Precision time protocol over LR-WPAN and 6LoWPAN

摘要

Precision time synchronization is critical for distributed sensing, and coordinated actuation in various low-range wireless applications in Internet of Things and Robotics. The state-of-the-art time synchronization protocol however, known as Precision Time Protocol (PTP) is designed for wired networks. In this work, we make an effort to enable PTP for Low Range Wireless Personal Area Networks (LR-WPAN). IPv6 over Low power Personal Area Network (6LoWPAN) represents the upper layers for LR-WPAN MAC and PHY layers in the protocol stack. Since 6LoWPAN offers additional advantages of software portability and interoperability with IPv6 based networks, we enable PTP over 6LoWPAN interface. We leverage PTP software abstractions and the networking stack to implement hardware timestamping feature for LR-WPAN and 6LoWPAN interfaces. To achieve precise timing, we expose 6LoWPAN interface as a Precise Hardware Clock (PHC) that enables accurate times-tamping of external events, precise hardware interrupts and pulse-per-second signals generation. We transform 6LoWPAN enabled ultra-wideband radios to wireless PHCs and achieve sub-nanosecond synchronization accuracy.