A raytracing model for wireless propagation in tunnels with varying cross section

Mandated by the 2006 United States Miner Act, reliable two-way communications in mines has drawn the interest of network engineers in recent years. Critical to the design of these systems is an accurate channel propagation model. Given the elementary geometry seen in most tunnels, models that approximate them as a rectangular waveguide have been developed. These models are extremely accurate in vehicular tunnels because - since the tunnel is typically cast from concrete - the cross section is uniform throughout and the surface roughness is negligible. Mines, however, do not conform to these two conditions. In this paper, we extend the waveguide model to tunnels with varying cross section and measurable surface roughness. The effectiveness of the proposed model is validated through in-house field measurements collected in a vehicular tunnel and in a coal mine. We show that while the original model performs well in the former, it falters in the latter. The extended model, however, predicts reliably in the mine as well.