Electromagnetic environment prediction and safety risk analysis of civil communication leakage coaxial cables in subway tunnels

Abstract

This study aimed to address the limitations of traditional electromagnetic numerical calculation methods in large-scale radio frequency (RF) space fields, accurately predict the electric field intensity of wireless communication signals in subway tunnels, and evaluate the safety of large-scale civil wireless communication electromagnetic environments in tunnels. To this end, COMSOL software was used to model the signal strength emitted by radiation terminals (leaky coaxial cables), which operate civil wireless communication systems of different types (3G, 4G, 5G) in small-scale space tunnels. Then, the simulation results for the small-scale space were theoretically calculated based on the radiation principle of a leaky coaxial cable. These results were used to derive the signal strengths corresponding to different civil communication frequency bands in the large-scale space of the tunnel. The prediction results of the signal received power in the tunnel were compared with the field measurement results: the root mean square error of the two was less than 1.58 dBm, thereby verifying the effectiveness of the signal strength model for different civil communication frequencies in a large-scale space tunnel. Subsequently, based on the calculated results of the signal strength, the extrapolation method was used to further calculate the maximum electric field intensities of 3G, 4G, and 5G in the civil communication environment within the large-scale space of the subway tunnel―0.143 V/m, 0.098 V/m, and 0.204 V/m, respectively. The calculated results of the electric field intensity were compared with the field measurement results in the tunnel: the root mean square error between the calculated and measured values was found to be less than 0.013 V/m. This result verifies the reliability of the proposed method for calculating the electromagnetic environment of civil communication in a large-scale space based on the signal strength modeling of a small-scale space. It further indicates that the proposed method effectively improves the calculation efficiency of the electromagnetic environment in the large-scale space inside a tunnel. The prediction results show that the maximum predicted power density of the electromagnetic environment in subway tunnels is only 0.005% of the public exposure limit of the International Commission on Non Ionizing Radiation Protection (ICNIRP), and the maximum predicted electric field strength is only 1.7% of the national electromagnetic environment control limit (GB 8702-2014), proving that the electromagnetic environment for civil wireless communication in subway tunnels is safe.

Keywords

• subway tunnel
• leaky coaxial cable
• large-scale space
• field strength prediction