Enormous fluid antenna systems (E-FAS), the system concept that utilizes position reconfigurability in the large scale, have emerged as a new architectural paradigm where intelligent surfaces are repurposed from passive smart reflectors into multi-functional electromagnetic (EM) interfaces that can route guided surface waves over walls, ceilings, and building facades, as well as emit space waves to target receivers. This expanded functionality introduces a new mode of signal propagation, enabling new forms of wireless communication. In this paper, we provide an analytical performance characterization of an E-FAS-enabled wireless link. We first develop a physics-consistent end-to-end channel model that couples a surface-impedance wave formulation with small-scale fading on both the base station (BS)-surface and launcher-user segments. We illustrate that the resulting effective BS-user channel remains circularly symmetric complex Gaussian, with an enhanced average power that explicitly captures surface-wave attenuation and junction losses. For single-user cases with linear precoding, we derive the outage probability and ergodic capacity in closed forms, together with high signal-to-noise ratio (SNR) asymptotics that quantify the gain of E-FAS over purely space-wave propagation. For the multiuser case with zero-forcing (ZF) precoding, we derive the distribution of the signal-to-interference-plus-noise ratio (SINR) and obtain tractable approximations for the ergodic sum-rate, explicitly revealing how the E-FAS macro-gain interacts with the BS spatial degrees of freedom (DoF). In summary, our analysis shows that E-FAS preserves the diversity order dictated by small-scale fading while improving the coding gain enabled by cylindrical surface-wave propagation.

翻译：超大规模流体天线系统（E-FAS）是一种利用大规模位置可重构性的系统概念，它已成为一种新的架构范式。在该范式中，智能表面从被动的智能反射器转变为多功能电磁接口，能够引导表面波在墙壁、天花板和建筑立面上传输，并向目标接收器发射空间波。这种扩展的功能引入了一种新的信号传播模式，从而实现了新型无线通信。本文对基于E-FAS的无线链路进行了分析性性能表征。我们首先建立了一个物理一致性的端到端信道模型，该模型将表面阻抗波公式与基站-表面段和发射器-用户段上的小尺度衰落耦合起来。我们证明了由此产生的有效基站-用户信道仍保持圆对称复高斯特性，其平均功率得到增强，并明确捕获了表面波衰减和连接损耗。对于采用线性预编码的单用户场景，我们推导了中断概率和遍历容量的闭合表达式，以及高信噪比渐近特性，这些结果量化了E-FAS相对于纯空间波传播的增益。对于采用迫零预编码的多用户场景，我们推导了信干噪比的分布，并获得了遍历和速率的易处理近似表达式，明确揭示了E-FAS宏增益如何与基站空间自由度相互作用。总之，我们的分析表明，E-FAS在保持由小尺度衰落决定的多样性阶数的同时，提升了由柱面表面波传播实现的编码增益。