  Relative localization between autonomous robots without infrastructure is
crucial to achieve their navigation, path planning, and formation in many
applications, such as emergency response, where acquiring a prior knowledge of
the environment is not possible. The traditional Ultra-WideBand (UWB)-based
approach provides a good estimation of the distance between the robots, but
obtaining the relative pose (including the displacement and orientation)
remains challenging. We propose an approach to estimate the relative pose
between a group of robots by equipping each robot with multiple UWB ranging
nodes. We determine the pose between two robots by minimizing the residual
error of the ranging measurements from all UWB nodes. To improve the
localization accuracy, we propose to utilize the odometry constraints through a
sliding window-based optimization. The optimized pose is then fused with the
odometry in a particle filtering for pose tracking among a group of mobile
robots. We have conducted extensive experiments to validate the effectiveness
of the proposed approach.
