A General Time-domain Artificial Noise Design for OFDM AF Relay Systems

While most existing artificial noise techniques cannot be applied to single antenna systems, in this paper, we consider the physical layer security of an orthogonal frequency division multiplexing (OFDM) relay system with an eavesdropper where each node is equipped with a single antenna. A general time-domain artificial noise (AN) scheme is proposed, where the source transmits signals bearing with time-domain AN to the relay while the destination sends jamming signals to the relay. The time-domain AN is designed for the source and the destination in this paper. The power allocation between the source signal and the ANs is optimized to maximize the secrecy rate. However, the optimization problem is non-convex. To solve the non-convex maximization problem, we propose an iterative inner convex approximation algorithm, which transforms the original problem into a sequence of convex approximated problems. Simulation results are provided to investigated the performance of the proposed scheme.