Radio wave propagation measurements in tunnel entrance environment for intelligent transportation systems applications

Underground environments are of great interest to intelligent transportation system (ITS) applications, since they occur frequently in both urban and rural situations, and have peculiar propagation characteristics. This investigation includes two of the major fields in ITS applications: road-to-vehicle, and vehicle-to-vehicle communications. Besides that, the propagation measurements presented also focus on the transition effects when moving between the regions outside and inside a tunnel, which represents its entrance environment. The experimental results of path loss and delay spread profiles are presented and analyzed.