This paper investigates the performance of physical layer security (PLS) in fluid antenna-aided communication systems under arbitrary correlated fading channels. In particular, it is considered that a single fixed-antenna transmitter aims to send confidential information to a legitimate receiver equipped with a planar fluid antenna system (FAS), while an eavesdropper, also taking advantage of a planar FAS, attempts to decode the desired message. For this scenario, we first present analytical expressions of the equivalent channel distributions at the legitimate user and eavesdropper by using copula, so that the obtained analytical results are valid for any arbitrarily correlated fading distributions. Then, with the help of Gauss-Laguerre quadrature, we derive compact analytical expressions for the average secrecy capacity (ASC), the secrecy outage probability (SOP), and the secrecy energy efficiency (SEE) for the FAS wiretap channel. Moreover, for exemplary purposes, we also obtain the compact expression of ASC, SOP, and SEE by utilizing the Gaussian copula under correlated Rayleigh fading channels as a special case. Eventually, numerical results indicate that applying the fluid antenna with only one active port to PLS can guarantee more secure and reliable transmission, when compared to traditional antenna systems (TAS) exploiting maximal ratio combining (MRC).

翻译：本文研究了在任意相关衰落信道下，流体天线辅助通信系统中物理层安全（PLS）的性能。具体考虑场景为：一个配备固定单天线的发射机向装备平面流体天线系统（FAS）的合法接收机发送机密信息，同时一个同样利用平面FAS的窃听者试图解码该消息。针对该场景，我们首先利用copula函数推导了合法用户和窃听者处等效信道分布的解析表达式，使得所得解析结果适用于任意相关衰落分布。随后，借助高斯-拉盖尔求积法，推导了FAS窃听信道平均保密容量（ASC）、保密中断概率（SOP）和保密能效（SEE）的紧凑解析表达式。此外，为便于示例说明，我们以相关瑞利衰落信道为特例，利用高斯copula函数进一步得到了ASC、SOP和SEE的紧凑表达式。最终数值结果表明，与传统采用最大比合并（MRC）的天线系统（TAS）相比，将仅含单个有源端口的流体天线应用于PLS可实现更安全可靠的传输。