A Two-Stage Analog Self-Interference Cancelation Structure for High Transmit Power In-Band Full-Duplex Radios

High transmit power in-band full-duplex (IBFD) systems are promising due to their tremendous advantages in both civilian and military applications. However, mitigating self-interference (SI) in such a high transmit power condition is significantly challenging. A two-stage analog filtering structure is proposed in this letter to tackle this problem successfully. The first stage is based on a vector modulator and a balun to cancel the direct leakage SI component. The second stage is constructed from an analog least mean square (ALMS) loop to adaptively cancel the residual SI. The performance of the second stage with nonlinear transmit signals is investigated analytically. Simulation results show that a total 75 dB of SI cancellation can be achieved by the proposed structure, ensuring the residual SI falls into the linear range of the analog-to-digital converter.