Mine electromagnetic wave analysis method based on mixed raytracing

The transmission distance of the mine wireless communication equipment is related to the installation position of the antennas. In order not to interfere with pedestrians and driving，the antenna of the wireless communication equipment is normally installed near the side of the tunnel. Consequently，it is necessary to study the analysis method and propagation characteristics of mine electromagnetic waves when the transmitting and receiving antennas are located in the above situation. Firstly，the received signal strength when the receiving and transmitting point is near the tunnel side or roof is calculated by the ray tracing method，which is markedly higher than that near the center of the roadway section. It is proved that the ray tracing method is not suitable for studying the electromagnetic wave propagation characteristics when the receiving and transmitting point is near the tunnel side at the same time. A corrected ray tracing model is proposed based on the traditional ray tracing method. The determination method of effective rays is designed when the transmitting antenna or receiving antenna is located on the boundary of the roof and the side of the tunnel or on the same roof or side. The path loss and reflection loss of incident energy at each reflection point are calculated，which reduces the fluctuation range of signal strength calculated by ray tracing method and extends the application range of this method in tunnel. In order to further improve the application of the ray tracing method in the whole tunnel section，a mixed ray model was proposed based on the corrected ray tracing model and the position attenuation coefficient. The definition and expression of the position attenuation coefficient are provided. The antenna location measurement experiment was carried out in the auxiliary transit tunnel of the mine. According to the simulation data of the corrected ray tracing model and the measured data，the attenuation coefficient of the horizontal location of the antenna along the tunnel is calculated. Experiments show that:The application range of modified ray tracing method outside the central area of the tunnel section is 25% higher than that of traditional ray tracing method under the same error condition. The longitudinal average error is less than 5 dB between the simulated values of mixed ray tracing method and measured values in the whole horizontal range of tunnel. It shows that the proposed method can more correctly compute the propagation characteristics of mine electromagnetic waves when the antennas are located near the tunnel side，expanding the application scope of the traditional ray tracing method. It provides guidance for the installation and optimal layout of the mine wireless communication equipment antenna.