Acquisition of GPS Signals at Very Low Signal to Noise Ratio

Mangesh M. Chansarkar and Lionel Garin

Abstract:	With the FCC E911 mandate, a new class of GPS applications has emerged as Wireless Aided GPS. In this case a handset position has to be determined quickly even in reception environments where a stand-alone GPS receiver usually does not operate. In particular, indoors positioning capabilities is a requirement. These applications have revived the interest in performance of GPS systems in cases where the Signal to Noise Ratio (SNR) is very low [1]. GPS signals are significantly attenuated due to foliage and buildings. In general the GPS signals inside buildings are at least 20 dB below their nominal levels as specified in the GPS ICD 200. It is well known that increasing the integration time during acquisition of GPS signals improves the sensitivity of the GPS acquisition. However it is not practicable to use very long integration times without GPS aiding as this leads to very long Time-to-Acquisition and consequently very long time to First Fix (TTFF). Even with sensitivity aid available, there is a theoretical limit to the expected improvements. This paper first discusses the theoretical limitations on use of very long integration times and then discusses the practical limitations on using long integration times in terms of acquisition performance. The effects of coherent and non-coherent integration on acquisition sensitivity is discussed along with the effects of signal movement. Simulation results are presented for acquisition performance under various signal scenarios.
Published in:	Proceedings of the 2000 National Technical Meeting of The Institute of Navigation January 26 - 28, 2000 Pacific Hotel Disneyland Anaheim, CA
Pages:	731 - 737
Cite this article:	Chansarkar, Mangesh M., Garin, Lionel, "Acquisition of GPS Signals at Very Low Signal to Noise Ratio," Proceedings of the 2000 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2000, pp. 731-737.
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