On the Accuracy of Measured Proximity of Bluetooth-Based Contact Tracing Apps

Qingchuan Zhao, Haohuang Wen, Zhiqiang Lin, Dong Xuan, Ness B. Shroff

Abstract: A large number of Bluetooth-based mobile apps have been developed recently to help tracing close contacts of contagious COVID-19 individuals. These apps make decisions based on whether two users are in close proximity (e.g., within 6 ft) according to the distance measured from the received signal strength (RSSI) of Bluetooth. This paper provides a detailed study of the current practice of RSSI-based distance measurements among contact tracing apps by analyzing various factors that can affect the RSSI value and how each app has responded to them. Our analysis shows that configurations for the signal transmission power (TxPower) and broadcasting intervals that affect RSSI vary significantly across different apps and a large portion of apps do not consider these affecting factors at all, or with quite limited tuning.