Differential Signal Processing Schemes for Enhanced GPS Acquisition

Surendran K. Shanmugam, Robert Watson, John Nielsen and Gérard Lachapelle

Abstract:	Recent attempts to enhance GPS performance in weak signal environments have focused on high-sensitivity GPS (HSGPS) and Assisted GPS (AGPS). High sensitivity can be realized in a stand-alone mode by using long non coherent integration times with relatively short coherent accumulations of between 1 and 20 ms. AGPS further enables weak-signal acquisition by narrowing code and frequency search spaces to reduce time to first fix (TTFF), and by potentially providing navigation data bits to allow long coherent integration without suffering the effects of 180° phase transitions. Major problems remaining with HSGPS and AGPS techniques include the additional system complexity required to provide assistance data, the limiting effect of local oscillator instability, and the major losses incurred by squaring weak signals for non-coherent integration techniques. A number of differential signal processing schemes have been proposed to address some of these issues. These schemes use the known properties of CDMA spreading codes to largely eliminate some of these issues, offering the potential for enhanced sensitivity, TTFF, or both, in systems with lower complexity than AGPS requires. This paper examines a set of differential processing schemes designed for the GPS L1 C/A signal both theoretically and with live GPS data. The results show benefits and limitations to all three techniques as compared with standard processing techniques. Suitable receiver applications for the various techniques are considered.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	212 - 222
Cite this article:	Shanmugam, Surendran K., Watson, Robert, Nielsen, John, Lachapelle, Gérard, "Differential Signal Processing Schemes for Enhanced GPS Acquisition," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 212-222.
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