Power spectrum estimation with low rank beamforming

When the size of the training samples is limited the performance of the full rank minimum variance distortionless response (MVDR) beamformer is deteriorated; and a low rank solution of the MVDR problem can yield a better performance. A new adaptive approach, indirect dominant mode rejection (IDMR), was introduced in previous work to solve the MVDR optimization problem. In the previous work the IDMR beamformer was used to extract the desired signal, while in this work we use the IDMR beamformer to estimate the power spectrum. We also introduce several modifications, which bring more robustness to the basic IDMR. These include root-music, forward/backward averaging of the sample covariance matrix and power window