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工业无线传感器网络高精度高安全时间同步方法研究
Alternative TitleTime Synchronization with High Precision and High Security in Industrial Wireless Sensor Networks
王照伟
Department工业控制网络与系统研究室
Thesis Advisor曾鹏
Keyword时间同步 工业无线传感器网络 高精度 安全
Pages121页
Degree Discipline控制理论与控制工程
Degree Name博士
2018-11-27
Degree Grantor中国科学院沈阳自动化研究所
Place of Conferral沈阳
Abstract

工业无线传感器网络中,传感器节点通常通过协同操作的方式完成特定的工业应用,这要求传感器节点要满足时间上的一致,即时间同步。但是,由于节点时钟模型的不确定、链路通信时延抖动、安全威胁和网络拓扑异构等不利因素,节点之间的时间很难实现同步。考虑到时间同步对工业无线传感器网络中很多应用的重要性,时间同步问题一直是学者研究的重点。然而,由于工业环境和应用需求的特殊性,包括,环境恶劣、时间同步的高精度、快速收敛、安全可靠、低能耗和异构兼容性等,传统的无线传感器网络时间同步机制无法直接应用到工业网络中。比如,分层结构的主从时间同步机制中会产生同步误差累积,并且相邻节点的同步精度很低;依赖邻居信息的相邻节点时间同步机制存在通信开销大、收敛速度慢的缺陷;时间同步安全防御机制欠缺;同步机制多基于同构网络,不支持异构工业网络等问题。本文结合国内外的最新研究现状,针对工业无线传感器网络的高精度、高安全需求,设计了相应的时间同步方法,主要贡献包括以下内容:针对分层结构的主从节点时间同步机制下的误差累积问题,设计了基于PTP的主从节点高精度时间同步方法,综合考虑了无线链路的非对称传播时延、中间节点的转发时延以及从节点的时钟源计时误差等因素。该方法首先建立主从时钟之间的时钟偏移以及时钟偏移率的状态空间模型,然后基于此状态空间模型,利用卡尔曼滤波方法对从节点的时间进行估计。仿真结果验证了本文的时间同步方法与现有工作相比具有更高的同步精度。针对相邻节点时间同步机制中的通信开销大、收敛速度慢等问题,设计了基于最大一致性理论的相邻节点间同步误差修正方法。该方法基于混合时钟模型实现相邻节点间的逻辑时钟同步以及与时间源的硬件时钟同步。时钟更新规则基于最大一致性理论。此外,结合分簇的网络拓扑,设计了理想链路条件下基于簇结构的相邻节点间时间同步方法,加快了算法收敛速度并降低了通信开销。进一步的改进方法克服了相邻节点之间的有界通信时延干扰。针对现有时间同步机制缺乏针对女巫攻击的防御问题,设计了基于节点身份识别的安全时间同步方法NiSTS,其核心思想是利用节点之间的时间戳相关性和节点时钟斜率的唯一性来检测非法信息,而不是简单的孤立可疑节点。在检测过程中,每个节点都以相对于其共同邻居的相对时钟斜率为基础,确定信息是否可靠,并过滤无效信息。NiSTS可以抵抗女巫攻击和信息操纵攻击,并对网络中女巫攻击者的个数不敏感。针对现有时间同步机制不支持异构工业网络的问题,设计了无线传感器网络与骨干网的高精度时间同步方法。提出的基于PTP的异构网络时间同步模型,可支持域内和域间的时间同步,解决了不同网络因通信模式、同步方法、信息格式不一致造成的无法同步问题。提出的链路时延实时补偿机制,降低了链路非对称性,解决了异构网络链路时延无法确定的问题,并与标准PTP协议兼容。开发了支持PTP透传时钟功能的交换机,基于已有硬件搭建了实验平台,验证了所提方法的有效性和兼容性。

Other Abstract

In IWSNs, sensor nodes usually accomplish special industrial applications using cooperative operations, which require that sensor nodes should meet the demand of time consistency, namely, network time synchronization. However, due to the uncertainty of a node’s clock model, delay jitter of the communication link, the heterogeneity of network topology, security threats, etc., it is very difficult and challenging to achieve time synchronization among nodes. As time synchronization is important for many applications in IWSNs, it has always been the focus of scholars. However, industrial environment and application requirements are very unique, concerning harsh environment; high precision time synchronization; fast convergence; safety and reliability; low energy consumption; compatibility of heterogeneous networks, etc. Hence, the traditional time synchronization mechanisms of WSNs can not be directly applied to industrial networks. For example, in the hierarchical time synchronization mechanisms between the master and slave nodes, synchronization error accumulates quickly with the increase of link hops; and the synchronization accuracy between adjacent nodes is very low. Communication overhead is high and convergence speed is slow concerning the time synchronization mechanisms among adjacent nodes that rely on time information about the neighbors. In addition, traditional synchronization mechanisms lack security defense technique and do not support heterogeneous industrial networks. Based on the latest research status, this paper designs the corresponding time synchronization methods to meet the high precision and high security requirements of IWSNs. The main contributions of this paper are summarized as follows: For the synchronization error accumulation problem in hierarchical master-slave time synchronization mechanisms, we design the PTP-based time synchronizaiton method with high precision between master and slave nodes. The method considers the asymmetric propagation delays of wireless links, the forwarding delays of intermediate nodes, and the timing error of the clocks of slave nodes. We first build the state-space models of the time offset and the time offset skew between the master clock and the slave clocks. Then, based on the formulated state space models, we estimate the clocks of the slave nodes using a Kalman filter. The simulation results show that the proposed method yields higher synchronization precision than currently exists. For the high communication overhead, the slow convergence speed, and other problems in the time synchronization mechanisms among adjacent nodes, we design the maximum-consistency-theory-based correction method of synchronization errors among adjacent nodes. This method can realize logical clock synchronization between adjacent nodes and hardware clock synchronization with time source based on the hybrid clock model. The clock update rule is based on the maximum consistency theory. Combined with the clustering network topology, a cluster-based time synchronization method for adjacent nodes under ideal link conditions is designed to speed up the algorithm convergence time and reduce the communication cost. Additionally, another improved method overcomes the interference of bounded communication delay between adjacent nodes. Addressing the problem of a non-defense mechanism against Sybil attacks in current synchronization mechnisms, we design the node-identification-based secure time synchronization (NiSTS) method. The main idea of NiSTS is to utilize the timestamp correlation among different nodes and the uniqueness of a node’s clock skew to detect invalid information rather than isolating suspicious nodes. In the detection process, each node takes the relative skew with respect to its public neighbor as the basis to determine whether the information is reliable and to filter invalid information. The information filtering mechanism renders NiSTS resistant to Sybil attacks and message manipulation attacks. Moreover, NiSTS is not sensitive to the number of Sybil attackers. Due to existing synchronization mechanisms not supporting heterogeneous industrial networks, we design the high precision time synchronization method between WSNs and backbone networks. The proposed PTP-based time synchronization model of heterogeneous networks can support time synchronization in domains and crossing domains. It solves the problem hindering different networks from synchronization with each other due to inconsistent communication modes, synchronization methods, and information formats. The proposed real-time link delay compensation mechanism reduces the link asymmetry and solves the problem of indeterminate link delay in heterogeneous networks. It is compatible with standard PTP protocol. An industrial switch supporting PTP transparent clock function is developed, and an experimental platform is built based on the existing hardware. The results verify the effectiveness and compatibility of the proposed method.

Language中文
Contribution Rank1
Document Type学位论文
Identifierhttp://ir.sia.cn/handle/173321/23640
Collection工业控制网络与系统研究室
Recommended Citation
GB/T 7714
王照伟. 工业无线传感器网络高精度高安全时间同步方法研究[D]. 沈阳. 中国科学院沈阳自动化研究所,2018.
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