Characterization of second-order fading statistics of 28GHz indoor radio propagation channels

Extension of usable frequency spectrum from microwave to millimeter-wave (mmWave) range is one of the key research direction in addressing the capacity demands of 5 ^th generation (5G) land mobile radio communication networks. This paper presents a thorough analysis on the second-order fading statistics of indoor mmWave range radio propagation channels. The well established analytical relationship of plain angular statistics of a radio propagation channel with the channel's fading statistics is utilized to study the fading characteristics of indoor mmWave radio propagation channels. The plain angle-of-arrival (AoA) measurement results published in the open literature for three different indoor radio propagation scenarios at 28GHz band are extracted by using different graphical interpretation techniques. The extracted plain AoA statistics are extended to study the dispersion of energy in angular domain and second-order fading statistics of the channel. The considered quantifiers for energy dispersion in angular domain and second-order fading statistics are true standard-deviation, angular spread, angular constriction, and direction of maximum fading; and spatial coherence distance, spatial auto-covariance, average fade duration (AFD), and level-crossing-rate (LCR); respectively. The conducted analysis on angular spread and second-order fading statistics is of high significance in designing antenna-beams, error-correction techniques, channel estimation and equalization schemes, modulation schemes, and interleaving algorithms; for 28GHz indoor radio propagation environments.