Research On Deterministic Scheduling Algorithms With Link Retransmission For Industrial Wireless Networks

Industrial wireless networks which are used for exchanging messages between industrial automation equipments have been widely applicated in the field of industrial process automation due to its low cost,flexible deployment,easy installation and maintenance.Industrial wireless field has strict requirements on the real-time performance of data transmission,and data must reach its destination within a certain time.Accordingly,deterministic scheduling technology is needed in industrial wireless networks.By running deterministic scheduling algorithm to allocate communication resources for data flow,industrial wireless networks allow each link to transmit data on the determined time slot and channel,so as to meet the deadline constraint of end-to-end field data.Besides,the transimission of filed data offten suffers from packet loss caused by complex industrial environment and various interferences.Existing researches on deterministic scheduling of industrial wireless networks mainly focus on the problem of how to obtain schedulable results,and fail to optimize the design of the mechanism of improving reliability such as link retransmission.The scheduling effect is easily influenced by network packet loss,which restricts the application of real-time scheduling algorithms in practical industrial wireless networks.Therefore,to solve the problems above,it is necessary to study the deterministic scheduling algorithm of industrial wireless networks on the basis of optimizing link retransmission in the scheduling process and thinking about the deadline constraint of data flow.The main work of this thesis includes:1.This thesis investigates the current research of deterministic scheduling in industrial wireless networks,and summarizes the existing problems.The basic principles of deterministic scheduling in industrial wireless networks are also analyzed.2.Aiming at the deterministic and reliability requirements of data transmission in industrial wireless networks,this thesis establishes the mathematical model of the network first,and then analyzes the schedulable conditions and dynamic priority determination criteria of data flow.Based on this,Deterministic Scheduling algorithm considering Continuous Retransmissions(DS-CR)is proposed.DS-CR which can improve the reliability of data transmission under the premise of ensuring the arrival of data within the deadline,takes the slot time margin of link as the dynamic priority criterion and adopts the continuous retransmission strategy.3.Considering the requirements of industrial wireless networks to complete link retransmission within a certain time range,this thesis proposes the Deterministic Scheduling algorithm considering Intra-Window Retransmissions(DS-IWR).DS-IWR schedules the released links and the retransmission links equally according to its priority determined by the slot time margin of link.By flexibly allocating communication resources,DS-IWR preferentially transmits the most urgent data and completes the retransmission of the link during the time window,thus it ensures the reliability of data transmission under the condition of meeting the deadline of data flow and the limit of retransmission time window.4.Simulation platform is set up to test the performance of both the two proposed scheduling algorithms and the comparison algorithms.The detailed analyses of test results are presented.The test results show that the two scheduling algorithms proposed in this thesis can meet the deterministic transmission requirements under the deadline constraint of data flow,and the reliability of data transmission can be improved when packet loss occurs in the transmission link.Hence,above researches bring some reference value for the development of deterministic scheduling technology in industrial wireless networks.