Research On DOA Estimation Of Coherent Wideband LFM Signals Based On Fractional Fourier Transform

As an important part of signal analysis and processing, array signal processing has become one of the key technologies in many fields, such as radar, sonar, communication, radio astronomy and medical imaging. In actual situation, due to the impact of the multi-path dissemination and the jamming of electronic warfare, there are many coherent signals which led to the traditional array signal processing means no longer apply. So, the research on the array signal processing in coherent signals environment becomes a new hotspot.Traditional Fourier transform can not describe the signals’ property in time-frequency domain. It does not apply to non-stationary LFM signals processing. As a generalized form of Fourier transform, fractional Fourier transform(FRFT) has good analysis performance for LFM signals processing. This paper applies FRFT to wideband array signals processing, and presents a new method for the direction of arrival(DOA) estimation of coherent wideband linear frequency modulation (LFM) signals based on FRFT. The main work and contributions of the dissertation are in the several aspects as follows:1. Characteristic of LFM signals is studied in fractional Fourier domain. Compared with the characteristic of LFM based on Wigner-Ville distribution (WVD) and short-time Fourier transform (STFT)), cross-terms can be avoided effectively in FRF domain.2. A new method for DOA estimation of Coherent wideband LFM signals is proposed based on FRFT. In allusion to the energy-concentrated property of LFM signal in the FRF domain, the proposed algorithm constructs the data model of array matrix and gains the ability of decorrelation by establishing a new Toeplitz matrix. Then, the DOA of coherent wideband LFM signals are obtained by performing a spectrum peak search. The new approach increases the ability of discernment under the same SNR without reducing the aperture of array.3. Discrete mathematical model of two dimension(2-D) DOA is established in FRF domain. Based on it, a new method for 2-D DOA estimation of coherent wideband LFM signals is presented. Forward/backward(FB) spatial smoothed DOA matrix is formed in FRF domain. Then, the signal and noise subspaces are estimated with the eigen-decomposition of the smoothed DOA matrix. Through eigenvalues and eigenvectors of signal subspaces, 2-D DOA of coherent wideband LFM signals are obtained, which means cross-terms, 2-D search and parameter alignment are avoided.