# LoRaWAN Networking in Mobile Scenarios Using a WiFi Mesh of UAV Gateways
## 1 Introduction  
Over the past few years, the ubiquity of the Internet and the miniaturization of computational devices created a new paradigm called Internet of Things (IoT). In many cases, IoT devices are subject to very strict power constraints. For this reason, a new range of low power wireless communication protocols has been developed in order to support Low Power Wide Area Networks (LPWANs) [1]. These networks are formed by simple devices that communicate infrequently over long distances at low bitrates. Long Range (LoRa) is one of the most promising and versatile technologies enabling LPWANs. LoRa [2] is a narrowband modulation technique based on Chirp Spread Spectrum (CSS) modulation, a technology that achieves high robustness against channel degradation factors, such as path loss, multipath fading, shadowing and Doppler shift. By taking advantage of Spread Spectrum (SS), chirp orthogonality and the good propagation properties of the sub-GHz spectrum, LoRa provides communication over long distances, at the expense of the bitrate and of the maximum time interval between transmissions due to duty cycle limitations in the bands used by the protocol. Air time, power consumption and data rates can be controlled by different Spreading Factors (SFs) (7 to 12) andbandwidth (125 kHz or 250 kHz) combinations. The LoRa modulation is the core of the PHY and MAC of LoRa Wide Area Networks Protocol (LoRaWAN) [3]. Unmanned Aerial Vehicles (UAVs), popularly called drones, are flying vehicles that work without a human pilot onboard. The exclusive prerogative of the military for many years, UAVs are now commercially available at low prices, thus making them appealing for a wide variety of applications. Drones come in different shapes, but the most common are quadrotors and fixed-wing drones. In case of a disaster, such as a flood or a wildfire, UAVs can be used to support the rescuers, to localize the victims and to create a backhaul network when communication facilities are disrupted. UAVs provide many advantages compared to other solutions: movement in an obstacle-free environment, better overview of the area, Line of Sight (LoS) with targets and faster data acquisition in large areas. However, UAVs still have a limited flying range, autonomy and flying time. UAV swarms are increasingly being considered as a possible solution to provide radio coverage in a target area. Integrating UAVs and LPWAN protocols in disaster scenarios may offer a new cost-effective and energy efficient way to solve problems arising during the operations of the rescuers. In this paper, a challenging scenario was selected: support of wildfire combat operations. Wildfires affect rural or suburban areas where the coverage of conventional networks (e.g., cellular networks) is weak or absent, or vulnerable to the fire itself. UAVs can therefore be used to establish a relay network between the command post managing the operations and the firefighters, therefore providing situational awareness to the rescuers. The mobility of firefighters represents a big challenge, since the UAV swarm has to maintain both area coverage and end-to-end connectivity to the Base Station (BS) of the command post. LoRaUAV, an UAV system based on LoRaWAN and Wireless Fidelity (WiFi), is designed to tackle these problems. Figure 1 shows a representation of the system architecture. In LoRaUAV, firefighters carry Global Positioning System (GPS) enabled LoRaWAN tags, which are used to transmit their position, as well as biometric data. They may also deploy tactical LoRaWAN sensors, which may detect when the fire has reached some selected locations. Firefighter tags and ground sensors will be henceforth designated Ground Nodes (GNs). In the target scenario, the LoRaWAN radio range is likely affected by additional attenuation due to terrain features and foliage. In the LoRaUAV system, a WiFi mesh network of autonomous UAV LoRaWAN gateways is dynamically deployed to provide LoRaWAN coverage during firefighting operations.