Mitigation of Continuous Wave Narrow-Band Interference in QPSK Demodulation Using Adaptive IIR Notch Filter

摘要

A Continuous Wave Narrow-Band Interference (CW-NBI) can reduce the effective signal-to-noise ratio (SNR), and the quality of the Signals-of-Interest (SoI) in any wireless transmission such as in a Digital Video Broadcasting (DVB-S2) receiver. Therefore, this paper proposes a novel low-complexity anti-jamming filter to mitigate unknown CW-NBI. The approach is to develop a robust least-mean-squared (LMS) algorithm for mitigating CW-NBI in QPSK demodulation but could be used in any communication system. The proposed filter is based on two open-loop Adaptive lattice Notch Filter (ALNF) structure and an LMS algorithm. Each ALNF is composed of a second-order Infmite-Impulse-Response (IIR) filter. The first ALNF is used to estimate the Jamming to Signal Ratio (JSR) and the frequency of the interference. In contrast, the second ALNF is used to remove the interference and adjust the depth of the notch according to the estimated JSR. On the other hand, the LMS algorithm is used to obtain and then track the interference. Simulation results show the performance of the proposed IIR notch filter with the LMS algorithm in reducing and mitigating interference. Also, it provides better output SNR of the notch filter for a given value of JSR and BER performance. For example, at the JSR value of -6 dB, the SNR output of the proposed IIR notch filter was enhanced by 9 dB compared to the case without a filter when E_b/N_o = 20 dB.