Influences of Vehicles on Signal Propagation in Road Tunnels

It is well known that the electromagnetic (EM) waves do not propagate well in road tunnels. The channel characteristics for empty tunnels have already been well analyzed by both theoretical and numerical/experimental methods. However, any road tunnels are full with running vehicles. Currently a few works have investigated the influence of the vehicles on the signal propagation in road tunnels. However, they are all limited to experimental or numerical results. This paper provides a theoretical mode-based analysis to give the straightforward description of the wireless channel in road tunnels with traffic flow. First the effects of a single vehicle in the tunnel are investigated. The analytical expressions of the in-mode loss and the mode coupling are provided using uniform theory of diffraction (UTD), Poisson summation formula and saddle point method. Then the channel model for a L-lane road tunnel with the Poisson traffic flow is provided basing on the analysis on single vehicle´s effect.