Optimized Low-cost HSGPS/IMU/WSS Land Vehicle Navigation System for Urban Navigation

摘要

Land vehicle navigation in urban areas, where masking effects are very frequent, is a major challenge for both the accuracy and the integrity of GPS-only solution. Several strong effects linked to urban canyon environments can seriously degrade the final position solution. Thus, the sole use of a GPS to navigate in urban areas has been proven to be challenging when high performances are expected in terms of accuracy and integrity of the computed solution. This paper proposes a "Smooth correction function" applied to the GPS received signals. This function works on the reliability of the pseudo-range measurements when affected by diverse sources of errors. Thus, to deal with different phenomena such as multipath or low C/No signals, a merging technique between the pseudo-range and Doppler measurements is proposed. The coupling of GPS with other positioning systems has been shown to be part of a solution to overcome satellites visibility problem in urban areas. The idea is to combine external measurements together with GPS measurements in order to improve the overall navigation system performance even during complete GPS signal outages. MEMS-based inertial sensors, such as accelerometers and gyros, are a classical solution to this problem. Nevertheless, due to the poor stability of these sensors, GPS is still required to correct their correlated errors and give an absolute position when available. This paper also looks at the potential benefits of the Wheel Speed Sensors (WSS) together with an Inertial Measurement Unit (IMU) will be studied for a complete land vehicle navigation solution. WSS provide wheel angular rate measurements and are fundamental components in the antilock braking system (ABS). Finally, this paper describes an hybridization technique optimised for land vehicle navigation in urban environment. The idea is to implement a high sensitivity multi-aided positioning system using the EKF (Extended Kalman Filter) where dead reckoning systems (INS and WSS) will help to keep track of the vehicle even during partial or complete GPS signal outages.