A Time-Robust Digital Self-Interference Cancellation in Full-Duplex Radios: Receiver Design and Performance Analysis

Abstract

In full-duplex radios, precise time synchronization between the received and reconstructed self-interference (SI) is the basis of the effective SI cancellation (SIC). However, due to the impacts of the hardware imperfections and the propagation environment, perfect time synchronization is impossible. More seriously, the time-varying SI propagation channel aggravates the difficulty of time synchronization. To overcome the above problems, a time-robust digital SIC (TR-DSIC) is proposed in this article, as a novel scheme to address the time synchronization error (timing error). Firstly, by comprehensively considering nonlinear distortion and multipath propagation with different time delays and time-varying gains, a revised general memory polynomial (RGMP) model of the received SI is presented. Then, based on the RGMP model of the received SI, the TR-DSIC is proposed to cancel the SI in the digital domain, which is robust to arbitrary timing error and no need additional processing for it. Finally, the performance of the proposed TR-DSIC is analyzed under imperfect estimations of the polynomial coefficients. The analytical expression of the variance of the estimation error is presented here, and the closed-form expression of the residual SI power introduced by imperfect estimations of the polynomial coefficients is derived. Simulation results reveal that the TR-DSIC is capable of eliminating the influence of arbitrary timing error. Specially, when the maximum timing error is $0.5T_{s}$ for the SI multipath channel, the TR-DSIC outperforms the traditional DSIC without considering the timing error between the reconstructed and received SI by 5.2 dB.