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）通过天线位置可重构性在紧凑外形内解锁大规模空间分集，使其成为6G用户终端（UT）的有前景推动技术。然而，实际端口切换会引入时延与信令开销，在有限块长操作下可能对超可靠低延迟通信（HRLLC）产生特别不利影响。本文通过显式捕获空间相关性、端口切换时延与有限块长编码的耦合效应，研究FAS赋能的HRLLC。我们推导了空间相关衰落信道上平均误块率（BLER）与平均可达速率的精确闭式表达式。分析揭示了一个基本设计权衡：增加端口数可提升分集增益，但会线性缩短有效块长，从而加剧有限块长惩罚。一项关键理论贡献是严格证明了可靠性、可达速率与能量效率在端口维度上呈严格单峰性，确保存在唯一最优端口配置。此外，我们刻画了一个显式切换时延阈值，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分隔开来。数值结果验证了分析结论，并表明当切换时延低于推导边界时，可实现显著的HRLLC性能增益。