Analog Self-Interference Cancellation Using Auxiliary Transmitter Considering IQ Imbalance and Amplifier Nonlinearity

In-band full-duplex communication, which transmits and receives simultaneously on the same frequency, causes self-interference (SI). In this paper, to cancel SI present in the radio frequency (RF) domain, we propose a novel nonlinear SI cancellation approach using an auxiliary transmitter which is effective in the presence of IQ imbalance and nonlinear distortion. The proposed approach estimates the local transceiver channel by using a time-domain least squares method and creates a signal for SI cancellation based on estimation results and a finite impulse response filter, whose coefficients are derived in this paper. Additionally, we theoretically calculate the SI cancellation limit of the proposed approach. Information about the SI cancellation limit due to phase noise is important for meeting SI cancellation requirements and being able to compare the effects of RF impairments such as IQ imbalance and nonlinear distortion. From simulation results, we show that the proposed approach outperforms the conventional approach and the case of using a general adaptive algorithm for the proposed approach. Furthermore, the SI cancellation limit is improved by adjusting the propagation delay of the SI signal and the canceling signal in addition to sharing one local oscillator in the local transceiver.