A Mixed Rays – Modes Approach to the Propagation in Real Road and Railway Tunnels

Nowadays, security and efficiency of transportation networks are usually supported by wireless communication systems. In all cases, the radio link reliability strongly depends on propagation properties, and therefore effective prediction tools and models are requested in the design and planning phases of the radio system. In this paper, a mixed rays – modes approach to the propagation modelling in real tunnels is presented. The propagating field is computed as the superimposition of many characteristic modes, whose amplitudes are properly estimated thanks to a limited and therefore fast ray-tracing procedure; the Geometrical Optics rules are also used to model the main effects of the possible tunnel curvature. Moreover, an equivalent wall roughness is introduced in order to approximately account for the actual tunnel transversal shape and for the presence of inner elements and objects. The model is compared with some other different existing models and also with measurements carried out inside an underground line in the neighbourhood of Naples. The achieved performance are in line with the published scientific data.