Performance Evaluation of Global Differential GPS (GDGPS) for Single Frequency C/A Code Receivers

Sundar Raman and Lionel Garin

Abstract:	Differential GPS is a technique that improves the accuracy of GPS. In its most common form, local differential GPS (LDGPS), high quality reference receivers are located at known, surveyed locations. These reference stations estimate the slowly varying error components of each satellite range measurement, form corrections and broadcast these corrections to local users within a range of 150 km (typical). In this paper, we will analyze the performance one type of differential GPS referred to as Global Differential GPS (GDGPS) [1]. GDGPS which is provided by NASA’s Jet Propulsion Laboratory (JPL), differs from LDGPS in that the corrections are valid globally. The rationale for using GDGPS over LDGPS is that the corrections are available from a single source and are uniformly valid. This avoids the degradation of the quality of corrections with distance from reference receivers inherent in LDGPS. GDGPS is primarily geared towards dual frequency receivers. In contrast, here, we will apply the corrections to a single frequency C/A code receiver. We will characterize the improvement in horizontal position accuracy obtained by using the GDGPS. In GDGPS, global corrections to the broadcast ephemeris and satellite clock corrections are computed using a global network of GPS reference sites, namely NASA’s Global GPS Network (GGN) which is operated by JPL. For ionospheric delay corrections, we will use their database of global grid points of ionosphere electron density. For purposes of evaluation, these corrections were provided offline by JPL. They were then included in the measurements and post processed to evaluate the improvement in performance.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1465 - 1469
Cite this article:	Raman, Sundar, Garin, Lionel, "Performance Evaluation of Global Differential GPS (GDGPS) for Single Frequency C/A Code Receivers," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 1465-1469.
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