基于级联随机共振的直接序列扩频信号的捕获方法

Capture method of direct sequence spread spectrum signal based on cascade stochastic resonance

在直接序列扩频信号的捕获中,针对低信噪(SNR)比以及大频偏对信号捕获产生影响的问题,提出了一种基于级联随机共振的直接序列扩频信号的捕获方法。首先将输入信号通过部分匹配滤波器进行处理,当本地伪码和输入信号伪码相位对齐时,输出信号仅剩下了残余多普勒频偏;然后将该信号进行级联随机共振,从而提高信号的输入信噪比;最后通过快速傅里叶变换(FFT)谱分析,可以在频谱上得到清晰的谱峰,进而求出多普勒频偏值。通过理论分析和实验仿真可知,在输入信噪比为-26 dB的情况下,所提方法能够提高直接序列扩频信号的捕获灵敏度,并且通过两级级联随机共振系统后输出信噪比提高了15 dB左右;同时与传统捕获算法相比,该方法的正确检测概率提高了4 dB左右。所提方法不但能抑制噪声,而且能将部分噪声能量转换为信号能量,同时能够改善大多普勒频偏的影响,在捕获弱信号方面有着极大的优越性。

In order to solve the influence of low Signal-to-Noise Ratio （SNR） and large frequency offset on signal acquisition in the capture of direct sequence spread spectrum signal, a new capture method of direct sequence spread spectrum signal based on cascade stochastic resonance was proposed. Firstly, the input signal was filtered by a partial matched filter, when the local pseudo code and the pseudo code phase of the input signal were aligned, only the residual Doppler frequency offset remained in the output signal, and then the signal was processed by the cascaded stochastic resonance to increase the SNR of the input signal. Finally, Fast Fourier Transformation （FFT） spectrum analysis was used to obtain the spectral peak on the frequency spectrum and then calculate Doppler frequency deviation. Theoretical analysis and experimental simulation shows that：the proposed algorithm can improve the acquisition sensitivity of direct sequence spread signals when the input SNR is -26 dB, and the output SNR is improved by 15 dB after two-stage cascade stochastic resonance system; at the same time, the correct detection probability of this algorithm is improved by about 4 dB compared with the traditional capture algorithm. The proposed method not only can suppress noise, but also convert some noise energy into signal energy; meanwhile it can decrease the influence of large Doppler frequency offset. Therefore, it has great advantages in capturing weak signals.