**2. Modeling approaches for wave propagation in confined environments**

The correct understanding of wave propagation in confined structures like tunnels has been an important area of research and development. They have been studied in the last 40 years for radio communication system deployment. Unfortunately, as we shall see, current models cannot be generally applied or they do not describe adequately the wave propagation. The purpose of this section is to provide an overview of the approaches for the problem of wave propagation in these structures.
