Closed-Loop Operation of GPS Aided INS

Gregory B. Johnson, Zdzislaw H. Lewantowicz

Abstract:	The Global Positioning System (GPS) aided inertial nav- igation systems (INS) that are implemented in fighter aircraft must be able to operate in a high dynamic and jammed signal environment. This paper investigates op- eration of a GPS aided INS during horizontal and verti- cal maneuvers of up to 9 g’s During these maneuvers, the GPS receiver carrier tracking loop is expected to loose lock and the code tracking loop is expected to re- ceive Doppler aiding from the INS velocity signal. These maneuvers are simulated using a nominal and decreased signal-to-noise ratio (SNR). The decreased SNR repre-sents jamming of the GPS receiver signal. The present implementation in the F-16 (and other aircraft) of the GPS aided INS (LN-39) is a suboptimal filter-driving- filter configuration. This use of two Kalman filters and a decreased code loop bandwidth for increased jamming resistance tends to destabilize the closed-loop operation of the GPS aided INS. The performance of three Kalman filter configurations is examined using time simulation analysis. The three configurations are an optimal full- ordered filter, single reduced-ordered filter, and the F- 16 filter-driving-filter configuration. All three configura- tions are evaluated in closed-loop and open-loop modes. Each configuration is simulated using nominal and de- creased SNRs. Results show that the GPS aided INS is stable for nominal operations. However, the closed-loop system becomes unstable in filter-driving-filter configu- ration with a low SNR.
Published in:	Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990) September 19 - 21, 1990 The Broadmoor Hotel Colorado Spring, CO
Pages:	461 - 470
Cite this article:	Johnson, Gregory B., Lewantowicz, Zdzislaw H., "Closed-Loop Operation of GPS Aided INS," Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990), Colorado Spring, CO, September 1990, pp. 461-470.
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