Fluid Antenna-Enhanced Symbol-Level Precoding for Multi-User MISO Communication Systems

Abstract

In this paper, we propose an fluid antenna (FA)-enhanced interference exploitation symbol-level precoding (SLP) for downlink multi-user multiple-input single-output (MU-MISO) systems, focusing on transmitter-side fluid antenna systems (Tx-FAS) that allow flexible spatial correlation effects while preserving user portability. First, we derive an explicit expression for the achievable rate of SLP under finite-alphabet inputs, and further establish a closed-form upper bound that quantifies the theoretical rate improvement achieved by spatial reconfigurability of Tx-FAS. Subsequently, a joint optimization problem involving SLP design and Tx-FAS port selection is formulated to maximize the minimum user signal-to-interference-plus-noise ratio (SINR) under strict transmit power constraints. Due to the highly non-convex nature of the problem, we devise a genetic algorithm (GA) to efficiently obtain a near-optimal solution. Moreover, based on the optimal channel structure of SLP, we further develop a low-complexity algorithm with a spatial filtering mechanism to obtain a sub-optimal solution to the considered problem. Simulation results confirm that the proposed FAS-enhanced SLP scheme delivers notable performance improvements over both conventional precoding techniques and the FAS-only transmission approach.