Research On Fast Acquisition Method Of High Dynamic DSSS Signals

Fast acquisition process of spread spectrum signals is crucial in direct sequence spread spectrum (DSSS) communications. The acquisition process has to search both carrier frequency Doppler shift and PN code phase, so the whole acquisition process is a two-dimensional search process. The high dynamic spread spectrum signals include high Doppler shifts which may exceed 100 kHz, which largely increases the difficulties of acquisition process. This dissertation utilizes an FFT-based acquisition method to search the correct code phase and estimate the carrier Doppler shifts simultaneously. By using this method, the former two-dimensional acquisition process becomes a one-dimensional process, which can significantly accelerate the acquisition process and reduce the acquisition time.The structure and the performance of the FFT-based acquisition method is analyzed in this dissertation. Several techniques for improving the performance of FFT-based method are also discussed, including the Welch spectral estimation method and adaptive threshold adjusting technique.The performance of the FFT-based method is simulated in this dissertation, and the simulation results show that the FFT-based method can efficiently perform the acquisition process of the high dynamic spread spectrum signals.