Noncircularity restoral for multi-antenna blind beamforming

Blind beamforming for extracting noncircular signals without the prior knowledge about the objective steering vector is considered. Three second-order blind techniques via NonCircularity REstoral (NCRE) are proposed to recover a dominant noncircular signal from circular interferences plus sensor noise with arbitrary and unknown correlation structure. These schemes are labeled as NCRE1, NCRE2, and NCRE3, respectively. For the high-rank environments where a number of rectilinear/circular interfering signals are present a Mixed-Order BEamspace (MOBE) technique, using simultaneously the second- and fourth-order cumulants, is developed. The performance of these proposed methods is studied based on numerical simulations. NCRE1 is computationally simple but performs well only in the case of very weak interferences and moderate noise, NCRE3 can provide good performance in the presence of medium or weak interferences, while NCRE2 is very suitable for adverse signal environments. NCRE2 outperforms NCRE1 and NCRE3 in terms of convergence rate, over a wide range of signal to interference plus noise ratio values. It is demonstrated that all the three NCRE methods are better than the traditional sample matrix inversion technique in the presence of look direction mismatch. They are also more attractive than the high-order cumulant method when non-Gaussian circular interferences are encountered. The MOBE method is shown to be competent for handling rectilinear/circular interfering signals, with respect to the attainable output signal to interference plus noise ratio.