Revealing the problems with 802.11 medium access control protocol in multi-hop wireless ad hoc networks

The IEEE 802.11 medium access control (MAC) protocol is a standard for wireless LANs, it is also widely used in almost all test beds and simulations for the research in wireless mobile multi-hop ad hoc networks. However, this protocol was not designed for multi-hop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multi-hop connectivity is one of the most prominent features. In this paper, we focus on the following question: can IEEE 802.11 MAC protocol function well in multi-hop networks? By presenting several serious problems encountered in transmission control protocol (TCP) connections in an IEEE 802.11 based multi-hop network, we show that the current TCP protocol does not work well above the current 802.11 MAC layer. The relevant problems include the TCP instability problem found in this kind of network, the severe unfairness problem, and the incompatibility problem. We illustrate that all these problems are rooted in the MAC layer. Furthermore, by revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multi-hop ad hoc networks. We thus doubt whether the current WaveLAN based system is workable as a mobile multi-hop ad hoc test bed. All the results shown in this paper are based on NS2 simulations, and are compatible with the results from the OPNET simulations.     

Reliable and Energy-Efficient Routing for Static Wireless Ad Hoc Networks with Unreliable Links

Energy efficient routing and power control techniques in wireless ad hoc networks have drawn considerable research interests recently. In this paper, we address the problem of energy efficient reliable routing for wireless ad hoc networks in the presence of unreliable communication links or devices or lossy wireless link layers by integrating the power control techniques into the energy efficient routing. We consider both the case when the link layer implements a perfect reliability and the case when the reliability is implemented through the transport layer, e.g., TCP. We study the energy efficient unicast and multicast when the links are unreliable. Subsequently, we study how to perform power control (thus, controlling the reliability of each communication link) such that the unicast routings use the least power when the communication links are unreliable, while the power used by multicast is close to optimum. Extensive simulations have been conducted to study the power consumption, the end-to-end delay, and the network throughput of our proposed protocols compared with existing protocols.     

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。     

军用无线移动自组织通信系统媒质接入技术概述

无线移动自组织网络的发展为新一代军事通信系统的发展注入了新的生命力。媒质接入技术是无线移动自组织网络的关键技术之一。本文介绍了美军近年来研发的基于移动自组织网技术的军用无线通信系统并对媒质接入问题进行了分析与总结。     

Ad hoc无线网络中的组播路由协议

由固定网络、基础结构移动网络和非基础结构无线网络组成的集成网络将成为未来互联网发展的趋势。同时,面向组计算和组通信的需求不断增长,要求未来的集成网络能为用户提供组播通信的功能。Adhoc无线网络是非基础结构无线网络的典型代表,具有带宽有限、拓扑结构易变和电池能源有限的特点,这些特性使得未来集成网络实现组播通信具有一定的挑战性。该文在分析Adhoc无线网络基本特性的基础上,综合评述了新近的Adhoc网络组播路由协议的研究现状,并对几种典型的Adhoc网络组播路由协议的特点进行了分类分析和比较,最后讨论了Adhoc无线网络组播路由协议的发展趋势和挑战。     

On the lifetime of node-to-node communication in wireless ad hoc networks

Lifetime of node-to-node communication in a wireless ad hoc network is defined as the duration that two nodes can communicate with each other. Failure of the two nodes or failure of the last available route between them ends their communication. In this paper, we analyze the maximum lifetime of node-to-node communication in static ad hoc networks when alternative routes that keep the two nodes connected to each other are node-disjoint. We target ad hoc networks with random topology modeled as a random geometric graph. The analysis is provided for (1) networks that support automatic repeat request (ARQ) at the medium access control level and (2) networks that do not support ARQ. On the basis of this analysis, we propose numerical algorithms to predict at each moment of network operation, the maximum duration that two nodes can still communicate with each other. Then, we derive a closed-form expression for the expected value of maximum node-to-node communication lifetime in the network. As a byproduct of our analysis, we also derive upper and lower bounds on the lifetime of node-disjoint routes in static ad hoc networks. We verify the accuracy of our analysis using extensive simulation studies.     

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.     

Survey of network coding-aware routing protocols in wireless networks

In recent times, there have been many advances in the field of information theory and wireless ad hoc network technologies. Regarding information theory progression and its connection with wireless ad hoc networks, this study presents fundamental concepts related to the application of the state-of-the-art Network Coding (NC) within wireless ad hoc networks in the context of routing. To begin with, this paper briefly describes opportunistic routing and identifies differentiation between NC-aware and NC-based routing mechanisms in wireless ad hoc networks. However, our main focus is to provide a survey of available NC-aware routing protocols that make forwarding decisions based on the information of available coding opportunities across several routes within wireless ad hoc networks. The taxonomy and characteristics of various representative NC-aware routing protocols will also be discussed. In summary, we provide a comparison of available NC-aware routing schemes and conclude that NC-aware routing techniques have several advantages over traditional routing in terms of high throughput, high reliability, and lower delay in a wireless scenario. To the best of our knowledge, this work is the first that provides comprehensive discussion about NC-aware routing protocols.     

移动自组织网络应用层组播研究

移动自组织网络的应用迫切要求组播支持。应用层组播是解决组播问题的一种有效的方案。针对目前移动自组网络中网络层组播出现的问题,深入研究了移动自组织网络应用层组播,并作了详尽的性能比较。深入分析了移动自组织网络覆盖组播的优势,并指出了移动自组织网络组播亟待解决的问题,为新的移动自组织网络应用层组播研究提供了非常有价值的研究方向。     

一种无线Ad Hoc网络动态混淆匿名算法

无线Ad Hoc网络的特殊性决定了它要受到多种网络攻击的威胁,现有的加密和鉴别机制无法解决流量分析攻击.在比较了抗流量分析的匿名技术基础上,提出混淆技术可以满足无线Ad Hoc网络的匿名需求,但现有的混淆算法在Ad Hoc网络下却存在安全与效率的问题.提出了一种动态混淆的RM(pseudo-random mix)算法,该算法主要对混淆器的管理部分进行重新设计.RM算法根据混淆缓冲区的情况进行决策,当缓冲区未满时采用时延转发方式,缓冲区满后采用随机数转发方式,这样既保证了无线Ad Hoc节点的匿名性,同时又解决了停等算法的丢包现象.对RM算法的安全性和效率进行了分析,仿真结果与理论分析相一致,表明RM算法在无线Ad Hoc网络下具有较好的自适应性和实用价值.     

Localized Operations for Distributed Minimum Energy Multicast Algorithm in Mobile Ad Hoc Networks

To explore the advantages of power saving offered by the wireless multicast advantage property, we consider the case of source-initiated multicast traffic. Current research activity for the minimum energy multicast (MEM) problem has been focused on devising efficient centralized greedy algorithms for static ad hoc networks. In this paper, we consider mobile ad hoc networks (MANETs) that use omnidirectional antennas and have limited energy resources. We propose the design and initial evaluation of the distributed minimum energy multicast (DMEM) algorithm for MANETs that attempts to reduce as much as possible the total RF energy required by the multicast communication. Several localized operations are presented for the DMEM algorithm, in which each node requires only the knowledge of and distances to all neighboring tree nodes. Through extensive simulation studies, we show that these operations are very efficient both in terms of energy saving and operation overhead     

Ad Hoc无线网络及其路由选择协议

AdHoc无线网络是一组无线移动主机组成的一个没有任务建立好的基础调和或集中管理设备的临时网络。文中介绍了adhoc无线网络的特点和设计，并根据表驱动和按需路由两大类重点介绍了adhoc无线网络的路由选择协议。     

无线Ad Hoc网络能量感知地理路由协议研究进展

无线Ad Hoc网络（以下简称为Ad Hoc网络）能量感知地理路由协议深度影响网络性能,具有降低网络能量消耗、延长网络寿命等功效,受到越来越多的关注.系统阐述了Ad Hoc网络能量感知地理路由协议的研究进展.首先介绍了Ad Hoc网络地理路由,进而详细概述了能量感知地理路由协议形成的背景、度量指标、节点选择规则、研究意义及分类;然后,详细介绍了典型能量感知地理路由协议,并从多角度对其进行了归纳总结与比较;最后,阐述了能量感知地理路由协议研究存在的问题,指出了未来需要研究的内容,并在此基础上进行总结.     

Differentiation, QoS guarantee, and optimization for real-time traffic over one-hop ad hoc networks

Nodes having a self-centrically broadcasting nature of communication form a wireless ad hoc network. Many issues are involved to provide quality of service (QoS) for ad hoc networks, including routing, medium access, resource reservation, mobility management, etc. Previous work mostly focuses on QoS routing with an assumption that the medium access control (MAC) layer can support QoS very well. However, contention-based MAC protocols are adopted in most ad hoc networks since there is no centralized control. QoS support in contention-based MAC layer is a very challenging issue. Carefully designed distributed medium access techniques must be used as foundations for most ad hoc networks. In this paper, we study and enhance distributed medium access techniques for real-time transmissions in the IEEE 802.11 single-hop ad hoc wireless networks. In the IEEE 802.11 MAC, error control adopts positive acknowledgement and retransmission to improve transmission reliability in the wireless medium (WM). However, for real-time multimedia traffic with sensitive delay requirements, retransmitted frames may be too late to be useful due to the fact that the delay of competing the WM is unpredictable. In this paper, we address several MAC issues and QoS issues for delay-sensitive real-time traffic. First, a priority scheme is proposed to differentiate the delay sensitive real-time traffic from the best-effort traffic. In the proposed priority scheme, retransmission is not used for the real-time traffic, and a smaller backoff window size is adopted. Second, we propose several schemes to guarantee QoS requirements. The first scheme is to guarantee frame-dropping probability for the real-time traffic. The second scheme is to guarantee throughput and delay. The last scheme is to guarantee throughput, delay, and frame-dropping probability simultaneously. Finally, we propose adaptive window backoff schemes to optimize throughput with and without QoS constraints.     

A survey of secure wireless ad hoc routing

Ad hoc networks use mobile nodes to enable communication outside wireless transmission range. Attacks on ad hoc network routing protocols disrupt network performance and reliability. The article reviews attacks on ad hoc networks and discusses current approaches for establishing cryptographic keys in ad hoc networks. We describe the state of research in secure ad hoc routing protocols and its research challenges.     

Group-Based Trust Management Scheme for Clustered Wireless Sensor Networks

Traditional trust management schemes developed for wired and wireless ad hoc networks are not well suited for sensor networks due to their higher consumption of resources such as memory and power. In this work, we propose a new lightweight group-based trust management scheme (GTMS) for wireless sensor networks, which employs clustering. Our approach reduces the cost of trust evaluation. Also, theoretical as well as simulation results show that our scheme demands less memory, energy, and communication overheads as compared to the current state-of-the-art trust management schemes and it is more suitable for large-scale sensor networks. Furthermore, GTMS also enables us to detect and prevent malicious, selfish, and faulty nodes.     

Energy saving and capacity improvement potential of power control in multi-hop wireless networks

This study investigates the potential of using transmission power control in wireless packet networks with differing number of hops between source and destination nodes. Here we exploit the benefits of power control in the context of multi-hop wireless ad hoc type networks with a distributed media access control. For our investigations we choose several general ad hoc network topologies and study the effects of power control with respect to energy consumption and network capacity. We show that power control largely improves the network capacity and energy savings in all investigated scenarios, and that utilizing a greater number of intermediate hops between source and destination nodes improves the energy savings though may cause a tradeoff in capacity, depending on the network topology considered.     

高能量节点驱动的按需距离矢量路由协议

无线自组织网络中的按需距离矢量路由协议(AODV)没有考虑到能量消耗的均衡性和网络生命期的问题。针对AODV的这一缺点,提出了一种高能量节点驱动的AODV协议(HN-AODV)。此协议将高能量节点驱动的策略应用于按需路由发现过程,尽量选择能量较高的节点来承担转发任务,以此来平衡网络能耗。仿真结果显示,HN-AODV在基本不降低数据传输性能的前提下,显著提高了网络生命周期。这种高能量节点驱动的方案同样可以运用在其它类似的反应式路由协议中。     

Efficient Communication Strategies for Ad Hoc Wireless Networks

An ad hoc wireless network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. This type of network is of great importance in situations where it is very difficult to provide the necessary infrastructure, but it is a challenging task to enable fast and reliable communication within such a network. In this paper we model and analyze the performance of so-called power-controlled ad hoc wireless networks: networks where the mobile hosts are able to change their transmission power. We concentrate on finding schemes for routing arbitrary permutations in these networks. In general, it is NP-hard even to find an n ^1-ε -approximation for any constant ε to the fastest possible strategy for routing a given permutation problem on n mobile hosts. However, we demonstrate here that if we allow ourselves to consider slightly less general problems, efficient solutions can be found. We first demonstrate that there is a natural class of distributed schemes for handling node-to-node communication on top of which online route selection and scheduling strategies can be constructed such that the performance of this class of schemes can be exploited in a nearly optimal way for routing permutations in any static power-controlled ad hoc network. We then demonstrate that if we restrict ourselves to the important case of routing between nodes distributed randomly in a Euclidean space, we can route in a time that is asymptotically optimal for any routing scheme. Received in final form January 31, 2000. Online publication October 10, 2000.     

与无线自组网相结合的配电通信网络延伸方案

针对配电通信网络存在网络盲区的问题,提出一种与无线自组网相结合的配电通信网络延伸方案;介绍了常用的无线自组织网络、WIA网络结构及性能分析、配电通信网络延伸方案的三层结构。该方案利用无线自组织网络的多跳性和自组织性,实现了盲区终端数据的回传。实际应用结果表明,该方案不但成本低、功耗低,且具有数据传输时延短、安全性高等优势。