IEEE 1588 Time Synchronization Optimization Based On OMNeT For Multi-hop WSNs

Wireless Sensor Networks (WSNs) is typical distributed network, has advantages in self-organizing, deployment flexibility and low cost, however, its reliability and stability are relatively lower. Time synchronization mechanism is the key technology to enhance the reliability and stability of WSNs. Although many time synchronization algorithms and protocols have been proposed for packet-exchange networks, such as Network Time Protocol (NTP), Flooding Time Synchronization Protocol (FTSP), and the recently proposed IEEE 1588 Precise Time Protocol (PTP) etc. NTP has lower accuracy, usually in tens of milliseconds, FTSP has higher requirements on communication bandwidth, while the IEEE 1588 PTP is able to obtain high synchronization accuracy by relatively low-bandwidth communication, and is expected to become the future standard for WSNs time synchronization. However, IEEE 1588 PTP is designed for wired industrial Ethernet, and has high requirements on the symmetry of propagation delay and the accuracy of time-stamps, how to apply it in multi-hop WSNs and achieve high time synchronization precision is still inconclusive.This paper studies how to establish a more realistic simulation platform to simulate performance of PTP protocol in multi hop WSNs, and the measures are proposed to improve the synchronization performance. More specifically, the main contents and contributions of this paper as follows:(1) On the basis of analysis of WSN’s oscillator clocks and PTP synchronization protocol, building the imprecise clock model and discrete model, the modeling of time stamp uncertainty, and the state space modelling of the PTP protocol, and the clock model is converted to a state transition equation and the PTP protocol model is converted to an observation equation, which lay a foundation for Kalman filter technique and state estimation technique, so as to research on how to improve and enhance the PTP synchronization algorithm.(2) A discrete event simulator TS3 (Time Synchronization Simulator) based on OMNeT is built, and a high realistic simulation for PTP time synchronization in multi-hop WSNs is implemented. The simulation results show that IEEE 1588 PTP can achieve high time synchronization precision, but adaptation of PTP should be improved in the multi-hop WSNs.(3) On the basis of the state-space model, servo clock algorithms based on Kalman filter are proposed. The simulation results show that PTP based on Kalman filter is able to upgrade the performance of multi-hop time synchronization and the scheme is suitable for multi-hop WSNs.