Radar Displacement Signal Processing for Heartbeat Harmonic Separation
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Solution Overview
Problem
Existing radar-based vital sign monitoring systems face challenges in accurately estimating heart rate due to interference from breathing harmonics, background noise, and random body movements, which can mask the heartbeat signal, especially in dynamic scenarios, requiring high signal-to-noise ratios and precise initial frequency estimates.
Innovation Solution
A method and system using an adaptive Nonlinear Least Squares (NLS) approach with individual search regions for each harmonic frequency estimate, combined with signal aggregation and bandpass filtering, to enhance heart rate estimation accuracy by adapting search regions and reducing computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If radar-based phase analysis is used to monitor vital signs, then contactless monitoring capability is achieved, but heartbeat signal detection accuracy deteriorates due to interference from breathing harmonics and background noise
Solution Approach 1:
The patent segments the frequency spectrum into distinct regions and applies different processing strategies to each. Specifically, it separates the fundamental heartbeat frequency from breathing harmonics by identifying and excluding frequency regions dominated by breathing-related components, thereby isolating the heartbeat signal for accurate detection
Solution Approach 2:
The patent extracts and removes interfering breathing harmonics from the displacement signal before heartbeat frequency estimation. By identifying breathing-related frequency components and eliminating them, the method isolates the heartbeat signal, enabling accurate heart rate monitoring without contact
2Device complexity
If conventional frequency estimation methods are used, then computational simplicity is maintained, but reliability of heart rate estimation deteriorates in dynamic scenarios with random body movements
Solution Approach 1:
The patent implements dynamic adaptation of search regions for frequency estimation. Instead of using fixed frequency ranges, the method adjusts the search regions based on previously estimated fundamental frequencies and observed signal characteristics, allowing the system to track heartbeat and breathing frequencies as they vary over time during dynamic activities
Solution Approach 2:
The patent employs feedback mechanisms where previously estimated frequencies inform subsequent estimation processes. The estimated fundamental frequencies from prior time windows are used to define search regions for current frequency estimation, creating a closed-loop system that continuously refines its estimates and adapts to changing physiological states
3Measurement precision
If high signal-to-noise ratio requirements are imposed, then heartbeat frequency estimation accuracy is improved, but system applicability deteriorates in real-world dynamic conditions
Solution Approach 1:
The patent converts the harmful effect of breathing harmonics into a beneficial filtering mechanism. By identifying breathing-related frequency components as markers for interference regions, the method uses these same components to define and exclude areas where heartbeat signals are masked, thereby transforming the problem of breathing interference into a solution for heartbeat isolation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method provides reliable and efficient heart rate estimation by accurately identifying fundamental frequencies despite interference, even in dynamic conditions, with improved signal-to-noise ratio and reduced computational burden.
Implementation Method 1
a transmitter for irradiating at least one body region of a person with radar radiation; a receiver for generating a receiver signal from reflected radiation from the at least one body region
Implementation Method 2
Radar-based vital sign processing relies on a phase analysis of a back-scattered signal, which corresponds to the chest-wall displacement induced by the breathing and the heartbeat mechanisms
Implementation Method 3
Doppler Vital Signs Detection in the Presence of Large-Scale Random Body Movements
Data Source
AI summary
A method for vital sign monitoring using a radar sensor system that includes a transmitter, a receiver, and processing device. The transmitter irradiates a body region of a person with radar radiation, the receiver generates a receiver signal from reflected radiation from the body region, and the processing device generates, for each of a plurality of processing windows, a displacement signal based on the receiver signal. The displacement signal characterizes a body motion having, as oscillating motions, a breathing motion and a heartbeat motion, and calculates an estimated fundamental frequency for at least one oscillating motion. The processing device applies an adaptive Nonlinear Least Squares method to calculate a plurality of frequency estimates, each of which corresponds to one of a plurality of harmonics of a first oscillating motion, wherein the processing device calculates a first estimated fundamental frequency for the first oscillating motion based on the frequency estimates.