Fluid antenna systems (FAS) exploit antenna position reconfigurability to unlock massive spatial diversity within compact form factors, making them a promising enabler for 6G user terminals (UTs). However, practical port switching incurs latency and signaling overhead, which can be particularly detrimental to hyper-reliable low-latency communications (HRLLC) under finite blocklength operation. This paper investigates FASenabled HRLLC by explicitly capturing the coupled effects of spatial correlation, port switching delay, and finite blocklength coding. We derive exact closed-form expressions for the average block error rate (BLER) and average achievable rate over spatially correlated fading channels. The resulting analysis reveals a fundamental design trade-off: increasing the number of ports improves diversity but linearly reduces the effective blocklength, thereby intensifying finite-blocklength penalties. A key theoretical contribution is a rigorous proof that reliability, achievable rate, and energy efficiency are strictly unimodal in the port dimension, ensuring a unique optimal port configuration. Furthermore, we characterize an explicit switching-delay threshold that separates regimes where FAS yields net gains over fixed-position antenna (FPA) systems. Numerical results validate the analysis and show that substantial HRLLC performance gains are achievable when the switching latency remains below the derived bound.

翻译：流体天线系统（FAS）利用天线位置的可重构性，在紧凑外形中实现大规模空间分集，使其成为6G用户终端（UT）的有前途使能技术。然而，实际端口切换会引入延迟和信令开销，这在有限块长操作下可能对超可靠低延迟通信（HRLLC）尤为不利。本文通过显式捕获空间相关性、端口切换延迟和有限块长编码的耦合效应，研究了FAS赋能的HRLLC。我们推导了空间相关衰落信道上平均块错误率（BLER）和平均可达速率的精确闭式表达式。所得分析揭示了一个基础设计权衡：增加端口数量可提升分集，但线性减少有效块长，从而加剧有限块长惩罚。一个关键理论贡献是严格证明了可靠性、可达速率和能量效率在端口维度上呈严格单峰性，确保了唯一的最优端口配置。此外，我们刻画了一个显式的切换延迟阈值，该阈值将FAS相对于固定位置天线（FPA）系统产生净增益的区域与不产生净增益的区域区分开来。数值结果验证了该分析，并表明当切换延迟低于所推导的界限时，可实现显著的HRLLC性能增益。