A Novel Algorithm for Ultra High-Sensitivity GPS Tracking

Why the traditional carrier loop is unsuitable for weak GPS signal tracking is discussed and a novel tracking scheme based on fast fourier fransform (FFT) technique is proposed. The relations between the point numbers of FFT and the rate-of-change of Doppler frequency are analyzed. The average rate-of-change of Doppler frequency is 0.54 Hz/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 errors of the carrier loop in this paper. The local carrier frequency should be adjusted only if the peak value of FFT is more than the threshold. Experimental results of the static GPS receiver show that our proposed method can track GPS signals using 128-point FFT when the power level is 163 dBm. Moreover,the sensitivity of the proposed scheme can be further improved if the rate-of-change of Doppler is compensated.