Wavelet-based feature extraction
After acquiring the vibration signals in the time domain, it is
processed to obtain feature vectors. The continuous wavelet transform
(CWT) is used for obtaining the wavelet coefficients of the
signals. The statistical parameters of the wavelet coefficients are
extracted, which constitute the feature vectors.
The term wavelet means a small wave. It is the representation
of a signal in terms of finite length or fast decaying waveform
known as mother wavelet. This waveform is scaled and translated
to match the input signal.
The continuous wavelet transform (Mallat, 1998) is defined as:
WsðsÞ ¼
R þ1
1 f ðtÞWs;jðtÞdt
where Ws;jðtÞ ¼ 1ffiffiffi
jsj
p W ts
s
is a window function called the mother wavelet, s is a scale and s is
a translation.