UWB-IMU-Odometer Fusion Localization Scheme: Observability Analysis and Experiments

In this article, we present a novel ultrawideband (UWB)-inertial measurement unit (IMU)-odometer fusion localization scheme for nonholonomic ground robots in global positioning system (GPS)-denied environments. To overcome the severe drift problems caused by the large acceleration bias of low-cost IMUs, rather than using the conventional IMU-only propagation model, a wheel odometer and a three-axis gyroscope are integrated to propagate the system states. Furthermore, the observability conditions of the proposed system with nonholonomic constraints are theoretically derived by a nonlinear observability analysis. The results reveal the minimum number of anchors (or leader robots) required for position observability (at least three anchors for UWB-time of arrival (ToA) measurements and one anchor for both ToA and angle-of-arrival (AOA) measurements). In addition, the system inputs (linear velocity and angular velocity along different axes) need to be excited for attitude observability. Simulations and experiments have verified that the proposed approach produces accurate position estimation and outperforms previous methods. Meanwhile, the position and attitude observability conditions have been verified through rich experiments, and the degenerated cases where the states cannot be observed are enumerated and tested, making the scheme complete.