基于Fr-AF与改进RIDT的QFM-PRBC伪码估计

针对二次调频-伪码调相(quadratic frequency modulated-pseudo random binary phase code,QFM-PRBC)复合信号伪码估计的难题,提出一种基于分数阶模糊函数(fractional ambiguity function,Fr-AF)和改进的三角窗抗干扰核函数(reduced interference distribution kernel based on the triangular window,RIDT)变换的伪码估计算法.应用平方法解决伪码与信息码相位突变问题,并用累加平均减小平方法带来的噪声影响,利用分数阶模糊函数估计平方累加后信号的最高项和次高项系数,重构信号对接收端信号降阶;采用奇异值分解(singular value decomposition,SVD)对基于三角窗减少干扰的核函数变换加以改进以提取降阶后信号的伪码序列.仿真实验表明了算法的有效性,当累加次数为20且信噪比在-4 dB以上时,伪码可以正确估计.

Estimation for PN code of reconnaissance signal combined with QFM-PRBC based on Fr-AF and modified RIDT

To estimate the pseudo noise (PN) code of reconnaissance signal combined by the quadratic frequency modulated (QFM) and pseudo-random binary phase code (PRBC), the paper presents an algorithm based on the fractional ambiguity function and a modified time-frequency analysis method using a reduced interference distribution (RID) kernel based on the triangular window. Firstly, the square method is computed to eliminate the phase mutation, and the accumulated method is used to reduce the bad effect of the square method. Secondly, fractional ambiguity is adopted to estimate second and third coefficients. Then the original signal is multiplied by the conjugated signal which is reconstructed by the estimated coefficients to get a new compound signal. Thirdly, the new compound signal consists of sine carrier and the PRBC signal,and the original PN code can be restored by the way of RIDT which is modified by the singular value decomposition (SVD). The simulation results show that the algorithm is feasible. The correct PN code is obtained when signal-to-noise ratio is more than or equal to - 4 dB,which shows good performance.