Study Of Beam Pattern Optimization Technique And Application Based On Second-order Cone Programming

As one of the key technology of modern sonar array signal processing,beamforming undertakes two main tasks which are direction of arrival estimation and signal receiving.According to the practical engineering requirements,how to improve the ability of underwater target location and detection through beam optimization which satisfied with kinds of performance indicators,is always one of the main tasks in the array signal processing.The new opportunity is brought to beam optimization with the application of second-order cone programming.The beam optimization algorithm based on second-order cone programming is systematically studied in the paper.And the applications of beam optimization algorithm in direction of arrival estimation,two-dimensional sonar imaging and desired signal receiving are deeply studied in theory and experiments.The concrete contents are as follows:1.The principle of beamforming and the achievement in time domain and frequency domain are introduced.The relationship between beam pattern and spatial spectrum is described.Through the performance criterions of beam pattern,the mathematic expression of beam design independent of data is proposed.The weights of beam pattern optimization is calculated by second-order cone programming.The optimized beam pattern which satisfied with kinds of performance indicators including main lobe precision,side lobe level,beam null depth and robustness is designed by constructing different optimization criteria.There is no requirement for the array shape,so the algorithm can be applied to any array shape.Because the optimized weights are designed entirely depend on the array manifold,the performance of beam optimization degrades when array manifold error occurrs.The correction of array manifold or robust optimization beamforming algorithm is needed.2.Waveform diversity MIMO sonar with co-located elements based on virtual array technology can improve the resolution of azimuth estimation in the premise of saving array elements.To improve the performance of system,the beam optimization of the virtual array is also needed.For the problem that bistatic MIMO sonar can not use the virtual array technology directly,the two-dimensional synthesis direction vector is converted into one-dimensional virtual array manifold.Target direction is obtained by the beamforming of virtual array manifold through combining the waveform diversity technology and bistatic system location.In the meanwhile,the advantages of target resolution improvement by virtual array technology is preserved.The relationship of beam patterns among virtual array in bistatic MIMO,transmitting array and receiving array is discussed.Due to the nonlinearity of angle domain mapping,it leads to serious performance degradation of the virtual array beamforming.A beam optimization algorithm based on second-order cone programming which can resist array manifold erros is proposed.The algorithm can not only control the side lobe and null of beam pattern,but also improve the tolerance of array manifold errors.The validity of the algorithm is verified by the pool experiment.3.Two meet the requirements of range and angle resolution at the same time in two-dimensional acoustic imaging,the sliding window is needed in time domain.Due to the mismatch between weights and steering vector computed by the sliding window,the performance of beam optimization degrades.An improved sliding window at a fixed distance is proposed.Through the computer simulation,the theoretical steering vector calculated by the improved sliding window,instead of the array manifold,is used to design the second-order cone programming weights.The performance of beam optimization is ensured,through the sacrifice of some distance resolution.The optimization of two-dimensional acoustic imaging with coherent interference is discussed.The coherent interference suppression in acoustic imaging is achieved through beam null designed at the interference location.The validity of the proposed method is verified by the pool experiment of coherent source and moving target.4.In order to obtain high precision broadband signal of beamforming output in time domain,and overcome the distortion defects of signal deviated from the spindle direction using norm beamforming,the broadband constant beamwidth beamforming based on FIR filter in time domain is studied.The array signal weights of each frequency is achieved by FIR filter with second-order cone programming.At the same time,the optimization of beam null is designed to suppress coherent interference of fixed direction.Due to the defect that two step design method can not meet the precision of sidelobe and beam null design,the global design method is proposed.The moving target echo is received by constant beamwidth beamforming using FIR filter in time domain.The frequency estimation algorithm using pulse pair signal is proposed to estimate the doppler shift of the moving target.The validity of receiving high precision broadband signal using constant beamwidth beamforming based on FIR filter is proved through the simulation and experiment.The benefit is got for signal detection and parameter estimation.