Research On Angle Estimation Methods For MIMO Radar Under Complex Electromagnetic Environment

As a new concept radar put forward in the early twenty-first Century,MIMO radar has shown prominent advantages in system analysis,waveform design,target detection,parameter estimation and electronic countermeasures.Target angle estimation,which is one of the research hotspots in MIMO radar,is actively and rapidly developed in recent years.However,current research usually assumes that no strong interference exists in the environment and the background noise is Gauss white noise,the practical methods for solving the high computing complexity problem when the number of virtual elements is large are also needed.Therefore the current research cannot adapt to the severe challenges brought by the increasingly complex electromagnetic environment.In order to solve the prominent problems such as coherent and incoherent mixed source,non ideal background noise,strong electronic jamming and large virtual cell number when MIMO radar is utilized as a military electronic reconnaissance device,the target angle estimation method for MIMO radar in complex electromagnetic environment is studied in this dissertation.The specific work can be summarized as the following five parts:In the first part,in order to solve the angle estimation problem of coherent sources in the colored background noise,a improved forward and backward Spatial Difference Smoothing(IFBSDS)algorithm is proposed by combining the improved spatial smoothing algorithm with the spatial difference algorithm.By the algorithm we can not only decoherent the coherent source,but also suppress the influence of the color noise.In order to further reduce the computational complexity of the IFBSDS algorithm,an improved forward and backward Spatial Difference Smoothing(MWF-IFBSDS)algorithm based on Wiener filtering is also proposed.Thus the eigenvalue decomposition operation of subspace class algorithm can be avoid,at the same time the same performance with the IFBSDS algorithm can be obtain,which is more consistent with the real demand of MIMO radar signal real-time processing.Theoretical analysis and simulation experiments show that the MWF-IFBSDS algorithm has better angle estimation performance than FSS,FBSS,MUSIC and ISDS algorithm under low SNR and small angle interval,and the proposed algorithm has stronger array element saving ability and source overload capability.In the second part,in order to solve the angle estimation problem of coherent sources in the impulsive background noise,a conjugate rotation invariant subspace(RCC-FLOM)algorithm based on reduced fraction and low order covariance matrix is proposed for single base MIMO radar.The fractional low order covariance is adopted to reduce the influence of impulsive noise and then the conjugate rotational invariant subspace method is utilized to decorrelate the coherent source,which makes up the defect that the two order statistical model algorithm is not suitable for impulsive noise.Then a infinite norm normalization preprocessing and sparse representation(INN-SR)based algorithm for bistatic MIMO radar is proposed.The influence of implusive noise is reduced by sing the infinite norm normalization preprocessing firstly,and then the target angle can be estimated by using the sparse decomposition construction recovery dictionary.This algorithm can realize the correct pairing of the direction of arrival and the direction of departure when the number of source is unknown.The simulation experiments show that the proposed algorithm has the advantages of high success probability in source number estimation and low estimation root mean square error in low signal-to-noise ration when compared with the FLOM-MUSIC algorithm and the FLOS-FAF algorithm.In the third part,in order to solve the angle estimation problem of coherent sources in non-stationary background noise,a slanting projection operator and Teoplitz matrix reconstruction(CVTR-OP)algorithm is proposed.The non-stationary noise is transformed into Gauss white noise through Toeplitz reconstruction method,then the independent and correlated source components in the echo covariance matrix are excluded by utilizing the oblique projection operator,finally the classical spectrum subspace method is utilized to estimate the angle of coherent sources.Theoretical analysis and simulation experiments show that the proposed algorithm has no array aperture loss and is suitable for various array structures.The performance of the algorithm is better than MWF algorithm in non-stationary background noise,and the ability of source overload and array element saving is also good.In the fourth part,in order to solve the angle estimation problem of weak sources in strong interference,the preserving orthogonality of signal source is defined and the condition of preserving orthogonality of strong and weak sources is analyzed.On this basis,an an improved interference blocking angle estimation(DO-JJM)algorithm is proposed.The interference source angle is firstly estimated by using the preserving orthogonality of source,and then the constructed blocking matrix is used to eliminate interference in the received data,finally the MUSIC algorithm is utilized to estimate the angle of target.The simulation results show that the algorithm has better performance in the success probability,estimation bias and RMS error than the JJM algorithm when the target angle has reconnaissance error,and the performance of these two algorithms is nearly the same when the target angle is precisely known.The less request for interference angle information of this algorithm makes it more suitable in the complex electromagnetic directional interference environment.In the fifth part,in order to solve the high complexity problem of angle estimation under the condition of large virtual elements number,two ESPRIT-like algorithms whose transmitted and received rotation invariant factors are tangent or cosine function are proposed by using the characteristics of non-circular signals and Euler formula.The computation amount of ESPRIT-like1 algorithm is minimum while that of ESPRIT-like2 algorithm is also moderate because that the unitary transform and spectrum peak search are not needed.The computation amount of the two algorithms is less than the CU-ESPRIT and PM-CU-ESPRIT algorithm.The simulation results show that the RMSE of ESPRIT-like1 algorithm is larger than the other algorithms,because the algorithm does not achieve the expansion of the array aperture,and the RMSE of ESPRIT-like2 algorithm is nearly the same as CU-ESPRIT algorithm.Overall,by the above research work,we solve some practical problems of MIMO radar angle estimation in complex environment to a certain extent,which can take promotion on the application of MIMO technology in military radar equipment.