Cell-free massive MIMO (multiple-input multiple-output) enhances spectral and energy efficiency compared to conventional cellular networks by enabling joint transmission and reception across a large number of distributed access points (APs). Since these APs are envisioned to be low-cost and densely deployed, hardware impairments, stemming from non-ideal radio-frequency (RF) chains, are unavoidable. While existing studies primarily address hardware impairments on the access side, the impact of hardware impairments on the wireless fronthaul link has remained largely unexplored. In this work, we fill this important gap by introducing a novel amplify-and-forward (AF) based wireless fronthauling scheme tailored for cell-free massive MIMO. Focusing on the uplink, we develop an analytical framework that jointly models the hardware impairments at both the APs and the fronthaul transceivers, derives the resulting end-to-end distorted signal expression, and quantifies the individual contribution of each impairment to the spectral efficiency. Furthermore, we design distortion-aware linear combiners that optimally mitigate these effects. Numerical results demonstrate significant performance gains from distortion-aware processing and illustrate the potential of the proposed AF fronthauling scheme as a cost-effective enabler for future cell-free architectures.

翻译：相较于传统蜂窝网络，无蜂窝大规模多输入多输出（MIMO）通过大量分布式接入点（AP）的联合传输与接收，显著提升了频谱效率和能量效率。由于这些接入点被设计为低成本且密集部署，由非理想射频（RF）链引起的硬件损伤不可避免。现有研究主要关注接入侧的硬件损伤，而硬件损伤对无线前传链路的影响尚未得到充分探索。本研究填补了这一重要空白，提出了一种专为无蜂窝大规模MIMO设计的新型基于放大转发（AF）的无线前传方案。以上行链路为焦点，我们建立了一个分析框架，该框架联合建模了接入点与前传收发器的硬件损伤，推导了由此产生的端到端失真信号表达式，并量化了每种损伤对频谱效率的独立贡献。此外，我们设计了失真感知线性合并器，以最优方式抑制这些影响。数值结果表明，失真感知处理带来了显著的性能增益，并证明了所提出的AF前传方案作为未来无蜂窝架构经济高效使能技术的潜力。