The signal processing and communication communities have witnessed the rise of many exciting communication technologies in recent years. Notable examples include alternative waveforms, massive multiple-input, multiple-output (MIMO) signaling, nonorthogonal multiple access (NOMA), joint communications and sensing, sparse vector coding, index modulation, and so on. It is inevitable that 6G wireless networks will require a rethinking of wireless communication systems and technologies, particularly at the physical layer (PHY), considering the fact that the cellular industry reached another important milestone with the development of 5G wireless networks with diverse applications [1]. Within this perspective, this article aims to shed light on the rising concept of reconfigurable intelligent surface (RIS)-empowered communications toward 6G wireless networks [2], [3]. Software-defined RISs can manipulate their impinging signals in an effective way to boost certain key performance indicators. We discuss the recent developments in the field and put forward promising candidates for future research and development. Specifically, we put our emphasis on active, transmitter-type, transmissive-reflective, and stand-alone RISs, by discussing their advantages and disadvantages compared to reflective RIS designs. Finally, we also envision an ultimate RIS architecture, which is able to adjust its operation modes dynamically, and introduce the new concept of PHY slicing over RISs toward 6G wireless networks.

中文翻译：

---

可重构智能地面通信的现在和未来 [观点]


近年来，信号处理和通信领域见证了许多令人兴奋的通信技术的兴起。值得注意的例子包括替代波形、大规模多输入多输出 (MIMO) 信令、非正交多址 (NOMA)、联合通信和传感、稀疏矢量编码、索引调制等。考虑到随着具有多种应用的 5G 无线网络的发展，蜂窝行业达到了另一个重要里程碑，6G 无线网络不可避免地需要重新思考无线通信系统和技术，特别是在物理层 (PHY) 方面 [1 ]。从这个角度来看，本文旨在阐明面向 6G 无线网络的可重构智能表面 (RIS) 授权通信的新兴概念 [2]、[3]。软件定义的 RIS 可以有效地操纵其冲击信号，以提高某些关键性能指标。我们讨论该领域的最新发展，并为未来的研究和开发提出有希望的候选者。具体来说，我们将重点放在有源、发射器型、透射反射和独立 RIS 上，讨论它们与反射 RIS 设计相比的优点和缺点。最后，我们还设想了一种终极的 RIS 架构，它能够动态调整其操作模式，并向 6G 无线网络引入基于 RIS 的 PHY 切片的新概念。