基于改进补零/差分的北斗弱信号捕获算法

北斗信号二次编码调制了速率为1kbps的NH码，频繁的比特跳变导致传统捕获算法的效果受到抑制，并且限制了积分时间的增长。为了实现北斗弱信号的捕获，提出了一种适合北斗弱信号的捕获算法，将补零算法和差分相干积分算法相结合并进行了优化设计。对补零算法和差分相干积分算法进行了改进，将差分延迟时间调整为20ms，有效消除了NH码的影响，并增加了积分时间，提高了信噪比。采用Monte Carlo仿真测试了在载噪比为20dBHz~38dBHz的条件下，此算法与传统算法的检测性能。结果表明，相比传统算法,此算法的捕获灵敏度提高了约10dB。此算法能够有效消除北斗NH码相位变化对信号捕获的影响，并提高信噪比，适用于弱信号条件下的北斗信号捕获。

Acquisition of Beidou Weak Signals Based on Modified Zero-padding and Differential Combination

A NH code with the velocity of 1kbps is modulated by the secondary code of Beidou navigation message. The conventional acquisition method is effected by the frequent bit jumps and the integration time is also limited. In order to realize the acquisition of Beidou weak signals, an acquisition algorithm based on the modified zero-padding and differential combination is proposed. Firstly, the zero-padding method and the differentially coherent integral method are modified and the differential delay time is set to 20ms to remove the influence of the NH code.The integration time is extended to increase the signal-to-noise ratio. Finally, the Monte Carlo simulation is used to analysis the detection performance of this algorithm comparing with the traditional algorithm under the carrier-to-noise ratio of 20dBHz~38dBHz. The results show that the acquisition sensitivity of this proposed algorithm is 10dB higher than the traditional method. This algorithm can effectively remove the effect of phase change of Beidou NH code toward signal acuisition and increase the signal-to-noise ratio, and is suitable for acquisition of Beidou weak signals.