ITERATIVE METHOD TO DERIVE AN APPROXIMATE MATCHED-FILTER TEMPLATE FORFETAL ELECTROCARDIOGRAM SIGNALS

Fetal electrocardiogram (FECG) signals that are extracted from the mat ernal abdomen have a signal-to-noise ratio that is so low that the det ermination of the times of location of the R-waves can be difficult. A matched filter could, in principle, be used, but in theory this requi res prior knowledge of the shape of the QRS complex of the FECG. In th e work that is described in this paper, a digital low-pass filter, wit h an impulse response that is triangular in shape, is applied to the f irst M complexes of a simulated FECG signal. An average based on the d etected fi-wave locations is determined and this is used as an approxi mation to the matched filter template for the next block of M complexe s. It is shown that this method can be iterated to obtain an effective ness in detecting R-wave locations that is competitive with the corres ponding performance that is obtained with the pure matched filter. The resilience of this technique to increasing noise levels is investigat ed.