Power Minimization for ISAC System Using Beyond Diagonal Reconfigurable Intelligent Surface

Reconfigurable intelligent surface (RIS) can benefit integrated sensing and communication (ISAC) systems. Recently, an emerging beyond-diagonal (BD)-RIS architecture exhibits superior beamforming capability over the conventional diagonal RIS. This paper investigates deploying BD-RIS to minimize transmit power of base station in ISAC network while assuring its communication and sensing quality. This task is challenging due to orthogonality and quartic inequality constraints induced by BD-RIS. By appropriately decoupling constraints and utilizing penalty-dual-decomposition (PDD) method, we develop an efficient algorithm. Numerical results verify the effectiveness of our algorithm and the benefit of BD-RIS deployment.