Cell-free (CF) massive multiple-input multiple-output (MIMO) and reconfigurable intelligent surface (RIS) are two promising technologies for realizing future beyond-fifth generation (B5G) networks. In this paper, we consider a practical spatially correlated RIS-aided CF massive MIMO system with multi-antenna access points (APs) over spatially correlated fading channels. Different from previous work, the electromagnetic interference (EMI) at RIS is considered to further characterize the system performance of the actual environment. Then, we derive the closed-form expression for the system spectral efficiency (SE) with the maximum ratio (MR) combining at the APs and the large-scale fading decoding (LSFD) at the central processing unit (CPU). Moreover, to counteract the near-far effect and EMI, we propose practical fractional power control (FPC) and max-min power control algorithms to further improve the system performance. We unveil the impact of EMI, channel correlations, and different signal processing methods on the uplink SE of user equipments (UEs). The accuracy of our derived analytical results is verified by extensive Monte-Carlo simulations. Our results show that the EMI can substantially degrade the SE, especially for those UEs with unsatisfactory channel conditions. Besides, increasing the number of RIS elements is always beneficial in terms of the SE, but with diminishing returns when the number of RIS elements is sufficiently large. Furthermore, the existence of spatial correlations among RIS elements can deteriorate the system performance when RIS is impaired by EMI.

翻译：无小区（CF）大规模多输入多输出（MIMO）和可重构智能表面（RIS）是实现未来超五代（B5G）网络的两项关键技术。本文考虑了一个在实际空间相关衰落信道上、配备多天线接入点（AP）的空间相关RIS辅助CF大规模MIMO系统。与以往工作不同，本文进一步考虑了RIS处的电磁干扰（EMI），以表征实际环境下的系统性能。在此基础上，推导了在AP处采用最大比合并（MR）和中央处理单元（CPU）处采用大规模衰落解码（LSFD）时系统频谱效率（SE）的闭式表达式。此外，为抑制远近效应和EMI，提出了实用的分数功率控制（FPC）和最大-最小功率控制算法以进一步提升系统性能。揭示了EMI、信道相关性及不同信号处理方法对用户设备（UE）上行SE的影响，并通过大量蒙特卡洛仿真验证了推导分析结果的准确性。结果表明，EMI会显著降低系统SE，尤其对信道条件较差的UE影响更为严重。此外，增加RIS元件数量在SE方面始终具有增益，但当RIS元件数量足够大时，该增益会呈现边际递减效应。同时，当RIS受到EMI影响时，RIS元件间的空间相关性会恶化系统性能。