User Equipment Based RAAS Experimentation

Tom Willems, Marijke Brondeel, Alain Muls and Alain De Wulf

Abstract:	The accuracy of differential GPS positioning is, as we all know, inversely proportional to baseline length. This is commonly labeled decorrelation, which can be decomposed into spatial decorrelation and temporal decorrelation. In order to overcome spatial decorrelation one needs to employ, either implicitly (e.g. in case of SBAS systems) or explicitly, data from different reference sites. For terrestrial applications, however, SBAS systems often cannot meet strict availability requirements. On the other hand, terrestrial networks providing differential data are often confined to slow data rates, which implies that they cannot conveniently accommodate WADGPS data. It is interesting against this background to investigate algorithms for merging different sources of differential data. Computation of networked differential corrections by the user equipment effectively implements regional area augmentation (RAAS). To gain a better understanding of decorrelation, it is interesting to look at scatter plots associated with long-range differential code fixes. These plots demonstrate a shift on the mean position in the direction away from the reference station. As with any parameter estimation process, the study of the propagation of random and systematic errors on the observation data into the results, is relevant to GPS observation data processing. In the context of long- range DGPS positioning, we focus on the propagation of residual ionospheric errors. We developed simulation software in which the only errors imposed on the measurements are ionospheric delays. Simulated corrected pseudorange data that is only affected by ionospheric decorrelation was generated and processed. The directional decorrelation effect is clearly recovered in the resulting simulated scatter plots. Next the simulation procedure is extended for studying the performance of user equipment based regional area augmentation. We present some results of tests that were carried out using different geometries of the reference nodes, different baseline lengths within the network, etc. and examine the residual decorrelation effects. To conclude we review user equipment based RAAS from different perspectives.
Published in:	Proceedings of the 2002 National Technical Meeting of The Institute of Navigation January 28 - 30, 2002 The Catamaran Resort Hotel San Diego, CA
Pages:	376 - 381
Cite this article:	Willems, Tom, Brondeel, Marijke, Muls, Alain, De Wulf, Alain, "User Equipment Based RAAS Experimentation," Proceedings of the 2002 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2002, pp. 376-381.
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