Closed-loop self-synchronized signal controlled constrained notch filter with application for rejection of arbitrary frequency variation speed sinusoidal interference

The closed-loop self-synchronized constrained notch filter (CLSS-CNF) is proposed, and its ability for retrieval of narrowband signals corrupted by a strong FM interference is studied. Self-synchronization is achieved through the estimation of the instantaneous phase of the FM interference to control time-varying coefficients of SC-CNF by using a closed-loop structure. The CLSS-CNF can overcome the tracking capability threshold of a conventional constrained adaptive notch filter (CANF), and reject a sinusoidal interference with arbitrary speed of frequency variation. Based on this approach, two such filters are discussed, and their system performances compared. It is shown that the proposed filters are superior to both the conventional CANF as well as the recently proposed SC-CNF with open loop structure. Use of closed loop and the specially developed projection scheme for time-varying coefficients allow one to achieve a signal to the interference ratio (SIR_O) of up to 20 dB compared to the input SIR_i of less than -20 dB