Adaptive beamformers (ABFs) seek to detect quiet sources in the presence of loud interferers. This challenge creates a tension between the long averaging window required to null loud interferers effectively and the short averaging window required to track the nonstationary interferers. The length of the averaging window determines the number of observations or snapshots used to form the Sample Covariance Matrix (SCM) in the process of computing the ABF array weights. The Dominant Mode Rejection (DMR) ABF is often used to address these challenges given that it is relatively numerically robust to short observation windows. However, observed notch depths for DMR fall dramatically short of those predicted theoretically from ensemble statistics. This talk bridges the gap between theoretical and observed performance by presenting a simple linear asymptotic model for the DMR notch depth for a single loud interferer in the spirit of a Bode plot approximation to a frequency response. The model is derived from random matrix theory results on the accuracy of the SCM eigenvectors. The model predicts the mean DMR notch depth as a function of the number of snapshots given the interferer-to-noise ratio (INR), the array size, and the interferer location relative to the look direction. The model predictions are validated through comparison with both simulation and data from the Philippine Sea 2010 field experiment. This work is a collaboration with Prof. Kathleen E. Wage of George Mason University. [Work supported by ONR Codes 321US and 322OA.]
Dr. John Buck is a Professor of Electrical and Computer Engineering at UMass Dartmouth. He received his Ph.D. from the MIT/WHOI Joint Program in Oceanographic and Electrical Engineering in 1996. His honors include the IEEE Education Society's Mac Van Valkenburg Early Career Teaching Award (2005), the UMass Dartmouth Faculty Federation Leo M. Sullivan Teacher of the Year Award (2008), an ONR Young Investigator Award (2000) and an NSF CAREER award (1998). He is a Fellow of the Acoustical Society of America. He has held visiting appointments at the Australian Defense Science and Technology Organisation, Sydney University, the University of New South Wales, and George Mason University. His research interests include array processing, underwater acoustics, animal bioacoustics and engineering pedagogy.