For high sensitivity and operation efficiency in weak signal acquisition of Global Positioning System (CPS) software receiver, a differential coherent accumulated acquisition algorithm based on Fast Fourier Transform ( FFT) was proposed. The limitation of coherent integration time was overcome by block accumulation of demodulated GPS intermediate frequency data. Based on FFT frequency shift characteristics, a Doppler circular frequency search was used to achieve low computation instead of frequency compensation search. The loss in frequency was resolved by different down conversions. Compared to the original incoherent accumulation, Signal-to-Noise Ratio ( SNR) was improved by differential coherent accumulation of coherent results. The weak signal in a - 39 dB poor SNR environment was successfully acquired in experiments. High sensitivity and operation efficiency of the proposed algorithm were confirmed by the experimental results.%为了解决全球定位系统(GPS)软件接收机中弱信号捕获存在灵敏度和运算效率低的问题,提出了一种基于快速傅里叶变换(FFT)改进的差分相干累积算法.通过对去载波后的中频信号进行块累加处理,解决了相干积分时间的限制；根据FFT频移特性,采用多普勒圆周移位搜索替代频率补偿搜索,减少了FFT运算量；同时采用了不同的下变频,降低了频域分量间的损耗；对相干积分结果进行了差分相干累积,相对于传统的非相干累积,提高了信噪比.实验结果表明,该算法在- 39 dB的低信噪比环境下仍能捕获到所有微弱信号,具有较高的灵敏度和运算效率.
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