Multi-wavelength photoplethysmography (MW-PPG) sensing technology has been known to be superior to signal-wavelength photoplethysmography (SW-PPG) sensing technology. However, limited by the availability of sensing detectors, many prior studies can only use conventional bulky and pricy spectrometers as the detectors, and hence cannot bring the MW-PPG technology to daily-life applications. In this study we developed a chip-scale MW-PPG sensor using innovative on-chip spectrometers, aimed at wearable applications. Also in this paper we present signal processing methods for robustly extracting the PPG signals, in which an increase of up to 50% in the signal-to-noise ratio (S/N) was observed. Example measurements of saturation of peripheral blood oxygen (SpO2) and blood pressure were conducted.
Conventional VLC receivers use photo-electronic devices with a fixed spectral response, and have no capability of canceling in-band interference from other users. We propose the use of filter array receivers equipped with data combing approaches to achieve interference rejection for wavelengthdivision-multiplexing visible-light-communication (WDM-VLC) systems. To reduce the computational cost of data combing as well as the error-propagation from corrupted sensors, we propose a selective combining method using the 1 l -norm algorithm to sparsely select the correct sensors. Simulation results show that a reduction rate of 61% for the sensor usage can be achieved using the proposed method, while still providing a competitive signal to interference plus noise ratio.
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