Information processing of optical sensor data in ambient applications

We have made use of the microbending fiber optic sensor to capture ballistocardiographic signals or data for vital signs monitoring in ambient settings, with applications ranging from serious games to ambient assistive living for ageing at home for the elderly. To remove noise and extract the vital signs, the first step of the signal data processing is filtering the signal. In this paper we consider the properties of the digital filter for filtering ballistocardiographic signals. The vital signs waveforms are derived from raw data captured by optical transducers that are placed in ambient locations that are in contact with, but not worn by the subject. Data has been collected from various locations and positions and a detailed trial has been conducted for one of these positions. We iteratively improve the filter design so as to lead to the best parameters. The baseline filter performed reasonably well on data collected in a trial study, with a mean error rate less than 10% for half of the subjects and below 20% for three quarters of the subjects. We also present results of an improved filter that improves the performance both in terms of responsiveness and sensitivity. The improved filter demonstrates consistently less than 12% mean error rate. Principles gleaned from this study may also be applied in designing filters for other types of sensors and for other applications in healthcare.