Time–frequency analysis of fusion plasma signals beyond the short-time Fourier transform paradigm: An overview

Performing a time–frequency (t–f) analysis on actual magnetic pick-up coil data from the JET tokamak, a comparison is presented between the spectrogram and the Wigner and Choi–Williams distributions. Whereas the former, which stems from the short-time Fourier transform and has been the work-horse for t–f signal processing, implies an unavoidable trade-off between time and frequency resolutions, the latter two belong to a later generation of distributions that yield better, if not optimal joint t–f localization. Topics addressed include signal representation in the t–f plane, frequency identification and evolution, instantaneous-frequency estimation, and amplitude tracking.