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Cyber-physical system (CPS) is a system featuring a tight combination and coordination between the system's computational and physical resources. As a CPS representative, the Weather Monitoring and Train Traffic Control Simulation System (WMT2CS2) includes two subsystems: the wireless sensor network front end and the train traffic control simulation subsystem. The sensing front end collects the real-time data of weathers(speeds and directions of winds and rainfalls, etc.), and connects to the simulation subsystem. The purpose of WMT2CS2 is to study the impact of weather on the train traffic control and envisions to enhance the safety of high-speed rail (HSR) system. However, the simulation system design faces new challenges such as accurate and fast time synchronization, fast data/command dissemination, and so on. In this paper, we propose an accurate and low-latency time synchronization protocol based on constructive interference (CI) to apply in the sensing front end of the hybrid simulation systems. As a recently discovered physical layer phenomenon, CI allows multiple nodes transmit and forward an identical packet simultaneously. By leveraging CI, the proposed Radio-Driven Time Synchronization protocol (RDTS) can realize microsecond time synchronization accuracy and milliseconds latency. Moreover, RDTS can directly utilize the time-stamps from the sink node instead of intermediate nodes, which avoids the error caused by the unstable clock of intermediate nodes.
Date of Conference: 15-19 July 2012