Reconfigurable intelligent surfaces (RISs) have emerged as one of the most studied topics in recent years, hailed as a transformative technology with the potential to revolutionize future wireless systems. While RISs are recognized for their ability to enhance spectral efficiency, coverage, and the reliability of wireless channels, several challenges remain. Notably, convincing and profitable use cases must be developed before widespread commercial deployment can be realized. The first sixth-generation (6G) networks will most likely utilize upper mid-band frequencies (i.e., 7-24\,GHz). This is regarded as the \textit{golden band} since it combines good coverage, much new spectrum, and enables many antennas in compact form factors. There has been much prior work on channel modeling, coexistence, and possible implementation scenarios for these bands. There are significant frequency-specific challenges related to RIS deployment, use cases, number of required elements, channel estimation, and control. These are previously unaddressed for the upper mid-band. In this paper, we aim to bridge this gap by exploring various use cases, including RIS-assisted fixed wireless access (FWA), enhanced capacity in mobile communications, and increased reliability at the cell edge. We identify the conditions under which RIS can provide major benefits and optimal strategies for deploying RIS to enhance the performance of 6G upper mid-band communication systems.

翻译：可重构智能表面（RIS）已成为近年来最受关注的研究课题之一，被誉为具有革新未来无线系统潜力的变革性技术。尽管RIS在提升频谱效率、覆盖范围和无线信道可靠性方面得到认可，但仍存在若干挑战。值得注意的是，在实现大规模商业部署之前，必须开发出具有说服力且具备盈利能力的应用场景。首批第六代（6G）网络极有可能采用中高频段（即7-24 GHz）。该频段被视为"黄金频段"，因其兼具良好覆盖能力、大量新频谱资源，并能在紧凑尺寸下实现多天线部署。此前已有大量关于该频段信道建模、共存机制及潜在实施场景的研究工作。针对RIS部署，存在诸多与频段特性密切相关的挑战，涉及应用场景设计、所需单元数量、信道估计及控制等方面。这些挑战在中高频段RIS研究中尚未得到系统探讨。本文旨在通过探索多种应用场景（包括RIS辅助的固定无线接入、移动通信容量增强及小区边缘可靠性提升），填补该领域的研究空白。我们明确了RIS能够产生显著效益的适用条件，并提出了优化部署策略以提升6G中高频段通信系统的性能。