# Unmanned Vehicles' Placement Optimisation for Internet of Things and Internet of Unmanned Vehicles
###### Abstract
WSNs are widely used for environmental monitoring in many fields, such as agriculture, disaster management (e.g., floods) and water monitoring, and a real problem resides in their further connection to the Internet infrastructure when they are deployed in isolated areas. Thus, UAVs can perform as data collection nodes to improve the energy consumption performance of WSNs and their coverage. In addition, the improvements consist of increased data transmission efficiency and lifetime [20]. On the other hand, when monitoring water quality, for example, WSNs may be deployed on buoys floating on the water surface and UAVs can collect their data as in [21] through the use of communication technology as such LoRa/LoRaWAN. The use of buoys, though, may support the increase in network coverage for WSNs found onshore, but usually, the interval between consecutive data transmissions is reduced, and the deployment of many such buoys would be expensive, as special protection enclosures are required. A more efficient approach would be to employ USVs and UAVs which are mobile and can serve more areas on demand. In addition, the adoption of a single communication technology determines the low scalability of the system to other applications. In the literature, when developing algorithms for UAV formation or USV formation, the propagation aspects (environment, different types of channels and propagation models) are usually neglected. If the employment of UAVs as access points was previously studied [22], the usage of USV as relays is less clear. When referring to SANET, the works found in the literature approach the large-scale maritime communications on different specific standards, such as ITU-R M.1842-1 [23] dedicated for very high-frequency (VHF) communications between industrial ships, but small-scale applications, such as those on rivers and lakes, are less represented. The usage of USVs as access points is motivated by the specific characteristics of some areas close to water environments and by many applications in regions transpassed by important rivers, such as the Danube (in Europe). Other regions of interest are those close to lakes that have a significant surface area. VHFcommunications would require very large antennas which are not affordable for small vehicles such as UAVs and USVs. Consequently, this paper intends to provide an algorithm for unmanned vehicles' (UVs, including UAVs and USVs) formation, such that communication is assured along a GW-UVs-WSN (Gateway-Unmanned Vehicles-Wireless Sensors Network) communication chain, where Wi-Fi communication is employed for quick data transfer, whereas LoRa/LoRAWN is employed for non-critical, low-throughput data transfer. Both technologies operate in unlicensed spectra and the necessary equipment to deploy them is miniaturised. The algorithm must determine the optimum position of each UV node such that they become Wi-Fi access points. Then, they are capable of fast-forwarding data from a wireless sensor network (WSN) to a gateway (GW). Based on the optimum positions computed through the algorithm, the equipment (sensors, cameras) and the performances of unmanned vehicles (in particular, UAVs and USVs), afterwards, a Cloud Center can assign different monitoring tasks to the UVs, their role being two-fold: data forwarders and monitoring data collectors. Concerning the contribution of the paper:  
* We highlight the importance of UAV and USV networks, and we propose the concept of Internet of Unmanned Vehicles over the concept of Internet of Drones or Internet of Unmanned Aerial Vehicles, which were narrower. We emphasise the current state of the art and how our proposal goes beyond this. * We propose an architecture comprising unmanned vehicles and a network of UAVs and USVs (UVs) that both assure reliable communication and fulfil tasks assigned by a Cloud Center (CC). * We offer the background for the communication link optimisation from the point of view of propagation.