12 Impulsive Noise

mpulsive noise consists of relatively short duration " on/off " noise pulses, caused by a variety of sources, such as switching noise, adverse channel environments in a communication system, dropouts or surface degradation of audio recordings, clicks from computer keyboards, etc. An impulsive noise filter can be used for enhancing the quality and intelligibility of noisy signals, and for achieving robustness in pattern recognition and adaptive control systems. This chapter begins with a study of the frequency/time characteristics of impulsive noise, and then proceeds to consider several methods for statistical modelling of an impulsive noise process. The classical method for removal of impulsive noise is the median filter. However, the median filter often results in some signal degradation. For optimal performance, an impulsive noise removal system should utilise (a) the distinct features of the noise and the signal in the time and/or frequency domains, (b) the statistics of the signal and the noise processes, and (c) a model of the physiology of the signal and noise generation. We describe a model-based system that detects each impulsive noise, and then proceeds to replace the samples obliterated by an impulse. We also consider some methods for introducing robustness to impulsive noise in parameter estimation.