Novel fine acquisition method for weak GPS signal

To improve the acquisition accuracy and sensitivity of GPS receiver in low signal-to-noise ratio (SNR) environment, a new kind of acquisition method for weak signal is proposed. This method makes use of differential coherent integration to reduce power loss, and breaks the restriction of searching step size on the estimation accuracy of carrier Doppler shift by utilizing the phase information of integration results. Moreover, based on the relationship between carrier and code Doppler shifts, this method can directly amends the local code phase. As a result, it ensures different correlation peaks' overlap with each other and can obtain accurate code phase of the received signal. Simulation results show that the estimation errors of carrier Doppler shift and code phase can be kept to less than 20 Hz and one sampling point respectively, and, in a given case, the acquisition sensitivity is improved by about 3.2 dB.