Kalman Filter Design Strategies for Code Tracking Loop in Ultra-Tight GPS/INS/PL Integration

D. Li and J. Wang

Abstract:	The integrated GPS/INS/PL system, with complementary characteristics to overcome the shortcomings of each individual part, can be achieved at different levels, namely loosely, tightly or ultra-tightly coupled. The next generation of integrated GPS/INS/PL navigation systems will be based on the ultra-tight coupled method. Ultratight coupled system offers numerous advantages, such as improved high-dynamic, anti-jamming and interference performance, due to its ability to maintain a narrow tracking loop bandwidth by employing unique integrated Kalman filter techniques. Under exposure to high dynamics, jamming or interference, the code tracking loop can sustain tracking with aiding Doppler derived from the ultra-tightly coupled Kalman filter. Hence, the code phase errors, i.e. the transmission time measurement errors and therefore the pseudorange errors, will be correlated with the inaccuracy of the velocity estimates. If these correlations are not considered in the design of the Kalman filter, it is likely to result in the instability of code tracking loop and even loss of lock. This paper focuses on the Kalman filter design strategies for the code tracking loop considering the correlations between the pseudorange and velocity errors. Initially, the error model of code tracking loop was investigated to derive the relationship between the code tracking loop errors, i.e. pseudorange errors, and the estimated velocity errors. The performance of the ultra-tightly integrated system was evaluated via comprehensive simulation tests comparing the solutions with the correlations taken into account and without. Experimental test results indicate that the stability of the integrated Kalman filter was improved remarkably based on this correlation analysis. Hence, the optimally estimated velocity could be derived to enhance the code tracking performance, even under high dynamics, jamming or interference by generating more accurate pseudorange measurements.
Published in:	Proceedings of the 2006 National Technical Meeting of The Institute of Navigation January 18 - 20, 2006 Hyatt Regency Hotel Monterey, CA
Pages:	984 - 992
Cite this article:	Li, D., Wang, J., "Kalman Filter Design Strategies for Code Tracking Loop in Ultra-Tight GPS/INS/PL Integration," Proceedings of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, January 2006, pp. 984-992.
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