Coverage Analysis of Fluid Antenna Systems in Poisson Cellular Networks

In this letter, we analyze the coverage performance of fluid antenna system (FAS)-equipped users in interference-limited heterogeneous cellular networks using stochastic geometry. In particular, we consider a downlink single-tier Poisson network where the user selects the antenna port that maximizes the instantaneous signal-to-interference ratio (SIR) from a set of spatially correlated ports within a finite aperture. A tractable framework is developed to characterize the coverage probability under arbitrary interference fading, with closed-form results for Rayleigh fading. The analysis shows that increasing the number of ports enhances coverage via spatial selection diversity, but the gains are fundamentally limited by spatial correlation and diminish beyond moderate port counts. Simulation results validate the analysis and highlight the joint impact of aperture size and port correlation on coverage performance.