Multi-robot Relative Pose Estimation and IMU Preintegration Using Passive UWB Transceivers

Ultra-wideband (UWB) systems are becoming increasingly popular as a means of inter-robot ranging and communication. A major constraint associated with UWB is that only one pair of UWB transceivers can range at a time to avoid interference, hence hindering the scalability of UWB-based localization. In this article, a ranging protocol is proposed that allows all robots to passively listen on neighboring communicating robots without any hierarchical restrictions on the role of the robots. This is utilized to allow each robot to obtain more range measurements and to broadcast preintegrated inertial measurement unit (IMU) measurements for relative extended pose state estimation directly on
$SE_{2}(3)$
. Consequently, a simultaneous clock-synchronization and relative-pose estimator is formulated using an on-manifold extended Kalman filter (EKF) and is evaluated in simulation using Monte Carlo runs for up to seven robots. The ranging protocol is implemented in C on custom-made UWB boards fitted to three quadcopters, and the proposed filter is evaluated over multiple experimental trials, yielding up to 48% improvement in localization accuracy.