Digital Domain Self-Interference Cancellation Based on Modified Variable Step-Size LMS Algorithm

As one of the key technologies of 6G, co-time co-frequency full duplex (CCFD) technology can more effectively utilize the spectrum and hardware resources of the radio system. However, the biggest challenge of this technology is how to cancel out the self-interference (SI) between the transmitter and receiver. In this paper, a time-varying least mean square (LMS) digital domain self-interference cancellation (SIC) algorithm with step-size parameters gradually decreasing with time is proposed. Our modified variable step-size LMS (M-VSLMS) algorithm establishes a new nonlinear function relationship between the step-size factor and the error signal, and controls the step-size factor to be updated by using the autocorrelation time mean of the error signal. The simulation results show that the proposed algorithm enhances the interference cancellation ratio (ICR), speeds up the convergence rate, and improves the abilities of channel tracking and anti-interference. Compared with the traditional variable step-size LMS algorithm, it improves the digital domain ICR by more than 2 dB and the convergence speed is increased by more than twice.