The BeiDou software receiver uses the fast Fourier transform (FFT) to perform the acquisition. The Doppler shift estimation accuracy should be less than 500 Hz to ensure satellite signals to enter a locked state in the tracking loop. Since the frequency step is usually 500 Hz or larger, the Doppler shift estimation accuracy cannot guarantee that satellite signals are brought into a stable tracking state. The straightforward solutions consist in increasing the sampling time and using zero-padding to improve the frequency resolution of the FFT. However, these solutions intensify the complexity and amount of computation. The contradiction between the acquisition accuracy and the computational load leads us to research for a more simple and effective algorithm, which achieves fine acquisition by a look-up table. After coarse acquisition using the parallel frequency acquisition (PFA) algorithm, the proposed algorithm optimizes the Doppler shift estimation through the look-up table method based on the FFT results to improve the acquisition accuracy of the Doppler shift with a minimal additional computing load. When the Doppler shift is within the queryable range of the table, the proposed algorithm can improve the Doppler shift estimation accuracy to 50 Hz for the BeiDou B1I signal.

中文翻译：

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基于查表的北斗软件接收机精细多普勒频移捕获算法

北斗软件接收器使用快速傅立叶变换 (FFT) 来执行采集。多普勒频移估计精度应小于500Hz，以保证卫星信号在跟踪环路中进入锁定状态。由于频率步长通常为500Hz或更大，多普勒频移估计精度不能保证卫星信号进入稳定的跟踪状态。直接的解决方案包括增加采样时间和使用零填充来提高 FFT 的频率分辨率。然而，这些解决方案增加了复杂性和计算量。采集精度和计算量之间的矛盾促使我们研究一种更简单有效的算法，通过查找表实现精细采集。在使用并行频率采集（PFA）算法进行粗采集后，该算法通过基于FFT结果的查表方法优化多普勒频移估计，以最小的额外计算负载提高多普勒频移的捕获精度。当多普勒频移在表的可查询范围内时，该算法可以将北斗B1I信号的多普勒频移估计精度提高到50 Hz。