基于PMF-FFT的北斗B1I弱信号捕获算法研究

Research on BeiDou B1I Weak Signal Acquisition Algorithm Based on PMF-FFT

北斗B1频点信号中,由于NH码调制的影响,使得相干积分时间限制在1 ms,因此,在弱信号条件下,使用传统的捕获方法将无法捕获到卫星信号。针对B1I信号特点,提出了弱信号的捕获算法,该算法以PMF-FFT为单元,采用改进的相干积分的算法并结合差分相干积分算法捕获北斗信号,改进的相干积分算法可以克服NH码调制的影响,而差分相干积分相对于非相干积分算法可以降低平方损耗。仿真实验结果表明,当取改进相干积分次数为10,差分相干积分次数为3时,该算法能够成功捕获信噪比为一37 dB左右的微弱信号。

In the BeiDou navigation satellite system, the signal is modulated with NH code, and the coherent integration time is limited within 1 ms. So, it is difficult to acquire weak signals. An acquisition algorithm of weak signals is proposed for the BeiDou satellite navigation signals. The acquisition algorithm is based on the PMFFFT, and the signals are acquired with the improved coherent integration method and the differential coherent integration method. The improved coherent integration method can overcome the impact of NH code, and the differential coherent integration reduces the impact of square loss. The simulation results show that the acquisition algorithm can acquire the weak signals of SNR - 37 dB with ten times of the improred coherent integration and three times of differential coherent integration.