Data Link Concept for Unmanned Aircraft in the Context of Operational Risk

Long-distance cargo transport is one of the manifold applications envisaged for highly automated unmanned aircraft (UA), which operate in the very low-level airspace below 150 m. Despite the level of automation, remote pilots need an interface for command and control of UA, which is typically provided by a digital data link. In this contribution, we investigate the impact of certification based on operational risk, which the European Aviation Safety Agency (EASA) introduced for UA within the specific category on the data link concept. In order to reach the required level of safety, which is the outcome of the Specific Operation Risk Assessment (SORA), the data link concept has to fulfill certain safety objectives. At the same time, the data link concept should be as cost-efficient as possible from an economical point of view. Keeping these boundary conditions in mind, we present an operation risk-based data link concept based on commercial off-the-shelf technologies. In dependence of the mission profile and the required safety level, cellular networks, satellite networks, as well as a combination of both, are viable options. Specifically, we evaluate by simulations the suitability of 4th generation Long Term Evolution (LTE) cellular networks for long-distance cargo UA. With regard to the concepts of operation, the goal of our simulations is estimating low-altitude cellular coverage in rural areas and we factor in radio propagation effects, link budgets, and the distribution of cellular base stations. The results of our system simulations with realistic flight routes show that LTE cellular networks offer good rural coverage in Germany and ensure operational safety in general. Nevertheless, connection disruptions in the order of some seconds can occur in valleys that are not served well by LTE and have to be considered in the risk assessment process.