Experimental Evaluation of High-Precision System Clock Synchronization with BeiDou for Wide-Area Industrial Internet-of-Things

High-precision clock synchronization is required for many industrial Internet of Things (IIoTs) supporting real-time monitoring and control for applications, such as the smart grid. For high-precision clock synchronization in IIoTs, several approaches can be used, such as the IEEE 1588 protocol, the Network Time Protocol (NTP), and the Global Navigation Satellite System (GNSS) based methods. Among them, the GNSS-based methods are more appropriate for IIoTs distributed in wide areas. It has been reported that nanosecond-level time synchronization can be achieved by GNSS receivers. However, the end-to-end accuracy of the system clocks in the application processor is a different story. In this study, an experimental testbed has been built using the open-source Linux system, the BeiDou receiver, and the open-source Raspberry Pi 4 hardware. The Pulse-Per-Second (PPS) signals from the BeiDou receiver are used as the reference to synchronize the system clocks. With a one-second synchronization interval, experiments indicate that the system clock achieves an accuracy of 1 µs with a success rate of 92.7% and 2 µs with a success rate of 99.7%. While increasing the synchronization interval, the system clock relies more on the local crystal oscillator, and the timing error increases to 100 µs in 500 seconds.