An Adaptive Approach to Compensate Crosscorelation Effects in Weak Signal Conditions for Satellite Positioning Systems

Catalin Lacatus, David Akopian and Mehdi Shadaram

Abstract:	During recent years location technologies have emerged as a research area with many possible applications. Many of these applications are using Global Positioning System (GPS) receivers. While GPS is designed for outdoor operation, recently many GPS receivers have been developed for indoor environments where the satellite signals are significantly attenuated. Still, these environments are very challenging for the receivers and their operation is not robust because of cross-correlation, colored noise, etc. This paper proposes an adaptive algorithm which may potentially improve the robustness of indoor operation. Our idea is based on the modification of pseudorandom codes in receivers to minimize cross correlation and other effects in weak or jammed signal conditions. The proposed method adaptively changes the codes to achieve an optimal synchronization. It is based on the convex optimization theory where the mean squared error (MSE) is regarded as a convex function in the dispreading code that is defined on a bounded convex set. The signal-to-interference-plus-noise-ratio (SINR) improvements of the optimal code in comparison with the conventional receivers are significant, e.g. between 3.75 dB and 22 dB for a bit error rate (BER) of 10-6 . Signals are typically attenuated for about 10-25dB in indoor environments causing strong interference phenomena. Thus, our approach helps to counter those along with the conventional integration techniques for signal enhancement. The proposed algorithm is analyzed and illustrated with numerical examples obtained from simulations.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	990 - 998
Cite this article:	Lacatus, Catalin, Akopian, David, Shadaram, Mehdi, "An Adaptive Approach to Compensate Crosscorelation Effects in Weak Signal Conditions for Satellite Positioning Systems," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 990-998.
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