Dual Frequency, Carrier Phase Differential GPS Augmentation
Report no. CTS 11-09
For many roadway applications, high-accuracy in-lane level vehicle position information is desired.
Unfortunately, in many roadway environments GPS dead zones hinder sufficient GPS position accuracy. These
roadway environments include underpasses, tree canopies, urban canyons, and any other locations where the view
to the sky is limited.
This report introduces a high-accuracy position estimator that augments GPS in areas where short-term (<
200 meter and < 15 second) GPS dead zones exist. The position estimator fuses differential GPS (DGPS) position
measurements, yaw rate measurements, and two-dimensional velocity measurements to provide in-lane level
accuracy position estimates. The estimator increases the availability of high-accuracy position estimates for
applications that demand continuous high-accuracy in-lane level positioning, such as lane departure warning
The position estimator was evaluated and the position accuracy was quantified. Seven vehicles were
outfitted with the position estimator system. Data was collected for 460 DGPS outages and the accuracy of the
system was analyzed. From the analysis the position accuracy of the estimator could be approximated based on the
distance and time since the DGPS outage began. This analysis provides a level of confidence in the position
estimates as a function of distance and time elapsed from the start of a DGPS outage. This level of confidence
measure allows applications to have a means to reject position estimates based on the outage time and distance if
those estimates are projected to have lower accuracy than the application requires.
Sponsored by: Hennepin County, ITS Institute (RITA), Minnesota Valley Transit Authority