Trajectory Design for Fairness Enhancement in Movable Antennas-Aided Communications

TL;DR

This paper proposes a trajectory design method for movable antennas at a base station to enhance fairness among users in multiuser uplink communication, optimizing antenna movement over time.

Contribution

It introduces an optimal solution for ideal fast movement and a heuristic for limited speed, improving user rate fairness in MA-assisted systems.

Findings

Optimal trajectories employ finite deployment patterns with time allocation.

Heuristic design performs well under limited movement speed.

Numerical results show improved fairness compared to benchmarks.

Abstract

Through adaptive antenna repositioning, the movable antenna (MA) technology enables on-demand reconfiguration of wireless channels, thereby creating an additional spatial degree of freedom in improving communication performance. This paper investigates a multiuser uplink communication system aided by MAs, where a base station (BS) equipped with multiple MAs serves multiple single-antenna users. Specifically, given that an optimized array geometry cannot guarantee rate fairness, we focus on designing antenna trajectory at the BS to maximize the minimum achievable rate among all users over a finite time period. The resulting optimization problem is fundamentally challenging to solve due to the continuous-time nature. To address it, we first examine an ideal case with infinitely fast MA movement and demonstrate that the relaxed problem can be optimally solved via the Lagrangian dual method. The obtained trajectory solution reveals that the BS should employ a finite set of MA deployment patterns, each allocated an optimal time duration. Building on this, we then study the general case with limited MA movement speed and propose a heuristic trajectory design inspired by the optimal patterns identified in the ideal scenario. Several insights are also gained by examining the simplified special case. Finally, numerical results are provided to validate the effectiveness of the proposed designs compared to competitive benchmarks.