Blind Self-Interference Analog Canceller with Differential Delay for Backscatter Communications

This paper demonstrates that the differential active self-interference canceller (DASIC), which does not require prior channel state information (CSI) of self-interference (SI), is effective in not only in-band full-duplex (IBFD) communications, but also backscatter communications. Unlike IBFD, backscatter communications have the characteristic that the desired signal is generated by nonlinear switching with rectangular pulse shape. Inspired by the characteristic, this paper proposes a method that enables cancellation in the analog domain by shortening the differential delay time of DASIC to a duration that can be implemented with a practical delay line. Additionally, focusing on the fact that the absolute value of the DASIC outputs remains constant regardless of the propagation delay time, an appropriate maximum a-posteriori probability (MAP) detector is designed for cases where the propagation delay time is unknown at the receiver. Finally, computer simulations confirm the efficacy of the proposed method by comparing the performance of MAP detectors when the propagation delay time is known and unknown, in terms of bit error rate (BER) performance.