The robust adaptive beamforming(RAB)algorithms reported in the literature are analyzed,to explain the serious performance degradation or even completely invalid in the presence of coherent interference.When the covariance matrix of the received data is decomposed into the description form of the array manifold matrix left and conjugate right multiplied by a matrix P.P is a non-diagonal matrix when the received data are interfered by the coherent signal sources,and the off-diagonal elements in the matrix Prepresent the coherences between the signal and interference sources as well as among interference ones,which are the main reasons for the failure of RAB algorithm reported in the literature.It is shown further that the insufficient number of snapshots can be regarded as a special case of coherent interference.In order to deal with these situations,a covariance matrix fitting method is proposed by constructing P as a diagonal matrix.Based on the fitted covariance matrix,an RAB method for non-smooth coherent interference is presented.The simulation results verify the effectiveness of the analytical ones.Meanwhile,they also show that the proposed method can still achieve the performances of the non-coherent interference RAB algorithms in the case of coherent interference,and has a faster convergence rate than the methods reported in the literature.
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