RESUMO
Airborne transmittable diseases such as COVID-19 spread from an infected to healthy person when they are in proximity to each other. Epidemiologists suggest that the risk of COVID-19 transmission increases when an infected person is within 6 feet from a healthy person and contact between them lasts longer than 15 minutes (also called Too Close For Too Long (TC4TL). In this paper, we systematically investigate Machine Learning (ML) methods to detect proximity by analyzing publicly available dataset gathered from smartphones' built-in Bluetooth, accelerometer, and gyroscope sensors. We extract 20 statistical features from accelerometer and gyroscope sensors signals and 28 statistical features of Bluetooth signal, which are classified to determine whether subjects are closer than 6 feet as well as the subjects' context. Using machine learning regression, we also estimate the range between the subjects. Among the 19 ML classification and regression methods that we explored, we found that ensemble (boosted and bagged trees) methods perform best with accelerometer and gyroscope data while regression trees ML algorithm performs best with the Bluetooth signal. We further explore sensor fusion methods and demonstrate that the combination of all three sensors achieves a higher accuracy of range estimation than when using each individual sensor. We show that proximity (< 6ft or not) can be classified with 72%-90% accuracy using the accelerometer, 78%-84% accuracy using gyroscope sensor, and with 76%-92% accuracy with the Bluetooth data. Our model outperforms the current state-of-the-art methods using neural networks and achieved a Normalized Decision Cost Function (nDCF) score of 0.34 with Bluetooth radio and 0.36 with sensor fusion.