# Unmanned Aerial Traffic Management System Architecture for U-Space In-Flight Services
## 2 Background
### U-Space  
U-space is a collaborative effort among researchers, industry, and regulators to enable the integration of UAS operations within the civil airspace, providing UAS situational awareness and digital communication with manned aviation, the ATM service providers, and the legal authorities. There exists a roadmap [11] to deploy U-space in Europe, consisting of the four phases depicted in Figure 3. Each phase will propose a new set of services with increasing complexity and integration level between UAS and manned aircraft, as well as an upgraded version of existing services in the previous phases. The detailed functional system architecture is still under development, but there is already a list of services defined for each deployment phase [14], and a report with the current progress of their implementation and deployment [15]. Table 1 depicts these services and their current level of implementation in Europe. Figure 3: The implementation roadmap for the U-space initiative [13], consisting of 4 deployment phases. The U-space framework proposes a UTM system as the software architecture that provides services to the different U-space actors. A possible classification for the services is depending on whether they are activated in the UAS pre-flight phase or during the flight:  
* Pre-flight services are those related with the functionalities needed to prepare and schedule a UAS operation. The vehicle and the operator need to register (_E-registration_), and the initial flight plan has to be handled before being accepted (_Flight planning management_). Then, the pilot may get assistance through information about predefined restricted areas (_Pre-tactical geofencing_) and the resolution of possible conflicts before flying (_Strategic deconfiction_). * In-flight services deal with the functionalities required to handle the operation after the UAS flight has started. This means the possibility to update the operator (_Tactical geofencing_) or the UAS itself (_Dynamic geofencing_) with geofencing information during the flight, and to track the current position and predicted trajectory for each UAS (_Tracking_). This updated information is then used to create a situation of the airspace (_Monitoring_) and to generate warnings and contingency actions under possible threats (_Emergency management_). Alternative plans could also be suggested in-flight to maintain the required separation between aircraft and with geofences (_Tactical deconfiction_). * There are other services that could be used either before flying or during the flight. These are functionalities that aim to provide identification (_E-identification_), weather forecasts (_Weather Information_), or more generic information (_Drone Aeronautical Information Management_), to create an interface with the ATC (_Procedural Interface with ATC_ and _Collaborative interface with ATC_), and to control and manage the UAS density in the airspace (_Dynamic Capacity Management_). According to Table 1 and to our study of the state of the art, in-flight services have been less addressed by UTM systems in general, with a notorious integration gap still