Signal processing method and apparatus
Inventors
GUAZZI, Alessandro • SHAH, Syed Ahmar • Tarassenko, Lionel
Assignees
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Publication Number
US-10993676-B2
Publication Date
2021-05-04
Expiration Date
Abstract
A method and apparatus for estimating the frequency of a dominant periodic component in an input signal by modelling the input signal using auto-regressive models of several different orders to generate candidate frequencies for the periodic component, generating synthetic sinusoidal signals of each of the candidate frequencies, and calculating the cross-correlation of the synthetic signals with the original signal. The frequency of whichever of the synthetic signals has the highest cross-correlation with the original signal is taken as the estimate of the frequency for the dominant periodic component of the input signal. The method may be applied to any noisy signal which has a suspected periodic component, for example physiological signals such as photoplethysmogram signals, and in the estimation of heart rate and breathing rate from such physiological signals.
Core Innovation
The invention analyzes an input signal to estimate the frequency of a periodic signal therein. It generates frequency domain candidates for the periodic signal by performing spectral analysis on the input signal to detect spectral components, where the detected spectral components constitute the frequency domain candidates. For each frequency domain candidate, a synthetic signal of the same frequency is generated.
A similarity of each synthetic signal with the input signal is calculated in time domain. A similarity threshold is defined, and the frequency of the synthetic signal with maximum similarity with the input signal is output as the estimate of the frequency of the periodic signal. The output is inhibited if the similarity of the synthetic signal with the maximum similarity with the input signal is below the similarity threshold.
In example implementations, the input signals are noisy signals and the estimated frequencies include respiration rate or heart rate. The approach is applied to physiological photoplethysmogram signals and video PPGi signals, including color channels such as red/green/blue channels.
Claims Coverage
The independent claim covers a frequency-estimation method that performs spectral analysis to form frequency-domain candidates, synthesizes time-domain signals at those candidate frequencies, computes a time-domain similarity measure against the input, selects the maximum-similarity candidate as the frequency estimate, and inhibits output when the maximum similarity is below a defined similarity threshold. The claim set includes refinements that add constraints on candidate frequency selection, autoregressive model fitting, similarity computation, and input segmentation/windowing.
Spectral analysis candidate frequencies
Generating frequency domain candidates for the periodic signal by performing spectral analysis on the input signal to detect spectral components of the input signal, the detected spectral components constituting the frequency domain candidates.
Synthetic signals matching candidate frequencies
For each frequency domain candidate generating a synthetic signal of the same frequency.
Time-domain similarity measure selection
Calculating in time domain a measure of the similarity of each synthetic signal with the input signal.
Similarity threshold controlled output
Defining a similarity threshold; outputting as the estimate of the frequency of the periodic signal the frequency of the synthetic signal with maximum similarity with the input signal; and inhibiting the outputting if the similarity of the synthetic signal with the maximum similarity with the input signal is below the similarity threshold.
Overall, the claims define estimating the periodic frequency by coupling spectral-analysis-based frequency-domain candidates with synthetic time-domain signals, selecting the candidate whose synthetic signal has maximum time-domain similarity to the input, and optionally inhibiting the estimate based on a similarity threshold.
Stated Advantages
Not explicitly described in patent.
Documented Applications
Estimating respiration rate from physiological PPG/PPGi signals.
Estimating heart rate from physiological PPG/PPGi signals, including video PPGi color channels (red/green/blue channels).
Using a reference capnometry comparison (reported as improved over prior AR-pole averaging versus reference capnometry).
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