Search

Knowledge of the Global Positioning System (GPS) signal-in-space (SIS) anomalies in history has a great importance for not only assessing the general performance of GPS SIS integrity but also validating the fundamental assumption of receiver autonomous integrity monitoring (RAIM): at most one satellite fault at a time. The main purpose of this paper is to screen out all potential SIS anomalies in the last decade by comparing broadcast ephemerides and clocks with precise ones. Validated broadcast navigation messages are generated from 397,044,414 navigation messages logged by on average 410 International GNSS Service (IGS) stations during the period 6/1/2000?8/31/2010. Both IGS and National Geospatial-Intelligence Agency (NGA) precise ephemerides/clocks are used as truth references. Finally, 1256 potential SIS anomalies are screened out. These anomalies show an improving SIS integrity performance in the last decade, from tens or hundreds of anomalies per year before 2003 to on average two anomalies per year after 2008. Moreover, the fundamental assumption of RAIM is valid because never have two SIS anomalies or more occurred simultaneously since 2004. [ABSTRACT FROM AUTHOR]

In safety-of-life applications of satellite navigation, the protection level (PL) equation translates what is known about the pseudo-range errors into a reliable limit on the positioning error. The current PL equations for satellite-based augmentation systems (SBAS) rely on Gaussian statistics. This approach is very practical: the calculations are simple and the receiver computation load is small. However, when the true distributions are far from Gaussian, such a characterization forces an inflation of the PLs that degrades performance. This happens in particular with errors with heavy tail distributions or for which there is not enough data to evaluate the distribution density up to small quantiles. We present a way of computing the optimal protection level when the pseudo-range errors are characterized by a mixture of Gaussian modes. First, we show that this error characterization adds a new flexibility and helps account for heavy tails without losing the benefit of tight core distributions. Then, we state the positioning problem using a Bayesian approach. Finally, we apply this method to PL calculations for the wide area augmentation system (WAAS) using real data from WAAS receivers. The results are very promising: vertical PLs are reduced by 50% without degrading integrity. [ABSTRACT FROM AUTHOR]

This paper develops an empirical confidence bound for barometric altimeter altitude errors and shows how this bound may improve the performance of GPS-based approach and landing systems. This empirical bound is developed using historical meteorological data collected at a set of geographically diverse locations over a thirty year period. The confidence bound developed is shown to provide a Gaussian overbound on altimeter altitude errors in standard atmospheric conditions between a 10-5 and 10-6 confidence level. This confidence bound is integrated into the standard methodology for analyzing the performance of GPS-based landing systems and the results of a performance trade study using the confidence bound are presented. The results show that incorporating the empirical barometric altimeter confidence bound provides an increase in the coterminous United States (CONUS) service volume for lateral precision with vertical guidance (LPV) type approaches. While this increase is approximately 2% for an L1 single-frequency GPS user, it jumps to roughly 40% for an L5 single-frequency user. [ABSTRACT FROM AUTHOR]

Among the receiver autonomous integrity monitoring (RAIM) algorithms treating multiple failures, multiple hypothesis solution separation algorithms (MHSS)—a type of solution separation algorithm—offer several advantages: First, the link between threat model, upper bound on the position error—the protection level and probability of hazardously misleading information is an easy and straightforward one; second, the calculation of the protection level does not involve complex steps. One of the critical steps in this algorithm is the allocation of the integrity and continuity budgets among the failure modes, as it determines the overall performance of the algorithm. After describing the baseline MHSS approach, we present an algorithm that simultaneously allocates the integrity and continuity budget among the failure modes to obtain the minimum protection level per satellite geometry. Then, we show how slope-based RAIM and solution separation RAIM are related through a little-known formula, which both unifies and highlights the differences between the two approaches. Finally, we apply the algorithm to evaluate the performance of RAIM for vertical guidance for a dual constellation, and find that even with a very large prior probability of satellite failure, vertical guidance can be achieved worldwide with high availability. [ABSTRACT FROM AUTHOR]