# Radio Wave Propagation and WSN Deployment in Complex Utility Tunnel Environments +
## 2 Materials and Methods
### Scenario Description  
In order to perform the radio wave propagation analysis within the tunnel, two scenarios were considered for the 3D-RL simulations: a real underground utility tunnel scenario located in the Old Town of Pamplona (Pamplona, Navarre, Spain) and a tunnel recreation of one of its gallery sections. The distribution of the considered experimental underground utility tunnels gallery is presented in Figure 3a with green lines on the map. As it can be seen from the figure, the tunnels have different sections, where the most remarkable characteristics are the different straight section lengths connected to one section with some intersections and slight curves. The dashed yellow line in the figure represents the straight tunnel section of 80-m-long where the experimental measurements were performed in order to calibrate the 3D-RL algorithm, as it is explained in Section 3. These tunnels were built in the early 2000s, under some specific streets, with the aim of easing maintenance operations. The tunnels consist of an outer layer of connected cement rings, with the inner part allocating several metallic trays for the corresponding utilities. The longest straight tunnel section is 327 m. A metallic hallway was also installed in order to provide access to the maintenance personnel, as can be seen in Figure 3b. Currently, they provide a route for the electrical connections, telephone connections, waste disposal and water distribution systems of the neighborhood. It is worth noting that slightly different utility tunnels have been built in newer neighborhoods of Pamplona, as can be seen in Figure 3c. Specifically, this picture corresponds to a recently repaired tunnel located in the suburb of Lezkairu, which began being built in 2008, and it has a total length of tunnels of 5600 m, plus 2300 m of sub-tunnels. Figure 2: Principle of operation of the in-house 3D-RL algorithm. Regarding security and safety, the utility tunnels include common intrusion detection and antifire systems, with their corresponding local alarms. However, one of the main problems of these types of tunnels is the lack of wireless coverage within the tunnel, which initially was planned to be provided by external infrastructures, such as municipal Wi-Fi or mobile networks (3G/4G). However, in reality, these technologies are unable to provide coverage to all tunnel sections, as signal attenuation can be very high in some sections due to the different tunnel depths. In this sense, one of the main concerns of municipal authorities has been this lack of wireless coverage within the tunnels, as coverage is needed in order to provide security and safety to the maintenance staff. Thus, a specific indoor coverage system is required, and therefore, a complete radio planning analysis before the deployment of the wireless system is needed in order to secure coverage and provide good performance at an affordable cost. As stated before, in order to characterize the variations of received power within the proposed utility tunnel, simulations by means of a 3D-RL code were performed. Material parameters were considered; basically, cement walls, aluminum trays and PVC tubes of different dimensions. A section of the simulation scenario is depicted in Figure 4, which corresponds with the same section where the experimental measurements were performed (see yellow dashed line in Figure 3a). The dimensions of  
Figure 3: Underground utility tunnels under analysis. (**a**) Tunnel location on the map of the Old Town of Pamplona. (**b**) Picture of the tunnel where the measurements were taken. (**c**) Picture of a newer tunnel built in the neighborhood of Lezkairu in Pamplona. the tunnel section are the following: width 2 m, height 3 m and length 80 m. Simulation results can be extended in length; however, due to measurement limitations, they will be considered up to the previously stated distance.