Autonomous GPS Integrity Monitoring Using the Pseudorange Residual

The use of GPS for navigation-critical applications such as aircraft nonprecision approach or harbor and river crossings requires the navigation data to be both extremely accurate and extremely reliable. This paper describes a method for autonomous GPS satellite failure detection and isolation (D/I). The test statistic for the D/I algorithm is the range residual parameter for six or more satellites in view. Based on experiments conducted at Stanford, nominal carrier-aided pseudorange measurement errors are modeled as Gaussian random variables with mean in the range from −5 m to + 5 m and standard deviation of 0.4 m. The theoretical statistical distribution of the range residual is given. Monte Carlo simulations present results of applying the algorithm to measurement sets containing a biased measurement. With a 100 m biased measurement present, successful detection is achieved 99.9 percent of the time, and successful D/I is achieved 72.2 percent of the time. The user is always aware when isolation is not possible. User positioning errors resulting from application of the algorithm are always the same or better than with the all-in-view solution.