Studies On The Passive Multi-target Resolving And DOA Estimation Techniques

The studies of passive multi-target resolving and DOA estimation techniques are very important in sonar,radar,and ocean exploration.This thesis discusses the theory and method of high resolution DOA estimation,and makes intensive research on the key technique of multi-target resolving.The main results are summarized as follows:1.The mathematical models of DOA estimation are constructed,and traditional high resolution narrowband algorithms including decorrelation methods and fast subspace approaches are explicit analyzed,and the results of simulation demonstrate the performance of these methods.To solve the heavy computational load of KR-MUSIC,new method which has lower computational burden is proposed,and it does not need the number of sources.Using the piecewise stationary feature and combining with Khatri-Rao product,new method can virtually augment array aperture and can estimate more signals DOA with less array elements.In new method,the effect of the noise is reduced by the orthogonal complement operator firstly,and then,by using the cyclic shift matrix,the dimension of array steering vector is reduced,finally,combining the idea of whole wighted MUSIC algorithm,it obtains signals DOA fastly without needing the number of sources.Simulation experiments show that the method is effective and it has higher precision.2.Incoherent signal subspace method(ISSM)and coherent signal subspace method(CSSM)are discussed.By deeply analyzing the principle the essence of focusing algorithm,two methods such as RSS and TCT are studied,and simulations results confirm the effectiveness of these methods.Test of orthogonality of projected subspace(TOPS)and test of orthogonality of frequency subspace(TOFS)are studied,and a fast DOA estimation for wideband coherent sources based on symmetrical spectrum is proposed.Using Toeplitz reconstruction,the decorrelation process can be realized,combining with real-valued transform,complex matrix can be changed into real matrix which can reduce the computational cost of subspace decomposition,then,utilizing noise subspace and its conjugate,new spatial spectrum can be obtained.According to the symmetric feature of spectrum,it can swiftly obtain the signals DOA through half scope search for spatial spectrum.Simulation results show that new method can deal with wideband coherent signals and has high precision and low computational cost.3.The DOA estimation algorithms for noncircular signals including of NC-MUSIC,real-valued NC-MUSIC and extended propagator method(EPM)are studied,and the simulations results are also given by computer simulation.MUSIC,ESPRIT and Unitary ESPRIT algorithms are studied with the coexistence of both noncircular and circular signals,in this circumstance,more signals DOA can be obtained for the expansion of signal subspace.To solved the computational burdens with the coexistence of both noncircular and circular signals,a fast algorithm is proposed which expands the unitary transform and multistage Wiener filtering technique into noncircular signals and reduces the computational complexity of the algorithm.Since circular signals angles could appear twice while noncircular signals only have once,we can distinguish circular and noncircular signals.The performance of the algorithm is verified by the simulation.4.The algorithms with the coexistence of both uncorrelated and coherent signals are studied,and the approaches based on the square and eigendecomposition of spatial difference matrix are discussed.To raise the probability of success detection,new method called difference Mini-Norm approval is proposed,which is not sensitive for the array parameter and has high success probability.A novel fast algorithm is proposed to overcome the problems of the spatial difference algorithm with heavy computational cost and aperture loss during the processing of decorrelation.By using new spatial difference technique,new method has lower aperture loss compared with the conventional spatial smoothing,and combining with real-valued transform and linear propagator method,it can obtain coherent signals noise subspace swiftly.The simulation experiments verify that new method has higher precision and lower computational complexity.5.Utilizing the real-valued transform and spatial difference techniques and combining with TOFS theoretics,a fast wideband signals DOA estimation under the coexistence of both wideband uncorrelated and coherent signals is proposed.Using the Hermitian feature of wideband covariance matrix at every frequency bin,complex matrix can be transformed into real matrix through unitary transform,thus,uncorrelated signals DOA can be acquired through real-valued TOFS.By using spatial difference and Toeplitz technique,new method can realize decorrelation with lower aperture loss compared with the conventional spatial smoothing,and combining with real-valued TOFS,it can swiftly obtain wideband coherent signals DOA.Simulation experiments verify that new method can estimate wideband uncorrelated signals and wideband coherent signals with lower computation,and it is effective when signal is overloading.