Study On Multipath Time Delay Estimation Algorithms Under Alpha-stable Noises

Time delay is one of the basic parameters representing signals. The research on time delay estimation and its related parameters is always an active subject in signal processing field. It has theoretical and practical significance. On the one hand, people use theories and techniques of digital signal processing, signal detecting and estimation, time series analysis and modeling and adaptive signal processing etc in the process of studying time delay estimation. This provides new power to boost the development of these theories and techniques. On the other hand, time delay estimation is quickly applied in military, industrial fields, underwater acoustics, seismology, biological medicine and other fields of study.Multipath propagation is one of the problems encountered often in radar, sonar and seismic domains. Under multipath environment, the main task is how to decompose superimposed signals in order to estimate time delays in multi-arrivals.Gaussian model is in dominant position of traditional signal processing field. This assumption is reasonable under many circumstances. It's easy to carry out theoretical analysis in designing signal processing methods using the Gaussian model. However, in fact there are a lot of non-Gaussian signals and noises with notable pulse characteristic, like underwater acoustic signals, low-frequency atmospheric noises and many other noises produced by human. If we still use Gaussian model to descript these processes, it will result in noticeable degradation of the algorithms, because the model doesn't match well with real signals or noises. Alpha-stable distribution is a very useful theoretical tool for this kind of process. So people usually use it to depict stochastic signals with a remarkable impulsive characteristic. Because alpha-stable distribution is generalized Gaussian distribution, which is to say Gaussian distribution is a special case of alpha-stable distribution. So alpha-stable model can be used in more widely range.But under lower order alpha-stable noises, multipath time delay estimation algorithms based on the second-order statistics cannot work properly, because the second-order statistics become unbounded. In this thesis, drawing on existing algorithms, three multipath time delay estimation algorithms based on fractional lower order moment (FLOM) theory under alpha-stable distribution model are developed. They are P-EM algorithm, RHMTDE algorithm and FLOCCS-ESPRIT algorithm. It shows that these new algorithms are robust for...