标题： RIS辅助的无线通信中的有限反馈：用例、挑战与未来方向 显示英文标题

标题： Limited Feedback in RIS-Assisted Wireless Communications: Use Cases, Challenges, and Future Directions

摘要： 信道状态信息（CSI）对于在无线通信系统中释放可重构智能表面（RIS）的潜力至关重要。 由于大量RIS元件通常不具有基带信号处理能力，因此在设计RIS的反射/折射系数时，需要有限的CSI反馈。 在本文中，从有限反馈的最新进展中提炼出RIS辅助信道的独特特征，例如与RIS位置相关的信道波动、超高维子信道矩阵以及结构稀疏性，并将其作为设计反馈方案的指导方针。 我们首先说明RIS反馈相关用例及其对应的挑战。 然后讨论如何利用诸如信道定制、结构稀疏性、自编码器等技术，在设计反馈方案时减少反馈开销和复杂度。 最后，通过考虑未解决的挑战、新的RIS架构以及与多模态信息和人工智能的集成，确定潜在的研究方向。 显示英文摘要

摘要： Channel state information (CSI) is essential to unlock the potential of reconfigurable intelligent surfaces (RISs) in wireless communication systems. Since massive RIS elements are typically implemented without baseband signal processing capabilities, limited CSI feedback is necessary when designing the reflection/refraction coefficients of the RIS. In this article, the unique RIS-assisted channel features, such as the RIS position-dependent channel fluctuation, the ultra-high dimensional sub-channel matrix, and the structured sparsity, are distilled from recent advances in limited feedback and used as guidelines for designing feedback schemes. We begin by illustrating the use cases and the corresponding challenges associated with RIS feedback. We then discuss how to leverage techniques such as channel customization, structured-sparsity, autoencoders, and others to reduce feedback overhead and complexity when devising feedback schemes. Finally, we identify potential research directions by considering the unresolved challenges, the new RIS architecture, and the integration with multi-modal information and artificial intelligence.