The emerging technology of fluid antenna systems (FASs) represents a promising next-generation reconfigurable antenna solution, capable of exploiting the full spatial diversity within a predefined space by finely reconfiguring the positions of radiating elements. In this paper, the performance of FAS over spatially correlated Rayleigh fading channels is investigated for two distinct scenarios: a multiple-input single-output (MISO) configuration, where a receiver with a single-antenna FAS is served by a multi-antenna transmitter (MISO-FAS), and a single-input single-output setup where single-antenna FASs are equipped at both the transmitter and receiver (Dual-FAS). Exact expressions and closed-form approximations for the outage probability (OP) of both the MISO-FAS and Dual-FAS models are derived as the core contributions of this work. To provide deeper insights into system performance, the diversity orders for each model are also derived and analyzed. Analytical results demonstrate that increasing the number of ports significantly enhances system performance. The theoretical analysis is corroborated by key findings from our simulations, demonstrating that: $i$) Both the MISO-FAS and Dual-FAS models achieve considerable performance gains as the number of ports is increased; $ii$) System performance for both configurations is inversely related to the level of port correlation; lower correlation leads to better performance; $iii$) In the high signal-to-noise ratio regime, the Dual-FAS model surpasses the performance of the MISO-FAS model.

翻译：流体天线系统（FAS）作为新兴技术，代表了一种有前景的下一代可重构天线解决方案，能够通过精细重构辐射元件的位置，在预定义空间内充分利用空间分集。本文研究了空间相关瑞利衰落信道下FAS在两种不同场景中的性能：多输入单输出（MISO）配置，其中配备单天线FAS的接收端由多天线发射端提供服务（MISO-FAS）；以及单输入单输出配置，其中发射端与接收端均配备单天线FAS（Dual-FAS）。作为本文的核心贡献，推导了MISO-FAS与Dual-FAS模型中断概率（OP）的精确表达式与闭合形式近似解。为深入理解系统性能，进一步推导并分析了各模型的分集阶数。理论分析表明，增加端口数量可显著提升系统性能。仿真结果验证了理论分析，并揭示以下关键发现：$i$）MISO-FAS与Dual-FAS模型均能通过增加端口数量获得显著性能增益；$ii$）两种配置的系统性能与端口相关性呈负相关，较低的相关性可带来更优性能；$iii$）在高信噪比区域，Dual-FAS模型的性能优于MISO-FAS模型。