I. Introduction
Direction-of-arrival (DOA) estimation has been widely used in wireless communications [1], [2]. As an important DOA estimation approach, multiple signal classification (MUSIC) has gained a lot of attention due to its super-resolution property in the presence of multiple signals [3]. Massive multiple-input multiple-output (MIMO) is one of the most important enabling technologies in 5G and its beyond [4]. Due to a large number of antennas, massive MIMO is essential to millimeter-wave bands because the large array gain can compensate for the high path loss. With massive MIMO, frequency resources at millimeter-wave bands can be exploited efficiently [5], [6].