Adaptive beamforming with low sample support via indirect dominant mode rejection

Low-rank MVDR beamformers such as conjugate gradients (CG) and principal components inverse (PCI) can yield a higher SINR than full-rank MVDR beamformer when the sample support is inadequate. However, a large drop in output SINR occurs if the low-rank beamformer operates at an improper rank. Indirect dominant mode rejection (IDMR) is proposed wherein one first employs a high-resolution spatial spectrum estimation technique to estimate the directions and powers of the dominant interferers. Subsequently, this information is used to construct an estimate of the signal-free (interference plus noise only) autocorrelation matrix (for a given look-direction). In this process, any residual correlations between the interferers and the signal arriving from the look-direction due to finite sample averaging is effectively removed. Simulations reveal that IDMR yields a dramatic improvement in output SINR relative to CG and PCI/DMR, even when the latter operate at the optimal rank.