  This paper studies the bearing-based time-varying formation control problem
for unicycle-type agents without bearing rigidity conditions. In the considered
problem, only a small set of agents, named as anchors, can obtain their global
positions, and the other agents only have access to the bearing information
relative to their neighbors. To address the problem, we propose a novel scheme
integrating the distributed localization algorithm and the observer-based
formation tracking controller. The designed localization algorithm estimates
the global position by using inter-agent bearing measurements, and the
observer-based controller tracks the desired formation with the estimated
positions. A key distinction of our approach is extending the
localization-and-tracking control scheme to the bearing-based coordination of
nonholonomic systems, where the desired inter-agent bearings can be
time-varying, instead of the constant ones assumed in most of the existing
researches. The asymptotic stability of the coupled localization-and-tracking
control system is proved, and simulations are carried out to validate the
theoretical analysis.
