Time-coordinated path following of multiple UAVs over time-varying networks using L₁ adaptation

Motivated by challenging mission scenarios, this paper tackles the problem of multi-Unmanned Aerial Vehicle (UAV) cooperative control in the presence of time-varying communication networks. Specifically, we address the problem of steering a fleet of UAVs along given paths (path following) so as to meet spatial and/or temporal constraints. One possible scenario is the situation where a fleet of vehicles is tasked to execute collision-free maneuvers under strict spatial constraints and arrive at their final destinations at exactly the same time. The paper builds on previous work by the authors on coordinated path following and extends it to allow for time-varying communication topologies. Path following control in 3D builds on a nonlinear control strategy that is first derived at the kinematic level (outer-loop control). This is followed by the design of an L₁ adaptive output feedback control law that effectively augments an existing autopilot and yields an inner-outer loop control structure with guaranteed performance. Multiple vehicle time-critical coordination is achieved by enforcing temporal constraints on the speed profiles of the vehicles along their paths in response to information exchanged over a dynamic communication network. We address explicitly the situation where each vehicle transmits its coordination state to only a subset of the other vehicles, as determined by the communications topology adopted. Further, we consider the case where the communication graph that captures the underlying communication network topology may be disconnected during some interval of time (or may even fail to be connected at any instant of time) and provide conditions under which the complete coordinated path following closed-loop system is stable. Hardware-in-the-Loop (HITL) simulation results demonstrate the benefits of the developed algorithms.