We propose a novel resource efficient analog over-the-air (OTA) computation framework to address the demanding requirements of the uplink (UL) fronthaul between the access points (APs) and the central processing unit (CPU) in cell-free massive multiple-input multiple-output (MIMO) systems. We discuss the drawbacks of the wired and wireless fronthaul solutions, and show that our proposed mechanism is efficient and scalable as the number of APs increases. We present the transmit precoding and two-phase power assignment strategies at the APs to coherently combine the signals OTA in a spectrally efficient manner. We derive the statistics of the APs locally available signals which enable us to to obtain the analytical expressions for the Bayesian and classical estimators of the OTA combined signals. We empirically evaluate the normalized mean square error (NMSE), symbol error rate (SER), and the coded bit error rate (BER) of our developed solution and benchmark against the state-of-the-art wired fronthaul based system

翻译：我们提出了一种新颖的资源高效型模拟空中计算框架，以应对无蜂窝大规模多输入多输出系统中接入点与中央处理单元之间上行前传的严苛需求。本文讨论了有线和无线前传方案的缺陷，并证明所提机制在接入点数量增加时仍保持高效性与可扩展性。我们提出了接入点的发射预编码与两阶段功率分配策略，以频谱高效的方式实现信号的相干空中合并。通过推导接入点本地可用信号的统计特性，我们获得了空中合并信号的贝叶斯与经典估计量的解析表达式。我们通过归一化均方误差、符号错误率以及编码比特错误率对所提方案进行了经验性评估，并与基于有线前传的最先进系统进行了基准对比。