一个高效的移动自组网广播协议

广播操作是无线移动自组网络中常用的操作,通常采用洪泛业实现。无控制的洪泛会带来大量重复消息,大大降低网络的吞吐率,称为广播风暴问题。鉴此,本文提出了一个高效的广播协议。通过在广播时有选择地转发消息,该协议能大大减少洪泛中的广播开销。模拟试验证明,本文提出的协议性能优于洪泛,可伸缩性强,实现简单,能有效地
地用于移动自组网中。     

一种最小连通支配集的分布式广播算法

研究移动自组网络中的广播算法,提出了一种适用于移动自组网络的基于最小连通支配集的分布式广播算法,并证明了新的广播算法与已有算法相比能够更加有效地解决网络采用洪泛(Flooding)方式进行广播时所可能产生的广播风暴问题。同时,算法是基于并行和分布式运行模式的,因此具有很好的扩展性和实用性。     

MANET与Internet互联时的自适应增强机制

移动自组网(MANET)与Internet的互联能有效扩展Internet覆盖和MANET应用范围。针对既有互联协议无法适应MANET动态变化的网络条件,在网关发现过程中形成广播风暴以及将全局路由建立于单向链路上等原因所导致的互联性能恶化,提出了一种具有自适应增强机制的互联协议,该协议一方面依据实际网络条件与Internet访问需求自动调整网关通告分组在MANET中的覆盖范围;另一方面,基于网络条件自适应调整发送间隔的HELLO分组可同时避免全局路由计算过程引入单向链路以及形成广播风暴。仿真结果表明,此自适应增强协议能够以合理的开销,在复杂而多变的应用环境下为MANET提供优化的互联性能。     

移动自组网络路由协议的安全性研究

分析了针对移动自组网络(MANET)路由协议的攻击方法,并基于优化链路状态路由协议(OLSR),提出了一种移动自组网络路由协议的安全解决方案。实验表明,增加安全模块后对协议性能的影响在可接受的范围之内。     

一种MANET认证方案的设计

移动自组织网(MANET)在军事领域、紧急场合等场所备受重视,但安全问题却是MANET的一个弱点。现设计了一种适用于MANET的OTP算法--HOTP,基于此算法设计了一种MANET簇成员的认证方案。分析表明,该方案能够有效地抵制网络监听、穷举攻击等攻击手段,较目前的认证方案[1,2]更为安全有效。     

MANET路由子层微移动管理

在采用无线自组网按需平面距离矢量(AODV)路由协议的移动自组网(MANET)网关设计中,针对MANET节点的微移动特性,提出应用于MANET路由子层的微移动管理策略,并在AODV路由协议中进行实现。在NS2平台上的仿真结果表明,采用微移动管理策略的MANET网关可有效降低MANET网络访问Internet的时延,并能减少MANET内控制报文的开销。     

一种基于信誉评估与能量辅助约束的混合MANET分簇协议

如今在移动自组网(MANETs)中,应用更多地依赖于层次结构的支持.簇结构是MANET中应用最广泛的层次结构.然而既有的方法往往比较片面,并且缺乏可信机制的支持.提出了一种基于信誉评估与能量辅助约束的混合MANET分簇协议--HMCPRE,并深入分析了其极大独立性.HMCPRE方法充分考虑到了簇首选择所要求的能量前提和高信誉要求,有效扩展了HELLO消息;协议在每个节点上运行时计算复杂性小,迭代次数为O(1)级,簇首消息数为O(N)级,各种开销较小.模拟实验表明:HMCPRE协议能够有效抑制恶意不合作节点对网络的影响,减轻能量耗损对分簇造成的动荡,从而能形成更稳定的簇结构.     

基于移动自组网的服务发现体系结构设计

移动自组网络(MANET)是自治的无基础设施的网络,在此基础上进行的服务发现体系有别于传统的服务发现体系,需要从网络传输、服务注册以及服务发现等方面充分考虑移动无线网络和移动设备的特性。现有的基于有线网络或者单点自组网络协议的相关服务技术标准及协议用于MANET,存在很大的局限性和不足。充分考虑移动自组网中设备的移动性和网络环境的不稳定性后,提出了一个基于分簇的体系架构设计,并在该体系架构中就服务传输协议、面向容错的分簇策略、非集中式的服务注册和服务发现机制等方面提出了针对性的设计方案。仿真结果显示,在移动自组网的特殊网络和设备环境下,这一新的体系架构和相关服务发现策略从服务匹配准确度、反馈时间等方面都优于传统方式的服务描述模式和服务发现机制。     

移动自组网络中的广播与路由技术研究

移动自组网络是由移动节点通过分布式协议自组织起来的一种网络 ,网络中可以没有基站等固定路由设施。当有线网络不可使用时 ,如在战场通讯等任务中 ,移动自组网络提供一种可行的地面通信和信息存取技术。本文研究具有平坦结构的移动自组网络中的广播与点点路由问题。移动自组网络中的广播问题不同于有线网络以及传统移动通信系统中的情形。当节点采用全向天线时 ,该问题可以归结为图论中的最小连通支配集( MCDS)问题。由于 MCDS问题是 NP完全问题 ,因而本文给出它的几种近似算法 ,包括 MCDS遣传算法、分布式广播生成树算法、虚拟骨干…     

自组网的网关选举算法的分布式实现

在MANET网络中，由于主机的移动，广播是一种非常重要的操作。在一个地理区域内，无线信号可能相互重叠，通过直接的广播(洪泛)操作常常花费很高的代价并将产生广播风暴问题。为了减少冗余广播以缓解该问题，该文提出并实现了基于最小id的分布网关选举方法。每两个相邻的簇之间仅仅需要一个网关。仿真结果表明，该方法可以有效地减少包转发数量，有助于减少维持拓扑信息的复杂度。通过将簇首和网关作为重播节点的机制，取得了比广播更好的可扩展性。     

A new dynamic counter-based broadcasting scheme for Mobile Ad hoc Networks

Broadcasting is an essential operation in Mobile Ad hoc Networks (MANETs) to transmit a message (data packet) from the sender to the rest of the network nodes. Although flooding is the simplest mechanism for broadcasting, where each node retransmits every uniquely received message exactly once, it is usually costly and results in serious redundancy, contention and collisions in the network. These problems are widely referred to as the broadcast storm problem. In the light of this, this study introduces a new counter-based broadcasting scheme to achieve efficient broadcasting in MANETs. This is achieved by using a counter-based scheme with a dynamic threshold to increase the successful delivery rate of packets and enhance the throughput of the network. Extensive simulation experiments have been conducted. Our results show that the new scheme outperforms the well known exiting schemes, namely the two counter-based broadcasting scheme and blind flooding.     

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.     

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.     

一种应用于城市环境中的车载自组网广播算法

针对城市环境中车载自组网信息发送面临的问题,本文提出一种可靠的车载自组网广播算法。首先,结合节点间的位置信息与移动方向将节点分类,基于距离机制选择中继节点,实现多跳广播;在十字路口处,为解决消息在各个路口进行广播,结合道路拓扑,将节点分为前向节点与后向节点两类;最后,针对车辆密度稀疏状况而出现通信空洞的问题,采用携带转发策略解决,节点主动探测空洞的发生,并验证消息发送方向上有节点进入通信范围,再次进行消息广播。仿真实验表明,算法在数据包延时、数据包成功发送率以及发送单一数据包平均负荷等方面具有较好的性能。     

Efficient DSR route request flooding with directional antennas

In this paper, an efficient scheme for flooding the DSR route request in ad hoc networks using directional antennas is proposed. The scheme makes use of the local neighbor information provided by the neighbor discovery scheme. Route request packets are forwarded to selected representative neighbors using directional transmissions instead of being broadcast to all neighbors. Two strategies are proposed to efficiently select the representative neighbors: fixed branching and honeycomb strategies. The fixed branching strategy selects one representative neighbor in each predefined forwarding direction, while the honeycomb strategy selects representative neighbors to create a hexagonal tiling pattern. Simulation results show that the proposed strategies are able to achieve a high route discovery success rate while keeping the number of involved nodes and the number of transmissions low.     

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.     

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。     

Flooding in wireless ad hoc networks

In an ad hoc network, each host assumes the role of a router and relays packets toward final destinations. This paper studies efficient routing mechanisms for packet flooding in ad hoc wireless networks. Because a packet is broadcast to all neighboring nodes, the optimality criteria of wireless network routing are different from that of the wired network routing. We show that the minimum cost flooding tree problem is similar to MCDS (Minimum Connected Dominating Set) problem and prove the NP-completeness of the minimum cost flooding tree problem. Then, we propose two flooding methods: self-pruning and dominant pruning. Both methods utilize the neighbor information to reduce redundant transmissions. Performance analysis shows that both methods perform significantly better than the blind flooding. Especially, dominant pruning performs close to the practically achievable best performance limit.