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In this paper, we investigate the problem of controlling multiple unmanned
aerial vehicles (UAVs) to enclose a moving target in a distributed fashion
based on a relative distance and self-displacement measurements. A relative
localization technique is developed based on the recursive least square
estimation (RLSE) technique with a forgetting factor to estimates both the
``UAV-UAV'' and ``UAV-target'' relative positions. The formation enclosing
motion is planned using a coupled oscillator model, which generates desired
motion for UAVs to distribute evenly on a circle. The coupled-oscillator-based
motion can also facilitate the exponential convergence of relative localization
due to its persistent excitation nature. Based on the generation strategy of
desired formation pattern and relative localization estimates, a cooperative
formation tracking control scheme is proposed, which enables the formation
geometric center to asymptotically converge to the moving target. The
asymptotic convergence performance is analyzed theoretically for both the
relative localization technique and the formation control algorithm. Numerical
simulations are provided to show the efficiency of the proposed algorithm.
Experiments with three quadrotors tracking one target are conducted to evaluate
the proposed target enclosing method in real platforms.
