Design and implementation of metasurfaces for enhancing non-line-of-sight communication in mining tunnels

Abstract

Coal mine tunnels contain numerous bends and branches that obstruct the direct propagation of wireless signals between transmitters and receivers, creating non-line of sight (NLoS) areas. Due to limitations on the transmission power of base stations within these tunnels, signal coverage holes are prevalent. Therefore, ensuring adequate signal coverage in coal mine tunnels is imperative. In this paper, we present a 900 MHz reflective metasurface to enhance the signal strength of mine tunnel signals in NLoS areas. The proposed metasurface unit has a two-layer structure, which achieves a 3-bit coverage of electromagnetic wave phase with a relatively small size, only 0.12λ. The metasurface allows for abnormal reflection of linearly polarized waves from −53° to +53° with the max RCS of 21.10 dBsm to 23.84 dBsm, respectively. Subsequently, a bend tunnel is established to simulate the underground propagation of electromagnetic waves in the tunnel. The metasurface is placed in the mine tunnel, and the simulation results are tested and validated in tunnel scenarios. The results show the proposed metasurface with an enhancement effect is 5 dBm on the signal in the NLoS area and filled the signal coverage by 60 m in this scenario within −100 dBm. The proposed metasurface effectively covers signals in NLoS areas, and appropriate deployment can reduce operational costs and be applied in various scenarios.