Research On Robust Adaptive Beamforming Algorithm Based On Coprime Sparse Array

Adaptive beamforming aims to design the weight vector of beamforming through certain mathematical criteria to achieve the purpose of enhancing the desired signal while suppressing interference signals and noise.In the scenario of model mismatch caused by various error sources,the performance of traditional beamformers based on dense uniform arrays is significantly reduced.As is known,the robustness of beamforming is closely related to degree of freedom(DOF)and array aperture.Coprime array possesses outstanding advantages in terms of array sparsity,high DOF and large aperture.However,the existing beamforming algorithms based on uniform arrays cannot be directly applied to the coprime array,so the design of a robust beamformer based on the coprime array remains to be solved.This thesis starts from two aspects.On the one hand,we design the robust beamformer using the subspace characteristics of the virtual domain.On the other hand,considering the amplitude and phase errors,we design the beamforming algorithm based on the matrix filling technique.In the aspect of virtual domain subspace characteristic extraction,the optimization of steering vectors is constrained by the orthogonality between the steering vectors of interference signal and its complement of signal subspace.Then the desired signal component is eliminated by the orthogonality between the desired signal and the interference signal subspace,based on which the interference power is estimated.Furthermore,the residual noise compensation is performed on the Capon spatial spectrum to obtain more accurate noise power and the desired signal steering vector.Finally,the interference plus noise covariance matrix is accurately reconstructed in the physical domain.This algorithm combines the advantages of virtual domain signal processing to optimize the steering vector mismatch situation,achieving relatively higher output performance under the same error conditions.In the aspect of considering the amplitude and phase error to dsign beamformer,we estimate the amplitude and phase error based on the auxiliary array element first,and perform error compensation on the received signal covariance matrix.Then,the compensated matrix is expanded into a high-dimensional Toeplitz matrix in the virtual domain,and filling holes to solve the steering vector of the signal.Finally,we construct a least squares problem to estimate the interference power,and reconstruct the interference plus noise covariance matrix according to the physical array structure.This algorithm achieves high output performance under relatively large amplitude and phase error through error compensation,and improves the anti-interference ability and the beam resolution ability by utilizing the received signal information of all virtual array elements.Of the above two algorithms,the former is suitable for improving the robust performancein the case of steering vector mismatch,and the latter is suitable for achieving the optimal output in the presence of amplitude and phase error.Both are designed based on sparse coprime array,which means that the distance between the array elements can be enlarged,and the mutual coupling effect of multi-antenna receivers can be suppressed,thus possessing a broad application prospect in the future high-frequency communication technology.