Fine Frequency Estimation in Weak Signals for GPS Receivers

P.K. Sagiraju, D. Akopian, and H. Valio

Abstract:	The goal of the acquisition stage of a GPS receiver is to find satellites visible in the sky. Technically the particular satellite signal is searched in two-dimensional space by correlating the input signals and locally generated replica with different (code phase, Doppler frequency) assumptions. As long as the signal is found an additional frequency refining could be necessary for tracking loops. From computational point of view during initial acquisition stage the right strategy is to find the signal with as coarse frequency grid as possible in order to accelerate the search. Then having the replica code aligned with the incoming signal in code dimension one can refine the frequency with only one-dimensional search in frequency. The frequency resolution is constrained by the coherent integration time during the correlation. This integration interval is limited due to 50 Hz navigation data bit. To achieve better resolution one should try to compensate the data modulation or apply other approaches. The focus of this paper is one such method for indoor environments to resolve in fine frequency without data bit demodulation.
Published in:	Proceedings of the 2006 National Technical Meeting of The Institute of Navigation January 18 - 20, 2006 Hyatt Regency Hotel Monterey, CA
Pages:	908 - 913
Cite this article:	Sagiraju, P.K., Akopian, D., Valio, H., "Fine Frequency Estimation in Weak Signals for GPS Receivers," Proceedings of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, January 2006, pp. 908-913.
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