Research And Implementation Of Cross-network Clock Synchronization Method For Industrial Internet Of Things

In industrial networks,devices possess a tight timing relationship between each other so that they need to maintain a consistent clock.And the precision time services are also needed when it comes to the scenarios such as data fusion,energy management,and deterministic scheduling.Therefore,precision clock synchronization is an important technology for industrial networks to function properly.The Internet of Things is widely applied in industrial automation,environmental monitoring and smart cities because of its comprehensive sensing,reliable transmission,and intelligent processing.Among them,the industrial internet of things,which is based on industrial wireless technology,is one of the mainstream development directions.In practical deployment,industrial internet of things integrates industrial backhaul networks with wireless field networks.Therefore,the implementation of clock synchronization across the industrial backhaul network and the wireless field network has become a challenging problem.In addition,in development and application,the border gateways of industrial internet of things mostly adopt modular design and are not equipped with hardware synchronization units.Therefore,it is an important problem that how to meet cross-network clock synchronization requirements with low complexity.In view of the above problems,a low-complexity cross-network clock synchronization method based on border gateway forwarding is proposed and implemented taking WIA-PA(Wireless Networks for Industrial Automation-Process Automation)as an example.The main contributions of this thesis include:Firstly,this thesis investigates the clock synchronization technology in industrial internet of things.The related technologies and current research status of clock synchronization in industrial backhaul networks,field wireless networks,and hybrid networks have been analyzed.Secondly,a low-complexity cross-network clock synchronization method based on border gateway forwarding is proposed to solve the problem of clock synchronization in industrial internet of things.The industrial wireless field network and the wired backhaul networks can get synchronized with software,and neither hardware synchronization unit nor extra protocol are required.Moreover,the mixed transmission of time synchronization data and network protocol data is supported.Thirdly,the low-complexity cross-network clock synchronization method based on border gateway forwarding is implemented taking WIA-PA as an example.And inside the border gateway,a timestamping method on serial interface driver layer is proposed and implemented to reduce the delay jitter caused by the non-real-time operating system's preemptive scheduling strategy.Finally,the proposed cross-network clock synchronization method is tested on experimental platform and the test results are analyzed.Test results show that the proposed method can meet cross-network clock synchronization requirement with low complexity and is convenient for unified management and IP transmission of the networks.The research of this thesis has a reference value for the practical application of clock synchronization in industrial internet of things.