Research On Wideband Multipath Beamforming Algorithm

With the development of array signal processing,beamfoming has been widely applied to radar,communication and electronic surveillance.Under ideal conditions,conventional beamforming method can enhance the signal of interest(SOI),and can suppress interference and noise.However,in many practical scenarios,multipath propagation cannot be avoided or ignored.Conventional beamforming method suffers from signal cancellation and has poor performance in multipath environment.To alleviate these problems,this paper focuses on narrowband multipath signal reception beamforming,and the wideband multipath interference suppression beamforming with low complexity and robustness.The main work and innovations obtained in this paper can be summarized as follows.1.To improve the performance in multipath environment,a novel beamforming method for narrowband multipath signal reception is proposed.The reason that conventional Capon beamformer suffers from signal cancellation is the phase difference between the array output corresponding to the SOI and multipath interferences is ??.This method uses anti-diagonal unit matrix to construct new covariance matrix and constrained steering vector.Then the weighting vector is obtained based on the MVDR criterion and the array output is performed.The proposed method does not have to estimate the directions of arrival(DOAs)of multipath interferences and uncorrelated interferences.Moreover,the array output can be better by adjusting the number of array elements.Simulations demonstrate the superior performance of proposed method comparing with the method of conventional Capon and multipath signal reception.2.The construction of sub-array covariance matrix of conventional spatial smoothing algorithm based on wideband time domain model will be complex,and the output performance of this method is poor.To resolve these problems,a novel wideband beamforming algorithm for multipath signal based on spatial smoothing is proposed.The proposed method rearranges the array received data based on time domain model,which reduces the structural complexity of sub-array covariance matrix of spatial smoothing algorithm.This method selects sub-array covariance matrix from original covariance matrix,which can cancel the SOI.Simulation results show that this algorithm can form nulling in the directions of multipath interferences adaptively,and has better performance than conventional wideband spatial smoothing algorithm.3.To improve the performance of Duvall-structure beamformer in the presence of both DOA estimation errors and several coherent interferences,a robust wideband multipath beamforming algorithm based on covariance matrix reconstruction is proposed.After Duvall-structure,this algorithm reconstructs the covariance matrix of array received data.The constraints in the directions of interferences are equal to the minimum output constraints.The proposed method can adaptively form nulling in the directions of coherent interferences when the number of coherent interferences is more than one.Then the robust beamforming is performed based on the worst-case performance optimization method and the spatial response variation(SRV)constraints.Analysis and simulation results show that the algorithm can suppress two or more strong coherent interferences,and attain better robustness.4.In order to solve the complexity of computation and the robust problems of conventional space-time wideband multipath beamformer structure,a robust wideband multipath beamforming algorithm based on phase constraints and energy focusing is proposed.Firstly,by analyzing the influence of frequency change and angle change on the phase of array response,the magnitude and phase constraints are imposed to compensate the phase differences between different frequencies for desired signal.Then,through introducing virtual interferences in sidelobe region to construct energy focusing matrix,the output beam sidelobe level is wholly controlled by iterative processing of mainlobe beamwidth,and the sidelobe energy is focused on mainlobe to achieve robust wideband multipath beamforming.Finally,the simulation and actual data analysis results show that the algorithm can suppress the multipath interference effectively,and attain better robustness and higher output signal to interference noise ratio(SINR).