Undecimated Lifting Wavelet Packet Transform with Boundary Treatment for Machinery Incipient Fault Diagnosis

Figure 2

One subband in the fourth layer decomposed using wavelet packet and preprocessed by different methods: (a) no extension, (b) zero-padding extension, (c) periodic extension, and (d) second-order Volterra series prediction.

(a)

(b)

(c)

(d)