Analysis of wireless transmission tests in mines and preferred working frequency bands for mining 5G

The development and deployment of mobile communication systems, personnel and vehicle positioning systems in mines require an analysis of wireless transmission characteristics, the selection of preferred working frequency bands, and the optimization of wireless communication base stations and positioning substations. In this study, wireless transmission tests were conducted in a large frequency range from 350 MHz to 6 GHz in mine environments such as curved tunnels, branch tunnels, main transportation tunnels, excavation tunnels, and fully mechanized mining faces. The test results were analyzed, revealing the characteristics of wireless transmission in mines: ① In curved tunnels, the lower the wireless transmission frequency, the smaller the attenuation, with the least attenuation in the 350 MHz to 900 MHz frequency band. ② In branch tunnels, the lower the frequency, the smaller the attenuation, with the least attenuation in the 350 MHz to 900 MHz frequency band. ③ In main transportation tunnels, the least wireless transmission attenuation was found in the 700 MHz to 900 MHz frequency band. ④ In excavation tunnels, the least attenuation was in the 700 MHz to 900 MHz frequency band. ⑤ In fully mechanized mining faces, the least attenuation was observed in the 433 MHz to 1 300 MHz frequency band. ⑥ With the same cross-sectional area of the tunnels, wireless transmission attenuation in curved tunnels was smaller than in branch tunnels, and the attenuation in branch tunnels emitted from branch sources was smaller than that emitted from main tunnels. Curves and branches in tunnels increased wireless transmission attenuation. Furthermore, this paper proposed the preferred working frequency bands and the best arrangement of antennas for wireless communication systems in underground coal mines, specifically in curved and branch tunnels: ① The working frequency bands for underground wireless communication systems should preferably be in the 700 MHz to 900 MHz range. ② To minimize the impact of curves and branches in tunnels on wireless transmission, wireless communication base stations, positioning substations, and their antennas should be set at the turning points of curved tunnels and at the branch points of branch tunnels. The research results have been applied to the People's Republic of China energy industry standards NB/T 11546-2024 General specification of 5G communication system for coal mines, NB/T 11523-2024 5G communication base station for coal mines, and NB/T 11547-2024 5G communication baseband controller for coal mines.