Hybrid Analog-Digital Beamforming in Cooperative mmWave MIMO Systems

This paper investigates hybrid beamforming design in cooperative millimeter-wave (mmWave) multiple-input multiple-output (MIMO) systems. We focus on the sum-rate maximization problem and aim to design the hybrid beamformer to maximize the weighted achievable sum-rate subject to the constraint of maximum transmit power for all base stations (BSs) and the constant modulus of phase shifters (PSs). Due to nonconvexity of the weighted sum-of-logarithmic function, we firstly transform the objective function into an equivalent form with the aid of fractional programming (FP) theory. Then, we propose an iterative hybrid beamforming algorithm, in which manifold optimization is first employed to solve analog beamformer and then a closed-form solution of digital beamformer is derived by Lagrange multiplier method. Numerical results demonstrate the remarkable advantages of proposed hybrid beamforming algorithm compared with other classical approaches.