[论文解读] Reconfigurable Intelligent Surfaces and Metamaterials: The Potential of Wave Propagation Control for 6G Wireless Communications

George C. Alexandropoulos, Geoffroy Lerosey+2 more|arXiv (Cornell University)|Jun 19, 2020

Advanced Wireless Communication Technologies参考文献 37被引用 112

一句话总结

本文评估可重构智能表面 (RIS) 与超材料作为主动控制电磁波在6G中的传播手段，介绍室内试验、硬件架构与未解决的挑战。

ABSTRACT

The future 6G of wireless communication networks will have to meet multiple requirements in increasingly demanding levels, either individually or in combinations in small groups. This trend has spurred recent research activities on transceiver hardware architectures and novel wireless connectivity concepts. Among the emerging wireless hardware architectures belong the Reconfigurable Intelligent Surfaces (RISs), which are artificial planar structures with integrated electronic circuits that can be programmed to manipulate an incoming ElectroMagnetic (EM) field in a wide variety of functionalities. Incorporating RISs in wireless networks has been recently advocated as a revolutionary means to transform any naturally passive wireless communication environment to an active one. This can be accomplished by deploying cost-effective and easy to coat RISs to the environment's objects (e.g., building facades and indoor walls/ceilings), thus, offering increased environmental intelligence for the scope of diverse wireless networking objectives. In this paper, we first provide a brief history on wave propagation control for optics and acoustics, and overview two representative indoor wireless trials at 2.47GHz for spatial EM modulation with a passive discrete RIS. The first trial dating back to 2014 showcases the feasibility of highly accurate spatiotemporal focusing and nulling, while the second very recent one demonstrates that passive RISs can enrich multipath scattering, thus, enabling throughput boosted communication links. Motivated by the late research excitement on the RIS potential for intelligent EM wave propagation modulation, we describe the status on RIS hardware architectures and present key open challenges and future research directions for RIS design and RIS-empowered 6G wireless communications.

研究动机与目标

• 推动在6G网络中实现智能电磁波传播控制的必要性。
• 介绍 RIS 与超材料作为低开销解决方案，将被动环境转变为主动无线介质。
• 展示基于室内 RIS 的实验，证明时空聚焦与多径富集。
• 综述 RIS 硬件架构与工作模式，以概述设计取舍与挑战。
• 确定推动在6G中实现全息无线通信的开放研究方向。

提出的方法

• 描述光学与声学中波传播控制的历史背景。
• 详细介绍在2.47 GHz的两项室内 RIS 实验，使用具有二进相位状态的被动 RIS。
• 解释 RIS 单元单元设计及其使用混合谐振器的二进制 pi/0 相位调制。
• 评述最先端的 RIS 硬件架构并对主动与被动、连续与离散 RIS 及工作模式进行分类。
• 讨论 RIS 支撑网络中的电磁信息建模、信道跟踪与算法设计等未解决的挑战。

实验结果

研究问题

• RQ1 RIS 与超材料如何操控电磁波以提升6G中的吞吐量、覆盖范围和定位精度？
• RQ2 RIS 实现的实际架构与工作模式是什么（主动、被动、连续、离散）？
• RQ3 RIS 支撑系统在建模、信道估计与算法设计方面的主要挑战是什么？
• RQ4 在复杂环境中，RIS 如何影响信道秩和多路复用？
• RQ5 实现全息无线通信需要哪些未来的研究方向？

主要发现

• 被动 RIS 能在 WiFi 频段的室内实验中改善空间聚焦与零点抑制。
• 一个102单元的 RIS 展示了稳定的二进制相位状态，在布置完毕的房间中实现时空控制。
• RIS 助力的实验显示多径散射的丰富化，以及在直射 LOS MIMO 链路中的潜在吞吐提升。
• 对 RIS 配置的迭代优化可在腔体环境中提高 MIMO 信道的有效秩。
• 被动 RIS 部署可以实现近零功耗运行，并实现对电磁波的节能环境控制。