University Events

Description: TOPIC: IMPROVED SAMPLE MATRIX INVERSION ADAPTIVE BEAMFORMERS FOR UNIFORM LINEAR ARRAYS USING ARRAY POLYNOMIALS

LOCATION: Dion Building, Room 109

ABSTRACT:
Adaptive beamformers (ABFs) place deep beampattern notches near interferers to suppress the interferers' power in the ABF output. The sample matrix inversion (SMI) Minimum Variance Distortionless Response (MVDR) ABF computes the beamformer weights by substituting the sample covariance matrix (SCM) for the unknown ensemble covariance matrix in the MVDR expression. Errors in the SCM estimate of interferer direction due to limited sample support or interferer motion distorts the ABF beampattern and degrades the ability of the ABF to suppress the interferer. For beamformers using uniform linear arrays (ULA), the beampattern can be represented as a polynomial. The array polynomial is the z-transform of the beamformer weights. Evaluating the array polynomial on the unit circle in the complex plane yields the beampattern. For the ensemble MVDR beamforming using a ULA, the array polynomial zeros are constrained to fall on the unit circle. But the SMI MVDR polynomial zeros generally do not fall on the unit circle. The first part of the dissertation develops a model for the ensemble MVDR polynomial zero locations assuming a single interferer present in white background noise. The model illuminates the trade off balancing the interferer suppression and the white noise gain by the ensemble MVDR. Secondly, the dissertation proposes the unit circle MVDR (UC MVDR) beamformer which projects the SMI MVDR polynomial zeros radially on to the unit circle to satisfy the constraint on the zeros of ensemble MVDR polynomial. Numerical simulations show that the UC MVDR beamformer suppresses interferers better than the SMI MVDR and diagonal loaded MVDR beamformer and also improves the white noise gain (WNG). Finally, the dissertation proposes the double zero (DZ) MVDR ABF as a new approach to notch broadening. The array polynomial for the DZ MVDR ABF has second-order zeros, producing broader and deeper notches in the interferer direction. The DZ MVDR ABF outperforms the SMI MVDR and covariance matrix tapered ABFs in simulations with stationary and moving interferers.

NOTE: All ECE Graduate Students are ENCOURAGED to attend.
All interested parties are invited to attend. Open to the public.

Advisor: Dr. John R. Buck

Committee Members:
Dr. Paul Gendron and Dr. Dayalan Kasilingam, Department of Electrical & Computer Engineering; Dr. Raj Rao Nadakuditi, University of Michigan; Dr. Christ D. Richmond, Advanced RF Techniques & Systems, MIT Lincoln Laboratory

*For further information, please contact Dr. John R. Buck at 508.999.9237, or via email at jbuck@umassd.edu.