Low-Complexity Planar Beyond-Diagonal RIS Architecture Design Using Graph Theory
It addresses the fabrication complexity of BD-RIS for wireless communication researchers, providing a practical design framework.
The paper uses graph theory to characterize beyond-diagonal RIS architectures that can be implemented on double-layer PCBs, identifying those with the most degrees of freedom for best performance under practical constraints.
Reconfigurable intelligent surfaces (RISs) enable programmable control of the wireless propagation environment and are key enablers for future networks. Beyond-diagonal RIS (BD-RIS) architectures enhance conventional RIS by interconnecting elements through tunable impedance components, offering greater flexibility with higher circuit complexity. However, excessive interconnections between BD-RIS elements require multi-layer printed circuit board (PCB) designs, increasing fabrication difficulty. In this letter, we use graph theory to characterize the BD-RIS architectures that can be realized on double-layer PCBs, denoted as planar-connected RISs. Among the possible planar-connected RISs, we identify the ones with the most degrees of freedom, expected to achieve the best performance under practical constraints.