Robust Nonlinear Interference Cancellation with Time Alignment Error in Full-Duplex Systems

In full-duplex (FD) systems, time alignment error between the received self-interference (SI) and the reconstructed one results in performance degradation of the SI cancellation. As a crucial part of SI cancellation, nonlinear interference (NI) cancellation is usually invested in the ideal situation, and the impact of the time alignment error on NI cancellation performance is rarely considered. In this paper, a robust NI cancellation algorithm is proposed to tackle the time alignment error in FD systems. At first, the impact of the time alignment error on NI cancellation is analyzed. The approximate expression of the residual NI power with time alignment error is derived to predict the NI cancellation performance. Then, an improved memory polynomial (IMP) model is derived to describe both time alignment error and nonlinearity. Finally, based on the IMP model, a novel NI cancellation algorithm with robustness to the time alignment error is proposed. Simulations present the impact of the time alignment error on NI cancellation capability, in which the theoretical value is coincident with the actual value. Besides, the proposed algorithm significantly enhances the NI cancellation performance. Specifically, when the time alignment error is 10% of the sampling interval and the interference to noise ratio is 60 dB, the proposed algorithm outperforms the conventional algorithm by 33 dB.