Radio propagation characteristics in curved tunnels

Radio propagation in curved tunnels of rectangular or arched cross-sections is modelled. The base station and tunnel parameters which have a significant influence on the propagation slope in curved tunnels are determined. The impact of these parameters on the propagation is then analysed and an optimum set of values is determined. Results are based on computed simulations utilising a ray launching approach with the Monte Carlo method. The obtained results show that the radio propagation slope depends on several practical planning parameters including the incident angle of the arrival signal, wall roughness, antenna location and antenna polarisation; especially in connection with tunnel shape. According to the results, antenna location and polarisation have a significant influence on the reflection angle, on reflection coefficient values, and thus on radio propagation. It is also shown that a tunnel cross-section size has only a minor effect on the propagation slope. Hence, the base station antenna configuration and the mobile antenna inclination have a superior impact on optimised coverage in curved tunnels.