Multiuser hybrid analog/digital beamforming for relatively large-scale antenna arrays

Power consumption and costs of the analog front-end (AFE) chains are often not negligible for large-scale antenna array systems. A low-complexity hardware architecture is to use a number of AFE chains that is less than the number of the antennas. Beamforming for this low-complexity hardware architecture involves both digital and analog beamforming, which is termed hybrid analog/digital beamforming. This paper focuses on the optimization for hybrid analog/digital beamforming to minimize the transmit power subject to the signal-to-interference-plus-noise-ratio (SINR) constraints. Properties on the feasibility and optimum of the considered problem are derived. Numerical algorithm based on semi-definite positive (SDP) relaxation is proposed in an attempt to solve the optimization problem. Numerical simulations show that the performance of hybrid analog/digital beamforming is highly related to the correlation of the channel coefficients of different subcarriers.