Accurate INS/GPS Positioning with Different Inertial Systems Using Various Algorithms for Bridging GPS Outages

Sameh Nassar, Eun-Hwan Shin, Xiaoji Niu and Naser El-Sheimy

Abstract:	For most of the current mobile mapping and navigation applications, integrated INS/GPS systems have become a standard tool. In such applications, GPS mainly provides position and velocity while the INS provides orientation. Since the early stages of inertial navigation and INS/DGPS integration, Kalman Filter (KF) proved to be the optimal method for the estimation and compensation of the system errors. Several KF approaches have been implemented such as the Linearized KF (LKF), Extended KF (EKF) and recently the sigma-point or Unscented KF (UKF). For any INS/GPS KF, the initial position, velocity and attitude are obtained from the INS mechanization. The position and velocity of this solution are compared to the GPS position and velocity (the KF updates) and the differences are used by the KF to estimate the system errors. Regardless of the implemented KF approach, any INS/GPS navigation system will suffer from the major problem of frequent occurrence of GPS signal blockages. To accommodate such problem, the INS is used for navigation as a stand-alone system until GPS signals are available again. In this case, position errors as well as the corresponding covariance increase rapidly with time. Therefore, positioning during GPS signal outages using INS is a partial solution. To improve the INS provided solution during GPS outages, bridging algorithms must be used. In this paper, two main bridging methods are used. The first method takes the KF outputs and applies an optimal backward smoothing. The second approach is called INS backward error modeling where an error model is derived and used backward in time during GPS outage intervals only. All discussed KFs and bridging algorithms are tested using two van INS/DGPS tests with different inertial systems (navigation-grade, tactical-grade and MEMS) and simulated GPS outage periods. In general, all bridging approaches showed substantial accuracy improvement of the obtained position errors during GPS outages by more than 90%.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1401 - 1410
Cite this article:	Nassar, Sameh, Shin, Eun-Hwan, Niu, Xiaoji, El-Sheimy, Naser, "Accurate INS/GPS Positioning with Different Inertial Systems Using Various Algorithms for Bridging GPS Outages," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 1401-1410.
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