Adaptive IIR notch filter with controlled bandwidth for narrow-band interference suppression in DS CDMA system

Suppression of NBI in a DS CDMA system using a fully adaptive IIR notch filter is investigated. An algorithm that requires no gradient signal generating filters for tracking the center frequency of the NBI is proposed. A gradient algorithm for adapting the notch bandwidth coefficient to a value that results in maximum SNR improvement factor and minimum BER is presented. Convergence behaviors of the algorithms are analyzed. Closed-form expressions for SNR improvement factor and BER of the system are derived. Simulations are shown to verify the analyses and compare the performance of the proposed scheme with that of a linear adaptive FIR prediction filter.