Secrecy communication of wireless information and power transfer system with green relay

In this paper, we propose a secrecy communication scheme for half-duplex amplify-forward relay networks in the presence of multiple eavesdroppers. Unlike conventional relay network, we consider that the relay is “green”, i.e., it is powered by the energy harvested from the relay observations. The transmission can be divided into two time slots. In the first time slot, the source and destination transmit signal and artificial noise (AN), respectively. The dual use of AN in jamming eavesdroppers and providing wireless energy for the relay is advocated. At the relay, the received signal is divided into two parts by power splitter and goes into energy harvester and information transceiver, respectively. In the second time slot, the “green” relay forwards the information to destination using the energy scavenged in the first time slot. The eavesdroppers can wiretap during both slots. Our scheme is to maximize the secrecy rate subject to the total transmit power constraint or minimize the total transmit power subject to the secrecy rate requirement. By applying successive convex approximation approach, we can convert these challenging non-convex problems into second-order cone program based iterative problems. Simulation results show the effectiveness of the proposed scheme.