Robust Secure Energy Efficiency Optimization for Active STAR-RIS Assisted ISAC Systems

In this paper, we consider the reflecting reconfigurable intelligent surface (STAR-RIS)-assisted integrated sensing and communication (ISAC) system under imperfect eavesdropper channel state information (CSI) and uncertain target angle estimation. On this basis, a robust secure energy efficiency maximization problem is formulated under several practical constraints. To solve the non-convex objective function, we first transform it into a subtractive form using the quadratic transform-based fractional programming method. Then, we decompose the problem into two subproblems via alternating optimization techniques. To solve each subproblem, we propose an iterative algorithm combining semidefinite relaxation, successive convex approximation, and S-Procedure techniques. Finally, the two subproblems are alternately solved until convergence. Simulation results verify the effectiveness of the proposed scheme.