基于FrFT的伪码-线性调频信号参数估计算法

伪码-线性调频(PRBC-LFM)信号是近些年来应用于低截获概率(LPI)雷达的一种常用复合调制信号。针对PRBC-LFM信号的特点提出了一种基于分数阶Fourier变换(FrFT)的参数估计算法，算法首先通过二维分数阶Fourier域峰值搜索找到最佳旋转角，估计调频斜率；然后对信号做相应阶数的FrFT，利用FrFT峰值点之间距离与调频信号参数的相互关系估计信号的调频带宽、起始频率、码元时宽、载波频率等参数；最后根据估计出的调频参数重构线性调频信号，与原信号每个码元共轭相乘去载波，通过对基带信号幅度符号的辨别识别出二相编码信号的编码规律。仿真实验表明，本文方法能在较低信噪比下实现PRBC-LFM信号参数有效估计。 

FrFT-based Parameter Estimation for PRBC-LFM Signals

PRBC-LFM signal is a combined modulation signal, which is widely used to design low probability intercept radar waveform. For the characteristic of the PRBC-LFM signal, a parameter estimation algorithm based on Fractional Fourier Transform is proposed. Firstly, search peak in two-dimensional time-frequency plane in fractional domain to get optimal rotating angular, estimating the chirp rate. Then, the FrFT with actually order is presented. The parameters, including bandwidth, initial frequency, code time width, carrier wave frequency of the signal, is estimated through the relation between the peaks’ distance and the parameters of the frequency modulation signal. Finally, the linear frequency modulation signal can be reconstructed and multiplied with the conjugated signal in every code to remove the carrier wave. The coding rule of the biphase coded signal can be identified through division the sign of the signal’s amplitude. Simulation results show that the algorithm in this paper can estimate the parameters of the PRBC-LFM signal effectively at low SNR.