# Sensors and Communication Simulation for Unmanned Traffic Management
## 2 Related Work  
In the literature, there are numerous simulation proposals oriented to drone flight simulation modeling aspects such as mission planning and drone navigation and control. In [21], we find an analysis of the existing commercial tools such as X-plane, Flight Gear, JMavSim, or Microsoft AirSim. These tools allow realistically simulating drone flight and control in a synthetic three-dimensional environment that can be visualized by the user. This simulation level can also be accomplished using the simulator developed by the manufacturer DJI for its drones [22]. DJI simulator allows using the physical drone controller to pilot within the simulation environment. There are other tools devoted to modeling mission planning and GCS behavior like QgroundControl or MAVProxy. This last tool allows simulating C2 link and the interchanged messages between the GCS and the drone using UDP (user datagram protocol) and MAVLink protocols.  
Simulation of C2 and V2V communications is presented in [23], where a simulation tool based on the Unity platform is proposed. This tool models aircraft specification, navigation, control, communications between different drones, and sense and avoid systems. Unlike previous simulators that were oriented to the simulation of a single drone, this one is designed to support simultaneous operations of several drones in order to analyze the operation of different sense and avoid algorithms. A multi-drone simulator is also proposed in [24], which presents a web architecture designed to simulate mission planning, execution, and monitoring of multiple UAVs within a virtual environment that can contain no-flight zones.  
A multi-agent simulation architecture is proposed in [25] to test how traffic distribution algorithms affect drone operations. Aside from the usual flight planning and trajectory simulation capabilities, this architecture also allows simulating the coverage of a communications network used by the drones, by defining a scenario that geographically positions the communication nodes.  
All the previous tools are self-contained and do not interconnect with UTM systems. If we focus on simulation oriented to UTM systems, the number of publicly available tools is very reduced. As a result of NASA's developments to investigate UTM systems, a set of tools [26] has been created that allows defining drone trajectories as a list of waypoints and simulating in real time drone movements in order to generate position report messages (telemetry). This simulator also allows manual control in order to introduce contingencies in the trajectories. In addition, all the tools are integrated (e.g., telemetry messages are injected into the system) with the UTM system so that they can be used for testing and evaluating it through simulated scenarios.  
To conclude, the available solutions do not offer a comprehensive simulation tool covering all the aspects that would be needed to evaluate a UTM platform effectively as will be detailed in the following section. In fact, no previous literature has been found for drone surveillance networks or sensors. Furthermore, simulators are not conceived to be integrated with a UTM system for evaluation (except the system proposed in [26])  
Figure 1: Proposed simulation framework and high-level unmanned traffic management (UTM) simulator integration.  
and thus data exchange with UTM platforms is disregarded focusing only on C2 and V2V communications.