With massive deployment, multiple-input–multiple-output (MIMO) systems continue to take mobile communications to new heights, but the ever-increasing demands mean that there is a need to look beyond MIMO and pursue the next disruptive wireless technologies. Reconfigurable intelligent surface (RIS) is widely considered a key candidate technology block to provide the next generational leap. The first part of this article provides an updated overview of the conventional reflection-based RIS technology, which complements the existing literature to include active and semiactive RIS, and the synergies with cell-free massive MIMO (CF mMIMO). Then, we widen the scope to discuss the surface-wave-assisted RIS that represents a different design dimension in utilizing metasurface technologies. This goes beyond being a passive reflector and can use the surface as an intelligent propagation medium for superb radio propagation efficiency. The third part of this article turns the attention to the fluid antenna, a novel antenna technology that enables a diverse form of reconfigurability that can combine with RIS for ultrahigh capacity, power efficiency, and scalability. This article concludes with a discussion of the potential synergies that can be exploited between MIMO, RIS, and fluid antennas.

中文翻译：

---

通过可重新配置的智能表面和流体天线系统，MIMO 演进至超越 5G


随着大规模部署，多输入多输出 (MIMO) 系统继续将移动通信提升到新的高度，但不断增长的需求意味着需要超越 MIMO 并追求下一个颠覆性无线技术。可重构智能表面（RIS）被广泛认为是实现下一代飞跃的关键候选技术块。本文的第一部分提供了对传统基于反射的 RIS 技术的最新概述，该技术补充了现有文献，包括主动和半主动 RIS，以及与无小区大规模 MIMO (CF mMIMO) 的协同作用。然后，我们扩大范围来讨论表面波辅助 RIS，它代表了利用超表面技术的不同设计维度。这超出了无源反射器的范围，并且可以使用表面作为智能传播介质，以实现卓越的无线电传播效率。本文的第三部分将注意力转向流体天线，这是一种新颖的天线技术，可实现多种形式的可重构性，可与 RIS 结合以实现超高容量、功效和可扩展性。本文最后讨论了 MIMO、RIS 和流体天线之间可以利用的潜在协同效应。