Optimal Element Allocation for RIS-Aided Physical Layer Security

In this paper, we investigate an innovative physical layer security (PLS) scheme for an uncertain reconfigurable intelligent surface-(RIS-) assisted communication system under eavesdropping attack. Specifically, in our proposed system, we consider that the uncertain RIS is known to the legitimate user while not to the eavesdropper (Eve). In this manner, the reflective elements of the uncertain RIS are adjusted to strengthen the keen signals for the legitimate user while suppressing the signals for Eve via jamming. We analyze the system by assuming legitimate and wiretap channels, respectively, where the secrecy capacity maximization problem is formulated and its exact closed-form expression is derived. Simulation results verifying the accuracy of our analysis demonstrate the validity and superiority of the uncertain RIS-assisted communication system against its counterparts.