Complete Propagation Model in Tunnels

The wave propagation in tunnels does not only depend on the carrier frequency and properties of the tunnel, but also differs along with the distance between transmitter (Tx) and receiver (Rx). This letter presents a complete structure and model for propagation in tunnels. Compared to existing models, the complete model unifies different academic viewpoints, reveals all possible propagation mechanisms, and localizes all the dividing points between every two adjacent propagation mechanism zones. When the user is close to the Tx, the propagation is dominated by the free-space mechanism, then the multimode mechanism is established. Afterwards, when the high-order modes have been largely attenuated, the fundamental-mode guided propagation is dominant. Finally, when the user is extremely far away, the waveguide effect vanishes because of attenuation of reflected rays. Measurements and simulations validate the model. This complete structure and model can be essential to establish a comprehensive understanding of the propagation in tunnels and can be applied for network planning and interference analysis of advanced communication systems.