Design of Joint Transmit Beamforming for Multi-User MIMO-OFDM Integrated Sensing and Communication Systems

To address spectrum scarcity and achieve the perceptive network, integrated sensing and communication (ISAC) systems have been extensively studied. However, research on multi-user ISAC systems utilizing multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) architectures remains incomplete. This paper aims to bridge this gap by exploring digital and hybrid beamforming designs for multi-user MIMO-OFDM ISAC systems. Specifically, the paper investigates the impact of beamforming on the range-Doppler domain of radar sensing and system capacity, and formulates a corresponding design problem. The paper then addresses the capacity maximization problem by converting it into a weighted minimum mean square error problem and employs successive convex approximation (SCA) to develop an iterative approach for digital beamforming design. Similarly, the paper formulates a hybrid beamforming design problem and proposes a design approach based on the alternating direction method of multipliers (ADMM) and SCA. The complexity of the proposed approaches is analyzed. Simulation results demonstrate that our approaches are effective and can outperform existing approaches in the literature.