A Radio Repeater Interference Cancellation Model for Mobile Communication Systems

When the gain of a radio repeater is larger than the isolation between the transmit and receive antennas of the repeater, the feedback signal that comes into the receive antenna from the transmit antenna of the repeater causes the repeater to go into feedback oscillation regardless of the input signal. To prevent feedback oscillation of the repeater by interference cancellation (ICAN), a feedback oscillation model of a radio repeater is first formulated. An ICAN model is then derived from that model. According to the ICAN model, iterative algorithms such as the least mean square (LMS) algorithm using the minimum mean square error criterion can be applied to perform the necessary ICAN. The validity of the ICAN model is confirmed by a computer simulation that shows the relationship among the level of ICAN, the repeater's gain, the estimated delay, and the filter length for the LMS algorithm.