High-Density Channels

In the future, fifth‐generation communications system (5G) is expected to provide reasonable mobile broadband experience to high‐density users in stadium, gym, shopping mall, etc. As the fundamental limitation is attributed to the propagation environments, it is essential to understand profoundly the high‐density channels, say, the propagation channel in the environments where the user density could be very high. In this article, seven different environments are considered. The targeted environments include stadium (or gymnasium), shopping mall, airport, hall, street canyon, indoor (or indoor office), and crowded area. The propagation investigations in the literature for the seven environments are reviewed in terms of channel sounding, parameter estimation, channel characterization and modeling, etc. The review of the high‐density channel facilitates the “great service in a crowd” defined in 5G.