This paper investigates fluid antenna systems (FASs) subject to finite-blocklength (FBL) constraints, motivated by the strict reliability-latency and ultra-massive connectivity requirements of future wireless networks. While FAS performance has been widely studied in the asymptotic regime, its behavior under FBL remains largely unexplored. Our objective is to develop a unified set of analytical tools for evaluating FASs under FBL that remains applicable across different spatial-correlation models. First, to establish accurate benchmarks for non-orthogonal finite-length user signature design, we characterize both the average and the worst-case correlation coefficients via extreme value theory (EVT) and derive closed-form predictions of the achievable correlation levels. Second, taking block error rate (BLER) as the fundamental FBL metric, we study joint detection and decoding in FAS-assisted links and derive a closed-form BLER expression that is universally applicable across channel models. Additionally, we revisit outage probability (OP) in the FBL regime and obtain tractable OP characterizations for both FASs and conventional multiple fixed-position antenna (FPA) systems. In order to reduce the computational burden for multi-fold integrals in correlated fading models, we further propose a Taylor-expansion-assisted mean value theorem for integrals (MVTI), thus enabling efficient performance evaluation with marginal accuracy loss. Numerical results validate the analysis and reveal that even single-antenna FASs can have superior spatial diversity relative to conventional multi-FPA systems. Moreover, under both FBL and interference-limited environments, FASs provide improved energy, spectral, and hardware efficiencies, hence highlighting FAS as a promising enabler for next-generation wireless networks.

翻译：本文研究了受有限块长约束的流体天线系统，其动机源于未来无线网络对严格可靠性-时延和超大规模连接的需求。尽管流体天线系统在渐近条件下的性能已被广泛研究，但有限块长下的行为仍基本未探明。我们的目标是建立一套统一的解析工具，用于评估有限块长下的流体天线系统，并使其适用于不同的空间相关模型。首先，为了为非正交有限长用户签名设计建立精确基准，我们通过极值理论刻画了平均和最坏情况相关系数，并推导了可达相关水平的闭式预测。其次，以误块率为基本有限块长指标，我们研究了流体天线辅助链路的联合检测与解码，并推导了适用于所有信道模型的闭式误块率表达式。此外，我们重新审视了有限块长条件下的中断概率，获得了流体天线系统和传统多固定位置天线系统的可处理中断概率表征。为降低相关衰落模型中多重积分的计算负担，我们进一步提出了泰勒展开辅助的积分中值定理，从而在精度损失极小的情况下实现高效性能评估。数值结果验证了理论分析，并揭示了单天线流体天线系统相比传统多固定位置天线系统可具有更优越的空间分集。此外，在有限块长和干扰受限环境中，流体天线系统可提供更高的能量、频谱和硬件效率，凸显了流体天线作为下一代无线网络有前景赋能技术的潜力。