2D-DOA Estimation for NLOS Environments via Intelligent Reflecting Surface

Direction-of-arrival (DOA) estimation provides the angle information about interesting targets for array radar systems. However, conventional algorithms are designed for line-of-sight (LOS) scenarios and thus cannot be used to estimate non-LOS (NLOS) targets. Recently, intelligent reflecting surface (IRS) has been applied to DOA estimation for NLOS environments. This paper proposes a geometric model utilizing IRS for DOA estimation in NLOS scenarios. First, we establish an IRS-aided DOA estimation framework, where one-pair-IRSs is used to manipulate the propagation direction of the detection signals. Then, we formulate the estimation task using the elliptic positioning technique. Subsequently, we derive a closed-form solution for the resultant problem. Furthermore, we improve the architecture using multi-pair-IRSs and then design a binary weighting method to enhance the accuracy of DOA estimation. In comparison with the existing methods, the proposed algorithm is able to estimate two-dimensional (2D) DOA for NLOS targets. Numerical simulations are conducted to validate the effectiveness of IRS for DOA estimation in NLOS environments.