Two-Slope Path Loss Model for Curved-Tunnel Environment With Concept of Break Point

The curvature of tunnels introduces an extra loss in the wave propagation. A simulation and measurement study are performed on the straight and the curved tunnels to investigate the extra loss in the curved tunnels in comparison with the straight tunnels at a frequency of 2.4 GHz. This study suggests the existence of two wave propagation mechanisms in the curved tunnel;
enhanced waveguiding mechanism
induced by rich multipath components from the curved tunnels and
degraded waveguiding mechanism
due to the blockage from the curved tunnel walls. For efficient radio planning, a new propagation model with curvature dependent break point is proposed. The proposed break point indicates the end of the
enhanced waveguiding mechanism
and the beginning of the
degraded waveguiding mechanism
. A two-slope radio wave propagation model is then proposed for radio communications inside curved tunnels by using the determined break point, with performance evaluation.