CheepSync: a time synchronization service for resource constrained bluetooth low energy advertisers

Clock synchronization is highly desirable in distributed systems, including many applications in the Internet of Things and Humans (IoTH). For IoTH, Bluetooth Low Energy (BLE) - a subset of the recent Bluetooth v4:0 stack - provides a low-power and loosely coupled mechanism for sensor data collection with ubiquitous units (e.g., smartphones and tablets) carried by humans. This fundamental design paradigm of BLE is enabled by a range of broadcast advertising modes. While its operational benefits are numerous, the lack of a common time reference in the broadcast mode of BLE has been a fundamental limitation. This work presents and describes CheepSync: a time synchronization service architecture for BLE advertisers. We implement CheepSync on custom designed nRF24Cheep beacon platforms (as broadcasters) and commercial off-the-shelf Android ported smartphones (as passive listeners); and show that the average (single hop) time synchronization accuracy is in the 10 μs range.