A Timing Asynchronous Self-interference Cancellation Method in Full-Duplex OFDM Systems

In the timing asynchronous self-interference cancellation (TASIC) of full-duplex (FD) orthogonal frequency division multiplexing (OFDM) systems, the relative delay between the signal of interest (SoI) and the self-interference (SI) may be greater than the length of the cyclic prefix (CP) due to the long distance transmission of the SoI and the access timing control, which causes a loss in the orthogonality of the SI when performing SI cancellation (SIC) in the frequency domain directly. In order to maintain the orthogonality of the SI pilots and estimate the channel response without the interference caused by the SoI, a channel estimation method is given utilizing either the complete or incomplete subcarriers. Based on it, a TASIC method is proposed to cancel the SI, where the expression of the time-domain SI is derived considering the influence of the multi-path channel and the relative delay between the SoI and the SI. The theoretical and simulation results show that the value of the residual interference (RI) power is stable and the SIC ratio (SICR) increases with the increase of the interference to signal ratio (ISR), and the proposed TASIC method can largely avoid the impairment brought by the relative delay between the SoI and the SI.