Research on direction of arrival estimation for mixed broadband signals

In practical applications, the signals received by a hydrophone array include coherent and incoherent signals, while estimating the direction of arrival (DOA) of coherent or incoherent signals has been studied for simplicity with poor performance for a mixed signal. The present study proposes a novel approach for estimating the DOA of mixed broadband signals to solve this problem, namely the oblique method. The unitary oblique method is simultaneously proposed to improve operational efficiency with the complex matrix shifted into a real valued matrix through a unitary transform. For independent signals, the incoherent signal subspace method (ISSM) is used to estimate the DOA. Matrix difference and oblique projection methods are adopted for multi-group coherent signals in order to eliminate the influence of incoherent signals and other groups of coherent signals. For broadband signals, the Tasseled Cap Transformation focusing transform is utilized to convert the broadband signal to the focusing frequency, and then the high-resolution Multiple Signal Classification algorithm method is employed to solve the problem. Simulation results indicate that the oblique method reconciles DOA estimation performance and computational efficiency and can be extended to other types of arrays.