A closed-loop adjusting strategy for wireless HART time synchronization

Wireless Highway Addressable Remote Transducer (HART) uses Time Division Multiple Access (TDMA) and channel hopping to communicate between devices. So it is important to keep high accurate time synchronization for a wireless network. This paper proposes a closed-loop adjusting strategy for time synchronization (CATS) which deals with the dramatic variation of oscillator drift rates. CATS is based on double sampling periods, i.e., a synchronization period and an adjusting period. The variation of relative drift rate between different nodes is estimated in the synchronization period. The closed-loop control law is carried out in the adjusting period, which is derived from the estimator of relative drift rate variation. The experimental results indicate that CATS achieves almost the same accuracy as the flooding time synchronization protocol (FTSP) with the regression table of 8(FTSP-8), and it outperforms FTSP-16. Furthermore, it's revealed that CATS achieves lower computational complexity and stronger environmental adaptation than FTSP does.