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Recovering one irregular signal in the presence of another stronger one--_in utero_ pulse ox

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(I posted this in comp.dsp a couple of weeks ago, but most of the actual 
DSP people seem to have disappeared, so the discussion petered out 
fairly fast.  Trying again here.)

Hi, all,

Hoping there are still some DSP folks round here despite the evil Google 
ban. (But I repeat myself.)

I'm working on a completely noninvasive sensor for fetal blood oxygen, 
using optical sensing through the mom's abdomen.  It's a very low SNR 
measurement on account of all the attenuation.

The mom's heartbeat modulates her pulse-ox signal, which is much 
stronger than the fetus's on account of the scattering and absorption in 
maternal tissue.

The data are several time series.  The main issue is the variability of 
both pulses, which smear out the spectra and therefore knock the peak 
heights way down towards the noise.  There are weak multiplicative 
effects between maternal and fetal signals, as you'd expect.

What I'm looking to do is something like:

1. Use a digital PLL to find the time-dependent maternal pulse rate.

2. Resample the data accordingly, and notch out the first 5 or so mom 
harmonics.

3. Do the PLL thing on the fetal pulse, and signal average to pull out 
the average fetal pulse ox signal.

Extra credit: sometimes the baby's pulse can cross the first or second 
harmonic of the mom's, and it would be good to preserve both pulse 
shapes accurately.

Resampling a noisy signal isn't necessarily the most well-conditioned 
operation, so I'd welcome suggestions for just how to do this.

Thanks

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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Recovering one irregular signal in the presence of another stronger one--_in utero_ pulse ox Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2021-06-06 14:38 -0400
  Re: Recovering one irregular signal in the presence of another stronger one--_in utero_ pulse ox Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2021-06-06 14:45 -0400
    Re: Recovering one irregular signal in the presence of another stronger one--_in utero_ pulse ox boB <boB@K7IQ.com> - 2021-06-10 22:53 -0700
      Re: Recovering one irregular signal in the presence of another stronger one--_in utero_ pulse ox Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2021-06-11 10:20 -0400

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