Inherent self-interference cancellation at 900 MHz for in-band full-duplex applications

This paper addresses the biggest practical obstacle of in-band full duplex (IBFD) communication systems, which is self-interference (SI) signals. We propose a novel analog self-interference cancellation technique for single antenna IBFD systems. In this technique, we use the secondary SI signal reflected by the antenna to cancel the primary SI signal leaked from the circulator transmitter port at the receiver. We use an adjustable mismatch impedance terminal (IMT) at the antenna port to modify the magnitude and phase of the secondary SI signal. We design and fabricate a prototype of single antenna IBFD in the ISM frequency band at 900 MHz. The measurement results show 40 dB SI cancellation over 35 MHz frequency bandwidth.