Synchronizing a digital GPS receiver

We investigate the synchronization behavior of a digital Global Positioning System (GPS) receiver. We focus our attention on code and carrier synchronization. Due to the large Doppler shift, the inaccurate receiver clock and the noisy environment, a combined time/frequency search is used for acquisition and tracking. Code acquisition is performed by a serial search algorithm. In the frequency domain a broken expanding window search is used. To achieve coherent demodulation, the uncertainty interval for the carrier frequency is minimized in discrete steps. Finally the correct frequency is found by a simple transform domain processing scheme to permit a narrowband digital PLL to lock