  Unmanned aerial vehicles (UAVs) suffer from sensor drifts in GPS denied
environments, which can cause safety issues. To avoid intolerable sensor drifts
while completing the time-critical coordination task for multi-UAV systems, we
propose a safety constrained bi-level control framework. The first level is the
time-critical coordination level that achieves a consensus of coordination
states and provides a virtual target which is a function of the coordination
state. The second level is the safety-critical control level that is designed
to follow the virtual target while adapting the attacked UAV(s) at a path
re-planning level to support resilient state estimation. In particular, the
time-critical coordination level framework generates the desired speed and
position profile of the virtual target based on the multi-UAV cooperative
mission by the proposed consensus protocol algorithm. The safety-critical
control level is able to make each UAV follow its assigned path while detecting
the attacks, estimating the state resiliently, and driving the UAV(s) outside
the effective range of the spoofing device within the escape time. The
numerical simulations of a three-UAV system demonstrate the effectiveness of
the proposed safety constrained bi-level control framework.
