Enhancing Spectral and Energy Efficiency with Multi-Sector Beyond-Diagonal RIS

Reconfigurable intelligent surfaces (RISs) have emerged as a spectrum-and energy-efficient technology to enhance the wireless communication networks. Recently, novel extensions of this technology referred to as multi-sector beyond diagonal RIS (BD-RIS) are proposed, where the configurable elements are divided into L (L ≥ 2) sectors and arranged as a polygon prism with each sector covering 1/L space. In this paper, we investigate the spectral and energy efficiency metrics of a network enhanced with a multi-sector BD-RIS. We derive closed-form expressions for the overall achievable spectral and energy efficiency and substantiate our analysis through simulations. The results demonstrate that, for a fixed number of configurable elements, increasing the number of sectors (and consequently reducing the elements per sector) leads to significant improvements in both spectral and energy efficiency gains compared to a configuration with fewer sectors but more elements per sector. In particular, our numerical results show a remarkable 138% improvement in energy efficiency when transitioning from a 2-sector to a 6-sector configuration.