Broadband Beamspace DOA Estimation: Frequency-Domain and Time-Domain Processing Approaches
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Research Article Broadband Beamspace DOA Estimation: Frequency-Domain and Time-Domain Processing Approaches Shefeng Yan Institute of Acoustics, Chinese Academy of Sciences, 100080 Beijing, China Received 1 November 2005; Revised 11 April 2006; Accepted 12 May 2006 Recommended by Peter Handel Frequency-domain and time-domain processing approaches to direction-of-arrival (DOA) estimation for multiple broadband far field signals using beamspace preprocessing structures are proposed. The technique is based on constant mainlobe response beamforming. A set of frequency-domain and time-domain beamformers with constant (frequency independent) mainlobe response and controlled sidelobes is designed to cover the spatial sector of interest using optimal array pattern synthesis technique and optimal FIR filters design technique. These techniques lead the resulting beampatterns higher mainlobe approximation accuracy and yet lower sidelobes. For the scenario of strong out-of-sector interfering sources, our approaches can form nulls or notches in the direction of them and yet guarantee that the mainlobe response of the beamformers is constant over the design band. Numerical results show that the proposed time-domain processing DOA estimator has comparable performance with the proposed frequency-domain processing method, and that both of them are able to resolve correlated source signals and provide better resolution at lower signal-to-noise ratio (SNR) and lower root-mean-square error (RMSE) of the DOA estimate compared with the existing method. Our beamspace DOA estimators maintain good DOA estimation and spatial resolution capability in the scenario of strong out-of-sector interfering sources. Copyright © 2007 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
Broadband direction-of-arrival (DOA) estimation has found numerous applications to radar, sonar, wireless communications, and other areas. Incoherent signal-subspace methods such as [1, 2] perform narrowband DOA estimation for each frequency bin and then statistically combine the resulting estimates to form a broadband DOA estimate. However, coherent signal sources cannot be handled by this approach. The coherent signal subspace (CSS) method was proposed by Wang and Kaveh [3] as an alternative method to deal with coherent signal sources. It decomposes the broadband data into several narrowband frequency bins and finds focusing matrices that transform the covariance matrices of each bin into the one corresponding to the reference frequency bin. Conventional narrowband DOA estimation methods such as MUSIC [4] may then be directly applied to find the directions of arrival. CSS methods have been found to exhibit better resolution at low signal-to-noise ratio (SNR) and lower estimate variance than incoherent methods. However, the design of focusing matrices in the CSS method requires preliminary DOA estimates in the neighborhood of the true directions of arrival.
Other broadband DOA estimation methods based on the beamspace preprocessing are proposed in [5
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