Optimal artificial noise design via equivalent channel analysis for RIS-assisted secure communication

This article delves into the optimal design of transmitting signals with artificial noise (AN) in reconfigurable intelligent surface (RIS) assisted secure communication system. Due to the introducing of RIS, injecting AN into null space of Alice-Bob channel is not optimal. Our approach commences with the formulation of the signal and AN design as an optimization problem, with the objective of maximizing the secrecy rate while conforming to the secrecy outage probability (SOP) constraint. Through constructing an equivalent channel model for the RIS-assisted communication scenario, we deduce the optimal solution which is represented as transmitting direction and corresponding power allocation for both information-bearing signal and AN. The research results contribute a theoretical objective for the practical design of AN transmission scheme in RIS-assited secure communication scenarios.