基于ST-FRFT的非合作水声脉冲信号检测方法

摘要

A detection method for underwater acoustic pulse under non-cooperative condition based on short time-fractional Fourier transform (ST-FRFT) is proposed in this paper. There are two kinds of underwater acoustic pulse signals, one is the Linear frequency modulation (LFM) signal and the other is the continuous wave (CW) signal. The matched filtering method cannot be used directly under non-cooperative situation due to lack of signal parameters information. The Fourier transform (FT) has good gain for the CW signal detection, but the gain decreases for the LFM signal detection, especially for the LFM signal with large modulation. The FR-FT has not only good energy-concentration for the LFM signal but also contains the FT for the CW signal, so that it can be used to detect the CW and the LFM signal. In order to obtain time domain and frequency domain features of the received signal simultaneously, the detector was designed by the short-time fractional Fourier transform (ST-FRFT) in this paper, that it can be used to detect intercepted the LFM and CW pulse signal without any information about the parameters of signals. The detection performance for the CW and the LFM signal was analyzed by using the ST-FRFT and the STFT respectively, the results show that the processing gain of the LFM based on the FT was affected by modulation rate and non-linear change with window length, so it is difficult to estimate optimal window length under non-cooperative situation. The processing gain of the matched filter can be obtained approximately by the FRFT, therefore, the detection performance of the LFM signal was improved. The simulation results and experimental results in lake demonstrate the correctness of the theoretical analysis and the effectiveness of the proposed method.%为解决非合作条件下水声脉冲信号检测与参数估计的难题,本文提出了一种基于短时分数阶傅里叶变换(ST-FRFT)的检测方法.线性调频(LFM)和单频(CW)脉冲信号是最常见的两种水下声脉冲信号,在非合作条件下,信号参数信息的缺失使得不能直接采用匹配滤波检测方法,傅里叶变换(FT)对CW信号具有良好的检测增益,但对LFM信号检测增益下降,尤其是具有较大调制率的LFM信号.分数阶傅里叶变换(FRFT)对LFM信号具有良好的能量聚集性特点,有利于LFM信号的检测,并且包含了Fourier变换,同样适用于CW信号的检测.为了同时获得接收信号的时域和频域特征,设计了基于短时分数阶傅里叶变换(ST-FRFT)的检测器,可以实现信号参数未知的情况下对LFM和CW信号的截获检测.理论分析了ST-FRFT与STFT方法针对LFM信号和CW信号的检测性能,基于FT的方法对LFM信号的处理增益受到调制率的影响,相对于CW信号增益下降,并且随窗长呈非线性变化,非合作条件下难以获得最佳窗长,而FRFT对LFM信号可以获得近似匹配滤波的处理增益,提高了LFM信号的检测性能.仿真结果和湖试数据处理结果验证了理论分析的正确性与该方法的有效性.