Research Of Direction Of Arrival Estimation Algorithms Based On Noncircular Radio Frequency Signals

Array signal processing technology is predominate in the entire signal processing field,which is widely used in many fields such as communications,radar,seismic survey and radio astronomy.It receives and processes the signals from the airspace through a sensor array with a specific shape,so as to obtain the parameter information of these signals,such as the number of sources,the powers,and the angles of arrival.This technology mainly focuses on the beamforming technology and the estimation of the direction of arrival(DOA).However,for noncircular signals,the performance of traditional algorithms is proven to be suboptimal,and algorithms of beamforming and DOA estimation modified according to the characteristics of noncircular signals always have better performance.This thesis focuses on improving the traditional algorithm to adapt to the noncircularity of the signals,and has done the following work:(1)The thesis gives a theoretical introduction to the basic knowledge of beamforming and DOA algorithms in array signal processing,especially the adaptive beamforming technology and the minimum variance distortionless response(MVDR)algorithm in beamforming,and the minimum variance method(MVM)and multiple signal classification(MUSIC)algorithm in DOA estimation.In addition,the thesis elaborates on the noncircularity of the signal,highlighting the inherent difference and connection between the noncircular and circular signals.(2)This thesis introduces the complex least mean square(CLMS)algorithm,which is proved suboptimal for the processing of noncircular signals.However,the augmented CLMS(ACLMS)algorithm formed after wide linearization is useful for processing specific noncircular input signals.On this basis,the thesis proposes a combination structure of ACLMS filters,which can speed up the convergence of the algorithm on the premise of getting a smaller mean square error(MSE).In addition,the thesis studies the connection between the performance of the new algorithm and the noncirculartiy of the input signals,and designs a practical algorithm to achieve the performance effect of the proposed combination algorithm.(3)The thesis introduces a widely linear(WL)MVDR algorithm in detail,and proves that this algorithm has absolute advantages in processing noncircular signals compared with traditional algorithms,and this advantage can even be observed in in-phase/quadrature(I/Q)channel.By defining new performance indicators,the thesis makes a comprehensive second-order performance analysis of the WL algorithm and find the connection between the MSE performance and the noncircularity of input signals,demonstrating the in-depth performance advantages of the WL MVDR in the I/Q channel.(4)The thesis introduces two WL MVDR beamforming algorithms,based on which two WL DOA estimation algorithms are proposed.These two algorithms are compared with the classic MVM algorithm to analyze their resolution and MSE performance,and prove that the WL algorithms are more suitable to process signals which have low signal to noise ratios(SNR),large noncircularity and close DOAs.In addition,based on the MUSIC algorithm,the thesis introduces a noncircular MUSIC(NC-MUSIC)algorithm to process noncircular signals.Similarly,the NC-MUSIC algorithm is more suitable to process signals which have low SNRs,large noncircularity and close DOAs.Moreover,the Cramér–Rao Bound(CRB)of the noncircular signal is introduced,and compared with the MSE performance of each DOA algorithm.Finally,the signal transmitted in the radio frequency identification(RFID)system is rectlinear so that the RFID system is very suitable for practical testing to prove the advantages of the DOA estimation algorithm proposed in the thesis when processing noncircular signals.The thesis uses the RFID system as a carrier,through a series of equipment such as antennas,tags and readers,to practically test the performance of each DOA algorithm.These tests highlight the performance advantage of the WL algorithms for processing noncircular signals.There is still a lot of room for research on noncircular signals in array signal processing.The thesis takes beamforming and DOA estimation as examples,while other fields still have traditional algorithms that are worth exploring and reforming,making them more effective in processing noncircular signals to achieve better performance results.