6G Metasurfaces: Signal Processing and Wireless Communications by Coding on Metamaterials

国际电信联盟（ITU）预测，到2030年，整体移动的数据流量将达到每月5泽字节（ZB）。多输入多输出（MIMO）是最著名的移动的技术，其以大规模MIMO的形式提供从2G到3G、从3G到4G以及最近从4G到5G的所需升级。在5G中，基站（BS）的天线数量已增加到64个，预计未来一代将有更多天线以科普不断增长的需求。然而，大规模MIMO的主要限制是在系统中并入大量RF链和线性功率放大器（PA）的成本。在用户设备（UE）处的大规模MIMO仍然是不可想象的。最近，软件控制的超材料或可编程超表面已经作为一种新的技术出现，以提高无线通信系统的性能。软件控制的超材料（或简称“超原子”）可以改变其电磁（EM）特性，以适应各种通信应用的目的。一方面，它们可以部署在大型表面上，通过优化元原子来提供智能无线电环境，以减少干扰，增强安全性，扩展通信范围等等。另一方面，它们也可以用于模拟MIMO的信号处理，而不需要增加RF链和PA的数量。这种基于超表面的MIMO在成本方面更具可扩展性，并且可能使超大规模MIMO在未来变得可行。尽管取得了早期的成功，但仍存在严重的挑战，极大地限制了元表面在移动的通信中的影响。从严重的路径损耗（传播效率差）到干扰控制的困难、元原子的窄带宽以及元表面MIMO的庞大，需要克服许多基本挑战才能真正释放元表面的潜力。在这个项目中，我们的目标是解决这些挑战。特别是，我们建议利用SWC（表面波通信），除了通常的空间波通信在一个新的方式为智能无线电环境和超大规模MIMO应用。所提出的研究利用了SWC的独特功能，并且是世界上第一个在移动的通信网络的设计中引入SWC的研究，该设计预计将通过使以下特性成为可能来彻底改变移动的通信：->有利的传播特性-SWC的使用在无线电环境中提供路径，以在智能无线电环境中具有少得多的传播损耗。->易于干扰管理-表面波被限制在表面，无线电波只出现在它们应该出现的地方。-> SWC辅助的元表面MIMO - SWC提供了一种新颖的架构，该架构简化了元表面MIMO的设计并大大提高了其能量效率，这将使大规模MIMO甚至在UE侧也成为可能。- 宽频元原子-此项目亦将设计一种新的元原子技术，具有更宽的带宽，并能在辐射元件、反射器、衍射器或传播介质之间切换。此项目将受惠于英国电信、东芝和香港城市大学的大力支持，以测试平台的实施和确保工业影响。

The forecast by International Telecommunication Union (ITU) predicts that by 2030, the overall mobile data traffic will reach 5 zettabytes (ZB) per month. Multiple-input multiple-output (MIMO) is the most celebrated mobile technology that provides the needed upgrade from 2G to 3G, from 3G to 4G and most recently from 4G to 5G in the form of massive MIMO. In 5G, the number of antennas at the base station (BS) has been increased to 64 and more are expected in future generation to cope with the rising demands. A major limitation of massive MIMO is however the cost of incorporating the large number of RF chains and linear power amplifiers (PAs) in the system. Massive MIMO at a user equipment (UE) remains unthinkable. Recently, software-controlled metamaterial or programmable metasurface has emerged as a novel technology to enhance wireless communications system performance. Software-controlled metamaterials (or "meta-atoms" in short) can alter their electromagnetic (EM) properties to suit the purpose of various communication applications. On the one hand, they can be deployed on large surfaces to provide a smart radio environment by optimising the meta-atoms for reducing interference, enhancing security, extending the range of communication, and many more. On the other hand, they can also be used to mimic the signal processing for MIMO without the need for the increase in the number of RF chains and PAs. This metasurface-based MIMO is much more scalable in terms of costs and may make ultra-massive MIMO feasible in the future. Despite the early successes, there are critical challenges that greatly limit the impact of metasurface in mobile communications. From severe pathloss (poor propagation efficiency) to the difficulty for interference control, narrow bandwidth of meta-atom, and the bulkiness of metasurface MIMO, many fundamental challenges need to be overcome to truly unleash the potential of metasurfaces.In this project, our aim is to tackle the challenges. In particular, we propose to utilise SWC (surface wave communications) in addition to the usual space wave communications in a novel way for both the smart radio environment and ultra-massive MIMO applications. The proposed research exploits the unique features of SWC and is the first in the world to introduce SWC in the design of mobile communications networks which is anticipated to revolutionise mobile communications by making possible the following characteristics: -> Favourable propagation characteristics - The use of SWC provides pathways in the radio environment to have much less propagation loss for a smart radio environment. -> Ease of interference management - Surface waves are made to be confined to the surface and radio waves appear only where they should be. -> SWC-aided metasurface MIMO - SWC provides a novel architecture that miniaturises the design of metasurface MIMO and improves its energy efficiency greatly, which will make massive MIMO possible even at the side of UE. - Wideband meta-atom - This project will also design a new meta-atom technology that has a wider bandwidth and the capability to switch between being a radiating element, a reflector, a diffractor or a propagation medium.This project will benefit from the strong support from BT, Toshiba and City University of Hong Kong for testbed implementation and ensuring industrial impact.