Highly accurate demodulation method of an IPFM model with an absolute refractory period

Abstract

An integral pulse frequency modulation (IPFM) model is a pulse generation mechanism model for the nervous systems and is one of the models which connects heart rate variability to autonomic nervous system activity. There is a refractory period just after a heart beat impulse occurs, in which no heart beat impulses occur at any rate. The IPFM model does not take the refractory period into account. It would be good to consider the refractory periods in order to make the IPFM model realistic. In this paper, we are examining the effects of the absolute refractory period on the spectral distortion properties and the demodulation accuracy. Spurious components, (which are caused by mutual interference among the frequency components), decreased as the absolute refractory period increased, while the side-band distortion around the input frequency components increased. The direct FFT method impairs demodulation accuracy as the absolute refractory period increases. Even the integral function (IF) method without taking the absolute refractory period into account can reduce the distortion that is peculiar to the absolute refractory period. Moreover, the IF method which took the absolute refractory period into account has higher demodulation accuracy in spite of the absolute refractory period.