Wideband Direction-of-Arrival Estimation via Covariance Fitting and Focusing

This paper studies the problem of direction-of-arrival (DOA) estimation for multiple wideband source signals using a uniform linear array. We propose a covariance fitting and focusing-based estimation method (COFFEE). Specifically, we develop a wideband covariance fitting criterion and formulate a corresponding bilevel optimization problem by introducing focusing operations on covariance matrices. We show that the upper-level problem for covariance fitting can be cast as a rank-constrained semidefinite programming (SDP) and the lower-level problem for the focusing matrices has a closed-form solution. We develop an alternating direction method of multipliers algorithm for the rank-constrained SDP. We further propose an alternating iterative algorithm to solve the overall bilevel optimization problem. Numerical results demonstrate that COFFEE outperforms existing methods.