Optimal Power Control and Link Selection Policy for Buffer-Aided Two-Hop Secure Communications

In this paper, secure communication over a buffer-aided two-hop communication link, in which a source sends data to a destination with the aid of a trusted half-duplex relay node in the presence of a passive eavesdropper, is studied. It is assumed that there is no direct link between the source and the destination, and the buffer-aided relay forwards the information to the destination by employing the decode-and-forward (DF) scheme. Both the source and the relay transmissions are assumed to be vulnerable to the eavesdropper. The perfect channel side information (CSI) of the network is assumed to be available at the source and the relay. Initially, conventional relaying protocols where equal partition of the time for the reception and transmission of the relay is considered. Then, the optimal time fraction with the optimal power control policy that maximizes the secrecy throughput is identified. Subsequently, the optimal joint link selection and power control policy that maximizes the secrecy throughput is derived. Numerical results demonstrate that the joint link selection and power control scheme can significantly improve the achievable secrecy throughput of the buffer-aided two-hop communication system.