Long-Term Prediction of GPS Accuracy: Understanding the Fundamentals

Ted Driver

Abstract:	This paper will explore the obstacles inherent in predicting GNSS-based navigation accuracy, discussing each obstacle in turn and attempting to bound navigation errors as a function of time. Depending on your definition of accuracy – this topic can be relatively easy or terribly difficult. For this analysis, we will focus on major contributors to navigation positioning errors, such as Dilution of Precision (DOP), and User Range Error (URE) behaviors. This paper is born out of the nascent need by organizations to plan missions based on future navigation accuracy – a need that is not easily met currently. I will look at the behaviors of each error contributor to the accuracy prediction problem, and attempt to mathematically or statistically bound the error produced by each. Complexities such as the non-Gaussian behavior of the errors must be addressed as well. The predictions will take on two forms: extrapolated instantaneous errors and statistical errors mapped to specific confidence levels. We’ll also show how these bounds can be converted to other accuracy parameters using standard methods. Some of the elements that make up the total navigation accuracy picture can be bounded fairly easily, given a few modeling parameters. Others are not so tame and will exhibit complex behaviors. I anticipate the results will show large variances in the different predicted error bounds and that this in turn will drive future work in the area. I anticipate writing follow on papers discussing the specific details of the different error contributors in the near future and encourage others to do so as well. Navigation error prediction is becoming more prevalent and as users get more sophisticated, dilution of precision predictions are no longer sufficient for their needs. Providing a framework to work from, this paper will allow users of position error predictions to better understand their specific problem. This work will also lead to further research in accuracy prediction, forming a foundation from which to grow.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	152 - 163
Cite this article:	Driver, Ted, "Long-Term Prediction of GPS Accuracy: Understanding the Fundamentals," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 152-163.
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