I. Introduction
Over the past decade, the future communication systems based on massive multiple-input-multiple-output (MIMO) [1] and millimeter wave [2] have been widely investigated. The available bandwidth at millimeter wave(mmWave) frequencies is hundreds of times larger than the conventional LTE(Long-Term Evolution) bands. The massive MIMO technique can improve the spectral efficiency by tens of times and compensate for the large propagation loss of mmWave signals. Meanwhile, the short wavelength of mmWave allows compact design of large antenna arrays. Therefore, the combination of massive MIMO and mmWave frequencies is attracting researchers from different areas in wireless communications, and the high-speed railway(HSR) communication is one of them.