A high-accuracy frequency estimation approach based on segmental-FFT for code fast acquisition

In this paper, to solve the problem of the Doppler estimation limited by FFT in the traditional code acquisition scheme based on FFT, a method of Doppler estimation for code acquisition based on segmental-FFT phase difference is proposed. First, the despreaded base band data with Doppler frequency is divided into two segments and the FFT is applied on them individually. Then, with the help of the phase difference of the two FFT spectrum at their maximum amplitude position, the Doppler frequency is estimated. At last, a coherent accumulation method is designed according to the phase difference. By theoretical analysis and simulation, the RMS errors of this frequency estimation method is close to CR bound, and the new coherent accumulation gain is higher than non-coherent accumulation gain but lower than the conventional coherent accumulation gain, meanwhile the calculating amount is less than the conventional coherent accumulation.