Secure precise transmission with multi-relay-aided directional modulation

In the conventional directional modulation (DM) system without relay aiding, when the eavesdropper locates within the main-beam of the desired direction, it can intercept the confidential message from source Alice. In this paper, we propose a strategy to enhance physical-layer security of direction modulation in wireless transmission with the help of multi-relay cooperation. In this scenario, the confidential messages are forwarded to the desired destination receiver, and the artificial noise (AN) is enforced to the eavesdroppers with the aid of multi-relays and direction modulation such that the eavesdropper can not successfully recover the useful information from its received signals. The simulation results show that the proposed method achieves a significantly higher signal-to-interference-plus-noise ratio (SINR) peak at the destination position than at other positions outside the main-beam of the desired position and its secrecy rate performance at undesired position is so poor that the secure transmission is guaranteed.