The flexibility and reconfigurability at the radio frequency (RF) front-end offered by the fluid antenna system (FAS) make this technology promising for providing remarkable diversity gains in networks with small and constrained devices. Toward this direction, this letter compares the outage probability (OP) performance of non-diversity and diversity FAS receivers undergoing spatially correlated Nakagami-$m$ fading channels. Although the system properties of FAS incur in complex analysis, we derive a simple yet accurate closed-form approximation by relying on a novel asymptotic matching method for the OP of a maximum-gain combining-FAS (MGC-FAS). The approximation is performed in two stages, the approximation of the cumulative density function (CDF) of each MGC-FAS branch, and then the approximation of the end-to-end CDF of the MGC-FAS scheme. With these results, closed-form expressions for the OP and the asymptotic OP are derived. Finally, numerical results validate our approximation of the MGC-FAS scheme and demonstrate its accuracy under different diversity FAS scenarios.

翻译：流体天线系统（FAS）在射频前端提供的灵活性和可重构性，使其成为在具有小型受限设备网络中实现显著分集增益的一项有前景的技术。基于此，本文比较了在空间相关Nakagami-$m$衰落信道下，非分集与分集FAS接收机的中断概率（OP）性能。尽管FAS的系统特性导致分析复杂度较高，但我们通过一种新颖的渐近匹配方法，为最大增益合并FAS（MGC-FAS）的中断概率推导出了简单而精确的闭式近似。该近似分两个阶段进行：首先近似每个MGC-FAS支路的累积分布函数（CDF），然后近似MGC-FAS方案的端到端CDF。基于这些结果，我们推导出了中断概率及渐近中断概率的闭式表达式。最后，数值结果验证了我们对MGC-FAS方案的近似，并展示了其在不同分集FAS场景下的准确性。