Browsing by Subject "Carrier phase"

Now showing 1 - 2 of 2
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    Analysis of GPS-based Real Time Attitude Determination System for ITS Application
    (Intelligent Transportation Systems Institute, Center for Transportation Studies, University of Minnesota, 2012-11) Gebre-Egziabher, Demoz; Lie, Fidelis Adhika Pradipta
    This work describes the development and testing of GPS-based attitude and heading determination system (AHRS) using single-frequency (L1) carrier phase differential GPS (CPDGPS). Vehicle's attitude can be uniquely determined from two non-collinear relative position vectors, known as the baseline vectors. The accuracy of the resulting attitude estimate depends on the accuracy of the baseline vector estimates and their respective magnitudes (length). The shorter the baseline, the higher the vector accuracy required to give the same attitude accuracy that can be obtained through longer baseline system. Issues such as ambiguity resolution and phase center variations are discussed. Test result shows that single-frequency CPDGPS is still a challenge, mainly caused by the integer ambiguity problem inherent to CPDGPS problem. A more feasible but less accurate method using a short baseline is also discussed. Phase center calibration remains a challenge for this attitude determination system.
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    Dual Frequency, Carrier Phase Differential GPS Augmentation
    (Center for Transportation Studies, 2011-05) Arpin, Eddie; Newstrom, Bryan; Shankwitz, Craig
    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 systems. 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.