# Unmanned Vehicles' Placement Optimisation for Internet of Things and Internet of Unmanned Vehicles
## 3 FSANET-WSN Networks: Proposed Architecture and Features  
We proposed the architecture of a Flying and Surface Ad Hoc NETwork serving Wireless Sensors Networks (FSANET-WSNs) on demand (Figure 1).  
Each WSN comprises a sink node (or central node) and sensor nodes. The wireless sensors network communicates with the rest of the network through a sink node, as emphasised in Figure 1. There are WSNs capable of communicating directly or/and by multi-hop with the gateway (S1-S4). Concurrently, there are also WSNs that are not in the range of the gateway (S5-S6). This situation appears when the WSNs are deployed in no or weak coverage areas.  
The architecture exploits the usage of UVs as an alternative to the costly and often not justified deployment of another fixed wireless infrastructure. UVs can perform several tasks while acting as mobile routers. In addition, given the use cases in which the sampling rate of the sensors nodes exceeds 30 min or even several hours, the wireless infrastructure may be reused and exploited in other locations. The monitoring is also performed on site, as in agriculture, where the sensors are deployed in fixed areas, and the wireless sensors networks are unavoidable. In the context of the Internet of Things, more beneficiaries can share their unmanned vehicles to deploy the on-demand network to cover a more extensive network than a beneficiary alone could have deployed with their own equipment.  
To ensure the communication between a WSN and the gateway (GW) through the use of FSANET, the optimum location of the UVs must be determined. To this end, the initial positions of the UVs must be known.  
The two communication technologies employed are LoRa/LoRaWAN and Wi-Fi (both in unlicensed spectra). LoRa/LoRaWAN is a low-power wide-area network technology used to transmit infrequent, low-throughput data. LoRa/LoRaWAN is used to send non-critical, non-frequent data inside WSNs and to communicate the Global Positioning System (GPS) coordinates of UVs when they are out of the range of Wi-Fi communication. LoRa refers to the modulation technique used in the physical layer, whereas LoRaWAN also embeds the data protocol to connect devices to the Internet infrastructure. LoRa/LoRaWAN have several limitations, among which include the limited number of messages per day a device can send to the gateway and the far more constrained downlink messages number [53]. From the gateway, the data are sent to the Cloud Center (CC). Here, the positions of the fixed nodes and the last positions of the UVs are stored in an InfluxDB database. In addition to the storage capability of the CC, it coordinates the UVs' tasks and executes the position optimisation algorithm.  
To enable multicast downlink transmission through LoRaWAN--as needed after the CC returns the results of the computation of the optimum positions of the UVs--a multicast node is required. It is in charge of sending a new position to each UV. To reduce the payload size, the Cloud Centre sends back the difference between the computed position and the position forwarded by UV to Cloud Centre to each UV.  
Wi-Fi technology is used for a fast transfer between a served WSN and the GW through the FSANET network due to its higher throughput, as FSANET nodes have power constraints related to their operation (for example, their propellers' functions).  
The paper focuses, as mentioned in Section 1, on the development of an algorithm that provides the optimum position for UVs to connect a certain terrestrial WSN to an IoT platform. This section aimed at presenting the framework and the simplified IoT architecture where such an algorithm is necessary. In Section 4, the theoretical background of the algorithm is presented.