Wireless Clock Synchronization Protocol For EtherCAT System

EtherCAT is an Ethernet which is used for control and automation, which usesring-type bus topology to promote real-time performance on physical layer. Due to itsadvantages in frame construction, transmission rate and real-time performance, it hasbeen used in various fields and has attracted more and more attention from industryand academic areas. It provides a new standard for the performance of real-time systemand flexibility in topology.There is a strong relationship between signal in real-time Ethernet and time,which puts emphasis on achieving time synchronization to collect valid data and toperform control in the system. To achieve time synchronization, the system requires areference time from outside and each subsystem’s clock board should be synchronizedwith it. Emphasis should also be put on a protocol which ensures that each slave clockboard and the time reference are in synchronization. This paper discusses how thereference time is accurately distributed to the EtherCAT system to achievesynchronization.Firstly, there is a brief introduction to the real-time Ethernet EtherCAT.Secondly the IEEE1588protocol, GPS, wireless sensor network clock synchronizationprotocol are analyzed and their advantages and disadvantages are discussed. Alongwith the analysis of the characteristics of the wireless network environment, a newwireless synchronization protocol for synchronization between the reference clock andEtherCAT clock board is proposed. The new protocol eliminates channel access delayby using reservation packets, fights with instability of wireless environent by usingmultiple frames to backup each other, adjusts the slave clock using statistical averagedelay. Finally, the correctness and feasibility of the algorithm are verified on the USRPplatform, the results show that it achieves the purposes.