I. Introduction
The 5th-generation mobile communication system (5G) employs a beamforming technology that uses massive multiple-input multiple-output (MIMO) as the radio access technology [1], [2]. By using a large antenna array and increasing the antenna gain, the received power at the terminal is substantially improved. In addition, by increasing the degree of freedom of the antenna, the number of spatially multiplexed streams also increase. These advantages contribute to the throughput improvement within a cell.