Fair Rate Maximization for Fluid Antenna Relay (FAR)-assisted Multi-user MISO Communications

Abstract: In this paper, we investigate the problem of max-min rate maximization in fluid antenna relay (FAR)-assisted multi-user uplink multiple-input single-output (MISO) wireless systems, where each user is equipped with a single fluid antenna (FA) and the base station (BS) is equipped with multiple FAs. Unlike most existing relevant work focusing on maximizing sum rate of the fluid antenna system (FAS), which may cause unbearable rate loss to weak users, we propose to maximize the minimal rate of the system to ensure fairness. The max-min optimization problem is formulated by jointly optimizing the positions of FAs with meeting the minimum distance requirements of FAs, maximum transmitting power limit, and feasible antenna region constraints. To solve this problem, we propose an alternating algorithm with utilizing the successive convex approximation (SCA) method. Simulation results demonstrate that the proposed method significantly outperforms conventional methods in terms of maximizing the minimal achievable rate across different signal-to-noise ratios (SNRs) and normalized region sizes.