Real-Time Failure Detection and Repair in Ionospheric Delay Estimation Using GPS by Robust and Conventional Kalman Filter State Estimates

The ionospheric delay is one of the main error sources for precise GPS positioning and navigation. Dual-frequency GPS receivers can be used to eliminate the ionospheric delay (to the first order) through a linear combination of L1 and L2 observations (Hofmann-Wellenhof et al., 1994). Taking advantage of this physical dispersive principle, one or more dual-frequency GPS receivers can be used to determine a model of the ionospheric delays over a region of interest and, if implemented in real-time, can support single-frequency GPS positioning and navigation applications.There are, however, several factors which may affect the accuracy of real-time ionospheric delay estimation. One of the dominant factors, the failure in the carrier phase observations, such as the occurrence of cycle slips (for example, Engler et al., 1995), is the topic of this paper. In order to improve the real-time ionospheric delay estimation performance a novel approach to addressing this problem is presented here.The concept and methodology of the proposed algorithm is introduced. Preliminary test results are presented to indicate the performance of this approach for real-time ionospheric delay estimation.