R.Shavelis and M.Greitans, “Extended Fourier Series Representation of Signals With Time-Varying Bandwidth”, ICICS 2013, Tainan, Taiwan, 10 – 13 December, 2013.

The paper proposes an extension of the classical
Fourier series for analysis of signals with time-varying spectral
content. This, in comparison to classical series, allows reducing
the number of coefficients that represent the signal if the
fundamental frequency of the extended Fourier series is chosen
according to the time-varying bandwidth of the signal. The
advantage of the proposed series is demonstrated by numerical
results for various test signals.