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

可重构智能表面（RIS）由于其通过近被动可重构元素操纵传播环境的潜力而获得了广泛的关注。已经注意到基于对角散射（相移）矩阵的RIS 1.0架构的使用，其中RIS的每个元素都连接到与其他元素断开的负载。这使得简单的RIS架构能够控制冲击波的相位并将波反射到所需的方向。该项目认为，要真正利用RIS在6G中的优势，RIS 2.0需要探索传统对角相移矩阵之外的架构。超越对角线（BD） RIS由PI首创，被视为RIS设计中的范式转变，它依赖于可重构阻抗网络和连接架构的合适设计，以智能地将RIS元素彼此连接，并利用散射矩阵的非对角线元素。BD-RIS通过控制反射波的相位和幅度，实现混合传输和反射模式，增加反射功率，提高频谱效率，增强各种部署的灵活性，并实现高度定向的全空间覆盖，为RIS 1.0提供了新的机会。在PI最近取得的成果的激励下，利用我们与科大、Interdigital和Viavi等学术和行业合作伙伴的独特互补技能，这个在伦敦帝国理工学院进行的富有远见的项目将把BD-RIS提升到一个新的水平，为BD-RIS辅助网络设计奠定基础，确定BD-RIS对下一代无线网络（通信、传感、电力）的全部潜在好处，并评估BD-RIS的可行性。这将是英国乃至全球首个基于BD-RIS的项目。为了将这一革命性的BD-RIS以可靠的方式组合在一起，该项目侧重于1)开发BD-RIS的物理和电磁兼容模型，2)构思新的BD-RIS架构，控制，优化和信号处理，3)发明新的无线系统范例和由BD-RIS支持的应用，4)通过原型设计和实验证明BD-RIS的可行性。该项目要求在微波理论、优化、多天线信号处理、无线通信、机器学习方面具有强大的跨学科记录，并且将在一个独特的研究小组中进行，该研究小组具有理论和实践技能的正确组合以及该领域的既定记录。综上所述，考虑到该主题的新颖性和原创性，研究成果将对改变无线网络的未来具有相当大的价值，并为业界提供一个新的和及时的洞察6G BD-RIS的发展，并推进英国在6G方面的研究。它的成功将从根本上改变无线接入网络的设计，对标准化和涉及未来通信、电力和传感网络的许多部门的应用产生巨大影响。

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.