移动Ad Hoc网络中基于ID的信道预约多址接入协议

为了在移动ad hoc网络中有效利用无线信道资源,提出一种基于ID的信道预约(ID-based channel reservation,简称IDBCR)多址接入协议.该协议在公共信道上发送Request-To-Send/Clear-To-Send(RTS/CTS)分组实现握手,采用基于节点ID的信道选择方案选择无冲突的业务信道传输数据分组,目的节点成功接收完数据分组后在另一个公共信道上回复acknowledgment(ACK)分组,有效避免了暴露终端问题.最后,仿真实现了IDBCR协议,并与CAM-MAC(cooperative asynchronous multi-channel MAC)多信道协议比较.结果表明,在总信道利用率、平均信道利用率和平均分组延迟性能上,IDBCR多址接入协议明显优于CAM-MAC协议.     

移动ad hoc网络中DOS攻击及其防御机制

移动ad hoc网络由于其动态拓扑、无线信道以及各种资源有限的特点,特别容易遭受拒绝服务(DOS)攻击．提出了移动ad hoc网络中一种新的DOS攻击模型——ad hoc flooding攻击及其防御策略．该攻击主要针对移动ad hoc网络中的按需路由协议,如AODV,DSR等．ad hoc flooding攻击是通过在网络中泛洪发送超量路由查询报文及数据报文,大量地占用网络通信及节点资源,以至于阻塞节点正常的通信．分析ad hoc flooding攻击之后,提出了两种防御策略：其一是邻居阻止,即当入侵者发送大量路由查询报文时,邻居节点降低对其报文的处理优先级,直至不再接收其报文．其二是路径删除,即目标节点将入侵者发送攻击报文的路径删除,以阻止其继续发送攻击报文．模拟实验证实,通过这两种方法的结合．能够有效地阻止网络中的ad hoc flooding攻击行为．     

中小型Ad hoc网络信道接入协议研究

在介绍了Ad hoc网络的概念及特点的基础上,系统地论述了Ad hoc网络的多址接入技术,并针对基于时分多址接入的网络系统提出了一种改进的无线自组网信道接入协议--信道预约多址接入协议.该协议通过对物理信道的动态划分,将控制信道与业务信道相分离,实现了网络控制信息和业务信息的无冲突发送,改善了网络的信道利用率和传输的可靠性.     

一种新的基于虚拟多信道的无线自组织网络

为了提高灾后应急通信网络频率资源利用效率,提出了基于多信道技术的虚拟多信道ad hoc网络方案。该方案采用单个控制信道和多个数据信道的虚拟多信道结构,通过跳频生成器实现收发机在不同跳频序列之间动态切换。控制信道使用所属子网占用的跳频序列,数据信道使用空闲跳频序列。设计了虚拟多信道路由协议VMCRP,提出了新的路由度量标准VMCM和控制信道分相广播机制CCSP。仿真结果表明:与传统网络相比,本方案能大幅增加网络容量和提升网络吞吐量。     

基于节点合作的Ad hoc网多信道MAC协议

针对Ad hoc网络的多信道隐藏终端问题,提出一种基于邻居节点合作通告机制的异步多信道媒介访问控制协议。该协议通过空闲邻居节点向未收到信道协商控制帧的节点发送通告广播帧,从而有效地解决了多信道隐藏终端问题。仿真结果表明,与IEEE 802.11、MMAC协议相比,该协议在提高网络平均吞吐量的同时,还能降低数据包平均延迟。     

一种适用于可扩展AdHoc网络的动态时隙分配算法

针对现有基于固定分配时隙的ad hoc网络MAC协议时隙利用率低,不能适应突发网络业务的局限性展开研究,并在此基础上提出了一种适用于规模可扩展的ad hoc网络的动态时隙分配算法(DTDMA).该算法利用较少的控制开销,通过节点间控制帧的交互,实现在网络负载较重的情况下,可以有效保证多个节点无冲突的接入信道,并针对不同优先级的网络业务提供相应优先级的时延保证.QualNet网络仿真环境中的仿真实验证明该算法能创建一个规模可扩展的无线自组织网络,且当网络中存在突发流业务时大大提高了网络吞吐量,减小了平均端到端时延,并实现了区分优先级服务.     

Ad Hoc网络中一种基于环状分层结构的组密钥协商协议

移动ad hoc网络是一种新型的移动多跳无线网络.其自身的特征,如网络规模庞大、动态的拓扑结构、有限的计算、通信和存储能力等,使得传统的密钥分配和管理机制无法直接应用于该网络.提出了一种新的适用于移动 ad hoc网络的组密钥协商协议.该协议在环状分层结构上基于多线性映射进行组密钥的协商和分配,使得节点在密钥协商过程中具有低计算开销与低通信开销的优势,较好地解决了在移动ad hoc网络中进行组密钥协商时所遇到的节点能量受限问题,适用于移动ad hoc网络.     

无线Ad Hoc网络支持QoS的研究进展与展望

无线ad hoc网络的应用环境以及与Internet的互连要求它必须提供一定的服务质量(QoS)保证,然而,无线信道固有的特点及节点移动造成网络拓扑的频繁变化,使得在无线ad hoc网络中支持QoS面临许多新的挑战.从无线ad hoc网络的QoS体系结构、QoS路由、QoS信令、支持业务区分和资源预留的介质访问控制协议这4个方面出发,对近年来国内外在该方向取得的研究成果作了全面的概括总结和比较分析,系统阐述了在无线ad hoc网络中支持QoS的问题,指出了亟待解决的问题和今后的研究方向.     

无线Ad Hoc网络QoS路由协议研究的进展与展望

无线ad hoc网络是一种无固定通信设备支持、节点可自由移动的多跳全分布式无线网络。无线ad hoc网络的应用环境以及与Internet的互连要求它必须提供一定的服务质量(QoS)保证,而QoS路由协议是无线ad hoc网络支持QoS的一个关键理论和技术,也是目前的一个研究热点。本文回顾了近年来国内外在无线ad hoc网络QoS路由协议研究方面取得的研究成果,对已有的无线ad hoc网络的QoS路由协议进行了分类．并对它们作了较全面的概括。总结和深入的比较分析,系统阐述了在无线ad hoc网络中实现QoS路由协议时需要考虑的因素,指出了亟待解决的问题和今后的研究方向。     

基于定长时隙的多跳Ad Hoc网络DCF协议马尔可夫链模型

指出了现有的基于不定长时隙的DCF协议马尔可夫链模型的局限性,并在详细分析多跳ad hoc 网络环境中DCF 协议建模的难点问题基础上,提出了一种基于定长时隙的多跳ad hoc 网络DCF 协议马尔可夫链模型.通过模型的求解,得到了反映多跳ad hoc 网络饱和吞吐量性能的相关性能指标的理论值,并结合GloMoSim 网络仿真环境中的仿真实验,证明了模型的有效性.     

The role of congestion in probabilistic broadcasting for ubiquitous wireless multi-hop networks through mediation analysis

Broadcast schemes play an important role in the performance of mobile ad hoc networks, which are a clear example of ubiquitous wireless multi-hop networks where nodes collaborate in a distributed way. They are widely used as a dissemination mechanism and as a part of the discovery phase of routing protocols. The simple flooding algorithm is the usual mechanism employed in mobile ad hoc networks, but its inefficiency has been demonstrated in congested scenarios due to the high number of collisions and contentions. However, these problems can be partially alleviated by using a probabilistic broadcast approach in which every node forwards the incoming packets according to a certain forwarding probability. In this paper, we use a simple probabilistic broadcast protocol to evaluate the effects of congestion on the performance of broadcasting in ad hoc networks through a mediation analysis. We hypothesize that the congestion mediates in the relationship between the forwarding probability (independent variable) and the output metric (dependent variable). We consider several output metrics according to the application of the broadcasting protocol such as reachability, broadcasting delay, packet delivery fraction and end to end delay. The simulation results show the existence of the mediating effects and how such effects may be counterbalanced depending on the target use of the probabilistic broadcast scheme.     

一个新的分布式最小连通支配集近似算法

在计算机网络中广泛使用广播来解决一些网络问题,设计有效的广播算法是一项重要的课题。文中提出一种分布地计算网络最小连通支配集的近似算法并给出了它的正确性证明。它只需要网络节点具有局部的网络状态信息,可伸缩性强。通过此算法可以在网络中自动形成一个虚拟骨干网,从而可为网络中的广播和路由操作提供一个有效的通信基础。模拟结果表明,文中提出的算法求得的连通支配集小,能较好地应用于一般网络以及移动自组网络中。     

Performance evaluation of dynamic probabilistic broadcasting for flooding in mobile ad hoc networks

In mobile ad hoc networks (MANETs), flooding is a required message dissemination technique for network-wide broadcast. The conventional blind flooding algorithm causes broadcast storm problem, a high number of unnecessary packet rebroadcasts thus resulting in high contention and packet collisions. This paper proposes a new probabilistic approach that dynamically fine-tunes the rebroadcasting probability of a node for routing request packets (RREQs) according to the number of neighbour nodes. We evaluate the performance of the proposed approach for the ad hoc on demand distance vector (AODV) routing protocol and compared against the blind flooding, fixed probabilistic and adjusted probabilistic flooding [L.M.M.M. Bani-Yassein, M. Ould-Khaoua et al., Performance analysis of adjusted probabilistic broadcasting in mobile ad hoc networks, International Journal of Wireless Information Networks 13(2) (2006) 127–140; M.B. Yassein, M.O. Khaoua et al., Improving route discovery in on-demand routing protocols using local topology information in MANETs, Proceedings of the ACM international workshop on Performance Monitoring, Measurement, and Evaluation of Heterogeneous Wireless and Wired Networks, Terromolinos, Spain, ACM Press, 2006, pp. 95–99.] approaches. The simulation results show that our proposed approach demonstrates better performance than blind flooding, fixed probabilistic and adjusted flooding approaches.     

Efficient broadcasting in ad hoc wireless networks using directional antennas

Using directional antennas to conserve bandwidth and energy consumption in ad hoc wireless networks (or simply ad hoc networks) is becoming popular. However, applications of directional antennas for broadcasting have been limited. We propose a novel broadcast protocol called directional self-pruning (DSP) for ad hoc wireless networks using directional antennas. DSP is a nontrivial generalization of an existing localized deterministic broadcast protocol using omnidirectional antennas. Compared with its omnidirectional predecessor, DSP uses about the same number of forward nodes to relay the broadcast packet, while the number of forward directions that each forward node uses in transmission is significantly reduced. With the lower broadcast redundancy, DSP is more bandwidth and energy-efficient. DSP is based on 2-hop neighborhood information and does not rely on location or angle-of-arrival (AoA) information. Two special cases of DSP are discussed: the first one preserves shortest paths in reactive routing discoveries; the second one uses the directional reception mode to minimize broadcast redundancy. DSP is a localized protocol. Its expected number of forward nodes is O(1) times the optimal value. An extensive simulation study using both custom and ns2 simulators show that DSP significantly outperforms both omnidirectional broadcast protocols and existing directional broadcast protocols.     

Repetition-based cooperative broadcasting for vehicular ad-hoc networks

In vehicular ad hoc networks, most of critical applications involved with safety rely on reliable broadcast communications with low latency. Recently, repetition-based protocols have been proposed to meet the requirements of timeliness and reliability for broadcasting. In these protocols, a sender repeatedly retransmits the broadcast message during the lifetime of the message. However, existing protocols face serious problems such as deterioration of the signal quality caused by wireless fading. In particular, since excessive repetitions might cause network congestion and waste channel resources, reliability of broadcasting should be achieved with as small a number of repetitions as possible. In this paper, we therefore propose a novel repetition-based broadcast protocol which exploits a cooperative diversity technique (called RB-CD) making a small number of repetitions robust for wireless fading. To support this cooperative diversity, neighboring nodes transmit the same message almost simultaneously (that is, using the same repetition pattern for each other) in order to form a virtual antenna array. The virtual antenna array achieves a diversity gain at the receivers. In the RB-CD protocol, the virtual antenna array consists of the source and some of its neighbors (called relays) which participate in repeating the transmission of a broadcast message. In addition, a new distributed relay selection algorithm is introduced in the RB-CD protocol. From the ns-2 simulation results, we verified that RB-CD provides a more reliable broadcasting service due to its capability of exploiting cooperative diversity.     

Modeling and performance analysis of ad hoc broadcasting schemes

Broadcasting is a technique widely used for distributing control packets in ad hoc networks. The traditional flooding scheme has been proven to unnecessarily consume network capacity and may lead to severe packet collisions in high-density networks. New schemes have been proposed for alleviating this so-called broadcast storm problem and their efficiencies are usually analyzed and compared by ns-2 simulations. However, little work has been done on mathematical modeling and rigorous analysis. In this paper, we focus on two popular ad hoc broadcasting schemes and provide their detailed analysis in one-dimensional and two-dimensional ideal networks. The statistical results obtained have revealed new relationships between network parameters and the performance metrics. These results are useful for optimally setting network parameters in designing protocols. It is also expected that the analytical methods developed will lay a solid foundation for the development of mathematical models for other ad hoc broadcast and multicast schemes.     

节点度估计和静态博弈转发策略的Ad Hoc网络路由协议

针对AdHoc网络路由发现过程中广播路由请求分组导致的广播风暴问题,提出了一种基于节点度估计和静态博弈转发策略的Ad Hoc网络路由协议NGRP.NGRP考虑边界影响,采用分段函数的思想将网络场景分为中心、边和角区域,分别估算网络中节点在不同区域的节点度,避免了周期性广播Hello消息获取节点度导致的开销;NGRP路由请求分组的转发采用静态博弈转发策略,利用节点度估算参与转发路由请求分组的节点数量,将转发和不转发作为策略集合,设计效益函数,通过纳什均衡获得节点转发路由请求分组的转发概率,从而减少了路由请求分组广播过程中产生的大量的冗余、竞争和冲突,提高了路由发现过程中路由请求分组的广播效率.运用NS-2对协议的性能进行大量的仿真,结果表明:NGRP的分组投递率、路由开销、MAC层路由开销和吞吐率这4项指标明显优于AODV+FDG,AODV with Hello和AODV without Hello协议.     

按需式ad hoc移动网络路由协议的研究进展

Ad hoc移动网络是一种完全由移动主机构成的网络，网络拓扑易变，带宽，能源有限是ad hoc移动网络的主要特点，针对这些特点，目前设计的ad hoc路由协议大多采用按需查找方式，该文介绍了这方面研究的最新进展，对几种典型的按需路由协议进行了说明，分析和综合比较，文中分析了目前协议存在的一些问题并提出了相应的改进方法，最后指出了下一步研究方向。     

基于模糊控制的Ad Hoc网络QoS优先调度算法

无线移动Ad Hoc网络(MANET)作为可移动分布式多跳无线网络,没有预先确定的网络拓扑或网络基础设施以及集中控制.由于移动Ad Hoc网络的动态性和资源的限制,在如此的网络中提供QoS保障是一个挑战性任务.Ad Hoc网络的分组优先级凋度算法将增进网络的性能.提出了一个基于模糊控制的Ad Hoc网络QoS优先调度算法,用于决定Ad Hoc网络中分组的优先级.利用NS2仿真软件对分组的传输率、平均端对端的延迟等做了性能分析,仿真结果表明,该方法高效、可行,可应用于Ad Hoc网络.     

无线传感网络低能耗时间同步的研究

低耗能是无线传感器网络时间同步算法的重要技术要求之一。为了降低同步过程中的能量消耗,提出了一种低能耗LECTS（Low Energy Consumption Time Synchronization）算法。该算法基于TPSN算法的基本思想,在两个阶段同时进行改进来降低能量消耗。在层次发现阶段利用节点之间的距离来限制部分节点广播,降低数据包的发送;在同步阶段结合单向广播和双向报文交换同步机制,也同样降低数据包的发送。通过仿真结果表明,与TPSN算法以及其改进算法STSP算法相比,算法能显著地降低无线传感器网络时间同步的能量消耗,且节点密度越大,节能越显著。