detect and remove motion artifacts from ppg signal using lms adaptive filter

fs=125;

frequency specifications

remove inband noise of motion artifacts from ppgsignal=(0.1 HZ or more);

allow freauency pulsatile portion=(0.5-4HZ); and resipiratory activity(0.2-0.35HZ);

[Israa]

I am facing the same issue. Could you please let me know if you found a tool to do it ?

Answer 1

[MULI]

Hi Rajesh,

I understand that you are looking for a method to remove noise from motion artifacts in a PPG signal.

You can follow the below steps to achieve this:

Design Bandpass Filter:

• The bandpass filter should be designed to pass both the pulsatile portion (0.5-4 Hz) and respiratory activity (0.2-0.35 Hz).

 bpFilt = designfilt('bandpassiir', 'FilterOrder', 4, ... 
            'HalfPowerFrequency1', 0.2, 'HalfPowerFrequency2', 4, ... 
            'SampleRate', fs); 
   filteredPPG = filtfilt(bpFilt, ppgsignal); % Apply the filter 
 

For more information and examples related to “designfit” and “filfilt”function you can refer to the following links:

https://www.mathworks.com/help/releases/R2021a/signal/ref/designfilt.html

https://www.mathworks.com/help/releases/R2021a/signal/ref/filtfilt.html

Simulate or Use Reference Signal:

• Use a reference signal that correlates with motion artifacts. If accelerometer data is unavailable, simulate a signal that mimics the artifact frequencies (e.g., starting from 0.1 Hz).

Apply LMS Adaptive Filtering:

• Now use an LMS filter to adaptively remove the motion artifacts. The LMS filter should be configured to minimize the error between the reference signal (motion artifact) and the PPG signal.

  filterOrder = 32; % Order of the adaptive filter 
   mu = 0.01; % Step size for the LMS algorithm 
   lmsFilter = dsp.LMSFilter('Length', filterOrder, 'StepSize', mu, 'Method', 'Normalized LMS'); 
   [filteredSignal, ~] = lmsFilter(referenceSignal, filteredPPG); 
 

For more information and examples related to “dsp.LMSFilter” function you can refer to the following link:

https://www.mathworks.com/help/releases/R2021a/dsp/ref/dsp.lmsfilter-system-object.html

By following these steps, you can isolate the desired physiological signals and minimize the impact of motion artifacts.