An Research On Beamforming Algorithm For Space-Time Interference

Blind beamforming algorithm,as an array signal processing algorithm for suppressing the same-frequency interference of Automatic Identification System(AIS),can effectively maintain the target signal while suppressing interference and noise by the estimated steering vector.In the traditional beamforming algorithms,it is assumed that the array received signals are synchronous,continuous and there is no relative time delay.However,such assumptions are far from realistic since there exists various error factors in the actual environment,resulting partial overlap of signals in adjacent time slots.Affected by this,the beamformer will suffer severe performance degradation.The main work and innovation of the thesis covers these points as following:(1)Based on the practical application of satellite AIS,clarify the research background and significance of beamforming algorithms for partially overlapped interferences,and describe the development history and research status at home and abroad in recent years.(2)Introduces the array data model and fundamentals of several classic beamforming algorithms.Theoretical and experimental results show that the traditional beamforming algorithms are insufficient under partial overlapping interference.It also researches the leading edge beamforming algorithms for such problems and discusses their advantages and disadvantages respectively.(3)For the problem that the performance of beamforming algorithm is seriously degraded when the target signal is subjected to partial overlapping signal interference from the near-incident direction,a partially overlapped interference suppression algorithm in super-resolution is presented,which firstly calculates the auto-regressive coefficient by auto-regressive model and performs the virtual array extrapolation.Then,the beamforming algorithm based on generalized singular value decomposition is utilized to estimate the target signal and suppress the partially overlapped interference.The weak capacity against signals from the closely incident angle in beamformer is strengthened.Simulation results show that the proposed algorithm based on the combination of array extrapolation and beamforming can effectively achieve the higher resolution than the original array without increasing the elements of actual array and presents a superior performance.(4)In order to solve the problem in AIS that the signal in the target slot cannot be correctly received due to partial overlap of signals in adjacent time slots,the paper introduces a new criterion: maximum expected signal power(MESP)and proposes a novel blind beamforming algorithm based on generalized singular value decomposition(GSVD)and orthogonal projection.The algorithm employs GSVD to estimate the signal subspace,and adopts orthogonal projection to project the received signal onto the orthogonal subspace of the non-target signal.Then,beamforming technique is used to maximize the output power of the target signal on the basis of MESP.Compared with other algorithms for interference suppression,the proposed method adopts a more efficient method of subspace partition without the assumption of known noise power.Experimental results show that the proposed algorithm has a better ability for interference suppression.