Research On DOA Estimation Algorithms For Coherent Multiple Targets Under Strong Interference

With the development of various target simulation technology,stealth technology and countermeasure technology,underwater multi-target battlefield environment becomes complex and changeable.It causes two main problems: one is that weak targets will be submerged by strong interference;the other is that conventional DOA estimation algorithms will invalid when signals are coherent.To solve the above problems,this paper will study DOA estimation of weak coherent signals under strong interference.Firstly,the DOA estimation algorithms are studied based on underwater uniform linear array(ULA),including CBF,MVDR,MUSIC and ESPRIT.The performances of these algorithms are verified by simulation and lake trial data.Their applicability is studied under the coherent signal model.In the simulation,the algorithms are low-resolution and sensitive to coherent signals except CBF.Then,in order to solve the problem that the classical estimation algorithms can not be applied to coherent signals,two kinds of methods are studied: non-dimension reduction processing and dimension reduction processing.In the dimension reduction method,the spatial smoothing algorithm and the ESPRIT-Like algorithm are studied.In the non-dimension reduction method,the modified MUSIC algorithm and the Toeplitz matrix reconstruction algorithm are studied.Taking DOA estimation accuracy and probability of detection as the evaluated standard,the ESPRIT-Like has higher accuracy and greater decoherence ability than the spatial smoothing algorithm,and the Toeplitz matrix reconstruction algorithm is better than modified MUSIC algorithm in the number of sources and DOA estimation ability.Some algorithms are verified by actual lake trial data.The ESPRIT-Like algorithm does not make full use of the ULA's conjugate symmetry.Therefore,an improved algorithm,named I-ESPRIT-Like algorithm,is proposed in this paper.The proposed is divided into three steps.Firstly,the array data are conjugate rearranged.Then the correlation values are averaged.And finally,a Hermitian Toeplitz matrix is constructed.The simulation results show that the proposed algorithm can effectively improve the performance of ESPRIT-Like,and has advantages when snapshots are less and signal-to-noise ratio is low.Finally,to estimate weak signals under strong interference we study three DOA algorithms: BNF(Bartlett Null-Forming),JJM(Jamming Jam Method)and noise subspace invariant method.Under the condition of known interference direction and unknown interference direction,the detection probability of weak signal and DOA estimation accuracy are compared among three alogrithms.The experiment results show that the BNF can form the zero point in the direction of interference.The direction information of interference is eliminated by rank reduction processing of the JJM.The noise subspace invariance method can estimate the signal and interference at once.