I. Introduction
Photoplethysmography (PPG) was a photoelectric method for measuring the volume of tissue blood, which was based on the change of blood volume in every cardiac pump. Compared to traditional method, PPG was a novel noninvasive method with the advantages of convenience and accuracy. Until now, PPG has been widely used for the detection of many basic physiological parameters [1], such as blood oxygen [2], heart rate, breath [3] and blood pressure [4]. Besides, PPG could also reflect some other important cardiovascular parameters, such as atherosclerosis etc. [5]. So there's great meaning to make a deep analysis of the PPG signal in order to extract various physiological parameters containing in it with high accuracy.