Impulsive noise reduction in digital phase-sensitive demodulation by nonlinear filtering

Abstract

Phase-sensitive demodulation is widely used in many systems, e.g. impedance measurement, communication, sonar and radar. In most cases, white noise is assumed in system design and analysis. However, impulsive noise is often encountered in many applications, which imposes challenges for a phase-sensitive demodulator (PSD). This paper presents a nonlinear filter for removing impulsive noise prior to the PSD. Unlike its linear counterparts, it is analysed in the time domain rather than in the frequency domain, making it easier to implement. The performance of the proposed method is compared to a standard PSD with a low-pass filter to suppress the impulsive noise and the theoretical limits of the signal-to-noise ratio (SNR) is analysed. The theoretical prediction has been validated by numerical simulation and experiment. Experimental results show that the proposed method can achieve SNR improvement of 10.8 dB or greater when impulse rate α = 0.01. Statistical analysis shows that 97.2% of the impulses can be rejected by the median filter of length 3 when impulse rate is less than or equal to 0.1.