  In this paper we study the distance-based docking problem of unmanned aerial
vehicles (UAVs) by using a single landmark placed at an arbitrarily unknown
position. To solve the problem, we propose an integrated estimation-control
scheme to simultaneously achieve the relative localization and navigation tasks
for discrete-time integrators under bounded velocity: a nonlinear adaptive
estimation scheme to estimate the relative position to the landmark, and a
delicate control scheme to ensure both the convergence of the estimation and
the asymptotic docking at the given landmark. A rigorous proof of convergence
is provided by invoking the discrete-time LaSalle's invariance principle, and
we also validate our theoretical findings on quadcopters equipped with
ultra-wideband ranging sensors and optical flow sensors in a GPS-less
environment.
