Sub-Optimality of the Prefilter in Deeply Coupled Integration of GPS and INS

Siva Sivananthan and Jay Weitzen

Peer Reviewed

Abstract:	A robust integrated receiver that integrates an Inertial Navigation System and a Global Positioning System and uses a Kalman filter to close the phase lock loops has been proposed recently in the form of an Ultra Tightly Coupled (UTC) receiver. One of the complexities of this receiver is establishing the mathematical relationship between the INS states and the GPS measurements. Many forms of the ultra tight coupling method have been proposed by linearizing these relationships to realize these highly non-linear relationships in the integrated system. Here, we analyze the optimality of such linearization and quantize how much accuracy is lost in the prefilter of a UTC receiver. The prefilter that models the relationship between the GPS signal quantities and receiver measurements is presented. A Posterior Cramer Rao Bound (PCRB) is derived. Simulation results show that the variance of the estimates from the prefilter is higher than the PCRB by as much as an order of magnitude.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 57, Number 3
Pages:	175 - 184
Cite this article:	Sivananthan, Siva, Weitzen, Jay, "Sub-Optimality of the Prefilter in Deeply Coupled Integration of GPS and INS", NAVIGATION: Journal of The Institute of Navigation, Vol. 57, No. 3, Fall 2010, pp. 175-184.
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