Hybrid MMSE Precoding and Combining Designs for mmWave Multiuser Systems

Hybrid analog/digital precoding architectures are a low-complexity alternative for fully digital precoding in millimeter-wave (mmWave) MIMO wireless systems. This is motivated by the reduction in the number of radio frequency and mixed signal hardware components. Hybrid precoding involves a combination of analog and digital processing that enables both beamforming and spatial multiplexing gains in mmWave systems. This paper develops hybrid analog/digital precoding and combining designs for mmWave multiuser systems, based on the mean-squared error (MSE) criteria. In the first design with the analog combiners being determined at the users, the proposed hybrid minimum MSE (MMSE) precoder is realized by minimizing the sum-MSE of the data streams intended for the users. In the second design, both the hybrid precoder and combiners are jointly designed in an iterative manner to minimize a weighted sum-MSE cost function. By leveraging the sparse structure of mmWave channels, the MMSE precoding/combining design problems are then formulated as sparse reconstruction problems. An orthogonal matching pursuit-based algorithm is then developed to determine the MMSE precoder and combiners. Simulation results show the performance advantages of the proposed precoding/combining designs in various system settings.