Performance assessment of the recent NDGPS recap - Initial simulation results

Document Type

Conference Proceeding

Date of Original Version



The Differential Global Positioning System (DGPS) is a ground-based augmentation system for GPS that uses a high-quality GPS receiver at a known location to measure the ranges to GPS satellites and compute the differences between the measured ranges and the theoretically expected ranges. These pseudorange corrections and the corresponding range-rate corrections are then broadcast to nearby users to allow them to improve their position accuracy. Within the U.S., the Coast Guard operates the nationwide differential GPS (NDGPS) service using 86 reference stations, broadcasting the correction data over a radio link in the marine radio-beacon frequency band. According to the NAVCEN website, NDGPS today provides 10-meter accuracy in all established coverage areas with typical accuracies in the 1 to 3 meter range. In 2003-2004 these authors undertook a study of the availability and accuracy of DGPS in harbor environments. This study included the questions: • "What is the absolute accuracy of the DGPS system and how does this compare to WAAS-aided GPS and raw (unaugmented, post SA) GPS?" • "How does DGPS accuracy vary with distance from the reference station site?" These activities focused on limited experiments, both static and dynamic, in several harbor locations around the U.S.; the results of these tests were reported in ION conferences during that time period. It was expected that the data would show an increase in position error for greater beacon distances due to the decorrrelation of the corrections. We did not find the expected decorrelation effect in these studies. Since the time of these studies the Coast Guard has significantly recapitalized the DGPS installations; this begs another examination of the performance of the system. These authors have begun a more comprehensive accuracy study. This paper describes our method of assessing accuracy in detail, providing some preliminary results.

Publication Title

Institute of Navigation International Technical Meeting 2012, ITM 2012



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