Beyond Diagonal RIS: Key to Next-Generation Integrated Sensing and Communications?

Reconfigurable intelligent surfaces (RIS) offer unprecedented flexibility for smart wireless channels. Recent research shows that RIS platforms enhance signal quality, coverage, and link capacity in integrated sensing and communication (ISAC) systems. This paper explores the use of fully-connected beyond diagonal RIS (BD-RIS) in ISAC. BD-RIS provides additional degrees of freedom by allowing non-zero off-diagonal elements in the scattering matrix, enhancing functionality and performance. We aim to maximize the weighted sum of the signal-to-noise ratio (SNR) at both the radar receiver and communication users using BD-RIS. Numerical results demonstrate the advantages of BD-RIS in ISAC, significantly improving SNR for both radar and communication users.