水下回波处理中分数阶傅里叶变换的带通采样实现方法

An implementation approach of fractional Fourier transform with bandpass sampling in the underwater echoes processing

主动声呐系统常采用线性调频信号探测水下目标。利用分数阶傅里叶变换处理线性调频回波时,可在低信噪比和强混响背景下获得目标参数的有效估计。主动声呐系统常通过增大发射信号的时间带宽积来提升系统的距离分辨力和速度分辨力,但却带来了计算复杂度的显著增加,尤其是奈奎斯特采样下基于分数阶傅里叶变换的回波处理方法,导致数据处理时间难以满足功耗和体积受限的无人水下航行器平台的实时性要求。针对此问题,该文提出分数阶傅里叶变换的带通采样实现方法,通过对线性调频信号时频特性直线在分数阶域的投影进行修正,使利用分数阶傅里叶变换方法处理带通采样的回波数据时,可获得正确的目标参数估计。计算机仿真数据和无人水下航行器湖试数据处理结果验证了分数阶傅里叶变换的带通采样实现方法的正确性,数据处理时间能够满足无人水下航行器平台处理的实时性要求。

Linear frequency modulated(LFM)signal is usually been used for underwater target detection in active sonar system.Fractional Fourier transform(FrFT)method has unique advantage when processing the LFM echos to obtain effective estimations of target parameters in a low SNR or high reverberation environments.A common strategy to improve the range and velocity resolution of active sonar system is to increase time bandwidth product of the transmitted signal.Then the computation complexity of method increases dramatically,especially the FrFT-based data processing method with Nyquist sampling.As a result,the method can hardly meet the real-time requirements of unmanned underwater vehicle(UUV)with constraints on the volume and power consumption.To address the problem,we proposed an approach to implement the FrFT method with band-pass sampling.By modifying the projection of time-frequency characteristic line of LFM signal on fractional domain,correct estimations of target parameters can be obtain by using FrFT method to process echo data with band-pass sampling.The processing results for simulation data and experimental data of UUV demonstrate the validity of the method,and the corresponding data processing time can meet the real-time requirements of UUV.