A Novel Algorithm Based on FFT for Ultra high-sensitivity GPS Tracking

X. Ba, H. Liu, R. Zheng, J. Chen

Abstract:	Recently, weak signal tracking has received a lot of interest in the research of high-sensitivity GPS receiver techniques. Traditionally, a GPS receiver uses the digital Costas loop as the carrier tracking loop. In this paper, the reason why the traditional carrier loop is unsuitable for weak GPS signal tracking is detailedly discussed and a novel tracking scheme based on Fast Fourier Transform (FFT) technique is proposed. The relations between the point number of FFT and the rate-of-change of Doppler frequency are analyzed. The average rate-of-change of Doppler frequency is 0.54Hz/s for static receiver and 128- point FFT can offer the maximum signal-to-noise rate (SNR) gain under this condition. A threshold based on Neyman-Pearson (NP) rules is presented in order to avoid the error of the carrier loop in the paper. The local carrier frequency should be adjusted only if the peak value of FFT is above the threshold. Experiment results of the static GPS receiver show that our proposed scheme can track GPS signals using 128-point FFT when the power level is -163dBm. Moreover, the sensitivity of the proposed scheme can be further improved if the rate-ofchange of Doppler is compensated.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	1700 - 1706
Cite this article:	Ba, X., Liu, H., Zheng, R., Chen, J., "A Novel Algorithm Based on FFT for Ultra high-sensitivity GPS Tracking," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 1700-1706.
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