Reconfigurable Intelligent Surfaces 2.0 for 6G: Beyond Diagonal Phase Shift Matrices

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Reconfigurable intelligent surface (RIS) 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 scattering (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 project argues that to truly exploit the benefits of RIS in 6G, RIS 2.0 need to explore architectures beyond conventional diagonal phase shift matrices. Beyond Diagonal (BD) RIS, pioneered by the PI and viewed as a paradigm shift in RIS design, relies on a suitable design of the reconfigurable impedance network and the connection architecture to smartly connect RIS elements to each other and exploit off-diagonal elements of the scattering matrices. BD-RIS has been shown to offer new opportunities over RIS 1.0 by controlling both phases and magnitudes of reflected waves, enabling hybrid transmissive and reflective mode, increasing reflected power, boosting spectral efficiency, enhancing flexibility in various deployments, and enabling highly directional full-space coverage.Motivated by those recent results by the PI and leveraging a unique set of complementary skills with our academic and industry partners HKUST, Interdigital and Viavi, this visionary project, conducted at Imperial College London, will take BD-RIS to the next level, by laying the foundations of BD-RIS aided network design, identifying the full potential benefits of BD-RIS for next generation wireless networks (communications, sensing, power), and assessing the feasibility of BD-RIS. This will be the first project on BD-RIS in the UK and in the world. To put together this revolutionary BD-RIS in a credible fashion, this project focuses on 1) developing physical and electromagnetic compliant models for BD-RIS, 2) conceiving new BD-RIS architecture, control, optimization, and signal processing, 3) inventing new wireless systems paradigms and applications enabled by BD-RIS, 4) demonstrating the feasibility of BD-RIS through prototyping and experimentation.The project demands a strong and inter-disciplinary track record in microwave theory, optimisation, multi-antenna signal processing, wireless communication, machine learning, and it is to be conducted in a unique research group with a right mix of theoretical and practical skills and an established track record in the area. With the above and given the novelty and originality of the topic, the research outcomes will be of considerable value to transform the future of wireless networks and give the industry a fresh and timely insight into the development of BD-RIS for 6G and advancing UK's research profile in 6G. Its success would radically change the design of radio access networks, have a tremendous impact on standardisation, and applications in many sectors involving future communications, power, and sensing networks.