## 5 Conclusions  
In this paper, the 3D ray-tracing method is used to simulate and analyze the transmission of wireless signals in a roadway:  
1. The spatial segmentation-based acceleration algorithm is used to segment the roadway model, which reduces the number of collisions during the path search process and improves the computational efficiency of the 3D ray-tracing method.
2. The results show that, for a wireless signal with a frequency of 700 MHz, the model can accurately reflect the waveform change and attenuation of the wireless signal during signal transmission in the roadway. However, the simulation model only considers relatively basic rectangular, long, straight roadways. In actual production operations, the cross-sectional shapes are trapezoidal and arched, and the roadway has L-shaped right angles and curvatures. This 3D ray tracing only includes the direct and reflected rays, and scattering and diffraction are not taken into consideration. Improvement of the roadway model and the propagation method of wireless signals in the 3D tracking method needs to be carried out in the future.  
Conceptualization, M.Z. and T.D.; methodology, Y.S.; software, B.L.; validation, B.L., T.D. and Y.S.; formal analysis, Y.S.; investigation, Z.N. and Q.W.; resources, Y.S. and T.D.; data curation, B.L.; writing--original draft preparation, B.L.; writing--review and editing, B.L., T.D. and Y.S.; visualization, Y.W.; supervision, Y.W.; project administration, T.D. and Y.S.;  
Figure 10: Signal strength simulation and actual measurement.  
funding acquisition, M.Z. and Z.N. All authors have read and agreed to the published version of the manuscript. This research was funded by National Key Research and Development Program of China (2022 YFC2904005), National Natural Science Foundation of China (U20A20148), Science and Technology Major Project of the Tibet Autonomous Region's Science and Technology Plan (XZ20201 ZD0004G01). Not applicable.  
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