Different Algorithms for Bridging Kinematic DGPS Outages Using SINS/DGPS Integration

Sameh Nassar

Abstract:	In recent years, the integration of a Differential GPS (DGPS) and a Strapdown Inertial Navigation System (SINS) has become a standard tool for high-precision kinematic systems. In SINS/DGPS integration mode, DGPS is used for positioning and the SINS is used for orientation. In case of DGPS outages that are caused by GPS signal blockages, the SINS is used instead for positioning as a stand-alone system until the standard DGPS mode is available again. The position errors in these cases are completely governed by the SINS errors. If accurate positions are required during these outages, some bridging algorithms should be used for estimating improved positions of these periods. In this paper, two different bridging methods have been applied. In the first method, the new positions are estimated using a backward smoothing algorithm. In the second method, the new positions are derived by a simple algorithm that has been developed for this purpose. The second method was initially tested using van and aircraft SINS/ DGPS data sets with a navigation-grade IMU (gyro drift 0.01 deg/h). The algorithm worked very well and removed most of the SINS errors accumulated at the end of the outage intervals. Therefore, the main goal of this paper is to analyze the performance of both bridging methods with different SINS grade categories and different kinematic data types. Three SINS/DGPS data sets will be used in the analysis, one of them is airborne while the other two are road vehicle data. The first road vehicle test utilized a navigation-grade IMU whereas the other one used a tactical-grade SINS (gyro drift 1.0-10.0 deg/h). The results show that both bridging methods reduce the SINS errors considerably for DGPS outages of 30 to 300 seconds. In general, the simple algorithm performs better than backward smoothing for all analyzed data sets. In this paper, both bridging algorithms are presented. Results obtained after applying each method will be discussed and their differences will be investigated.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1474 - 1482
Cite this article:	Nassar, Sameh, "Different Algorithms for Bridging Kinematic DGPS Outages Using SINS/DGPS Integration," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1474-1482.
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