Radio Wave Propagation in Arched Cross Section Tunnels - Simulations and Measurements

For several years, wireless communication systems have been developed for train to infrastructure communication needs related to railway or mass transit applications. The systems should be able to operate in specific environments, such as tunnels. In this context, specific radio planning tools have to be developed to optimize system deployment. Realistic tunnels geometries are generally of rectangular cross section or arched shape. Furthermore, they are mostly curved. In order to calculate electromagnetic wave propagation in such tunnels, specific models have to be developed. Several works have dealt with retransmission of GSM or UMTS [1], [2]. Few theoretical or experimental works have focused on 2.4 GHz or 5.8 GHz bands [3]. In this paper, we propose an approach to model radio wave propagation in these frequency bands in arched shape cross section straight tunnels using tessellation in multi-facets. The model is based on a Ray-Tracing tool using the image method. The work reported in this paper shows the propagation loss variations according to the shape of tunnels. A parametric study on the facets size to model the cross section is conducted. The influence of tunnel dimensions and signal frequency is examined. Finally, some measurement results in an arched cross section straight tunnel are presented and analyzed in terms of slow fadings and fast fadings.