Abstract: Aiming at the problem of spread spectrum signal acquisition with long period pseudo-noise（PN）code under the condition of high Doppler frequency and low signal-to-noise ratio，an improved algorithm based on circular correlation for fast acquisition of spread spectrum signals was proposed.Since the algorithm used fast Fourier transform（FFT）to estimate the frequency offset of the results obtained by circular correlation and expanded the frequency sweep step of the traditional circular correlation method，the frequency sweep step was no longer limited by the tracking loop bandwidth.The theoretical analysis and simulation results indicate that the algorithm can correctly estimate the PN code phase and Doppler frequency under the signal-to-noise ratio of -34dB when the Doppler frequency is 500kHz.With the same sensitivity，the mean acquisition time of the proposed algorithm is shortened by about 47% in comparison to the traditional circular correlation algorithm，and about 88% in comparison to the FFT-based parallel frequency search algorithm.In addition，the FFT points used for frequency estimation only account for 1% of the circular correlation points.The algorithm is proved to be a straightforward logic-controlling solution，which can significantly increase the real-time performance of the satellite communication system with a high Doppler frequency，low signal-to-noise ratio，and long period PN code.

Key words: satellite communication system, direct sequence spread spectrum, signal acquisition, circular correlation, fast Fourier transform