy Harvesting Relay Network

The security performance in an amplify-and-forward dual-hop untrusted relay network is considered. It is assumed that the source and multiple destinations are equipped with multiple antennas, and the information transmission is aided by a single-antenna but energy-constrained relay. On the one hand, the relay can harvest the energy from its received signals by applying power splitting relaying and time switching relaying protocols and then forward the information to the destinations. To enhance the reliability performance, multiple destinations are exploited to receive the information simultaneously. On the other hand, the relay may be a potential passive attacker and eavesdrop the received information, but this kind of illegal activity may not be discovered by the sources. To investigate the security and the reliability performance, the secrecy outage probability (SOP) and the connection outage probability (COP) of the considered system are especially examined. In particular, the exact closed-form expressions of SOP and COP are derived. Since the SOP and COP are contradictory metrics, the effective secrecy throughput (EST) performance is further characterized to comprehensively examine the security and the reliability performance. Moreover, the asymptotic analysis of EST in high signal-to-noise ratio (SNR) regime is provided. The theoretical analysis and simulations reveal the impact of different parameters on the system performance, such as the transmit SNR, the power allocation coefficient, the antenna numbers, and other parameters. The Monte Carlo simulations are in excellent agreement with the theoretical expressions.