基于线性调频信号二次相位变换的主动声呐目标速度估计

Velocity estimation of active sonar based on quadratic phase transform of linear frequency modulation signal

分数阶傅里叶变换常用于主动声呐线性调频信号的分析,通过搜索变换参数可以估计目标的相对速度。但是由于其参数搜索计算量偏大,在自主式水下航行器等计算力有限的小平台难以实时处理。针对该问题提出了一种基于二次相位变换的线性调频信号速度估计方法,根据多普勒频移后线性调频信号的二次相位变换的解析解,分析了二次相位变换后变换域频谱展宽与多普勒频移之间的对应关系。二次相位变换是分数阶傅里叶变换的简化,使用二次相位变换变换后幅度谱的展宽来估计相对速度,有效降低了对变换参数二维扫描的计算量。数值仿真结果显示,该方法可有效估计目标相对速度,参数搜索计算量降低了一个维度,估计精度可以达到1 m·s^(-1)。

Fractional Fourier transform(FrFT)is often used to analyze the linear frequency modulation(LFM)signal in active sonar.The relative velocity of the target can be estimated by searching the transform parameters.However,the parameter search process in this approach costs large amount of computations,and it is a heavy burden for small platforms with limited computation resource such as autonomous underwater vehicles.To reduce the computational complexity of FrFT,a method based on the quadratic phase transformation(QPT)is proposed to estimate the relative velocity.The close-form solution for the QPT of LFM signal with Doppler frequency shift is derived,which reveals the relationship between the spectrum broadening in the transformation domain and the Doppler frequency shift.In this method,the relative velocity is estimated by amplitude spectrum broadening after QPT,so transformation parameter scanning is avoided.The numerical results show that the proposed method decreases computational cost and provides precise velocity estimation of 1 m·s^(-1).