GNSS can provide high accuracy via real-time-kinematic (RTK) positioning, but RTK currently works only if there is a free line-of-sight between user and GNSS satellite. In urban areas the GNSS signal is often obstructed or reflected. The availability of a RTK solution in urban areas is less than 50-70 % (depending on the type of the buildings), which renders RTK virtually useless for safety critical applications. For example, we can currently not imagine that an UAV flies autonomously in a city, e.g. for traffic monitoring.
This project targets to increase the RTK availability in urban areas by using GPS+Galileo L1/E1 and L5/E5a signals and by inertial aiding. A cost efficient microelectromechanical (MEMS) gyro and accelerometer (a so-called inertial measurement unit – IMU) is used to detect cycle-slips within the GNSS carrier phase measurements. Cycle-slips are the main reason for the low RTK availability in urban areas. A GPS/Galileo RTK module is developed which is integrated with an ultra-tightly coupled GNSS/IMU receiver, to achieve continuous GNSS signal tracking even if obstructions are present. To mitigate multipath the principle of a synthetic antenna aperture is used. The Kalman filter is extended based on IMU calibration campaigns and a parameter sensitivity analysis. This shall allow to use more cost efficient IMUs or to bridge longer GNSS signal outages (e.g. in an underpass).
For verification, a ring-laser IMU based reference system is integrated within a measurement vehicle. This allows establishing the ground truth with ~ 1 cm accuracy. The measurement vehicle also carries competitive solutions used for comparisons. A fish-eye camera allows identification of GNSS signal degradations and is used to optimize the developed algorithms.
This project was funded by the Austrian Promotion Agency (FFG) within the programme line "ASAP".
Dorn, M.; Filwarny, J. O.; Wieser, M.:
Inertially-Aided RTK Based on Tightly-Coupled Integration Using Low-Cost GNSS Receivers - in: European Navigation Conference (ENC). Lausanne, 11.05.2017.