# US 11,998,312 B2 · Systems and methods for breathing detection and rate estimation using wireless communication signals

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- Number: US 11,998,312 B2
- Document ID: US11998312B2
- Status: Granted
- Kind: B2
- Application number: 17/038,456
- Filed: 2020-09-30
- Published: 2022-03-31
- Granted: 2024-06-04
- Earliest claimed: 2020-09-30
- Assignees: NXP USA, Inc.
- Applicants: NXP USA, Inc.
- Inventors: Xilin Cheng; Xiayu Zheng; Zhipei Chi
- Web page: https://patentgrep.com/patent/US11998312B2

## CPC

- A61B 5/0816: {Measuring devices for examining respiratory frequency (measuring frequency of electric signals G01R23/00)}
- G16H 50/20: for computer-aided diagnosis, e.g. based on medical expert systems
- A61B 5/0004: {characterised by the type of physiological signal transmitted}
- A61B 5/7214: {using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths}
- A61B 5/7257: {using Fourier transforms}
- G16H 50/30: for calculating health indices; for individual health risk assessment
- H04W 24/08: Testing, {supervising or monitoring} using real traffic
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G16H: HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

Various embodiments relate to a method for estimating a breathing rate, including: receiving a plurality of channel state information (CSI) from a wireless device; selecting an initial reference CSI from the plurality of CSI; computing a perturbation index using the initial reference CSI and a portion of the plurality of CSI; determining an optimal reference CSI based upon the perturbation index; re-computing the perturbation index using the optimal reference CSI on a portion of the plurality of CSI subsequent to the optimal reference CSI; and determining a breathing rate from the perturbation index using a frequency analysis of the perturbation index.

## Claims

### Claim 1

A method for estimating a breathing rate, comprising:
receiving at a first wireless communication device a wireless signal from a second wireless communication device;
measuring, by the first wireless communication device, a plurality of channel state information (CSI) data points from the wireless signal, wherein breathing-related motion over time changes the CSI data points between the first and second communication devices;
selecting, by the first wireless communication device, an initial reference CSI data point from the plurality of CSI data points;
computing, by the first wireless communication device, a first perturbation index curve for the wireless signal using the initial reference CSI data point and a portion of the plurality of CSI data points;
finding, by the first wireless communication device, an optimal reference CSI data point from within the plurality of CSI data points associated with a maximum perturbance index value from within the first perturbation index curve;
computing, by the first wireless communication device, a second perturbation index curve for the wireless signal using the optimal reference CSI data point and a portion of the plurality of CSI data points subsequent to the optimal reference CSI; and
determining, by the first wireless communication device, the breathing rate from the second perturbation index curve using a frequency analysis.

### Claim 2 (depends on 1)

The method of claim 1, wherein computing either the first or second perturbation index curves includes using channel nulling.

### Claim 3 (depends on 2)

The method of claim 2, wherein channel nulling includes:
calculating a nulling matrix; and
applying the nulling matrix to the plurality of CSI data points.

### Claim 4 (depends on 1)

The method of claim 1, wherein computing either the first or second perturbation index curves Γn includes computing:
Γn=10 log10|Σk,k+1∈ΨΔhkn HΔhk+1n|−10 log10Σk,k+1∈Ψ∥hkn∥2,
where Δhkn is channel change information for CSIn, hkn is the CSI for sample n, Ψ is the set of all the available tones, and k is tone index.

### Claim 5 (depends on 1)

The method of claim 1, wherein the frequency analysis of the second perturbation index curve includes applying a fast Fourier transform (FFT).

### Claim 6 (depends on 1)

The method of claim 1, wherein determining the breathing rate includes:
calculating a standard deviation of the second perturbation index curve over a window set of CSI data points; and
indicating a breathing detection failure when the standard deviation is below a predetermined threshold value.

### Claim 7 (depends on 1)

The method of claim 1, wherein the frequency analysis includes:
performing a frequency transformation of the second perturbation index curve over a window set of CSI data points; and
determining the breathing rate as a frequency with a highest value.

### Claim 8 (depends on 7)

The method of claim 7, further comprising:
calculating a peak-to-total power ratio using the frequency with the highest value; and
indicating a breathing detection failure when the peak-to-total power ratio is below a predetermined threshold value.

### Claim 9 (depends on 7)

The method of claim 7, further comprising sliding the window set of CSI data points and re-calculating the breathing rate.

### Claim 10 (depends on 7)

The method of claim 7, further comprising:
determining a breathing rate detection failure;
computing an average of the second perturbation index curve values corresponding to the window set of CSI data points;
indicating motion when the average of the second perturbation index curve values corresponding to the window set of CSI data points is above a predetermined threshold; and
indicating no motion when the average of the second perturbation index curve values corresponding to the window set of CSI data points is below a predetermined threshold.

### Claim 11

A breathing rate estimation device, comprising:
a first wireless communication device configured to:
receive a wireless signal from a second wireless communication device;
measure a plurality of channel state information (CSI) data points from the wireless signal, wherein breathing-related motion over time changes the CSI data points between the first and second communication devices;
select an initial reference CSI data point from the plurality of CSI data points;
compute a first perturbation index curve for the wireless signal using the initial reference CSI data point and a portion of the plurality of CSI data points;
find an optimal reference CSI data point from within the plurality of CSI data points associated with a maximum perturbance index value from within the first perturbation index curve;
compute a second perturbation index curve for the wireless signal using the optimal reference CSI data point and a portion of the plurality of CSI data points subsequent to the optimal reference CSI; and
determine the breathing rate from the second perturbation index curve using a frequency analysis.

### Claim 12 (depends on 11)

The system of claim 11, wherein computing either the first or second perturbation index curves includes using channel nulling.

### Claim 13 (depends on 12)

The system of claim 12, wherein channel nulling includes:
calculating a nulling matrix; and
applying the nulling matrix to the plurality of CSI data points.

### Claim 14 (depends on 11)

The system of claim 11, wherein computing either the first or second perturbation index curves Γn includes computing:
Γn=10 log10|Σk,k+1∈ΨΔhkn HΔhk+1n|−10 log10Σk,k+1∈Ψ∥hkn∥2,
where Δhkn is channel change information for CSIn, hkn is the CSI for sample n, Ψ is the set of all the available tones, and k is tone index.

### Claim 15 (depends on 11)

The system of claim 11, wherein the frequency analysis of the second perturbation index curve includes applying a fast Fourier transform (FFT).

### Claim 16 (depends on 11)

The system of claim 11, wherein determining the breathing rate includes:
calculating a standard deviation of the second perturbation index curve over a window set of CSI data points; and
indicating a breathing detection failure when the standard deviation is below a predetermined threshold value.

### Claim 17 (depends on 11)

The system of claim 11, wherein the frequency analysis includes:
performing a frequency transformation of the second perturbation index curve over a window set of CSI data points; and
determining the breathing rate as a frequency with a highest value.

### Claim 18 (depends on 17)

The system of claim 17, wherein the first wireless communication device is further configured to:
calculate a peak-to-total power ratio using the frequency with the highest value; and
indicate a breathing detection failure when the peak-to-total power ratio is below a predetermined threshold value.

### Claim 19 (depends on 16)

The system of claim 16, wherein the first wireless communication device is further configured to slide the window set of CSI data points and re-calculate the breathing rate.

### Claim 20 (depends on 16)

The system of claim 16, wherein the first wireless communication device is further configured to:
determine a breathing rate detection failure;
compute an average of the second perturbation index curve values corresponding to the window set of CSI data points;
indicate motion when the average of the second perturbation index curve values corresponding to the window set of CSI data points is above a predetermined threshold; and
indicate no motion when the average of the second perturbation index curve values corresponding to the window set of CSI data points is below a predetermined threshold.