CheepSync: A Time Synchronization Service for Resource Constrained Bluetooth Low Energy Advertisers

TL;DR

CheepSync introduces a novel time synchronization service for BLE advertisers, enabling high-precision clock alignment on resource-constrained devices, which enhances IoT applications' efficiency and scalability.

Contribution

It presents a BLE-compatible synchronization framework utilizing low-level timestamping and error compensation, achieving microsecond-level accuracy on constrained hardware.

Findings

Achieves approximately 10 microseconds synchronization accuracy

Demonstrates effectiveness on custom and commercial BLE platforms

Validates performance through extensive empirical evaluations

Abstract

Clock synchronization is highly desirable in distributed systems, including many applications in the Internet of Things and Humans (IoTH). It improves the efficiency, modularity and scalability of the system, and optimizes use of event triggers. 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 paper presents and describes CheepSync: a time synchronization service for BLE advertisers, especially tailored for applications requiring high time precision on resource constrained BLE platforms. Designed on top of the existing Bluetooth v4.0 standard, the CheepSync framework utilizes low-level timestamping and comprehensive error compensation mechanisms for overcoming uncertainties in message transmission, clock drift and other system specific constraints. CheepSync was implemented on custom designed nRF24Cheep beacon platforms (as broadcasters) and commercial off-the-shelf Android ported smartphones (as passive listeners). We demonstrate the efficacy of CheepSync by numerous empirical evaluations in a variety of experimental setups, and show that its average (single-hop) time synchronization accuracy is in the 10us range.