| Wireless sensor network (WSN) is a distributed sensing network. This paper is a sub-topic of The Geomagnetic-anomalies-detection Based Hidden Targeting Positioning System. The whole system is made up of several wireless sensor network nodes which communicate with each other via ZigBee protocol. The nodes should acquire the signal of the magnetic field generated by the magnetic targets in three-dimensional space with high speed and synchronization. So that the magnetic field signal acquired by monitoring nodes has zero phase difference. Hence, it is very important to study a solution of time synchronization applied to ZigBee network.This paper designed a set of the WSN measurement and control systems-Nebula. The nodes in the system are constructed upon EMZ3018wireless sensor network development kit with core of STM32W MCU. The system clock is revised in order to increase the timing accuracy of the node. To meet the need of high-precision time synchronization algorithm research. The time synchronization protocol design is based on the IEEE1588protocol, which is simplified the original time of interactions and the data amount in every interaction of the protocol. So that the protocol can apply to a low-data transmission rate and low-power ZigBee network. Additionally, some supporting function of the nodes is designed. The timing system of the node is designed by combining a16-bit register and a32-bit software variable together as a accurate timer running in UTC mode. The time synchronization algorithm and hibernation of the nebula measurement and control system is implemented. The task scheduling is arranged when the node is waked up. The above-mentioned functions are all implemented on the hardware target with C language. All the code is debugged on-line via J-link. The process of network formation, communication, data acquisition and time synchronization are verified by Tektronix TDS2024digital oscilloscope and SSCOM32debugger. Through the experiments, the time synchronization performance is evaluated. The phenomenon of synchronization accuracy between the wireless sensor network nodes get papers up to about5us, the entire network time synchronization accuracy meets the application error precision requirements. |
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