Wideband Channel Capacity Maximization With Beyond Diagonal RIS Reflection Matrices
<|reference_start|>Wideband Channel Capacity Maximization With Beyond Diagonal RIS Reflection Matrices: Following the promising beamforming gains offered by reconfigurable intelligent surfaces (RISs), a new hardware architecture, known as \emph{beyond diagonal RIS (BD-RIS)}, has recently been proposed. This architecture enables controllable signal flows between the RIS elements, thereby providing greater design flexibility. However, the physics-imposed symmetry and orthogonality conditions on the non-diagonal reflection matrix make the design challenging. In this letter, we analyze how a BD-RIS can improve a wideband channel, starting from fundamental principles and deriving the capacity. Our analysis considers the effects of various channel taps and their frequency-domain characteristics. We introduce a new algorithm designed to optimize the configuration of the BD-RIS to maximize wideband capacity. The proposed algorithm has better performance than the benchmarks. A BD-RIS is beneficial compared to a conventional RIS in the absence of static path or when the Rician $\kappa$-factor is smaller than $10$.<|reference_end|>
@article{demir2024wideband,
    title={Wideband Channel Capacity Maximization With Beyond Diagonal RIS
  Reflection Matrices},
    author={"Ozlem Tuu{g}fe Demir and Emil Bj"ornson},
    journal={arXiv preprint arXiv:2404.00982},
    year={2024},
    archivePrefix={arXiv},
    eprint={2404.00982},
    primaryClass={eess.SP cs.IT math.IT}
}