Feedback interference cancellation system for WCDMA radio repeater

In this paper, a feedback interference cancellation system (FICS) is investigated in order to prevent the feedback signal from the transmit antenna coming into the received antenna when the repeater´s gain is larger than the isolation between transmit and receive antennas of a radio repeater. Adaptive filters based on a least mean square (LMS) algorithm and a recursive least square (RLS) algorithm are also studied comparatively. The delay estimation algorithm based on a zero-padded autocorrelation technique is proposed. It can be shown that the proposed FICS achieves a lower error vector magnitude, especially for the RLS adaptive algorithm. In addition, the proposed delay estimation algorithm yields a highly accurate estimated delay of the first channel path. Furthermore, the proposed FICS does not need the feedback signal from the amplifier making the installation easier.