Robust widely linear beamformer based on a projection constraint

For noncircular signals, optimal widely linear (WL) minimum variance distortionless response (MVDR) beamformer has a powerful performance by exploiting the noncircularity of the received signals. Though, the noncircularity rate can be estimated by the steering vector (SV) of the signal of interest (SOI), the performance degrades as there exist errors in the SOI's SV. This paper introduces a new robust WL beamformer. In the proposed approach, the assumed extended steering vector (ESV) of the SOI is used to construct an interference-plus-noise subspace projection matrix, and the new ESV is estimated by maximizing the WL beamformer output power under a constraint that prevents the ESV from converging to the interference. The proposed algorithm only needs imprecise knowledge of the antenna array geometry and the SOI's angular sector. Simulations verify the effectiveness of the proposed algorithm.