As a critical component of beyond fifth-generation (B5G) and sixth-generation (6G) mobile communication systems, ultra-reliable low-latency communication (uRLLC) imposes stringent requirements on latency and reliability. In recent years, with the improvement of mobile communication network, centralized and distributed processing schemes for cellfree massive multiple-input multiple-output (CF-mMIMO) have attracted significant research attention. This paper investigates the performance of a novel scalable cell-free radio access network (CF-RAN) architecture featuring multiple edge distributed units (EDUs) under the finite block length regime. Closed expressions for the upper and lower bounds of its expected spectral efficiency (SE) performance are derived, where centralized and fully distributed deployment can be treated as two special cases, respectively. Furthermore, the spatial distribution of user equipments (UEs) and remote radio units (RRUs) is examined and the analysis reveals that the interleaving RRUs deployment associated with the EDU can enhance SE performance under finite block length constraints with specific transmission error probability. The paper also compares Monte Carlo simulation results with multi-RRU clustering-based collaborative processing, validating the accuracy of the space-time exchange theory in the scalable CF-RAN scenario. By deploying scalable EDUs, a practical trade-off between latency and reliability can be achieved through spatial degree-of-freedom (DoF), offering a distributed and scalable realization of the space-time exchange theory.

翻译：作为第五代移动通信系统（B5G）和第六代移动通信系统（6G）的关键组成部分，超可靠低时延通信（uRLLC）对时延和可靠性提出了严格要求。近年来，随着移动通信网络的演进，面向无蜂窝大规模多输入多输出（CF-mMIMO）的集中式与分布式处理方案引起了广泛研究关注。本文研究了一种具有多个边缘分布式单元（EDU）的新型可扩展无蜂窝无线接入网络（CF-RAN）架构在有限块长机制下的性能。推导了其期望频谱效率（SE）性能上下界的闭式表达式，其中集中式与完全分布式部署可分别视为两种特例。进一步分析了用户设备（UE）与远端射频单元（RRU）的空间分布，研究表明在特定传输错误概率的有限块长约束下，与EDU关联的交错式RRU部署能够提升SE性能。本文还将蒙特卡洛仿真结果与基于多RRU分簇的协同处理进行对比，验证了时空交换理论在可扩展CF-RAN场景中的准确性。通过部署可扩展EDU，可利用空间自由度（DoF）实现时延与可靠性的实际权衡，为时空交换理论提供了一种分布式且可扩展的实现方案。