Joint Beamforming, User Association, and Antenna Position Optimization in Movable Antenna-Assisted Cell-Free Massive MIMO

Jian Zhu, Lei Feng, Xudong Wang, Hongyang Du, Shaoyong Guo

Abstract: This paper proposes a downlink transmission optimization framework for cell-free massive MIMO (CF-mMIMO) systems enhanced by movable antennas (MAs). The proposed architecture significantly expands the spatial degrees of freedom. Moreover, it enhances user-centric cooperation among distributed access points (APs). We formulate a joint optimization problem to maximize the system weighted sum-rate (WSR) by simultaneously optimizing beamforming, user association, and antenna positions. To tackle the problem's non-convexity and coupling, we develop an efficient Joint Beamforming, User Association, and Movable Antenna Position (JBUM) algorithm within a two-loop iterative framework. In the outer loop, dynamic cosine-weighted particle swarm optimization (DCWPSO) is employed to search for optimal antenna locations. In the inner loop, we solve the beamforming subproblem using fractional programming (FP) and address the relaxed user association subproblem using successive convex approximation (SCA). Simulation results demonstrate that, compared with traditional PSO-based optimization, fixed-antenna CF architectures, and single-AP systems, the proposed MA-enhanced scheme achieves performance gains of 5.9%, 21.6%, and 58.8%, respectively. These results validate the effectiveness of integrating movable antennas into CF-mMIMO systems, and highlight its significant advantages in improving both system throughput and optimization flexibility.

External IDs:doi:10.1109/tnse.2025.3639312