In a 3GPP-based system such as 4G-LTE and 5G-NR, a UE transmits a PRACH (Preamble Random Access Channel) signal in the initial connection with a base station. As a result, the interference canceling repeater suddenly receives a high-power narrow-band signal continuously in a no user signal state, so that the interference cancellation algorithm may malfunction and the system is likely to cause oscillation. In this paper, we propose an adaptive algorithm that can maintain the interference cancellation function without oscillation even for narrow band input with an abrupt change of the spectrum and power.
