Physical-Layer Secure Wireless Transmission via Active Reconfigurable Intelligent Surfaces

The development of Internet of things (IoT) has substantially increases the number of access users and their transmission rates. When the number of access users is increasing, however, the channels from the base station (BS) to the user and the eavesdropper are highly correlated, which brings about the severe problem of physical-layer security. To address this problem, in this paper, we propose a physical-layer secure transmission system, where active reconfigurable intelligent surface (ARIS) is employed for enhancing the BS-user link while simultaneously degrading the BS-eavesdropper link. Moreover, we develop the signal model of the proposed system, and formulate the corresponding optimization problem for maximizing the secure rate (SR). To solve this non-convex optimization problem, we propose a low-complexity approximated joint precoding (LCAJP) algorithm based on alternating optimization (AO). Simulation results show that, the proposed physical-layer secure transmission system as well as the LCAJP algorithm can increase the SR of the system, which provides solutions for the security problem.