【作者】 秦绍华；

【导师】 陈冬岩；

【作者基本信息】 山东大学 ， 控制理论与控制工程， 2014， 博士

【摘要】 随着无线传感器网络在工业测控、医疗监护、高效农业和智能建筑等领域的广泛应用,对网络通信性能的要求也不断提高。多信道通信技术的应用,可以有效地提高网络通信的可靠性和吞吐量,解决由于网络内节点众多而引起的通信竞争,以及由于通信信道受干扰而造成的网络瘫痪等问题。但是多信道通信技术的应用,也对网络通信协议的设计提出了更高的要求,如何有效地利用现有的多个信道,如何扩展已有的信道资源都是需要解决的问题。多信道通信在提高网络通信能力的同时,也带来了一些新的问题,由于网络内节点分散在不同信道,使得在单信道下容易实现的广播问题变得困难。另外,随着无线传感器网络应用的扩展,网络的安全问题也日益引起人们的重视,目前的安全研究主要集中在通信协议,密钥分配和管理等方面,对于时间同步协议安全的研究较少。时间同步是多信道通信稳定运行的基础,也是无线传感器网络实现各种与时间相关应用的前提条件,因此,一个安全的时间同步协议是实现多信道通信的基础。本文对多信道通信涉及到的多信道MAC协议,多信道频谱感知,多信道广播和时间同步的安全问题进行了研究。主要进行了如下工作：首先,对多信道通信的应用背景进行了分析。无线传感器网络是由部署在监测区域内的大量廉价微型传感器节点,通过无线通信方式形成的一种多跳的自组织网络。相比于传统的网络,无线传感器网络具有自组织,多跳通信和以数据为中心等特点,无线传感器网络节点众多,节点之间的通信竞争严重。因此,传统无线网络的通信协议并不适用于无线传感器网络,需要研究专门的通信协议。同时,无线传感器网络节点受成本和体积的限制,其计算能力,存储能力和通信能力都很弱,决定了节点不能运行复杂的程序,并且无线通信的可靠性较低。最重要的一点是,节点依靠电池供电,能源受限,而无线通信是节点主要的能量消耗方式。无线传感器网络的以上特点,对通信技术的可靠性,复杂性和能量效率都提出了极高的要求。多信道通信在无线传感器网络中应用多个信道进行信息传输,避免了网络内众多节点聚集在单一信道上而引起的通信竞争严重的现象。节点可以使用多个信道同时进行通信,也避免了节点间的相互干扰,使得一跳内的多对节点可以同时进行信息交换,而不会引起相互干扰,提高了网络的吞吐量。网络有多个信道可以使用,也避免了单信道情况下,由于所用信道受到干扰而造成整个网络瘫痪的危险。多信道通信有着诸多的优点,但是也增加了通信协议的复杂性。多个信道资源如何在众多的网络节点内进行分配,处于不同信道上的节点如何相互通信,如何减少通信协议的控制开销等问题都需要解决,另外,多信道引起的无线广播无法实现问题,以及如何避免使用受干扰信道,如何对授权信道进行机会接入等问题,都是多信道通信技术需要研究的。本文对已有的多信道通信MAC协议进行了研究。以McMAC为代表的并行协商类多信道MAC协议具有分布式控制,控制开销少和不依赖于控制信道等特点。并行协商类多信道通信中,节点按照自己的默认序列在多个信道上进行切换,不需要管理节点进行信道分配,分布式控制方式提高了协议的可靠性和可扩展性。节点的信道切换序列通过伪随机序列产生,节点可以通过本地计算得到对方节点所处的信道,减少了控制信息的交换。并行协商类多信道通信不依赖于控制信道,避免了众多节点在控制信道上竞争而造成的拥塞,以及控制信道受干扰而造成整个网络通信的崩溃。但是,传统的并行协商类多信道通信,还存在消失节点和节点之间通信竞争不公平等问题。本文在原有协议的基础上,设计了一种基于随机时间片的并行协商多信道MAC协议——RTMAC协议。该协议引入时间片机制,节点在一个周期内的某个时间片上苏醒,进行信息接收,而在其余时间片上休眠。节点苏醒周期的选择按照伪随机序列的方式进行。伪随机时间片的应用,不但可以让节点能够定时休眠,减少能量消耗,而且解决了消失节点问题,减少了通信失败的概率,同时也保证了网络内节点具有平等的通信竞争权利。仿真实验证明,RTMAC协议具有良好的网络吞吐量和能量利用率。无线传感器网络与无线局域网的无线信道存在重叠,当二者处于同一环境中时,不可避免的造成相互干扰,由于无线传感器网络的资源受限性,其在竞争中处于劣势地位,如何避免使用受干扰的信道,是多信道通信在实际应用中面临的现实问题。在无线信道资源紧张的条件下,有效地扩展无线传感器网络可利用的信道资源,是多信道通信进一步发展的方向,无线认知传感器网络的出现为多信道通信的发展开辟了新的道路,但是其关键问题是如何有效地进行频谱感知。有效地频谱感知不但是无线认知传感器网络的应用前提,也是避免使用受干扰信道的需要,但是传统的来源于认知无线电领域的频谱感知技术,因其复杂性较高,并不适应于无线传感器网络的应用。本文基于有限维随机矩阵理论,提出一种简单可靠的协作频谱感知算法。该算法利用准确,简洁的随机矩阵的DCN表达式,进行检测阈值的计算。仿真结果表明,该算法相比于渐进式的检测方案,具有需要检测数据少,检测性能可靠等优势,本方法为多信道频谱感知在无线传感器网络中的应用,提供了一种可行的方案。多信道在提高无线传感器网络通信能力的同时,也引起了一些单信道中不存在的问题。在单信道环境中,利用无线电波的广播特性,节点通过广播的形式,可以很方便地向邻居节点发送信息。无线传感器网络中的很多应用,以及路由协议的实现,都依赖于广播功能。但是在多信道环境中,邻居节点分布于不同的信道,节点在某个信道上发送的广播包,处于其他信道上的节点无法接收到,而且休眠机制的加入,使得节点在不同时刻苏醒,也增加了广播实现的难度。因此如何在多信道环境中,实现广播功能是多信道通信必须要解决的问题。本文设计了一种基于分布式广播树的广播协议——DTB协议。广播包的发起节点,采用发送广播训练包的方式建立指数型广播树,当其发起广播时,广播包按照树型路径进行转发。指数型广播树的建立,保证了网络内的节点都能接收到广播包,同时也避免了广播包的冗余发送。仿真实验表明,DTB协议具有广播路径建立快,广播包覆盖性好,广播延迟小等优点。随着无线传感器网络应用领域的日趋广泛,其安全性也越来越受到重视。时间同步协议是无线传感器网络众多与时间有关应用的基础,也是网络通信协议运行的前提。多信道通信时间片的划分,节点信道切换时间的估计,都需要可靠的时间同步。但是已有的时间同步协议大都关注于如何提高时间同步的精度,而在安全性方面缺乏措施,因此传统的时间同步协议存在诸多的安全问题,容易受到攻击而影响其时间同步的精度。本文从安全角度对已有的时间同步协议进行了分析,设计了一种具有容错能力的时间同步协议—FTTSP协议。该协议具有入侵检测机制,能够对恶意节点针对时间同步发起的攻击进行检测。对于偏差较小的缓慢攻击,以及时间同步中存在的发送时间误差,能够基于信息融合的原理,根据不同节点的时间同步信息的质量,采用随机加权平均的方法进行本地节点的时间校正。仿真实验表明,FTTSP时间同步协议具有良好的入侵检测能力和容错运行能力。总之,本文对无线传感器网络多信道通信的不同方面进行了分析,主要对多信道通信MAC协议的设计,多信道频谱感知,多信道广播以及时间同步协议的安全等问题进行了研究,给出了自己的解决方法。这些问题的解决,必将促进多信道通信在无线传感器网络中的应用,对促进无线传感器网络技术的发展,具有积极的意义。更多还原

【Abstract】 As wireless sensor networks are widely used in the field of industrial monitoring, medical care, efficient agriculture and intelligent buildings, the requirements to network communication performance are increasing. Multichannel communication technology can effectively improve the reliability and throughput of networks, and solves the communication competition due to the numerous nodes and the network breakdown as a result of the channel be interfered. But the application of multichannel communication technology also has higher requirements to the design of networks communication protocol, such as how to effectively use the available multiple channels, how to extend the available channel resources, these are problems needed to be solved. Although multichannel communication can improve the ability of network communication, it also brings some new problems, the broadcast is difficult because the nodes live in different channels, as this is easy to realize in single channel. In addition, with the expansion of the wireless sensor networks applications, networks security attracted more attention, time synchronization is the base of multichannel communication, it is also the condition for wireless sensor networks to realize some applications related to time. So a security time synchronization protocol is the foundation of multichannel communication.In this thesis, some problems related to multichannel communication were studied, such as multichannel MAC protocols, multichannel spectrum sensing, multichannel broadcast and security time synchronization. The main work of this thesis is as follows:First, the background of multichannel communication is analyzed. Wireless sensor networks are multi-hop self-organizing networks, which are formed by a large number of cheap micro sensor nodes in a region, connected with wireless communication to monitor. Compared with the traditional network, wireless sensor networks are self-organizing, multi-hop communication and data-centric, the quantity of nodes is numerous, and the communication competition among nodes is serious. So traditional wireless network communication protocols are not suitable for wireless sensor networks. On the other hand, restricted with cost and size of wireless sensor networks nodes, their computing power, storage capacity and communication capability are all weak, so they can not run complex programs, and their reliability of wireless communication are very low. Another we should consider is the node runs with battery, and its energy is restricted, and the wireless communication consumes most energy in a node. The above characteristics of wireless sensor networks, are challenges to the reliability, complexity and energy efficiency of communication technology.Multichannel communication uses multiple channels to transmit information in wireless sensor networks, avoiding serious communication competition caused by many nodes gathered in single channel. Nodes can simultaneously communicate with multiple channels, avoiding interfered with each other, and this improved the network throughput. The usage of multiple channels avoids the breakdown of networks caused by the single channel being interfered. Multichannel communication has many advantages, but also increases the complexity of the communication protocol. How to assign multiple channels to many nodes, how to make the nodes in different channels to communicate with each other, and how to reduce the control overhead of communication protocols, all these problems need to be solved. In addition, the problems about broadcasting in multiple channels, avoiding interfered channel, opportunity accessing the authorized channel, all need to be studied in multichannel communication technology.In this thesis, many traditional multichannel MAC protocols have been studied. Many multiple rendezvous multichannel MAC protocols, such as McMAC, are distributed controlled, have low control overhead and do not depend on control channel. In multiple rendezvous multichannel MAC protocols, the nodes switch in different channels according to their default sequence, do not need management node to assign the channels, this improves the reliability and scalability of protocols. The default sequence is generated from a pseudo-random sequence, each node can get the default sequence of other node with the local computing, and this method reduces the exchange of control information. The operation of multiple rendezvous multichannel MAC protocols do not rely on control channel, this avoids the congestion caused by the communication competition, and avoids the breakdown of the network caused by the control channel being interfered. But the traditional multiple rendezvous multichannel MAC protocols still have some problems, such as the disappear node and unfair communication competition. Based on the original protocols, the time slot mechanism is used in this thesis. In one period, the node wakes up in one slot to receive the information and sleeps in other slot. The awake slot is selected according to a pseudo-random sequence. The usage of pseudo-random time slot not only reduces the energy consumption with the sleep mechanism, but also resolves the problems about the disappear node and unfair communication competition. Simulation results show that this protocol has good network throughput and energy efficiency.There is an overlapping problem between the channels of wireless sensor networks and wireless local area networks, they will interfered each other when they located in the same area. Because wireless sensor networks are resource-constrained, which are weak in competition. How to avoid using interfered channel in multichannel communication, this is a practical problem need to be resolved. As the frequency resource is scarce, it is important for multichannel communication to find new method to use more channels. Cognitive radio sensor networks present a new approach to develop multichannel communication, and the key problem is how to do spectrum sensing in sensor networks. Effective spectrum sensing is not only the foundation of cognitive radio sensor networks, but also the requirement of avoiding interfered channel, but the spectrum sensing come from the cognitive radio, does not adapt the wireless sensor networks because of its high complexity. In this thesis, we proposed a simple and reliable cooperative spectrum sensing algorithm, based on finite-dimensional random matrix theory. In this algorithm, the detection threshold is calculated from the accurate and simple expression of DCN in random matrix. Simulation results show that, compared to the asymptotic method, the algorithm needs fewer measurements and has more reliable detection performance. This algorithm proposed a practicable method to use spectrum sensing in wireless sensor networks.Multichannel can improve the communication capability of wireless sensor networks, but also caused some problems that do not exist in single channel. In the single channel, using wireless broadcast advantage of the wireless radio, the node can easily transmit message to its neighbours with broadcast. Many applications of wireless sensor networks and routing protocols are depend on the broadcast. But in multichannel, the neighbour nodes locate in different channels, they can not receive the broadcast packet sent by a node in a fixed channel, and the sleep mechanism increases the difficulty of broadcasting, because it makes the nodes waking at different time. So how to broadcast in multichannel is a key problem of multichannel communication in wireless sensor networks. In this thesis, a broadcast protocol based on distributed broadcast tree is proposed. In this protocol, the node which initiates the broadcast will establish an index broadcast tree with training broadcast packets. When it begins to broadcast, the broadcast packet will be forwarded according to the tree. Broadcast tree ensures that all nodes in the network can receive the broadcast packets, and without redundant broadcast packets. Simulation results show that the broadcast tree can be established quickly, and the protocol has good performance in broadcast coverage and broadcast delay.As the expansion of wireless sensor networks applications, its security attracted much attention. Time synchronization protocol is related to many applications of wireless sensor networks, and it is also the foundation of many network protocols. The dividing of time slot and the estimating of channel switching time all need time synchronization. But most traditional time synchronization protocols focus on the accuracy of time synchronization, and do not consider the security, so there are some security vulnerabilities in traditional time synchronization protocols, and this will affect their accuracy. In this thesis, we analyzed the security of the traditional time synchronization protocols, and proposed a fault-tolerant time synchronization protocol. This protocol has intrusion detection function, it can detect the attacks against time synchronization from the malicious nodes. Using random weighted average method, the node can calibrate its local time with fusing many synchronization information from different nodes, this can resist smaller slow attacks with smaller deviation, and reduce the inherent error of transmit time in synchronization packets. Simulation results show that this time synchronization protocol has good performance in intrusion detection and fault tolerance.In this thesis, we analyzed different aspects of multichannel communication in wireless sensor networks. We mainly studied the design of multichannel communication MAC protocols, multichannel spectrum sensing, broadcast in multichannel, and security time synchronization protocols, we gave our own solutions to these problems. These solutions will promote the application of multichannel communication in wireless sensor networks, it is important to the development of wireless sensor networks.更多还原