Research On Frequency Invariant Broadband Beamforming In Time-domain

With the increasing development of array signal processing, its status in modern signal processing has become significant and has been applied in many fields, such as radar,communications, radio astronomy and medical diagnosis. Adaptive beamforming is an important part of array signal processing; its target is to obtain the optimal output by assigning different factor to every array element. The bandwidth of wideband signal is large enough to transfer a large amount of information and the correlation of background reverberation is weak. So wideband signal is not easily affected in channel transmission process. And it has more advantages on these aspects such as target detecting,parameter estimating and feature extracting.Firstly, in the focus transform idea we convert the different frequency sub-band data to the frequency of a reference signal by the focus transformation matrix. We derive the expressions of the frequency domain output data of each sub-band in a matrix form and the focus transformation matrix in the RSS method. Then design a beamwidth constant and large nulling region beamforming by MVDR beamforming. Secondly, in SDL delay line array we studied a frequency invariant and minimum sidelobe beamforming by SRV constraints. The beamforming achieve good frequency invariant effect in the area of the main lobe and sidelobe region. Then based on this we propose a frequency invariant and minimum sidelobe MVDR algorithm which imposed MVDR constraints to reduce the effects of interference and noise signals. We improve the algorithm . After simulation study and performance analysis we prove the two algorithms can implement frequency invariant and form nulling on the direction of interference. When there are two interference signals in a small number of samples the frequency invariant and minimum sidelobe LSMI algorithm has a smaller main lobe and more prominent nulling effect on the directions of interference. Once more, we focus on beamforming algorithm in steering vector mismatching and derive the formation process with some guidelines in detail. By introducing the ellipsoid set of constraints,we achieve the distortion free reception of the signal with arbitrary direction vector mismatch. The algorithm can be transformed into a convex optimization problem under certain conditions and the optimal weight can be obtained by interior point method. Finally the algorithm is applied to frequency invariant beamforming algorithm of wideband signal. We present the frequency invariant MVDR beamforming in steering vector mismatch. Simulation results verify that the algorithm reduce the errors caused by sample autocorrelation matrix and the direction vector mismatch. The algorithm can implement frequency invariant and form nulling on the direction of interference. It has good robustness and output performance.