This paper considers Cell-Free Massive Multiple Input Multiple Output (MIMO) systems with the assistance of an RIS for enhancing the system performance. Distributed maximum-ratio combining (MRC) is considered at the access points (APs). We introduce an aggregated channel estimation method that provides sufficient information for data processing. The considered system is studied by using asymptotic analysis which lets the number of APs and/or the number of RIS elements grow large. A lower bound for the channel capacity is obtained for a finite number of APs and engineered scattering elements of the RIS, and closed-form expression for the uplink ergodic net throughput is formulated. In addition, a simple scheme for controlling the configuration of the RIS scattering elements is proposed. Numerical results verify the effectiveness of the proposed system design and the benefits of using RISs in Cell-Free Massive MIMO systems are quantified.

中文翻译：

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RIS 和无蜂窝大规模 MIMO：严苛传播环境的结合

本文考虑了在 RIS 的帮助下的无细胞大规模多输入多输出 (MIMO) 系统，以提高系统性能。在接入点 (AP) 考虑分布式最大比合并 (MRC)。我们引入了一种聚合信道估计方法，它为数据处理提供了足够的信息。通过使用渐近分析来研究所考虑的系统，这使得 AP 的数量和/或 RIS 元素的数量变大。为有限数量的 AP 和 RIS 的工程散射元素获得了信道容量的下限，并制定了上行链路遍历净吞吐量的闭式表达式。此外，还提出了一种用于控制 RIS 散射元件配置的简单方案。