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.