Adaptive Filters and Applications - Digital Signal Processing: Fundamentals and Applications - page 478

Abdominal
lead

Chest leads
Abdominal
lead

dn ()

Reduced
Mother's
ECG

Chest leads

xn
1 ()

0 ()

sn () en ()

xn
2 ()

Adaptive
Algorithm

xn
3 ()

yn ()

xn

(a)

(b)

Mother
Fetus

(c)

Fetus

Mother

(d)

FIGURE 10.20

Canceling the maternal ECG in fetal monitoring.

(electrodes) are used to acquire the reference inputs: x 0 ðnÞ , x 1 ðnÞ , x 2 ðnÞ , and x 3 ðnÞ , with the
assumption that these channels only contain the mother's ECG (see Figure 10.20 (b)). One lead
(electrode) placed on the mother's abdomen is used to capture the fetal information dðnÞ , which
may be corrupted by the mother's ECG as shown in Figure 10.20 ( c). An adaptive filter uses its
references to predict the mother ECG, which will be subtracted from the corrupted fetus signal.
Then the fetal ECG with the reduced mother's ECG is obtained, as depicted in Figure 10.20 (d).
One possible LMS algorithm is listed below:

For k ¼ 0 ; 1 ; 2 ; 3

y k ðnÞ¼w k ð 0 Þx k ðnÞþw k ð 1 Þx k ðn 1 Þþ / þ w k ðN 1 Þx k ðn N þ 1 Þ

yðnÞ¼y 0 ðnÞþy 1 ðnÞþy 2 ðnÞþy 3 ðnÞ

sðnÞ¼eðnÞ¼dðnÞyðnÞ

For k ¼ 0 ; 1 ; 2 ; 3

w k ðn iÞ¼w k ðn iÞþ 2 meðnÞx k ðn iÞ; for i ¼ 0 ; 1 ; / N 1