A LORAF-based coherent sidelobe canceller for narrowband adaptive beamforming applications

A direction-of-arrival (DOA) based coherent sidelobe canceller is proposed which utilizes the recently developed low-rank adaptive filter, or LORAF, to track the DOA´s (and corresponding power levels) of r narrowband sources impinging on a N-element (uniform linear) array. This approach differs from previously proposed block-based superresolution methods in which the computed DOA´s (and the corresponding power levels) of the sources are passed onto a processing block which computes the Wiener optimal spatial filter weights. The powerful block-based methods tend to be non-recursive which limits the rate at which the beampattern can be updated and thus the overall nulling capability in a non-stationary operating environment. In contrast, the LORAF is computed recursively and, like many of the superresolution methods, exploits the low-rank nature of the problem. Conventional full-rank adaptive methods such as LMS and RLS fail to exploit the low-rank nature of the problem and consequently suffer in their ability to determine the DOA´s of the sources under the stressing cases of low SNR or closely spaced sources.