  This paper presents a distributed approach to provide persistent coverage of
an arbitrarily shaped area using heterogeneous coverage of fixed-wing unmanned
aerial vehicles (UAVs), and to recover from simultaneous failures of multiple
UAVs. The proposed approach discusses level-homogeneous deployment and
maintenance of a homogeneous fleet of fixed-wing UAVs given the boundary
information and the minimum loitering radius. The UAVs are deployed at
different altitude levels to provide heterogeneous coverage and sensing. We use
an efficient square packing method to deploy the UAVs, given the minimum loiter
radius and the area boundary. The UAVs loiter over the circles inscribed over
these packing squares in a synchronized motion to fulfill the full coverage
objective. An top-down hierarchy of the square packing, where each outer square
(super-square) is partitioned into four equal-sized inner squares (sub-square),
is exploited to introduce resilience in the deployed UAV-network. For a failed
sub-square UAV, a replacement neighbor is chosen considering the effective
coverage and deployed to the corresponding super-square at a higher altitude to
recover full coverage, trading-off with the quality of coverage of the
sub-area. This is a distributed approach as all the decision making is done
within close range of the loss region, and it can be scaled and adapted to
various large scale area and UAV configurations. Simulation results have been
presented to illustrate and verify the applicability of the approach.
