Compensation of Doppler Effect in Direct Acquisition of Global Positioning System using Segmented Zero Padding

Because of the very high chip rate of global positioning system (GPS), P-code acquisition at GPS receiver will be challenging. A variety of methods for increasing the probability of detection and reducing the average time of acquisition have been provided, among which the method of Zero Padding (ZP) is the most essential and the most widely used. The method using the Fast Fourier Transform (FFT), searches phase codes of the uncertainty region in a parallel method to find the desired code for correct acquisition. ZP method is sensitive to Doppler frequency so that the increase in Doppler frequency drastically reduces the probability of detection and consequently the average time of acquisition increases. The presented method in this paper, that called Segmented Zero Padding (SZP), reduces the Doppler effects on probability of detection at the acquisition of GPS receiver. Also, it will be shown that using the proposed algorithm proper mean acquisition time at high Doppler frequencies is achievable. Based on the comparisons made in this paper, we prove that the proposed algorithm in comparison to ZP algorithm, maintains the capability of parallel search and finally has a lower average acquisition time.