Polarization Oblique Projection Based Self-Interference Cancelation in Full Duplex with Nonlinear PA

Abstract

In MIMO full duplex (FD) system, power amplifier (PA) nonlinearity degrades the self-interference (SI) cancelation performance significantly. Since the polarization state (PS) of the SI is completely determined by the structure of the transmit antenna and is unaffected by the PA nonlinearity, we propose a polarization oblique projection based SI cancelation method which exploits the PS information of the SI to resist the PA nonlinearity in this paper. This method can project the nonlinear SI to the null space of the operator, and the major merit of it is the non- necessity of the PA nonlinearity coefficients estimation, which can avoid the estimation error caused by the mismatch between the estimated PA model and the actual PA property. Numerical results demonstrate that the proposed method can cancel the nonlinear SI effectively. Moreover the signal to interfere and noise ratio (SINR) gain and the achievable sum rate of the proposed method do not deteriorate when the transmit power is high compared with the existing cancelation methods. Further, the achievable sum rate can be more than twice that of the half duplex when the depolarization effect of the wireless channel is the most severe. Meanwhile the system equipped with orthogonally dual-polarized transmit antennas can obtain better performance than that equipped with uni- polarized transmit antennas.