High-resolution DOA Estimation Algorithms For Noncircular Signals

In recent years,the use of the statistical properties of the signals to enhance direction-of-arrival(DOA)estimation algorithm has become an important research field of array signal processing.Among them,the non-circular signals get more and more attention due to their excellent performance on extending array aperture and improving estimation accuracy.The non-circular signals are pervasive in modern communications,such as AM,BPSK,and UQPSK,which do not have rotational invariance.At the same time,with the growing requirements on the resolution and accuracy of DOA estimation in modern radar and communication systems,the demand for high-performance DOA estimation algorithms is becoming more and more urgent.Therefore,the study of high-resolution DOA estimation algorithm based on non-circular signals has significant theoretical and practical value.Although the study of this problem has made some achievements,the research for arbitrary non-circular rate signals and coherent non-circular signals is not sufficient yet.In this dissertation,based on the previous results,we made further research in this field and the main work can be summarized as follows:1.In order to improve the DOA estimation performance of arbitrary non-circular rate signals,a high-resolution DOA estimation algorithm based on centrosymmetric array is proposed,which combines the properties of the non-circular signal and the centrosymmetric array.Most of the arrays in practical applications are centrosymmetric,such as uniform linear array,symmetrical linear array and uniform planar array.Since the centrosymmetric array is symmetric about the center point,the delays of impinging signals received by symmetric sensors are opposite relative to the center point.Thus,the array steering vector has a conjugate symmetry characteristic.By using the conjugate symmetry of the steering vector and the non-circular property of the signals,the estimation of the steering vector of each signal can be obtained directly.And then,according to the relationship between the steering vector and the corresponding DOA,we can estimate all the DOAs easily.We not only present the one-dimensional DOA estimation method,but also the two-dimensional DOA estimation method based on uniform planar array and uniform circular array as examples.And the simulation results show that the proposed algorithm has significant advantages in terms of resolution,estimation accuracy and robustness to noise.2.With regard to the DOA estimation for non-circular signals in the presence of multipath propagation,the existence of coherent signals leads to the rank loss of signal covariance matrix,which results in the invalidity of the conventional high-resolution algorithms.To solve this problem,a multi-group DOA estimation algorithm for coherent non-circular signals is proposed.Firstly,the group steering vector of each coherent group is estimated by using the non-circular property,and both forward and backward group steering vectors are exploited to construct the corresponding composite Toeplitz matrix.By decomposing these matrices,the initial DOA estimation of each group can be obtained by utilizing the conventional high-resolution algorithms.In order to further improve the estimation accuracy,the group steering vectors are reformed using the initial estimates,and the more accurate DOA estimates are obtained by employing the matrix oblique projection and the forward and backward spatial smoothing techniques.As a result,the requirement for the number of sensors is reduced,whereas the estimation accuracy is improved.Simulation experiments demonstrate the superior performance of the proposed algorithm,especially in the condition of low signal-to-noise ratio and small snapshots.