A hybrid model for propagation loss prediction in tunnels

The Fresnel zone theory is employed to determine the boundary to distinguish propagation regions for line-of-sight topographies in tunnels. The formula for calculating the break point distance is obtained. A hybrid propagation model combining the free space propagation model and the modified waveguide propagation model is proposed. The hybrid model and the break point distance formula are validated with our own and other published experimental data in various tunnels and at different frequencies. It is shown that the free space propagation model can be used to predict propagation loss in the region prior to the break point, while the modified waveguide propagation model offers excellent prediction of propagation loss after the break point. This novel hybrid model has obvious application in tunnel microcell design.