Two-Timescale Design for Fluid Antenna Enhanced Multiuser Mimo System with Imperfect CSI

This paper proposes an uplink two-timescale transmission scheme for a fluid antenna-enhanced multi-user multiinput multi-output system (MU-MIMO-FAS), where antenna positions are optimized based on statistical channel state information (CSI), and beamforming at the base station (BS) adapts to rapidly-varying instantaneous CSI. Using a Rician channel model with imperfect CSI, we employ the linear minimum mean square error (LMMSE) method for channel estimation and a maximal ratio combining (MRC) detector to derive a closed-form expression for the achievable rate. Subsequently, we formulate a minimum user rate maximization problem for antenna position design, subject to movement and spacing constraints, and utilize a genetic algorithm (GA) to solve this non-convex problem. Numerical results demonstrate that the proposed two-timescale MU-MIMO-FAS design significantly outperforms the traditional fixed-position antenna (FPA) system.