ECE Seminar - Beyond Diagonal Reconfigurable Intelligent Surfaces: A New Frontier in Wave Domain Processing

Reconfigurable intelligent surface (RIS) is expected to be a key technology in future wireless systems to manipulate the propagation environment and perform processing and computation in the electromagnetic wave domain efficiently and cost-effectively. In conventional RIS, each RIS element is independently controlled by a tunable load disconnected from the other elements. Thus, conventional RIS results in a diagonal scattering matrix, also known as a phase shift matrix, which has limited passive beamforming and wave control capabilities. To enhance the flexibility of RIS, beyond diagonal RIS (BD-RIS) has been introduced as a generalization of conventional RIS, in which the scattering matrix is not restricted to being diagonal. In this talk, I review the emerging concept of BD-RIS, showing its promising benefits in terms of performance, coverage, deployment, and flexibility in wave manipulation over conventional RIS and STAR-RIS. We discuss the modelling and architectures of BD-RIS, and compare the performance and circuit complexity of BD-RIS architectures with conventional RIS. We also discuss potential applications of BD-RIS in various wireless communications and sensing systems and its implementation in Stacked Intelligent Metasurfaces, and outline future research directions for the special interest group on BD-RIS in IEEE Communication Society https://sites.google.com/view/ieee-comsoc-rcc-sig-bdris .