A Comparison of Measured GPS Performance with Model Based Predictions in an Equatorial Scintillation Environment

Mark Knight, Manuel Cervera and Anthony Finn

Abstract:	Ionospheric scintillations are rapid variations in the amplitude and phase of radio signals resulting from density irregularities in the ionosphere. At GPS frequencies and in the mid-latitudes, scintillation effects are generally negligible. However, at low latitudes and in the hours immediately after sunset, scintillation activity can become a problem for GPS. This is particularly true during periods of high solar activity when the ionosphere is at its most active. At present, solar activity is near the maximum of its 11 year cycle. It is therefore anticipated that scintillation activity will be close to its peak and will remain at this level for the coming few years. Scintillations have the potential to affect all GPS systems, including both single, and dual frequency SPS and PPS receivers and both code and carrier phase Differential GPS (DGPS). The effects of scintillations include an increase in errors on the code and carrier phase range measurements, and an increase in the probability of losing lock. Depending on the geometry of the satellite constellation and the locations of the irregularity patches within the ionosphere, these effects can translate into poorer navigational accuracy for a receiver. However, it is anticipated that the most significant effects will only be observed on the L2 tracking loops of codeless and semi-codeless receivers and for carrier phase DGPS. Previously, models of the code and carrier tracking loops of GPS receivers have been combined with predictions provided by the Wide Band Ionospheric Scintillation Model (WBMOD [1]) to predict the impact of scintillations on GPS [2]. The objectives of this paper are as follows: 1) To investigate the performance of semi-codeless GPS receivers in equatorial regions during the peak of the current solar cycle, 2) To compare the predictions of GPS receiver performance with measurements made by co-located Novatel Millennium and PAQ12 Ionospheric Scintillation Monitoring (ISM) receivers [3], and 3) To use the ISM data to evaluate the Wide Band Ionospheric Scintillation Model (WBMOD) for the South East Asian region during solar maximum.
Published in:	Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000) June 26 - 28, 2000 The Catamaran Resort Hotel San Diego, CA
Pages:	588 - 601
Cite this article:	Knight, Mark, Cervera, Manuel, Finn, Anthony, "A Comparison of Measured GPS Performance with Model Based Predictions in an Equatorial Scintillation Environment," Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000), San Diego, CA, June 2000, pp. 588-601.
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