Design of Local Area DGNSS Architecture to Support Unmanned Aerial Vehicle Networks: Concept of Operations and Safety Requirements Validation

Abstract

Local-area differential global navigation satellite systems (LAD-GNSS) support unmanned aerial vehicles (UAVs) with high integrity and accuracy. This study investigates three major issues in fully establishing LAD-GNSS and analyzes their performance. First, we define the concept and requirements of UAV operation, including segregation of UAV operation coverage in low-altitude airspaces, and the derivation of navigation requirements, such as alert limits (ALs), for each operational coverage. Second, we design a LAD-GNSS architecture by simplifying the hardware and monitoring algorithms of both the ground facility and onboard module, using the well-established ground-based augmentation system (GBAS) as a starting point. Lastly, we perform theoretical performance evaluations comparing position uncertainty bounds, which are represented by protection levels (PLs), to the corresponding navigation requirements for each coverage airspace. We derive and compare PLs and ALs under both nominal and malfunction cases. In addition, we describe a method for deriving PLs for excessive acceleration and code-carrier divergence fault scenarios, which are bounded by using a maximum-allowable error in range. Using these PLs, integrity/continuity allocations are ideally and dynamically assigned to each single-fault hypothesis to obtain optimized PLs that are identical for all fault scenarios. We find that vertical protection levels (VPLs) are reduced by approximately 16% when implementing the optimal allocation method.