# Radio Wave Propagation and WSN Deployment in Complex Utility Tunnel Environments +
## 1 Introduction
), considering aspects such as multi-variable optimization (energy consumption, node density and transmission rate as a function of the coverage area under analysis) and the impact of elements such as user density variation, estimation of cell edge conditions or interference background levels [6; 7; 8; 9; 10; 11]. With the progressive adoption of wireless sensor networks, radio-planning tasks have been adapted to optimize network configuration [12; 13; 14; 15; 16; 17; 18]. In this case, the specific considerations given by the wireless sensor network (WSN) operation have to be taken into account, such as the random node location, the existence of predominant non-line-of-sight operation conditions or the inherent energy consumption and processing constraints, among others. In this way, a wireless channel analysis can be effectively employed in order to assess elements such as cooperative MAC schemes, optimizedrouting protocols or specific data aggregator policies in order to optimize the overall system operation. One of the main challenges in this case is to consider accurate radio channel conditions, given the large variability of node location and configuration within the wireless network layout, usually leading to the use of empirical/analytical-based channel estimation models. Radio propagation has been studied for different wireless systems within the interiors of galleries and tunnels [19; 20; 21; 22], as well as for different tunnel geometries [23]. Other approaches have developed diffraction-based models, such as the alternate direction implicit parabolic equation method [24], boundary element method [25], numerical calculation of a vector parabolic equation [26] or application of the perturbation theory, among others. Another approach is based on the use of deterministic methods, such as ray launching (RL) or ray tracing (RT). One of the main issues of these approaches is the inherent divergence within the RL calculation as the distance increases between the transmit and receive antenna. In this case, solutions in scaled frequency models have been given by reconstructing the initial wave front of the source, achieved by ray density normalization [27]. One of the approaches adopted to perform wireless characterization within tunnels has been the adoption of dielectric waveguide models, in which the tunnel is emulated by a waveguide with dielectric walls [28]. These models, however, do not take into account the additional complexities, which appear in underground service tunnels, such as ducts, walkways or distribution trays, among others. Complete modeling can be achieved by employing full-wave electromagnetic simulation techniques, such as the finite difference time domain (FDTD) or frequency domain finite element techniques [29; 30]. However, the computational cost of these techniques can be very high, due to the large size of the tunnel structures as compared to the wavelengths considered in conventional wireless communication systems. Moreover, the tunnels analyzed are usually devoted to road traffic or trains, with inherently larger cross-sections and lower structural complexity as compared with utility tunnels, with dense obstacle distributions. In this paper, an in-house developed three-dimensional ray-launching (3D-RL) code is employed to analyze the wireless propagation in a real urban utility tunnel scenario at 868-MHz operation frequency. The aim of the article is a thorough analysis of the real results of measurements in the tunnels in order to obtain the optimal parameters for the simulation's 3D-RL algorithm, so that, after their application, the simulated and experimental results show good agreement. By adequately modeling the tunnel gallery structure, a precise characterization for the complete extension of the tunnel system can be obtained, which can aid in the deployment of wireless communication and monitoring systems. Furthermore, a complete radio wave propagation analysis is performed, and a WSN deployment is proposed for the considered real underground utility tunnel system gallery.