Tutorials

Duration: 1 hour

Speaker: Prof. Bruno Clerckx

Abstract: Reconfigurable intelligent surface (RIS), also called intelligent Reflecting Surface (IRS), has gained much traction due to its potential to manipulate the propagation environment via nearly-passive reconfigurable elements. Attention has been drawn to the use of RIS 1.0 architectures based on diagonal phase shift matrices where each element of the RIS is connected to a load disconnected from the other elements. This enables simple RIS architectures to control the phase of the impinging wave and reflect the wave in the desired direction. This lecture argues that to truly exploit the benefits of RIS in 6G, RIS needs to explore architectures beyond conventional diagonal phase shift matrices.  This lecture bridges microwave theory and RIS communications, introduces the audience to Beyond Diagonal (BD) RIS, and shows the benefits of BD RIS architectures in terms of controlling both phases and magnitudes of reflected waves, enabling simultaneous transmission and reflection, increasing reflected power, boosting sum-rate and flexibility in various deployments, enabling omnidirectional and sectorized coverage, etc.

Duration: 50 minutes

Speaker: Prof. Bruno Clerckx

Abstract: Reconfigurable intelligent surface (RIS) is expected to be a key technology in 6G to enhance wireless systems by efficiently and cost-effectively manipulating the propagation environment. 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, we 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 modeling 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.