标题： 多RIS赋能的通信系统：容量分析与优化 显示英文标题

标题： Multi-RIS-Empowered Communication Systems: Capacity Analysis and Optimization

摘要： 本章中，利用统计物理方法，给出了在存在多个可重构智能表面（RISs）的情况下，多天线发射机-接收机对的互信息均值和方差的渐近显式表达式。虽然这些结果在大系统极限下名义上有效，但研究表明，即使对于中等规模的天线阵列和超表面，推导出的互信息高斯近似也相当准确。上述结果在快速衰落条件下特别有用，这使得信道估计变得具有挑战性。推导的分析表明，当接近RIS的信道相关时，例如由于较小的角扩展（这对于载波频率不断上升的无线系统来说是合理的），通信链路从统计RIS优化中显著受益，带来的增益比几乎不相关的场景要高得多。更重要的是，RIS上入射和传出信号的相关矩阵的新型渐近特性可以用于优化超表面，而无需暴力数值优化。数值研究显示，当任意RIS的期望反射明显偏离几何光学时，超表面可以被优化以提供稳健的通信链路，而无需对其最优位置进行显著依赖。 显示英文摘要

摘要： In this chapter, using statistical physics methods, asymptotic closed-form expressions for the mean and variance of the mutual information for a multi-antenna transmitter-receiver pair in the presence of multiple Reconfigurable Intelligent Surfaces (RISs) are presented. While nominally valid in the large-system limit, it is shown that the derived Gaussian approximation for the mutual information can be quite accurate, even for modest-sized antenna arrays and metasurfaces. The above results are particularly useful when fast-fading conditions are present, which renders channel estimation challenging. The derived analysis indicates that, when the channel close to an RIS is correlated, for instance due to small angle spread which is reasonable for wireless systems with increasing carrier frequencies, the communication link benefits significantly from statistical RIS optimization, resulting in gains that are surprisingly higher than the nearly uncorrelated case. More importantly, the presented novel asymptotic properties of the correlation matrices of the impinging and outgoing signals at the RISs can be deployed to optimize the metasurfaces without brute-force numerical optimization. The numerical investigation demonstrates that, when the desired reflection from any of the RISs departs significantly from geometrical optics, the metasurfaces can be optimized to provide robust communication links, without significant need for their optimal placement.