SonicPACT: An Ultrasonic Ranging Method for the Private Automated Contact Tracing (PACT) Protocol
This work addresses the problem of inaccurate proximity estimation for contact tracing applications, which is a critical issue for public health authorities and app developers.
The paper introduces SonicPACT, a protocol that uses near-ultrasonic signals on smartphones to estimate distances via time-of-flight measurements. This method aims to improve the accuracy of device proximity estimation for contact tracing apps, addressing the challenges faced by Bluetooth Low Energy (BLE) signals.
Throughout the course of the COVID-19 pandemic, several countries have developed and released contact tracing and exposure notification smartphone applications (apps) to help slow the spread of the disease. To support such apps, Apple and Google have released Exposure Notification Application Programming Interfaces (APIs) to infer device (user) proximity using Bluetooth Low Energy (BLE) beacons. The Private Automated Contact Tracing (PACT) team has shown that accurately estimating the distance between devices using only BLE radio signals is challenging. This paper describes the design and implementation of the SonicPACT protocol to use near-ultrasonic signals on commodity iOS and Android smartphones to estimate distances using time-of-flight measurements. The protocol allows Android and iOS devices to interoperate, augmenting and improving the current exposure notification APIs. Our initial experimental results are promising, suggesting that SonicPACT should be considered for implementation by Apple and Google.