A survey on channel measurements and models for underground MIMO communication systems

The high reliability of the communication system is critical in metro and mining applications for personal safety, channel optimization, and improving operational performance. This paper surveys the progress of wireless communication systems in underground environments such as tunnels and mines from 1920 to 2022, including the evolution of primitive technology, advancements in channel modelling, and realization of various wireless propagation channels. In addition, the existing and advanced channel modeling strategies, which include the evolution of different technologies and their applications; mathematical, analytical, and experimental techniques for radio propagation; and significance of the radiation characteristics, antenna placement, and physical environment of multiple-input multiple-output (MIMO) communication systems, are analyzed. The given study introduces leaky coaxial cable (LCX) and distributed antenna system (DAS) designs for improving narrowband and wideband channel capacity. The paper concludes by figuring out open research areas for the future technologies.