Finite-Blocklength Fluid Antenna Systems With Spatial Block-Correlation Channel Model

Finite blocklength (FBL) effects are often overlooked in analyses based on outage probability, where the assumption of vanishing decoding error can lead to overly optimistic performance predictions. Although fluid antenna systems (FASs) have been shown to deliver substantial spatial diversity for various system designs, their behavior under FBL constraints has not been adequately studied. Leveraging the simplicity, tractability, and accuracy of the spatial block-correlation channel model for FAS, this work investigates therandom coding performancelimits of FBL-coded systems equipped with fluid antennas. We analytically characterize how FAS contributes to performance enhancement under the FBL assumption and validate the findings through numerical evaluations. Both analytical and simulation results reveal that FAS offers pronounced advantages over conventional systems employing multiple fixed antennas in FBL-coded communication scenarios.