Research On Main Lobe Interference Suppression Method Of Underwater Acoustic Array Signal Based On Adaptive Beamforming

Beamforming is the core technology of underwater acoustic array signal processing.The underwater acoustic signal beamforming method of underwater array is a spatial filter,which is usually used as sending or receiving equipment of underwater acoustic communication by arranging transducers in a certain shape in space to form underwater array.Using beamforming technique can obtain a scalar output by weighted sum of received data.By designing the weight vector,it can receive the desired signal in the direction of the main lobe to the maximum extent,and at the same time suppress the interference and noise in other directions,and improve the signal receiving quality.However,when the interference enters from the main lobe of the array pattern,the main lobe of beamforming will be distorted and the sidelobe level will rise.In particular,when the sampling data of the desired signal with,and the main lobe interference power is larger,which leads to the main peak of the beam offset,side lobe zero in disappear.In view of the above questions this thesis launches the research,and proposes an improved eigen-projection Matrix Preprocessing(EMP)based main lobe interference suppression method for underwater acoustic array signals.The main work of this thesis is as follows:(1)An improved method based on EMP for main lobe interference of underwater acoustic array signal is proposed.In view of the sample data mixed the desired signal causes the problem of the main lobe offset,this thesis improves the way the reconstruction of the interference noise covariance matrix.The interference covariance is reconstructed by the Capon algorithm integrating the uncertain set of all the interference signals,which improves the estimation accuracy.In addition,the noise covariance matrix is reconstructed by means of the low noise eigenvalues in the sample covariance matrix.The eigenvalue decomposition of the interference noise covariance matrix was carried out,the corresponding eigenvectors of the main lobe interference were screened,and the eigen-projection matrix was constructed to eliminate the main lobe interference components.The simulation results show that the improved covariance matrix has less estimation error and can determine the main lobe disturbance more accurately.(2)Aiming at the problem that the high interference power of the main lobe leads to the sidelobe level rising and the sidelobe zero trap becoming shallow,this thesis improved the constraint conditions by adding the equality constraint matrix of the desired signal and the sidelobe interference subspace,which ensures the direction gain of the desired signal and deepens the sidelobe interference zero trap.In addition,the method minimizes the modulus of the adaptive weight vector and thus minimizes the noise gain,so as to eliminate the disturbance of the eigenvalue with low noise and reduce the sidelobe level.Simulation results show that this method can not only preserve the beam shape,but also deepen the sidelobe zero sink,thus improving the output signal-to-interference-noise ratio of the whole system.To sum up,considering the mixing of sampling data with expected signals in practice,aiming at the strong interference problem faced by underwater acoustic array signals in complex Marine environment,this thesis proposes an improved anti-mainvalve interference method for underwater acoustic array signals based on EMP from two aspects of reconstructing the covariance matrix of interfering noise and improving the linear constraint conditions.The proposed method can not only preserve the shape of the beam,but also strengthen the suppression of sidelobe interference and improve the receiving quality of underwater acoustic signal,which is of great significance to the acquisition and transmission of information between underwater Marine equipment and the realization of ocean observation.