The frequency pull-in process of traditional GPS receiver is time-consuming and its success rate is low under weak GPS signal environments. In order to solve this problem, FFT-based fine frequency estimation methods are presented. To overcome data bit phase transition, new input variables of FFT are constructed by using the squaring or differential algorithm. The experimental results show that the frequency detection probability is above 95% using differential algorithm when C/N0=21 dBHz if prior information of the navigation data is unknown. The frequency detection probability is above 95% using squaring algorithm when C/N0=19 dBHz if prior information of the navigation data is known.
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