Study On The High Performance Robust Adaptive Beamforming In Antenna Arrays

With the continuous development of electronic information science and technology,antenna array is widely used in more and more fields.As one of the key technologies of adaptive arrays,beamforming can make the main lobe of the array antenna point at the desired signal direction and form nulls adaptively at the interference directions,so as to effectively suppress the interference and improve the output signal-to-interference-to-noise ratio(SINR).In practical applications of antenna array,various errors and mismatches may exist inevitably,such as fast motion interference,desired signal direction of arrival(DOA)estimation error,wavefront distortion,local coherent scattering,array element position error and element mutual coupling,etc.,and the traditional beamforming suffers serious output performance degradation in the presence of these errors.Therefore,how to improve the robustness of antenna array beamforming in nonideal conditions has become a hot topic in recent years.Most robust beamforming algorithms are proposed for a specific error,and hence the comprehensive robustness is limited.The main problems are the large gap between the output SINRs and theoretical optimum,and donot consider the situation that different errors coexist,as well as lack of systematic research on the high performance robust beamforming.Aiming at the existing problems,this paper studies on the high performance robust beamforming method to further improve the anti-jamming performance and the output SINR,and study the robust beamforming method under condition that various errors coexist.The main research work of this paper is summarized as follows:Aiming at the interference suppress problem of fast motion interference or relative angle of antenna array and interference change rapidly,this paper proposed a novel null widening beamforming method based on projection and diagonal loading(PDNBB),the PDNBB algorithm overcomes the null depth shallower problem in the covariance matrix tapers(CMT)null widening method,and hence the interference suppression performance and the robustness of the algorithm are greatly improved.The reason why the subspace projection transformation can broaden the jammer null and enhance the null depth was analyzed theoretically.We find that the projection transform operation can expand the incident direction of the interference and strengthen the signal-plus-interference subspace,which is equivalent to enhance theinterference power.and thus the null is broadened and deepened..The PDNBB algorithm has a good performance on suppressing the fast motion interference,and the output SINR can close to the theoretical optimal.What's more,the PDNBB can control of the null depth by choosing the number of basis vectors.In addition,the amplitude response constraint technique is introduced into the PDNBB algorithm,which can control the width and response of the main lobe,and thus improve the robustness of the algorithm in the presence of the fast motion interference and the steering vector mismatch.Aiming at the problem that the performance of traditional beamforming degraded seriously due to the desired signal steering vector mismatch,and the existing high performance beamforming suffers a high computation complexity.An efficient robust beamforming algorithm based on variable diagonal loading(VLRB)is proposed in this paper,the VLRB method first estimates the input SNR and then the diagonal loading can be adjusted adaptively according to the change of the input SNR.The VLRB algorithm can obtain the analytical expression of the weighted vector without iterative solution.Compared with the existing robust beamforming method,the VLRB algorithm can improve the output SINR significantly with low computational complexity.In addition,an improved modified norm constraint Capon beamforming(MNCCB)is proposed to combat large desired signal DOA mismatches.The MNCCB method is realized by projecting the negative exponential power of the covariance matrix to the weight vector,and the then impose a norm constraint on the projection.The MNCCB method strength the orthogonal constraint on the weight vector,and thus enhance the robustness of the beamformer against large DOA mismatch,which can achieve better anti-jamming performance than other methods.Considering the problem that the performance adaptive beamforming degraded seriously in the presence of array manifold errors which may caused by element position error,array element mutual coupling error,two robust beamforming algorithms against array manifold error are proposed.Firstly,robust adaptive beamforming based on interference subspace reconstruction(ISRRB)is proposed.The ISRRB method estimate the accurate interference steering vectors within angular sectors in which the interferences may existed,and the interference subspace is constructed based on the corrected steering vector.Then projecting the covariance matrix to the interference subspace and combined with diagonal loadingtechniques to get a new covariance matrix.Compared with the existing method,the proposed method can greatly improve the robustness of the beamformer against the array manifold errors,and the output SINR is more close to the optimal value.Then a robust beamforming method based on covariance matrix hybrid reconstruction(CMHRRB)is proposed.The interference plus noise covariance matrix is derived from the weighted combination of the two parts.The proportion of the two parts can be adaptive adjustment according to the input SNR by designing the weighting factor reasonably.The proposed method improves the anti-jamming performance of the beamforming in the presence of array manifold errors,and the output SINR is superior to the current method.In order to improve the robustness of the beamformer against the desired signal steering vector mismatch and the array manifold errors,a robust beamforming algorithm based on steering vector double estimation(SVDE)is proposed.The SVDE method overcomes the performance degradation by correcting the steering vector twice.On the base of SVDE,the CMT null widening method is introduced,and the SVDE-CMT algorithm is proposed to achieve the purpose of broadening null width in the presence of array manifold errors.The SVDE-CMT method can suppress the fast motion interference,and further improve the robustness of the beamformer in the complex environment.The SVDE-CMT method does not need any iteration,and the low computation complexity can be obtained.The simulation results demonstate the effectiveness of the proposed algorithm.