Research On Noise Cancellation In Heart Rate Monitoring System

With the development of society and the improvement of living standard,people are paying more attention to healthy problem.Demand for real-time monitoring physical condition is ascending.Heart rate is a key indicator which reflects physical condition.Knowing about the real-time heart rate in different states helps people discover health problems and adjust their lifestyle in time,it is of great help in preventing heart disease and maintaining heart health.Moreover,heart rate monitoring for physical exercise facilitates arranging reasonable exercise intensity.As a result,real-time,noninvasive and accurate heart rate monitoring has been further developed,followed by various wearable heart rate monitoring device rising.At present,wristband is the most common device in the market,and it generally uses Photoplethysmography(PPG)as the heart rate measurement method.However,PPG is susceptible to various types of noise.The noise interference is more serious during exercising,reducing the accuracy of heart rate monitoring.This thesis was aimed at solving the problem of noise interference in heart rate monitoring system.Thus noise interference cancellation technique was studied and an algorithm of motion noise interference cancellation based on adaptive filtering was proposed.Combined with the peak search and tracking algorithm,the algorithm achieves accurate heart rate monitoring.The main contents and achievements of this thesis are as follows:1.The heart rate detection technology based on PPG was studied.The types of noise interference in PPG signal and their characteristics were analyzed and the noise cancellation algorithms for different kinds of noise were studied.The motion artifact is the most complicated noise in PPG,therefore the cancellation algorithm for motion artifact was studied in detail.Since the prior knowledge of motion artifact cannot be obtained,adaptive filtering is more suitable than the other algorithms to remove motion artifact.The algorithms of extracting heart rate based on the time domain and the frequency domain were studied.The result showed that the latter one had the better anti-interference ability.2.A multi-level adaptive filtering algorithm based on three-axis acceleration signal was proposed.It achieves cancellation of motion artifact.A spectrum peak searching and tracking algorithm based on frequency domain was designed and thus accurate heart rate monitoring was realized.The average absolute error of heart rate estimation is 2.34 BPM(Beat per Minute),the average absolute error percentage is 1.67%.3.An adaptive filtering algorithm based on acceleration signal synthesis was proposed.It achieves cancellation of motion artifact.A spectrum peak searching and tracking algorithm based on frequency domain was designed and thus accurate heart rate monitoring was realized.The average absolute error of heart rate estimation is 1.26 BPM,the average absolute error percentage is 0.96%.Compared to other estimation algorithms for heart rate monitoring,this algorithm has the advantages of high accuracy,simple and good real-time performance.