Multi-UAV formation geometries for cooperative navigation in GNSS-challenging environments

This paper focuses on the problem of autonomous UAV navigation in GNSS-challenging environments. The proposed approach is based on the idea of supporting the flight of a ("son") UAV in challenging environments, by means of one or more cooperating ("father") UAVs flying under nominal satellite coverage. Relative sensing and information sharing are the basic cooperation mechanisms. Different sensing architectures are presented in terms of filtering schemes, with the focus set on measurement equations and the relevant covariance matrices. The concept of generalized dilution of precision is introduced as a way to predict the son positioning accuracy resulting from available GNSS observables and cooperative measurements, and can thus be used to individuate optimal formation geometries and navigation performance bounds. Both numerical simulations in different scenarios, and first results from experimental datasets, demonstrate a good consistency with the achieved navigation accuracy. Experimental data show how proper formation geometries allow cooperative visual measurements to provide meter-level positioning accuracy for relatively long timeframes, even exploiting only two available pseudoranges.