In this work, we investigate the impact of channel aging and electromagnetic interference (EMI) on spatially correlated reconfigurable intelligent surface (RIS) assisted cell-free massive multiple-input multiple-output (MIMO) systems. To effectively handle channel aging and EMI, we employ a novel two-phase channel estimation scheme with fractional power control-aided pilot assignment during the uplink channel estimation phase. This scheme provides improved channel estimates compared to existing approaches. The closed-form uplink and downlink spectral efficiency (SE) expressions incorporating fractional power control are derived to enable system performance evaluation. Additionally, we introduce the system's power consumption model to analyze energy efficiency (EE). Our numerical results illustrate the theoretical results and demonstrate the system performance with channel aging and EMI. Specifically, the proposed two-phase channel estimation scheme enhances estimation accuracy, compensating for performance degradation caused by channel aging and EMI. We find that increasing the number of access points (APs), RISs, antennas per AP, and elements per RIS can help to mitigate the SE performance degradation. We also find that an optimal number of APs can be selected to achieve energy efficiency (EE) maximization. However, in severe EMI environments, the benefits of deploying more RISs cannot be fully realized.

翻译：本文研究了信道老化与电磁干扰（EMI）对空间相关性可重构智能表面（RIS）辅助的无蜂窝大规模多输入多输出（MIMO）系统的影响。为有效应对信道老化与EMI，我们在上行信道估计阶段采用了一种新颖的两阶段信道估计方案，该方案结合了分数功率控制辅助的导频分配。相较于现有方法，该方案提供了更优的信道估计性能。我们推导了包含分数功率控制的上行与下行频谱效率（SE）闭合表达式，以支持系统性能评估。此外，我们引入了系统的功耗模型以分析能量效率（EE）。数值结果验证了理论分析，并展示了系统在信道老化与EMI影响下的性能表现。具体而言，所提出的两阶段信道估计方案提升了估计精度，有效补偿了由信道老化与EMI引起的性能下降。研究发现，增加接入点（AP）数量、RIS数量、每个AP的天线数以及每个RIS的单元数，有助于缓解SE性能的恶化。同时，可通过选择最优的AP数量以实现能量效率（EE）最大化。然而，在强EMI环境下，部署更多RIS所带来的性能增益无法完全实现。