FRFT在水声信道时延-频移联合估计中的应用

Application of FRFT in time-delay and frequency-shift joint estimation for underwater acoustic channels

由于水声信道的复杂性和多变性,信号在水声信道传播中将伴随着多径时延与多普勒频移,二者是水声信道估计中两个重要的参数。基于分数阶傅里叶变换(fractional Fourier transform,FRFT)的时延和频移特性,提出一种采用多分量线性调频(linear frequency modulated,LFM)信号的水声信道估计方法,通过分析分数阶傅里叶域上峰值的偏移,联立不同阶次的时延和频移方程,可得到水声信道的时延和频移值。理论推导及仿真结果表明,该方法计算量小,且随着LFM信号分量数和调频率差值的增大,能在一定程度上减小估计的时延误差和频移误差。水池实验中选用具有相反调频率的双LFM信号作为估计信号,估计出多径时延与运动目标的多普勒频移,并给出了水下目标的运动速度。实验结果表明,FRFT估计法简单有效,在水声信道多径时延与多普勒频移估计上具有较好的实际应用价值。

Because of the complexity and variability of the underwater acoustic（UWA）channel,signal transmitting in the UWA channel is accompanied with multi-path time-delay and Doppler frequency-shift,which are important parameters in UWA channel estimation.Based on the time-delay and frequency-shift characteristics of fractional Fourier transform（FRFT）,a novel method of UWA channel estimation is proposed,using multi-component linear frequency modulated（LFM）signals.By analyzing the shift of signal peak in the fractional Fourier domain（FRFD）and solving the time-delay and frequency-shift errors equations of different orders,the time-delay and frequency-shift values can be figured out.The theoretical derivation and simulation results show that the time-delay and frequency-shift decrease to some extent with the increase of the number of LFM signals and the difference of frequency modulation rates using the proposed method,with low computational complexity.A pair of LFM signals with contrary frequency modulation rates is chosen to estimate the multi-path delay and Doppler frequency-shift in the pool experiment,and the velocities of underwater moving targets are presented.The experiment results demonstrate the proposed method is simple,effective and practical in the multi-path time delay and Doppler frequency-shift estimation.