The Study Of Robust Adaptive Beamforming Algorithms

The array signal processing as an important branch of the signal processing domain is applied for many areas such as radar, sonar, communication and biomedical testing. It can exploit sufficiently the information of the signal by sampling the signal in time-spatial domain to suppress the interference and increase the SINR of the system. The adaptive array signal processing can obtain good performance in the ideal cases. But the errors in the system always severely affect the performance of the array signal processing. So many researchers are trying to research robust array signal processing algorithms. This paper introduced several algorithms to improve the robusness, which makes the system more robust for the complicated scenario.Firstly, a robust adaptive beamforming algorithm in the presence of the pointing error is proposed by the steering vector rotation method aiming at the shortcoming of the MVDR sensitive to the pointing error, and proposed the choice criterion of the angle rotation quantity. Secondly, a NULL-broadening method is proposed by the interference steering vector rotation, which increases the MVDR algorithm's robustness when the interference moves quickly.Analyzing the forward-backward covariance by the numerical analysis, we reached a conclusion that the backward smoothing matrix is the rearrange of the forward smoothing matrix, and the covariance matrix includes itself the all information of the smoothing submatrix by analyzing the steering vector of the uniform linear array. As a result, the computation effort of the spatial smoothing algorithm can be reduced. The algorithm also makes the spatial smoothing processing more flexible.Due to the computation complexity of the higher order cumulant(HOC), the algorithms of HOC exists in the theoretical analysis stage. This paper analyzies the extension of the MUSIC-LIKE method for uniform linear array, and reduces the size of cumulant matrix to (2M-Y)×(2M-1) which leads the reduction ofthe computation effort. On the other hand, this paper analyses the problem of the generalized steering vector in the presence of the coherent signals, and combines the blind adaptive beamforming with eigen-analysis algorithm to improve the performance of the blind algorithm for the weak signal cases.The most signals in the communication system have the cyclostationary property. Many algorithms based on the cyclostationary of the signal in the array signal processing have been exploited, such as SCORE, CAB and so on. But the performance of the algorithms have periodic zero point as the number of snapshot increasing when there is the error of the cycle frequency in the system due to the effect of the sine function. This paper assumes that the distribute of the cycle frequency is uniform in the specific interval and cumulant the all cycle autocorrelation matrix, then perform the CAB operation utilizing the cumulant cycle autocorrelation matrix, which can improve the robustness of the algorithm when the correct cycle frequency exists in this interval. At the end, this paper studies the problem of the DOA in the presence of the coherent signal utilizing the cyclostationary property of the signal, and obtains some significant conclusions.