A comparative study on estimation of instantaneous frequency by means of LMD

In order to solve the problem of calculating the instantaneous frequency by means of local mean decomposition, four methods were introduced such as Hilbert transform, Teager energy operator, direct quadrature and inverse cosine. By analysis of the advantages and disadvantages of various methods, the following conclusions could be made: first, the phenomenon of end swing by Hilbert transform was obvious; second, Teager energy operator method was easy to susceptible to signal form and noise, and the error was relatively large; third, inverse cosine method could be influenced by signal extreme points and brought in the mutations of instantaneous frequency. To solve the mutations of instantaneous frequency by inverse cosine method, an improved algorithm was proposed, which used cubic B-spline interpolation to obtain the instantaneous frequency of signal extreme points. It was shown from simulation and experimental results that the improved inverse cosine method could avoid the phenomenon of mutation and the error of instantaneous frequency was smaller.