Beamforming Optimization for Distributed MIMO Systems Over Practical Line-of-Sight Near-Field Channels

Distributed multiple-input multiple-output (D-MIMO) systems is a key architecture for next-generation communications, offering enhanced capacity and coverage. However, designing beamforming for D-MIMO systems in line-of-sight (LoS) near-field conditions remains challenging. In this letter, we incorporate the effective antenna aperture for accurate channel modeling and investigate near-field beamforming optimization in collaborative D-MIMO systems. To address this high-dimensional non-convex problem, we propose a near-field collaborative beamforming (NCB) algorithm to maximize the system sum rate. The NCB algorithm iteratively updates the solution and guarantees convergence to a closed-form stationary point. Specifically, we employ the Lagrangian dual transformation and quadratic transformation to convert the original problem into a series of mathematically tractable convex problems. The primal-dual subgradient method is then applied to reduce the optimization complexity. Simulation results verify the effectiveness of the proposed NCB algorithm.