Traditional mobile communication systems mainly work on the licensed frequency band near or below 3 GHz; however, this band is becoming increasingly crowded. On the other hand, there are abundant unlicensed spectrum resources in higher frequency bands, e. g. , 6 GHz, 15 GHz, and 28 GHz, and if those bands are applied, the current spectrum shortage problem could be effectively alleviated. However, the wireless channel characteristics and models are important but still unknown, and thus in this st
