Study On Clock Network Structure And Synchronization In Distributed Test System

Network based distributed test is a complex and hard work. Different from theindependent test system, in a network based distributed test system, each node needs towork cooperatively to complete a test task. All the nodes need to work in the commonsense of time, and they must be synchronized to a reference clock. There are two waysto improve the synchronization precision: hardware and algorithms. The hardwaremethod can significantly improve synchronization precision at the expence of thehardware cost and the power consumption. However, considering the power limitedwireless distributed test system, the hardware way is inapplicable. In this case, thesoftware algorithm is a preferable way, and it is also the focus of this dissertation. Basedon the project of my research, this dissertation studies the clock synchronization in thedistributed system and some key issues in precise time protocol (PTP). The main workis as follows:1. PTP clock synchronization behavioral model establishment. Based on the IEEE1588clock synchronization protocol, we establish the PTP clock synchronization modelbased on the OMNeT++software. Also we construct the mathmatcal model for themaster-slave nodes clock synchronization in the context of the PTP protocol, andanalyse several critical issues for the synchronization precision. This model can providethe simulation platform for the study of synchronization algorithms.2. Study on the choice of the master clock in the distributed test system. In theinitial process of the distributed test and control system, we must decide which node canbe served as the master clock in the context of the current situation of network. There isanother case that, due to the inner or external influence, the choosed master clockfails, and we must choose a substituted master clock. Since the synchronizationprecision of the whole network highly depends on the property of master clock. Theresearch of the optimal master clock choice is very important to the clocksynchronization. Based on the research of the post-impact on the synchronization afterfailure of the master clock in the process of synchronization, this dissertation presents aclock group based algorithm to handle the choice of the master clock. The experimental results indicate that, after the failure of the master clock, the introduced method cansignificantly reduce the influence on the coming synchronization.3. Considering the noise in the time measurement, the dissertation studies on theKalman filter to improve the synchronization precision. In IEEE1588clocksynchronization protocol, the clock difference between master node and slave node ismeasured using the PTP message. However, any measurement will be corrupted bynoise. Based on the machenism of the different noise source, we construct themathmetical models for both the clock offset and the clock skew. In order to employ theKalman filter algorithm to estimate the clock offset and the clock skew, the stateequation and the observation equation are established. The clock difference is calibrated,and the slave clock model parameters are corrected. In practical application, the clockskew will be subject to environment. To address this problem, synchronizationalgorithm based on the second order Kalman filter is introduced. With an adptive modelselection method, clock model can be detected on line, and the optimal clocksynchronization algorithm can be employed.4. Study on the clock synchronization based on the linear topology structurenetwork. For the case that there are multiple middle nodes in the communication linkbetween the master node and slave node in a linear topology structure network, thesynchronization precision will decrease with the increasing of the number of middlenodes. This dissertation studies on the applications of boundary clock and transparentclock in the clock synchronization in a distributed network with linear topologystructure. The comparison between boundary clock and transparent clock has been made.The clock model for different middle clock and the different number of middle nodes inlinear topology structure network is also considered.