航空自组网的现状与发展

近年来,随着移动Ad Hoc网络研究与应用的不断深入,许多研究机构和学者正在将其应用于航空通信中,产生了崭新的研究领域——航空自组网。本文概述了航空自组网的基本概念、主要特点及应用场合,介绍了在这一领域比较活跃的研究机构以及其主要工作,分析了航空自组网的关键技术,并展望了未来的发展方向。     

移动自组网中的典型位置服务协议比较

到目前为止,移动自组网已经开发很多基于不同策略的路由协议,这些路由协议可分为基于网络拓扑的路由协议和基于位置信息的路由协议。本文主要介绍基于位置信息的路由协议及几种典型协议的分析比较。     

自组网中功率控制的MAC协议分析

针对无线自组网中网络资源缺乏的问题，在MAC协议中引入优化控制传输功率的机制，可以有效地开发现有资源，提高网络性能。本文详细分析了PCMA协议的思想、机制以及对网络性能的影响，指出了协议的缺陷。     

自组网路由协议综述

自组网路由协议用于监控网络拓扑结构变化,交换路由信息,定位目的节点位置,产生、维护和选择路由,并根据选择的路由转发数据。本文综述了自组网路由协议研究方面的一些最新工作,描述了设计自组网路由协议所面临的问题,并着重对该研究开展以来所提出的各种主要协议进行了对比、分析和分类阐述,为进一步的研究提出了新的课题。     

无线自组网可信路由协议的研究

本文分析了无线自组网面临的安全风险,介绍了现有安全路由与不足之处,提出了一个以可信计算为基础、信任机制为辅助的可信路由方案,对其中涉及的具体问题进行了分析和研究。     

自组网的路由协议及其QoS保障

自组网是一种新型的移动计算机网络，它应用广泛，并具有重要的商业价值。首先介绍了自组网的概念和特点，然后分析了自组网路由协议的特点与设计思路，并丰此基础上讨论了在自组网环境下实现QoS的策略与方法。     

车载自组网中的网络与信息安全

因自组织网络无中心的特点,传统有中心网络中成熟的安全保障机制无法得到直接应用。为了使车载通信技术得到更加广泛的应用,安全问题必须得到很好的解决。文章对车载自组网的安全需求及目标进行分析,然后从安全路由、密钥管理和入侵检测3个方面对车载自组网安全研究的现状进行介绍。在这3个方面中,安全路由研究最为广泛,而密钥管理则是保障车载自组网安全的关键。     

高动态无线自组网路由协议设计

针对节点快速移动过程中网络建立时间较长,数据端到端传输时延无法得到可靠保 障,并且由于维护动态网络连接性造成网络开销较大等方面的问题,提出了一种无线自组网 路由协议,通过分簇算法快速将网络分为多个簇,每个簇包括簇首节点、成员节点和簇间网 关节点。该协议能够应用于快速移动节点构成的高动态无线自组织网络中,实现了先应式和 反应式路由算法进行了有机结合,能够在快速变化的拓扑结构中为未知路由提供优化的路由 结果,利用较小的网络开销实现网络快速构建和数据端到端的实时传输。     

无线自组网络的技术研究

随着通信技术的快速发展和人们对通信要求的提高,无线自组织网成为当今网络的重要研究内容。无线自组织网络由几个可移动的无线节点自组织形成的一个多跳、灵活、无中心的网络,这些特点为它在军事和民用通信领域提供了有利保证。文章首先介绍了无线自组网的特点和应用;其次对现有路由协议存在的问题进行了研究;最后针对无线自组网存在的能量消耗,多路径,多播等问题归纳出了的六种方法对系统进行优化,提高了无线自组网络的传输性能。     

Quality of service challenges for wireless mobile ad hoc networks

Wireless mobile ad hoc networks consist of mobile nodes interconnected by wireless multi‐hop communication paths. Unlike conventional wireless networks, ad hoc networks have no fixed network infrastructure or administrative support. The topology of such networks changes dynamically as mobile nodes join or depart the network or radio links between nodes become unusable. Supporting appropriate quality of service for mobile ad hoc networks is a complex and difficult issue because of the dynamic nature of the network topology and generally imprecise network state information, and has become an intensely active area of research in the last few years. This paper

1 This article, except for some minor changes, is essentially the same as one that appears in 103 . The latter is a revised and updated version of 51

presents the basic concepts of quality of service support in ad hoc networks for unicast communication, reviews the major areas of current research and results, and addresses some new issues. The principal focus is on routing and security issues associated with quality of service support. The paper concludes with some observations on the open areas for further investigation. Copyright © 2004 John Wiley & Sons, Ltd.     

Stable routing protocol based on fuzzy logic system in vehicular ad hoc networks

Vehicular ad‐hoc networks have several roles in alert messages dissemination between vehicles in danger, the most important role is to provide helpful information for drivers (eg, road traffic state). But, some performance improvements are frequently needed in terms of routing. Hence, several clustering approaches have been proposed to optimize the network services. These approaches are based on increasing data delivery, reducing data congestion, and dividing the traffic into clusters. However, a stable clustering algorithm is always required in order to ensure the data dissemination in a dense, mobile, or a large‐scale environment. Therefore, in this paper, we have proposed a stable routing protocol based on the fuzzy logic system, which can deliver alert messages with minimum delay and improve the stability of clusters structure by generating only a small number of clusters in the network. In this work, the fuzzy logic system has been used to create the clusters and select a cluster head for each cluster. We have used the network simulator (NS2) to generate the results. As a result, we could reduce the cluster head changes and increase the cluster member lifetime compared with recent approaches.     

Vulnerability assessment of ad hoc networks to MAC layer misbehavior

This paper describes a new vulnerability for the IEEE 802.11 protocol and studies its impact on degrading the performance of ad hoc networks. A host that exploits this new simple, but practical, vulnerability could cause devastating effects on the proper operation of the network protocols and hence severely degrade the performance. In this work, a misbehaving node fully cooperates by forwarding packets for other nodes and completely adheres to the proper selection of backoff intervals; however, it maliciously forces the forwarding operation to fail in order to either disrupt the route discovery process or to cause damage to existing flows routed though that node. As a result, the medium around the misbehaving node will be less congested and hence the node will obtain an increased unfair access to the channel. We use network simulations to show that such malicious misbehaviors have devastating effect on demoting the network performance and disrupting the protocol functioning. Hence, necessary extensions for existing detection systems are required to mitigate the effects of these new vulnerabilities. Copyright © 2006 John Wiley & Sons, Ltd.     

Sparsely‐deployed relay node assisted routing algorithm for vehicular ad hoc networks

In this paper, we study the issue of routing in a vehicular ad hoc network with the assistance of sparsely deployed auxiliary relay nodes at some road intersections in a city. In such a network, vehicles keep moving, and relay nodes are static. The purpose of introducing auxiliary relay nodes is to reduce the end‐to‐end packet delivery delay. We propose a sparsely deployed relay node assisted routing (SRR) algorithm, which differs from existing routing protocols on how routing decisions are made at road intersections where static relay nodes are available such that relay nodes can temporarily buffer a data packet if the packet is expected to meet a vehicle leading to a better route with high probability in certain time than the current vehicles. We further calculate the joint probability for such a case to happen on the basis of the local vehicle traffic distribution and also the turning probability at an intersection. The detailed procedure of the protocol is presented. The SRR protocol is easy to implement and requires little extra routing information. Simulation results show that SRR can achieve high performance in terms of end‐to‐end packet delivery latency and delivery ratio when compared with existing protocols. Copyright © 2013 John Wiley & Sons, Ltd.     

SDMAC: Selectively Directional MAC protocol for wireless mobile ad hoc networks

Using directional antennas in wireless mobile ad hoc networks can greatly improve the transmission range as well as the spatial reuse. However, it will also cause some problems such as deafness problem and hidden terminal problem, which greatly impair the network performance. This paper first proposes a MAC protocol called Selectively Directional MAC (SDMAC) that can effectively address these problems and significantly improve the network throughput. Then two improvements on SDMAC are proposed. The first one is to improve the network throughput by scheduling the packets in the queue (a scheme called Q-SDMAC), thus the head-of-line (HOL) blocking problem can be addressed. The second one is to relax the assumption that each node knows the relative directions of its neighboring nodes and use caches to buffer those relative directions (a scheme named Q-SDMAC using cache). Extensive simulations show that: (1) SDMAC can achieve much better performance than the existing MAC protocols using directional antennas; (2) The network throughput can be significantly improved by scheduling the packets in the queue; (3) Using caches can still achieve high network throughput when nodes are moving; and (4) Network throughput decreases when directional antennas have side lobe gain.

Contention-based forwarding for mobile ad hoc networks

Existing position-based unicast routing algorithms which forward packets in the geographic direction of the destination require that the forwarding node knows the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages each node sends out periodically.

Due to mobility, the information that a node receives about its neighbors becomes outdated, leading either to a significant decrease in the packet delivery rate or to a steep increase in load on the wireless channel as node mobility increases. In this paper, we propose a mechanism to perform position-based unicast forwarding without the help of beacons. In our contention-based forwarding scheme (CBF) the next hop is selected through a distributed contention process based on the actual positions of all current neighbors. For the contention process, CBF makes use of biased timers. To avoid packet duplication, the first node that is selected suppresses the selection of further nodes. We propose three suppression strategies which vary with respect to forwarding efficiency and suppression characteristics. We analyze the behavior of CBF with all three suppression strategies and compare it to an existing greedy position-based routing approach by means of simulation with ns-2. Our results show that CBF significantly reduces the load on the wireless channel required to achieve a specific delivery rate compared to the load a beacon-based greedy forwarding strategy generates.     

Towards efficient data collection mechanisms in the vehicular ad hoc networks

Recently, the fast growth of communication technology has led to the design and implementation of different types of networks in different environments. One of these remarkable networks is vehicular ad hoc network (VANET). The ubiquitous connectivity among vehicles is possible through VANET in the absence of fixed infrastructure. Moreover, it provides safety and comfort to people sitting in the vehicles. In this regard, collecting information from vehicles that are moved constantly is an essential challenge. To develop an efficient method for data collection in the VANET, some parameters must be considered such as data aggregation, latency, packet delivery ratio, packet loss, scalability, security, transmission overhead, and vehicle density. Since data collection has a significant importance in the VANET, the aim of this study is to investigate the existing methods and describe the types of important issues and challenging problems that can be addressed in data collection in the VANET. The data collection techniques are investigated in four primary groups, namely, topology‐based, cluster‐based, geocast‐based, and fog‐based. Also, the mentioned parameters are important to compare all of the presented techniques.     

Interference minimum network topologies for ad hoc networks

This paper investigates the topology control problem with the goal of minimizing mutual interferences in wireless ad hoc networks. It is known that interference is considered as a relationship between link and node in previous works. In this paper, we attempt to capture the physical situation of space‐division multiplex more realistically by defining interference as a relationship between any two bidirectional links. We formulate the pair‐wise interference condition between any two bidirectional links, and demonstrate that the interference condition is equivalent by employing the equal‐power allocation strategy and by employing the minimum‐power allocation strategy. Then we further study the typical interference relationship between a link and its surrounding links. To characterize the extent of the interference between a link and its surrounding links, a new metric, the interference coefficient, is given, and its property is explored in detail by means of analysis and simulation. Based on the insight obtained, a centralized algorithm, BIMA, and a distributed algorithm, LIMA, are proposed to control the network interference. Our simulation indicates that BIMA can minimize the network interference while conserving energy and maintaining good spanner property, and LIMA has relatively good interference performance while keeping low node degree, compared with some well‐known algorithms. Besides, both BIMA and LIMA show good robustness to additive noises in terms of interference performance. Copyright © 2010 John Wiley & Sons, Ltd.     

基于双信道的一种ad hoc网络路由策略

利用多个信道接口来改善ad hoc网络信道容量。即一个信道周期性的广播节点状态信息分组来维护全网所有节点的状态信息，而另一个信道利用此信息采用最短路径搜寻算法来获得到目的节点的路由并完成数据传输。这样充分结合了表驱动路由方法和按需式路由方法的优点。另外，信息维护与数据分组分别在两个信道内同时进行，避免了信息维护对数据分组传输的影响，提高了网络性能。