Improving Autonomy in GNSS-Challenging Environments by Multi-UAV Cooperation

Cooperative navigation is a promising strategy to enable safe autonomous flight in GNSS challenging environments. This paper discusses a cooperative strategy that guarantees bounded navigation error for an UAV flying in poor GNSS coverage conditions ("son"), exploiting the support of a cooperative vehicle ("father") and the available GNSS observables. A customized path planning strategy is developed for the father UAV, which is aimed at minimizing son positioning uncertainty. In view of real time implementation, path planning is complemented by proper cooperative guidance strategies. Planning and guidance approaches are verified in simulations that take into account three-dimensional environment and multi-GNSS constellation coverage. Cooperative navigation potential is demonstrated in experiments carried out flying two quadrotors in formation. In these flight tests, GNSS-challenging conditions are simulated off-line by assuming a virtual three-dimensional environment and removing GNSS satellites that would not be in view.