Self-Interference Suppression with Length-Adaptive Digital Filter in In-Band Full-Duplex Relay

The emerging in-band full-duplex (IBFD) system is a promising technique to enhance spectral efficiency and reduce latency in the beyond 5G systems. However, effectively mitigating self-interference (SI) is crucial for leveraging IBFD advantages. This paper presents a dual-stage approach to suppress SI, constructing feedforward linear finite impulse response (FIR) filters in the digital domain by carefully considering processing delays and error vector magnitude (EVM). In this sense, the analog self-interference cancellation (ASIC) filter coefficient is first calculated through the least squares (LS) estimator, whereas the digital self-interference cancellation (DSIC) filter is obtained by optimizing both the estimation error and filter length using the dual gradient descent method. The simulation results validate the effectiveness of this method in mitigating SI while reducing the processing delay at the relay.