Active RIS with Artificial Noise Assisted Downlink Physical Layer Secure Transmission

Active RIS is a technology that combines an active antenna array and a reflective smart surface. It is a novel smart surface technology, the core of which is a two-dimensional array consisting of a large number of programmable antenna units. These antenna units can not only reflect the incident beam, but also amplify or modulate the signal, thus possessing the ability to actively transmit and receive signals. On this basis, we investigate active RIS-assisted downlink physical layer secure transmission while the user maximizes the security rate by sending artificial noise to the eavesdropper while receiving the message. Jointly, we optimize the base station beamforming, the active RIS beamforming, and the power allocation between the active RIS and the artificial noise.The paper proposes an alternating optimization algorithm to solve the problem. Since the optimization problem is non-convex, we use the successive convex approximation algorithm (SCA) and the semi-positive definite relaxation algorithm (SDR) to solve the problem. Finally, the effectiveness of the algorithm is verified by experimental simulation results.