Abstract: The very minimum chirp keying (VMCK) is a novel ultra-narrow band communication scheme in which the up-chirp or down-chirp waveform corresponds to one or zero. This paper proves that VMCK is a kind of wavelet signal. The Mexican hat wavelet is used in time-frequency analysis of VMCK communications. Multi-cycle VMCK signal is also discussed. The results show that the spectrums of VMCK signals are arranged in different ways. The spectrum of up-chirp signals shifts to high frequency in the bit symbol, while the downchirp is in the opposite way. With the multi-cycle VMCK signals, the greater the modulation factor, the more the frequency shifts. The results show reliability of the wavelet analysis.

Key words: time-frequency analysis, ultra-narrow band (UNB), VMCK, wavelet