Suppression of narrow-band interference in DS-spread spectrum systems using adaptive IIR notch filter

This paper proposes an algorithm for the suppression of narrow-band interference in direct sequence spread spectrum systems, based on the open-loop adaptive IIR notch filtering. In the open-loop notch filtering schemes, it is assumed that the frequency and power estimates are given or obtained by time-frequency analysis of input signal. In this paper, we estimate the frequency and power of the interference by using the adaptive lattice IIR notch filter. Another lattice IIR notch filter of the same structure is placed in front of the receiver, the notch of which is controlled by the frequency estimate in order to remove the interference. However, since the conventional IIR notch filters have zeros constrained on the unit circle, they also remove the information signal at the notch frequency while removing the interference at the same time. Hence, we adjust the depth of the notch with respect to the interference power, for the trade-off between data distortion and interference reduction. The objective function for adjusting the depth of the notch is defined as the overall signal to noise ratio (SNR). The SNR is expressed as a function of filter parameters, and the notch depth that maximizes the SNR is found. Simulation results show that the proposed algorithm yields comparable or better performance than the open-loop FIR notch filter, conventional FIR LMS, and nonlinear adaptive filters with long taps.