In this study, the authors propose a cooperative transmission scheme with energy-harvesting (EH) relays under wiretapping of an eavesdropper. In this scheme, the relays harvest energy from radio-frequency (RF) signals of a source through power-splitting receivers, and process arrived signals by amplify-and-forward (EH-AF protocol) and decode-and-forward (EH-DF protocol) technologies. In the proposed protocols, a best relay is selected at the destination so that the end-to-end achievable secrecy rates are maximal. Exact and asymptotic secrecy outage probability expressions are used to evaluate the EH-AF and EH-DF protocols, respectively, and are confirmed by Monte Carlo simulations. The simulation results show that (i) the EH-DF protocol outperforms the EH-AF protocol, and both proposed protocols are improved when the number of cooperative relays and the distances of the relay–eavesdropper links increase and the relays move toward the destination, (ii) the secrecy performance of the EH-AF and EH-DF protocols is the best at optimal power-splitting ratios, which are obtained by the golden section search method, (iii) the energy conversion efficiency and the noise at RF-to-baseband conversion units seriously affect the proposed protocols, and finally, (iv) the theoretical analysis results fit those of the Monte Carlo simulations.
['Pham Ngoc Son', 'Hyung Yun Kong']
Cooperative communication with energy-harvesting relays under physical layer security