Iterative method to derive an approximate matched filter template for fetal electrocardiogram signals

Fetal electrocardiogram (FECG) signals that are extracted from the maternal abdomen have a signal-to-noise ratio that is so low that the determination of the times of location of the R-waves can be difficult. A matched filter could, in principle, be used, but in theory this requires prior knowledge of the shape of the QRS complex of the FECG. In the work that is described in this paper, a digital low-pass filter, with an impulse response that is triangular in shape, is applied to the first M complexes of a simulated FECG signal. An average based on the detected R-wave locations is determined and this is used as an approximation to the matched filter template for the next block of M complexes. It is shown that this method can be iterated to obtain an effectiveness in detecting R-wave locations that is competitive with the corresponding performance that is obtained with the pure matched filter. The resilience of this technique to increasing noise levels is investigated.