A Robust Foot-Mounted Positioning System Based on Dual IMU Data and Ultrasonic Ranging

Foot-mounted positioning system (FPS) is regarded as an important application for GPS-denied scenes, including but not limited to emergency rescue, medical health, and individual soldier positioning. With the assistance of zero-velocity update technology (ZUPT), the basic positioning function can be realized, while the largest problem is that the accumulation of systematic heading drift and positioning error cannot be completely constrained. This article presents a robust FPS based on dual inertial measurement unit data and ultrasonic ranging (FPS-DU). Bidirectional long short-term memory (Bi-LSTM) network is developed for the recognition of quasi-static (QS) period for the performance enhancement of ZUPT, and multilevel constraints are modeled for decreasing the cumulative error of the single foot-mounted model. In addition, a unified Kalman-based location estimator is developed combining dual foot-mounted inertial data and sphere constraint-based ultrasonic ranging results, enhanced by a robust ultrasonic outlier detector. Comprehensive experiments demonstrate that the proposed FPS-DU realizes much more accurate and robust positioning accuracy (between 0.371% and 0.548% under different test environments and traveled distances) compared with traditional single FPSs (S-FPSs).