In weak GNSS signal environments, due to navigation data bit, the dynamic of receiver and the quality of receiver' s oscillator, the traditional carrier loop cannot use long coherent integration time to enhance input SNR of the loop. A navigation data bits estimation method based on FFT is proposed, which just needs to calculate the FFT of one combination of data bits' signs. The FFT of the received signal under any other data bits combination can be obtained through a few additions. The proposed method reduces the calculation complexity of navigation data bits' signs estimation. Based on the estimation of the signs and bit edges of navigation data bits, the proposed method can adopt short coherent integration time samples over long time and FFT to discriminate doppler frequency error, which can overcome the SNR degradation introduced by receiver' s dynamic and doppler frequency estimation error over long coherent integration time and enhance the output SNR of the loop. Simulation results show that the proposed carrier tracking method can track carrier frequency in weak signal and low dynamic environments.%在弱GNSS信号环境中,基于传统环路的GNSS载波跟踪方法受导航电文、接收机动态和晶振稳定性的制约,难以使用较长相干积分时间提高环路输入信噪比.本文提出了一种基于FFT的电文估计方法,该方法只需计算一种电文组合下的相干积分值序列的FFT,其他电文组合下的FFT只需少量加法运算即可完成,降低了电文符号估计的计算量.通过对导航电文符号和边沿的估计,可以使用较长时间的相干积分值序列的FFT变换鉴别载波环跟踪误差,这可以克服长积分时间中接收机动态和多普勒频率估计误差造成的损耗,从而提高鉴频器的输出信噪比.仿真结果表明,本文提出的跟踪方法能够在低动态弱信号条件下跟踪载波频率.
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