Maximum Likelihood Channel Estimation for Millimeter-Wave MIMO Systems with Hybrid Beamforming

In a millimeter-wave massive multiple-input multiple-output system, the accurate estimation of the angle of departure is crucial to benefit from a high array gain. In this paper, a novel algorithm is proposed for the maximum likelihood estimation of angles of departure in the multiuser downlink scenario. The proposed approach is based on discrete Fourier transform beamforming vectors to estimate the angle of departure. The discrete Fourier transform matrix can efficiently be implemented in the analog domain by a so-called Butler matrix. Finally, we derived the Cramer-Rao lower bound to assess the performance of our proposed algorithm.