An Off-grid DOA Estimation Method for Passive Sonar Detection Based on Iterative Proximal Projection

Traditional direction of arrival (DOA) estimation methods based on sparse reconstruction commonly use convex or smooth functions to approximate non-convex and non-smooth sparse representation problems. This approach often introduces errors into the sparse representation model, necessitating the development of improved DOA estimation algorithms. Moreover, conventional DOA estimation methods typically assume that the signal coincides with a predetermined grid. However, in reality, this assumption often does not hold true. The likelihood of a signal not aligning precisely with the predefined grid is high, resulting in potential grid mismatch issues for the algorithm. To address the challenges associated with grid mismatch and errors in sparse representation models, this article proposes a novel high-performance off-grid DOA estimation approach based on iterative proximal projection (IPP). In the proposed method, we employ an alternating optimization strategy to jointly estimate sparse signals and grid offset parameters. A proximal function optimization model is utilized to address non-convex and non-smooth sparse representation problems in DOA estimation. Subsequently, we leverage the smoothly clipped absolute deviation penalty (SCAD) function to compute the proximal operator for solving the model. Simulation and sea trial experiments have validated the superiority of the proposed method in terms of higher resolution and more accurate DOA estimation performance when compared to both traditional sparse reconstruction methods and advanced off-grid techniques.