Diagonal Loading of Robust General-Rank Beamformer for Direction of Arrival Mismatch

This study presents a technique which utilizes the movement of the peak of the main beam towards the presumed signal direction with negative diagonal loading for robust general-rank beamformer. The main beam symmetry along presumed signal direction is improved by this movement. When desired signal is contained in the data snapshots, the conventional beamformers face the problem of performance degradation even if there is a small mismatch between the presumed and the actual signal direction. Diagonal loading is a popular technique to mitigate this problem. There is no definite criterion to find diagonal loading level. A new diagonal loading method has been proposed in the literature which utilizes the movement of the peak of main beam towards the presumed signal direction with positive diagonal loading. The proposed technique works iteratively for the selection of negative diagonal loading level to move the main beam at a position to get the beam symmetry at desired level and hence the desired robustness. The mismatched signal will not be cancelled as long as it is within the half of the width of the main beam. But there is the tradeoff between this robustness and interference cancelling capability.