Study On Real-time Scheduling Methods Based On Proportion Deadline For Industrial Wireless Networks

Industrial wireless network is a prevalent technology on industrial automation field,which can realize the communication among industrial field devices and contributes to the production of the industrial field.In industrial wireless networks,data is requested to transmit with a deterministic and real-time way to avoid underlying hazard caused by timeout arriving.Real-time scheduling is a key technology to achieve deterministic and realtime transmission by effectively allocating time slots and channel resources in industrial wireless networks.The uncertain channel collisions and link collisions over the tranmission process will result in the waste of time slots and channel resurces,which prevents the complete transmission from arriving within the specified deadline.How to allocate multiple channel resources in the network to links at each time slot to avoid conflicts,and improve data transmission efficiency is a challengable problem of realizing deterministic data transmission in industrial wireless networks.Therefore,to solve the above problems,this thesis proposes two real-time scheduling methods based on the method of earliest proportional deadline first,while combining with the characteristics of data flows in industrial wireless networks,in order to satisfy the request of transmission deadline.The proposed scheduling methods is verified by simulation,and the main work of this thesis are follows:1.The current literature of industrial wireless networks real-time scheduling technology is studied,the existing problems are summarized,and the related basic knowledge of industrial wireless network real-time scheduling is analysed by this thesis.2.Considering the senario where the link of the data flow encounters conflicts in current time slot,a method based on local link conflict degree and max proportional deadline is proposed on the basis of the established network model and the method of earliest proportional deadline first.This method in first calculates the ratio of the conflict number of data flow released link and the unscheduled links to deadline time,and then schedules the network according to the obtained ratio above.The proposed method can improve the scheduling success ratio effectively.3.Considering the urgency of data flow which is affected by the conflicts of all unschedulded links on the data flow path,a method based on the link of path conflict degree and max proportional deadline is proposed.At each slot,this method not only considers the conflicts of data flow released link,but also calculates the conflict number of all unscheduled links behind the released link.Therefore,the method can further improve the scheduling success ratio.4.The performance of the proposed scheduling methods is verified and is compared with the exsited real-time methods on the simulation platform.The simulation results show that the method based on local link conflict degree and max proportional deadline can improve scheduling success ratio in a lower time complexity way,and is adopted to networks with limited computing resources.Tough the method based on the link of path conflict degree and max proportional deadline has a relatively higher time complexity,it can achieve a higher scheduling success ratio and is adopted to the network with rich computing resources.The two scheduling methods proposed in this thesis can satisfy the real-time request of data transmission,and have a reference value for the development of real-time scheduling technology in industrial wireless networks.