UWB-aided GNSS/INS Fusion for Resilient Positioning in GNSS Challenged Environments

The fusion of Inertial Navigation System (INS) and Global Navigation Satellite System (GNSS) is a well established technique to provide resilient positioning even in GNSS challenged environments. However, when GNSS reception conditions are persistently degraded, the inherent drift of inertial navigation can result in insufficient accuracy (e.g. greater than 1m), especially when using industrial or tactical grade Inertial Measurement Unit (IMU). This study introduces the tightly coupled integration of Ultra-Wideband (UWB) ranging measurements with fixed beacons to a loosely coupled GNSS/INS fusion. The algorithm uses an Error-State Kalman Filter (ES-KF) that supports Velocity Constraints (VC) and Zero-Angular Rate Updates (ZARU)/Zero Velocity Updates (ZVU). It details the necessary pre-processing of UWB measurements to correct for clock drift, velocity and latency errors, and provides two calibration techniques suitable for guided and generic use cases, resulting in ranging accuracy of better than 3cm and 11cm, respectively, based on 28 field tests. The benefits of UWB measurements in fusion are demonstrated through a field trial with severely degraded GNSS conditions, resulting in horizontal accuracy better than 40cm (compared to 2.1m without UWB) and improved rejection of poor GNSS measurements.