MicroSync: Sub-Micro Second Accuracy Wireless Time Synchronization Service

• Published in: IEEE access 2024-01, Vol.12, p.124478-124494
• Main Authors: Ohara, Ryotaro, Izumi, Shintaro, Imanaka, Shoya, Yamamura, Tetsuo, Toru, Ishii, Kawaguchi, Hiroshi
• Format: Article
• Language: English
• Subjects: Accuracy; Bluetooth; Bluetooth Low Energy; Clocks; Communication; Frequency drift; Global Positioning System; Internet of Things; Power consumption; Power demand; Power efficiency; Protocols; Real time; receivers; Scheduling; Synchronization; Time synchronization; Timing devices
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2024.3446668

This paper proposes MicroSync, a high-accuracy and low-power synchronization method based on two ideas: a hybrid timer and communication scheduling. The hybrid timer is implemented by combining two types of timers: a real-time clock and high-frequency clock timers. While high-frequency clock timers offer high resolution at the cost of increased power consumption, real-time clocks operate at lower frequencies, providing power efficiency but lower time resolution. The combination of these two timers results in a synchronized timer with low power consumption and high accuracy. Furthermore, we proposed two types of communication scheduling using this hybrid timer: high-accuracy and low-power scheduling. High-accuracy scheduling leverages Slave Latency, a feature of Bluetooth Low Energy (BLE), to minimize communication frequency, reduce the time gap between communication and synchronization, and prevent error accumulation caused by frequency drift. Both synchronization schemes were implemented on a commercially available Bluetooth transceiver IC. The evaluation results show that the high-accuracy scheduling achieves 400-ns synchronization accuracy with less than 300~\mu W power consumption. The low-power scheduling also achieves 1- \mu s synchronization accuracy with less than 150~\mu W power consumption under same conditions.