Adaptive tightly-coupled, a low cost alternative anti-jam INS/GPS integration technique

P.D. Groves, D.C. Long

Abstract:	In an INS/GPS integrated navigation system, the GPS receiver may exploit the inertial aiding by operating with narrow tracking loop bandwidths in order to increase interference resistance. However, wider bandwidth tracking loops are more responsive to dynamics and provide more frequent statistically independent GPS measurements. Where a low grade INS is used, such as in a guided weapon, the wider bandwidths are needed to calibrate the INS errors effectively. This is important for GPS tracking loop aiding and sole-means inertial navigation during jamming. To obtain both effective INS calibration and jamming resistance, it is desirable to adapt the GPS tracking loop bandwidths according to the measured signal to noise ratio to attain high dynamics or high noise resistance tuning as appropriate. However, if the INS/GPS integration algorithm is tuned to the GPS receiver’s wide bandwidth setting to optimise INS calibration, the Kalman filter can become unstable when the bandwidths are narrowed, with the potential for positive feedback through the tracking loop aiding to destabilise the whole navigation system. To address this, an adaptive tightly-coupled (ATC) INS/GPS integration technique has been developed that adapts with the GPS receiver to varying jamming levels. This enables robust GPS calibration of the INS to be maintained under moderate jamming, whilst maintaining the established tightly-coupled integration architecture. The ATC technique has been assessed over a series of simulations, examining different jamming scenarios, different bandwidth adaptation algorithms, different grades of INS and the effect of transfer alignment. The results have shown that the ATC technique provides a significant anti-jam margin over an INS/GPS with fixed tracking bandwidths selected for INS calibration. Compared to the deep (or ultra-tightly-coupled) integration techniques currently under development, ATC is a low cost anti-jam integration technique as it does not require a complete re-design of the navigation architecture and does not impose a significantly higher processing load.
Published in:	Proceedings of the 2003 National Technical Meeting of The Institute of Navigation January 22 - 24, 2003 Disneyland Paradise Pier Hotel Anaheim, CA
Pages:	429 - 440
Cite this article:	Groves, P.D., Long, D.C., "Adaptive tightly-coupled, a low cost alternative anti-jam INS/GPS integration technique," Proceedings of the 2003 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2003, pp. 429-440.
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