Auto-focusing and tracking techniques for enhancement of coherent signal-subspace methods

The authors formulate the wideband minimum variance distortionless response (MVDR) as the auto-focusing criterion. By emulation results of single-group and multi-group sources, they show that the optimal focusing angles can achieve the wideband MVDR criterion and result in minimum output power of the beamformer. The steepest descent algorithm is suggested for iteratively updating the focusing angles for beamformers to null both stationary and nonstationary interferences. For direction finding applications, the same auto-focusing procedures can be applied directly by presuming a dummy looking direction. Simulation results show that the performances of beamforming and direction finding applications are greatly improved by the proposed auto-focusing algorithm