To ensure coherent signal processing across distributed Access Points (APs) in Cell-Free Massive Multiple-Input Multiple-Output (CF-mMIMO) systems, a fronthaul connection between the APs and a Central Processor (CP) is imperative. We consider a fronthaul network employing parallel radio stripes. In this system, APs are grouped into multiple segments where APs within each segment are sequentially connected through a radio stripe. This fronthaul topology strikes a balance between standard star and bus topologies, which deploy parallel or serial connections of all APs. Our focus lies in designing the uplink signal processing for a CF-mMIMO system with parallel radio stripes. We tackle the challenge of finite-capacity fronthaul links by addressing the design of In-Network Processing (INP) strategies at APs. These strategies involve linearly combining received signals and compressing the combining output for fronthaul transmission, aiming to maximize the sum-rate performance. Given the high complexity and the stringent requirement for global Channel State Information (CSI) in jointly optimizing INP strategies across all APs, we propose an efficient sequential design approach. Numerical results demonstrate that the proposed sequential INP design achieves a sum-rate gain of up to 82.92% compared to baseline schemes.

翻译：为确保无蜂窝大规模多输入多输出（CF-mMIMO）系统中分布式接入点（AP）间的相干信号处理，AP与中央处理器（CP）间的传输网络连接至关重要。本文研究采用并行无线条带的传输网络架构。在该系统中，AP被划分为多个区段，每个区段内的AP通过无线条带顺序连接。这种传输网络拓扑在标准星型与总线拓扑之间取得了平衡，后者分别采用全部AP的并行或串行连接方式。我们聚焦于设计采用并行无线条带架构的CF-mMIMO系统上行链路信号处理方案。针对传输链路容量有限的问题，我们致力于设计AP端的网络内处理（INP）策略。这些策略通过对接收信号进行线性组合，并对组合输出进行压缩以实现传输网络传输，旨在最大化系统和速率性能。考虑到跨所有AP联合优化INP策略的高复杂度及对全局信道状态信息（CSI）的严苛要求，我们提出了一种高效的顺序设计方法。数值结果表明，与基线方案相比，所提出的顺序INP设计可实现高达82.92%的系统速率增益。