Research Of Time Synchronization Estimation Method In Industrial Wireless Sensor Networks Based On Timing Response

Time synchronization is one of the key technologies for wireless sensor networks.Time synchronization estimation method based on timing response is a novel clock synchronization method that has received much attention in recent years.This method does not need the interaction of specialized synchronization packets which carry timestamps,and estimation of clock synchronization parameters can be obtained during the transmission and reception process of ordinary data packets.Therefore,the time synchronization method based on timing response has the advantages of low synchronization overhead,high security,and easy embedding into existing network traffic.However,this kind of timestamp-free synchronization protocol needs the following response data packet,and the corresponding synchronization parameter estimator is derived by least square method based on the following response data packet model.Aiming at the above problems,this thesis proposes a timing response time synchronization method based on sequence number mapping.The proposed method has the characteristics of without interaction of timestamps and second response packet,the integration with the actual industrial wireless sensor networks(IWSNs)can be achieved easily.The maximum likelihood estimation method is used to derive the clock synchronization parameter estimator under the Gaussian random delay model.The main works of the thesis includes:1.Analyses of clock model,the delay that affecting time synchronization,the three mainstream standards of IWSNs are presented.Various time synchronization methods,including time synchronization method based on timing response are also discussed.2.For the existing timestamp-free synchronization method,it is necessary for a following response packet,which is inconvenient to integrate into the actual IWSNs.Thus,a timing response synchronization method based on sequence number mapping is proposed.Based on the fact that slot-based IWSNs generally adopt an acknowledgment frame mechanism,the timestamp-free synchronization can be embedded into the common data packet transmission and confirmation process.A mechanism of the response time for acknowledgment frame based on the data packet sequence number mapping is proposed,which eliminates the dependence of the following response packets.In this case,the synchronization overhead is further reduced and it is easy to integrate into the IWSNs,such as ISA100.11 a.In the scenario where the random delay meets the Gaussian distribution,the mathematical model of the synchronization process based on the timing response is established,and the maximum likelihood estimator of the clock skew and fixed delay is obtained.The corresponding CRLB is derived as the evaluation reference indicator for the performance of estimators.3.The Monte Carlo simulation method is used to verify the performance of the proposed time synchronization estimation algorithm.The simulation results show that the clock synchronization estimation method proposed in the thesis can reach the performance of the timestamp-free synchronization method which needs following response packets.Additionally,the synchronization overhead of our method is very low.The MSE curve of the estimators is close to its CRLB,and the good performance of estimators is verified.Therefore,the proposed method is valuable for synchronization technology in the actual IWSNs.