TCP performance over mobile ad hoc networks

TCP is a transport protocol that guarantees reliable ordered delivery of data packets over wired networks. Although it is well tuned for wired networks, TCP performs poorly in mobile ad hoc networks (MANETs). This is because TCP's implicit assumption that any packet loss is due to congestion is invalid in mobile ad hoc networks where wireless channel errors, link contention, mobility and multipath routing may significantly corrupt or disorder packet delivery. If TCP misinterprets such losses as congestion and consequently invokes congestion control procedures, it will suffer from performance degradation and unfairness. To understand TCP behaviour and improve the TCP performance over multi-hop ad hoc networks, considerable research has been carried out. As the research in this area is still active and many problems are still wide open, an in-depth and timely survey is needed. In this paper, the challenges imposed on the standard TCP in the wireless ad hoc network environment are first identified. Then some existing solutions are discussed according to their design philosophy. Finally, some suggestions regarding future research issues are presented.     

几种典型Ad hoc路由协议的仿真分析

路由算法是无线自组网的重要组成部分,路由的好坏直接影响网络的性能.文章以无线自组网在电力系统通信中的应用为出发点,研究了DSDV,DSR,AODV和OLSR四种典型的路由协议,采用定性比较和仿真实验的方法,分析了静止节点在不同规模和负载流量场景下,路由协议的分组投递率、时延、吞吐率以及路由控制开销的变化情况,并在此基础上,对4种协议的性能进行了比较和评估,为基于无线自组网的电力系统通信提供了路由选择参考.     

Challenges of intervehicle ad hoc networks

Intervehicle communication (IVC) networks, a subclass of mobile ad hoc networks (MANETs), have no fixed infrastructure and instead rely on the nodes themselves to provide network functionality. However, due to mobility constraints, driver behavior, and high mobility, IVC networks exhibit characteristics that are dramatically different from many generic MANETs. This paper elicits these differences through simulations and mathematical models and then explores the impact of the differences on the IVC communication architecture, including important security implications.     

一种分布式车联网路由恢复方法

针对移动自组网路由协议在用于车联网时路由恢复延迟长、效果差的问题,提出了一种独立于具体路由协议的路由恢复方法。主要用于高速公路无基站情况下车与车之间的通信。能在通信路径断开后快速恢复并保证恢复后的通信路径有较高的可靠性。仿真实验表明,算法有效地降低了路由恢复延迟和开销,提高了路由修复成功率和路径生存时间。     

基于无线MPLS的Ad hoc网络路由研究

通过对现有路由协议的研究发现,目前提出的Ad hoc网络路由协议繁多,大多只能提供尽力而为的服务,而不能保证服务质量。在Ad hoc网络中,由于节点故障或节点移动造成的链路故障,使网络拓扑不断变化,计算所得路由的生命周期很短,因此,自愈恢复技术在移动Ad hoc网络中显得尤为重要。文章基于WMPLS协议体系并结合Ad hoc网络的特点,提出了一种具有一定自愈恢复能力的QoS路由协议———LDSR,并对如何运用LDSR协议建立和恢复LSP的过程进行了详细地阐述。     

一种有效的具有负载意识的按需路由协议

移动Ad hoc网络是由一组无线移动终端构成的临时性网络,不依赖于固定的基站或现有的有线骨干网。由于网络拓扑结构动态变化的特性和网络资源的有限性,开发一种性能优越的Ad hoc网络路由协议是一项具有挑战意义的工作。在本论文中,提出了一种有效的具有负载意识的按需驱动路由方案。该方案将网络负载信息作为路由选路的主要标准。对提出的方案作了仿真,并且和Dynamic Source Routing（DSR）协议进行了比较。结果表明网络负载在总体上得到了平衡,包传递率和平均端到端时延的性能也得到了有效的改善。     

基于位置信息的车联网路由恢复方法

利用方向性天线的高空间复用度和高传输能力,提出了一种基于位置信息的车联网路由恢复方法。为了减少路由修复过程中因目标节点移动对路由修复造成的影响,方法利用GSP定位装置提供的行车参数信息,对路由修复过程中目标节点的移动轨迹进行了预测并对目标节点位置进行修正。仿真实验表明:方法有效提高了路由修复成功率、降低了路由修复延迟和路由修复开销。     

基于城市配电网的无线自组传感器网络结构研究

数据通信是变配电自动化系统不可或缺的重要组成部分.在10kV以下的电力系统中,对电网数据的采集、处理、显示和控制尚无统一的通信组网模式.运用图论的方法分析城市配电网架构模式,提出一种基于改进的Dijkstra最短路径算法的无线自组传感器网络路南算法,在仿真结果的理论依据上实现了无线传感器节点的合理部署,使得无线自组传感...     

基于网络仿真器NS2的Ad hoc网络路由协议仿真

NS2是一种免费的功能强大的网络仿真器。无线Ad hoc网络作为一种典型的自组织网络,其路由协议一直是应用研究的重点问题。本文介绍了基于Linux平台的NS2仿真器针对Ad Hoc网络路由协议的仿真过程。以仿真AODV(Ad hoc on-demand distance vector)协议为例介绍了NS2仿真路由协议的详细步骤,给出了仿真中使用的TCL脚本程序、gawk性能分析程序、仿真结果图和一些性能分析。结果表明,业务源数目增加的情况下,分组投递率、路由发现频率、归一化路由开销和端到端平均时延等性能都有所下降。     

自组网在变电站自动化系统中的应用研究

随着无线通信技术的发展,变电站自动化系统采用无线通信已成为可能.文章提出了基于无线自组网的变电站自动化通信方案,分析了变电站自组网的性能和组成.自组网具有无中心、自组织、多跳路由和动态拓扑的特点,文章结合自组网及变电站自动化通信的特点,分析了变电站自组网的信道访问及路由机制,并提出了一种变电站自组网的网络协议.     

An efficient medium access control protocol for mobile ad hoc networks using antenna arrays

In recent years, the use of directional antennas in wireless networks has been widely studied. Since the medium access control (MAC) protocol of the IEEE 802.11 standard was initially designed for systems with omnidirectional antennas, it cannot perform efficiently when directional antennas are used. In this paper, an efficient two-channel MAC protocol is designed for ad hoc networks that are equipped with directional antennas. The proposed protocol utilizes the large throughput offered by directional antennas using two frequency-division multiplexed channels. The first channel is used for control information, and the second for user-data transmission. The proposed MAC protocol operates in two main modes: the omnidirectional mode, in which one antenna is used for the transmission of users? control frames, and the directional mode, in which antenna arrays are used for the transmission of data frames. The proposed protocol is assessed by means of computer simulations based on randomly generated network topologies reflecting the random movement of nodes in the network. Based on these topologies, performance comparisons with the existing MAC protocols are presented for different system parameters. In all cases, the proposed MAC protocol is shown to offer a significant throughput improvement relative to the existing protocols.     

基于行车参数信息的车联网网络分割解决方法

首先对车联网网络分割的判定方法、发生网络分割的可能性进行了分析。在分析的基础上,为了解决车联网中由于网络拓扑结构的动态变化引起的网络分割的问题,提出了一种基于行车参数信息的车联网网络分割解决方法。方法利用GPS定位装置提供的行车参数信息,对网络分割解决过程中目标节点的移动轨迹进行了预测并对目标节点位置进行修正。仿真结果表明该方法有效降低了网络端到端的延时,提高了网络分割修复成功率和分组转发成功率。     

基于负载感知和伪流言机制的高稳定性路由协议

通过建立无人机自组网可以有效满足无人机集群作战的组网通信需求,但相较于传统移动自组网,无人机自组网具有节点移动速度更快,网络拓扑高度动态变化的显著特征.针对链路频繁断开带来网络性能下降严重的问题,提出了一种基于负载感知和伪流言机制的高稳定性路由协议.网络拥塞和节点移动性是影响路径稳定性的两个主要因素.针对网络拥塞问题,提出了基于节点负载预测的伪流言受限洪泛机制,在发起路由请求过程中,通过动态调整节点转发概率,均衡了网络负载的同时降低了控制开销.针对无人机节点的高移动性特征,基于接收到分组信号功率强度,提出了链路稳定性的联合度量指标.仿真结果表明,与AODV协议及其他改进型协议相比,该协议有效减少了网络的控制开销,提高了分组投递率,降低了平均端到端时延,显著改善网络性能,增强了数据传输的实时性和可靠性.     

电力系统中无线自组网软件平台架构研究

针对无线网在电力系统中广阔的应用前景，进一步研究了无线自组网在电力系统中的应用，重点讨论了如何利用NDIS(network driver interface specification)中间驱动程序实现电力系统中的无线自组网软件平台架构，介绍了基于Passthru的程序框架、最优化链路状态路由协议及程序模块的实现原理，并讨论了网络平台的特性，展望了其应用前景。     

基于网络划分的VANET路由构建及数据传输方法

为提高车载自组网的路由扩展性,提出了一种基于网络划分的车载自组网路由构建及数据传输方法。首先,提出了一种新的车载自组网划分算法来把网络划分为多个子网,随后,搭建和维护各子网中的头尾节点间路由,最后,所有路由的搭建和维护都基于各个子网的头尾节点间路由。该方法将链路失败的影响局限于包含该链路的子网中,并且能够多次复用子网中的路由信息。仿真表明,在网络节点数和路由数目不断增多的情况下,相对于直接在网络中应用相关路由算法,文中方法显著地减小了路由代价,提高了网络性能。仿真结果充分地说明了文中方法的有效性。     

A distributed Synchronous reservation multiple access control protocol for mobile Ad hoc networks

This study proposes a new multiple access control protocol named distributed synchronous reservation multiple access control protocol, in which the hidden and exposed terminal problems are solved, and the quality of service (QoS) requirements for real-time traffic are guaranteed. The protocol is founded on time division multiplex address and a different type of traffic is assigned to different priority, according to which a node should compete for and reserve the free slots in a different method. Moreover, there is a reservation acknowledgement process before data transmit in each reserved slot, so that the intruded terminal problem is solved. The throughput and average packets drop probability of this protocol are analyzed and simulated in a fully connected network, the results of which indicate that this protocol is efficient enough to support the real-time traffic, and it is more suitable to MANETs. Translated from Journal of Xidian University, 2006, 33(1): 28–32 [译自: 西安电子科技大学学报]     

无线自组网在变电站综自系统中的应用探讨

剖析了多种变电站自动化系统的通信网络,明确了各自的适用范围,并指出随着电力系统和通信技术的发展,无线通信将在变电站自动化系统中崭露头脚.提出了变电站无线自组网方案,根据变电站具体情况和对目前主流的路由控制和MAC协议的分析,选择了适合变电站自组网的路由算法和MAC协议.     

A Programmable Framework for the Deployment of Services and Protocols in Mobile Ad Hoc Networks

Mobile ad hoc networks (MANETs) are characterized by their heterogeneity and the diverse capabilities of their nodes given that almost any device with a wireless network interface can join such a network. In such an environment it is difficult to dynamically deploy services and protocols without a common understanding among the participating nodes and their capabilities. A deployment/provisioning framework must cope with the high-level of device heterogeneity, degree of mobility, and should also take into account the potentially limited device resources. This paper presents a context-based programmable framework for dynamic service/protocol deployment that allows the nodes of a mobile ad hoc network to download and safely activate required service/protocol software dynamically. Downloading and activation can be triggered through preconditions evaluated according to available contextual information. This strategy leads to the alignment of the nodes' capabilities so that common services and protocols can be deployed even if they are not available at every node. In addition, dynamic context-driven deployment may lead to a degree of network self-optimization. We present the programmable framework and functionality and evaluate its various aspects through testbed experimentation, simulation and analytical modeling. The results demonstrate good performance with respect to the supported functionality.     

Detecting the vehicle direction changes for routing algorithms and applications of vehicular ad hoc networks

Vehicular ad hoc networks will enable a variety of applications for safety, traffic efficiency, driver assistance, and infotainment in modern automobile designs. For many of these applications as well as for improving the stability of vehicular ad hoc network routing algorithms, it is necessary to know whether a steering wheel rotation has led to a change in the vehicle motion path. The problem is that some steering wheel rotations are temporary and do not lead to a change in the vehicle motion path. In this paper, a GPS‐free fuzzy sensor is designed for detecting the change of vehicle motion paths. The implementation results show acceptable precision. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.