I. Introduction
The shortage of global wireless spectrum resources has prompted people to explore millimeter-wave (mmWave) bands [1]. Thanks to the deployment of large-scale antenna arrays at the base stations (BSs), massive multiple-input multiple-output (MIMO) could serve a plurality of user terminals (UTs) over the same physical layer resources and remarkably increase the system spectral efficiency. Combining mmWave transmission with massive MIMO is a practical point of view and causes widespread concern [2]. The short wavelength in mmWave signals allows a small physical space to encapsulate a large antenna array. Meanwhile, high beamforming gains of massive MIMO can solve the problem of high propagation path loss of mmWave transmission.