Acquisition of weak GPS signals requires long Predetection, Integration Time (PIT). The double-block zero-padding (DBZP) algorithm can use long PIT without any assisting information to acquire weak GPS signals. Modified double-block zero-padding (MDBZP) algorithm accounts for the Doppler effect on the code duration. It also develops the Doppler frequency bin elimination method during the noncoherent integration steps. The fast modified double-block zero-padding (FMDBZP) algorithm based on MDBZP algorithm eliminates the redundant FFT computations by considering possible data bit combinations and bit edge positions. Although the computation burden of FMDBZP is lower than that of MDBZP, it may still be very heavy. This paper aims to reduce the computation complexity and save memory space further. Three methods are introduced to improve the FMDBZP algorithm. One consists of unlikely data bit combination path elimination during coherent integration steps. The second one perform unlikely code phase elimination during noncoherent integration steps. The third one perform unlikely bit edge elimination also during noncoherent integration steps. The good performance of the proposed improved FMDBZP algorithm is illustrated using both simulation and real data.
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