Beyond Diagonal Reconfigurable Intelligent Surfaces with Mutual Coupling: Modeling and Optimization

This work studies the modeling and optimization of beyond diagonalreconfigurable intelligent surface (BD-RIS) aided wireless communicationsystems in the presence of mutual coupling among the RIS elements.Specifically, we first derive the mutual coupling aware BD-RIS aidedcommunication model using scattering and impedance parameter analysis. Based onthe obtained communication model, we propose a general BD-RIS optimizationalgorithm applicable to different architectures of BD-RIS to maximize thechannel gain. Numerical results validate the effectiveness of the proposeddesign and demonstrate that the larger the mutual coupling the larger the gainoffered by BD-RIS over conventional diagonal RIS.