Fine Frequency Resolving Acquisition Methods for GPS Receivers

David Akopian, Harri Valio and Seppo Turunen

Abstract:	The goal of the acquisition stage of a GPS receiver is to find satellites visible on the sky. Technically the particular satellite signal is searched in two-dimensional space correlating 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 defined by the coherent integration time during the correlation. This integration interval is limited due to 50 Hz navigation message and the sensitivity of the system is reducing beyond 20 msec integration. To achieve better than 50 Hz resolution one should try to compensate the data modulation or apply other approaches. The methods to resolve in fine frequency without navigation data demodulation are presented next.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2515 - 2523
Cite this article:	Akopian, David, Valio, Harri, Turunen, Seppo, "Fine Frequency Resolving Acquisition Methods for GPS Receivers," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2515-2523.
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