A Practical Oblique Projection Methods for GPS Cross-Correlation Interference Mitigation

Kwame N. Edjah, H. Howard Fan

Peer Reviewed

Abstract:	Current state of the art GPS receivers employ various techniques for acquisition of weak GPS signals at a negative SNR level. In reality, receivers located in places like urban canyons or under forest canopies receive weak GPS satellite signals that may co-exist with other strong GPS satellite signals. The strong GPS satellite signals may cause interference to weak GPS satellite signals. The 1023 chip Gold code sequences of the GPS C/A spreading code limit the dynamic range of a typical GPS receiver to less than 24dB for successful acquisition of a weak GPS signal in presence of other strong GPS signals. When this condition is not satisfied, the Cross Correlation Interference (CCI) experienced during acquisition of a weak signal due to high cross correlations at the correlator output can cause difficulties in false acquisition or complete loss of the weak signal, and subsequently tracking failures. Successive Interference cancellation, Parallel Interference Cancellation and the Delayed Parallel Interference Cancellation methods have been proposed for CCI mitigation in GPS. But the difficulty in applying these methods is the need for continuous and accurate tracking of the amplitudes of the strong interfering satellite signals for effective cancellation. The Subtractive Orthogonal Projection method eliminated such a need. But it may suffer from partial cancellation of the desired weak signal. In addition, it is quite sensitive to Doppler and code phase estimation errors. In this paper we present a new method using an oblique projection operator for very effective removal of all strong GPS satellite signals relative to a weak GPS satellite signal being acquired. The undesirable partial cancellation of the weak signal by the subtractive orthogonal projection method is much reduced. The resulting signal from this oblique projection method is void of any strong GPS signal interference that produces large CCI, making the acquisition process for the weak satellite signal much more reliable. In addition, the proposed method is more robust against code phase and Doppler estimation errors. All these advantages are shown in both theoretical derivation and in simulations, and are compared favorably with the subtractive orthogonal projection method.
Published in:	Proceedings of the 2015 International Technical Meeting of The Institute of Navigation January 26 - 28, 2015 Laguna Cliffs Marriott Dana Point, California
Pages:	493 - 503
Cite this article:	Edjah, Kwame N., Fan, H. Howard, "A Practical Oblique Projection Methods for GPS Cross-Correlation Interference Mitigation," Proceedings of the 2015 International Technical Meeting of The Institute of Navigation, Dana Point, California, January 2015, pp. 493-503.
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