【作者】 李本亮；

【导师】 王厚军；

【作者基本信息】 电子科技大学 ， 测试计量技术及仪器， 2011， 博士

【摘要】 基于无线局域网(Wireless Local Area Networks,WLAN)的分布式测试系统的实时性和时钟同步是当前分布式测试系统研究的热点课题。无线分布式测试系统数据传输的实时性是系统性能的重要指标,保持数据传输的可靠性,减少数据传输的延时是很多无线分布式应用系统的基本要求。时钟同步是无线分布式测试系统的核心技术之一,时钟同步的实现将使得各个分布式测试终端能够实现自主的数据采集,减少测试总线的控制信息传输,显著的提高测试的效率和精度。论文的主要研究工作及成果如下:(1)基于无线局域网的分布式测试系统的实时性研究。论文提出了基于WLAN的分布式测试系统模型,分析了影响分布式系统实时通讯的性能指标。针对系统实时性的要求建立了网络仿真场景,研究了无线分布式测试系统的不同MAC层接入机制的在数据流量递增的情况下实时性通讯的具体性能变化,并且研究了不同的物理层对系统的实时性能和丢包率的影响,为基于无线局域网的分布式测试系统设计提供了参考数据。(2)基于IEEE802.11 DCF(Distributed Coordination Function)的无线分布式测试系统实时性研究。DCF是无线局域网最常用的媒介接入机制,论文分析了IEEE802.11的DCF基本接入机制和RTS/CTS(Require To Send /Clear To Send)机制以及分片机制的工作原理。针对不同的MAC(Media Access Control)层接入机制分析了影响分布式系统性能的指标,研究了不同MAC层接入机制的无线分布式测试系统的实时性。论文在改进的MARKOV模型基础上,引入了Z变换,分析了IEEE802.11的DCF机制MAC延时性能,研究了从非饱和到饱和信道状态的延时性能。通过MATLAB数值分析和OPNET10.0网络仿真,基于MARKOV模型的MAC延时分析能够和网络仿真的MAC延时很好的吻合,验证了分析模型的在预测媒介接入延时方面的有效性,为进一步的系统设计提供了理论依据。(3)基于IEEE1588的无线分布式系统时钟同步应用问题研究。论文分析了IEEE1588网络拓扑的选择及域的划分对PTP(Precision Time Protocol)时钟同步的影响,提出了在无线分布式测试系统中应用IEEE1588协议的两种典型网络拓扑,研究了不同无线分布式网络拓扑下以及不同调度机制下PTP时钟同步精度,通过引入偏移估计和斜率补偿提高了无线分布式测试系统中PTP时钟同步的精度。研究结果对IEEE1588在无线分布式测试系统中的应用有重要的参考价值。(4)SPTP(Simplified Precision Time Protocol)时钟同步机制的研究。针对PTP时钟同步过程在无线分布式网络中应用面临问题,提出了一种新的无线分布式测试系统SPTP时钟同步机制。SPTP吸收了PTP同步机制的优势,同时又利用了RBS和PBS算法的优点。通过仿真比较了SPTP与PTP时钟同步精度差异,指出了SPTP时钟同步机制在无线分布式测试系统中的显著应用优势。(5)MBBS(Management and Boundary Broadcast Synchronization)时钟同步机制研究。针对无线分布式网络时钟同步中误差及信息的数目随层数增长过快的问题,提出了基于管理和边界时钟广播的MBBS时钟同步算法,详细介绍了MBBS的思想来源以及实现步骤。MBBS算法与PBS算法相比,虽然在每轮同步中增加一条同步信息,但是同步的从时钟数目增加了一层。实验结果表明,在多层网络拓扑下,MBBS减少了全局时钟同步所需的信息数目,提高了网络时钟同步的精度。MBBS算法的提出对无线分布式测试系统的时钟同步精度的提高有着重要的应用价值。更多还原

【Abstract】 The real-time performance and clock synchronization of Wireless local area network (WLAN)-based distributed measurement systems attract much attention from both academia and industry nowadays. The real-time performance of data transfer is one of the most important parameters in wireless distributed measurement systems. Maintaining reliable data transmission with minimum data transmission delay is a basic requirement in many wireless distributed systems. As a key technology in wireless distributed systems, clock synchronization allows all terminals to achieve data acquisition separately, which reduces the transmission of control information in data bus and significantly improves the efficiency and accuracy of the measurement. The main achievements and contributions of this dissertation are as follows:(1) The research on real-time performance of WLAN based distributed measurement system. The model of WLAN based distributed measurement system is proposed and the performance of the real-time communications is analyzed in this thesis. By using simulation for the real-time communication network, the performance variation of real-time communication through different MAC mechanisms with the gradually increase of the data traffic is investigated. In addition, the influence of different PHY layers on real-time performance and data packet miss probability of is studied. It provides reference data for further design of WLAN based wireless distributed system.(2) The research on real-time performance of distributed measurement system based on DCF of IEEE 802.11. DCF is a fundamental Media Access Control (MAC) mechanism in WLAN. Basic Access Mechanism, RTS/CTS mechanism and RTS/CTS-Fragment principle of DCF are all analyzed. Real-time performance of different wireless distributed MAC layer access mechanisms is studied. This thesis provides an improved MARKOV model and introduces Z transform to analyze and calculate the MAC delay of 802.11 DCF, which includes delay performance of the non-saturation and saturation transmission channel. The numerical analysis of MAC delay in MATLAB matches the network simulation in OPNET10.0, which proves accuracy of the analysis model in MAC delay predication. Furthermore, this thesis provides a theoretical basis for further system design.(3) The research on implementations of IEEE1588 for clock synchronization in wireless distributed system. This thesis analyzes effects of the network topology choice and domain partition of PTP,and studies the PTP clock synchronization accuracy in different network topology and different scheduling mechanisms. In addition, by using offset estimation and skew compensation to improve the accuracy of the PTP clock synchronization in wireless distributed measurement system. The research results are of most value in implementation of IEEE1588 in wireless distributed measurement system.(4) The research on SPTP clock synchronization mechanism. Focusing on problems of PTP clock synchronization in wireless distributed network applications, a new wireless distributed measurement system clock synchronization mechanism SPTP (Simplified Precision Time Protocol) is proposed. SPTP has the advantages of PTP, RBS and PBS methods. The clock synchronization accuracy of SPTP is compared with that of PTP by simulation. SPTP clock synchronization mechanism has obvious advantage in wireless distributed measurement system.(5) The research on MBBS clock synchronization mechanism. Focusing on rapid increasing of clock synchronization error and message amount in wireless distributed networks, Management and Boundary Broadcast Synchronization (MBBS) wireless distributed clock synchronization algorithm is presented. The main idea and realization steps of MBBS are described in detail. Comparing with PBS, MBBS adds a piece of message in each synchronization round, but solves another layer slave clocks’synchronization. It is demonstrated by simulation results that MBBS reduces the messages needed for global synchronization and reaches higher clock synchronization accuracy in multilayer topology. The proposition of MBBS algorithm is of most value in improving clock synchronization accuracy for wireless distributed measurement system.更多还原