| Time delay estimation is an important research content in the field of signal processing,and is widely used in wireless positioning,radar,sonar,geophysical exploration,biomedical engineering,and other fields.In practical application scenarios,signal propagation environments are complex and diverse,and the existence of multipath effects poses challenges to time delay estimation.The time delay estimation method under the influence of multipath effect is a difficult and hot research topic at home and abroad.In order to improve the accuracy of multipath time delay estimation,this paper combines the alpha stable distribution and subspace theory to study the multipath time delay estimation method in impulsive noise environments and the multipath time delay estimation method in small sample conditions,respectively.The specific research content is as follows:(1)To address the degradation of multipath time delay estimation algorithms based on second-order statistics in impulsive noise environments,a multipath time delay estimation algorithm based on sigmod transformation and correlation entropy is proposed.The multipath received signal is nonlinear preprocessed using the sigmod transformation,and then the maximum correlation entropy criterion in the correlation entropy theory is used to estimate the multipath delay parameters combined with the relaxation search idea.The simulation results show that the algorithm has a strong ability to resist impulse noise,and its dependence on prior knowledge of impulse noise is lower than that of FLOS method.(2)To solve the problem of accurately estimating the multipath time delay of LFM signals in impulsive noise environments,a P-NAT function with different nonlinear transformation characteristics from traditional NAT functions is designed,and a multipath time delay estimation method for LFM signals based on the P-NAT function is proposed.The transmitted signal and the noisy multipath received signal after P-NAT function transformation are respectively subjected to the optimal order fractional Fourier transform.According to the relationship between the peak position offset and the time delay in the FRFT domain,multipath time delay estimation for LFM signals is achieved.Simulation results show that the method is suitable for multipath time delay estimation of LFM signals in low generalized signal-to-noise ratio and strong impulsive noise environments.(3)Aiming at the poor performance of traditional subspace algorithms in multipath time delay estimation under small sample conditions,a multipath time delay estimation method based on improved MUSIC algorithm is proposed.This algorithm combines the technology of spatial smoothing,uses the conjugate information of measured data to construct a new covariance matrix,and uses the modified noise eigenvalues to construct weighted values to weight the traditional estimation spectrum,which achieved optimization of the MUSIC time delay estimation method.The simulation results show that the optimized method has higher time delay estimation accuracy under small samples and low signal-to-noise ratio conditions. |
