# Radio Wave Propagation and WSN Deployment in Complex Utility Tunnel Environments +
## 1 Introduction  
The evolution of wireless communication has led to their adoption in a wide range of applications, including utilities and administrative authorities. In addition, the growth in population, as well as in the services offered in cities, has led, in some cases, to the construction of underground tunnels in order to reduce the visual impact within the city center, as well as facilitating maintenance and operation works of utilities. In recent years, the underground sector has seen the use of wireless networking for certain projects, i.e., tunneling construction [1], but they do not make full use of the benefits offered by wireless communications. The utilization of wireless networking in the underground environment offers the potential for major benefits in productivity and safety. Currently, most of the communications infrastructure in operational tunnels such as transport tunnels are provided by cables. However, if it is an infrequently accessed tunnel, a wired communication infrastructure will not generally be available; therefore, the maintenance, upgrade and inspection of those tunnels will rely on wireless communications [2]. Nevertheless, one of the issues that local authorities have considered is the fact that, inherently, underground service tunnels lack coverage from exterior wireless systems, such as mobile networks or municipal wireless local area networks (WLAN), which can lead to potentially dangerous situations for maintenance personnel working within the tunnel. Therefore, wireless coverage should be deployed within the underground installation in order to guarantee real-time connectivity. In emergency situations, such as fires, explosions or earthquakes, the normal wired communication infrastructure of an underground environment could be inoperable. Due to that, sometimes, it is necessary for the emergency services to have a wireless communication infrastructure following a serious incident. Rescue services normally are equipped with very high-frequency (VHF) or ultra-high-frequency (UHF) radio equipment, which is effective aboveground, but such radios have a very poor range in tunnels. The use of leaky feeder cables [3] is usually used to extend the coverage of VHF and UHF systems. However, the use of microwave frequencies provides a much greater range, without expensive leaky feeder systems, in such environments, and, also, they offer greater bandwidths. In addition, leaky feeders are also susceptible to damage during a fall or explosion. In [4], a system including both wired and wireless communications was described that enabled voice communication, as well as the exchange of photographs, video streams or other data, inside the tunnel. In [5], a wireless-based personnel tracking system to track people in an underground environment was presented, showing that the system can reduce the time taken for rescuers to reach any casualties. The characterization of wireless channel behavior within complex heterogenous underground environments, such as utility tunnel systems, enables to perform link-balance estimations, which lead to coverage/capacity estimations. In this sense, an adequate estimation of losses is relevant in order to characterize the complex operation conditions, such as those given by high-obstacle density, with a high percentage of non-line-of-sight conditions and multipath propagation buildup owing to scatterers distributions within the scenarios under test or the effect of diffuse scattering, among others. This information is relevant in order to perform radio-planning tasks, which are required in order to design the network topology, node configuration and device-related parameters, such as antenna location/type. A radio-planning analysis was studied for different types of wireless networks (e.g., broadcasting systems, trunk radios, public land mobile systems, microwave transport links, etc.