Composition of Safety Constraints for Fixed-Wing Collision Avoidance Amidst Limited Communications

This paper considers how to ensure that a system of fixed-wing unmanned aerial vehicles (UAVs) can avoid collisions. To do so, a novel method is developed for creating a barrier function, which is similar to a Lyapunov function and can be used to ensure that a system can stay safe for all future times. After introducing the general approach, it is shown how to ensure that collision avoidance for two vehicles can be guaranteed for all future times. The construction is then extended to the case of arbitrarily many vehicles by addressing how to satisfy multiple safety objectives simultaneously. This is done while ensuring that output actuator commands are within specified limits. Because this formulation requires communication of control values and may therefore reduce throughput of other important messages, it is then shown how to reformulate the solution without this significant communication overhead while still ensuring that safety is maintained and actuator limits are respected. The theoretical developments of this paper are validated in the simulator SCRIMMAGE with a simulation of 20 UAVs that maintain safe distances from each other even though their nominal paths would otherwise cause a collision.