Cross Layer Approach and ANFIS based Optimized Routing in Wireless Multi-Hop Ad Hoc Networks

Wireless Personal Communications - Mobile ad hoc networks are non-dependent on any wired infrastructure and provide exceptional benefits during typical situations like conference, fair/exhibition,...     

多跳对基于802.11的Ad Hoc网络TCP流公平性的影响

多跳是Ad Hoc网络主要的特点,也是很多问题(如TCP流不公平、不稳定以及吞吐量下降等)产生的原因.文中基于NS2仿真平台研究了跳数及接入时间对TCP流公平性的影响,给出了不同TCP流的信道接入能力,深入分析了多跳TCP流公平性下降的原因,并在此基础上提出了改进公平性的建议.研究的结果表明,不同跳数的TCP流共存时,跳数较少的TCP流会占优甚至垄断信道.当跳数相同时,提前接入的TCP流会占优甚至垄断信道.     

Bandwidth Estimation for IEEE 802.11-Based Ad Hoc Networks

Since 2005, IEEE 802.11-based networks are able to provide a certain level of Quality of Service by the means of service differentiation, thanks to the IEEE 802.11e amendment. However, no mechanism or method has been standardized to accurately evaluate the amount of resources remaining on a given channel. Such evaluation would however be a good asset for bandwidth-constrained applications. In multi-hop ad hoc networks, such evaluation becomes even more difficult. Consequently, despite the various contributions around this research topic, the estimation of the available bandwidth still represents one of the main issues in this field. In this article, we propose an improved mechanism to estimate the available bandwidth in IEEE 802.11-based ad hoc networks. Through simulations, we compare the accuracy of the estimation we propose to the estimation performed by others state of the art QoS protocols, BRuIT, AAC and QoS-AODV.     

Throughput Analysis of IEEE802.11 Multi-Hop Ad Hoc Networks

In multi-hop ad hoc networks, stations may pump more traffic into the networks than can be supported, resulting in high packet-loss rate, re-routing instability and unfairness problems. This paper shows that controlling the offered load at the sources can eliminate these problems. To verify the simulation results, we set up a real 6-node multi-hop network. The experimental measurements confirm the existence of the optimal offered load. In addition, we provide an analysis to estimate the optimal offered load that maximizes the throughput of a multi-hop traffic flow. We believe this is a first paper in the literature to provide a quantitative analysis (as opposed to simulation) for the impact of hidden nodes and signal capture on sustainable throughput. The analysis is based on the observation that a large-scale 802.11 network with hidden nodes is a network in which the carrier-sensing capability breaks down partially. Its performance is therefore somewhere between that of a carrier-sensing network and that of an Aloha network. Indeed, our analytical closed-form solution has the appearance of the throughput equation of the Aloha network. Our approach allows one to identify whether the performance of an 802.11 network is hidden-node limited or spatial-reuse limited     

Quorum-Based Asynchronous Power-Saving Protocols for IEEE 802.11 Ad Hoc Networks

This paper investigates the power mode management problem for an IEEE 802.11-based mobile ad hoc network (MANET) that allows mobile hosts to tune to the power-saving (PS) mode. There are two major issues that need to be addressed in this problem: (a) wakeup prediction and (b) neighbor discovery. The former is to deliver buffered packets to a PS host at the right time when its radio is turned on. The latter is to monitor the environment change under a mobile environment. One costly, and not scalable, solution is to time-synchronize all hosts. Another possibility is to design asynchronous protocols as proposed by Tseng et al. in [25]. In this paper, we adopt the latter approach and correlate this problem to the quorum system concept. We identify a rotation closure property for quorum systems. It is shown that any quorum system that satisfies this property can be translated to an asynchronous power-saving protocol for MANETs. Thus, the result bridges the classical quorum system design problem in the area of distributed systems to the power mode management problem in the area of mobile ad hoc networks. We derive a lower bound for quorum sizes for any quorum system that satisfies the rotation closure property. We identify a group of quorum systems that are optimal or near optimal in terms of quorum sizes, which can be translated to efficient asynchronous power-saving protocols. We also propose a new e-torus quorum system, which can be translated to an adaptive protocol that allows designers to trade hosts' neighbor sensibility for power efficiency. Simulation experiments are conducted to evaluate and compare the proposed protocols.     

A Cross Layer Metric for Discovering Reliable Routes in Mobile Ad Hoc Networks

Host mobility in mobile ad hoc networks causes failure of wireless links between nodes and breaks all the routes that use these links. Consequently, route reconstructions are needed, which is one of the most critical problems for this type of wireless networks. The number of route reconstructions can be reduced if more reliable wireless links are used. Also by these links, stable clusters can be constructed as is needed in cluster based protocols. Reliable routing protocols for mobile ad hoc networks use many link reliability metrics for finding these links; four of the most commonly used are ??Link Expiration Time??, ??Probabilistic Link Reliable Time??, ??Link Packet Error Rate?? and ??Link Received Signal Strength??. It is shown that these metrics enhance the reliability and reduce the number of route reconstructions, but to the best of our knowledge there is no report that compare their efficiencies. In this paper, we make this comparison in different network conditions and discuss their optimal applications. Then, a new cross layer metric is proposed that combines the aforementioned metrics according to their efficiency by means of a unit weight function. Simulation results show that by using all these metrics, the number of route reconstructions is reduced, and for the proposed one the result is better than the others.     

IEEE802.11移动自组织网络节点竞争窗口长度的概率分布

 在基于IEEE 802.11的移动自组织网络中,MAC(Medium Access Control)层提供了DCF(Distributed Coordinate Function)以控制节点对无线信道的争用.DCF包括了BEB (Binary Exponential Backoff)算法.该文对BEB的重要参数——竞争窗口CW(Contention Window)进行研究,通过随机建模,导出了竞争窗口长度的概率分布,并进行数值分析.研究结果可应用于IEEE 802.11移动自组织网络.     

Performance Evaluation of IEEE 802.11 DCF in Single Hop Ad Hoc Networks

The mathematical modeling of IEEE 802.11 CSMA/CA has received considerable attention in the past few years. However there is lack of significant work considering the presence of buffer in wireless networks. Also most of the work has not followed IEEE specifications regarding inclusion of retry limits. This paper presents a new analytical model for performance evaluation of IEEE 802.11 single hop networks. The work presented here takes into consideration the presence of first order memory buffer along with the effect of traffic arrival which obeys Poisson distribution. In addition, we have considered the short retry limit to accommodate IEEE 802.11 specifications. On one hand, lack of buffering leads to high delays and under utilization of the channel. Also the absence of short retry limit tends to overestimate the throughput. By accommodating both the shortcomings, it has been proved that our model predicts the behaviour more accurately. We have been carrying out extensive simulations to validate results of our model. We have presented the performance evaluation of both the access mechanisms present in 802.11 MAC protocol.     

Analysis of TCP Performance over Mobile Ad Hoc Networks

Mobile ad hoc networks have attracted attention lately as a means of providing continuous network connectivity to mobile computing devices regardless of physical location. Recent research has focused primarily on the routing protocols needed in such an environment. In this paper, we investigate the effects that link breakage due to mobility has on TCP performance. Through simulation, we show that TCP throughput drops significantly when nodes move, due to TCP's inability to recognize the difference between link failure and congestion. We also analyze specific examples, such as a situation where throughput is zero for a particular connection. We introduce a new metric, expected throughput, for the comparison of throughput in multi-hop networks, and then use this metric to show how the use of explicit link failure notification (ELFN) techniques can significantly improve TCP performance.     

基于802.11 MAC的移动Ad Hoc网络AODV路由协议改进算法

基于802.11的Ad Hoc网络AODV路由协议会引入通信盲区问题,使路由发现信息建立的路由不能很好地满足高速数据分组的传输,本文在传统通信盲区解决方案的基础上提出一种AODV路由协议改进算法.Opnet仿真表明,改进算法能有效地提高Ad-hoc网络性能.     

移动自组网中联合优化设计的MAC/路由协议

文章针对节点数量多、密度大的一类移动自组网提出了一种跨层联合设计的MAC/路由协议.在MAC层上采用基于调度的信道分配算法以减少通信冲突,在网络层上结合使用表驱动路由和基于地理位置的路由来提高协议适应动态拓扑的能力,并设计了适合TDMA MAC协议的高效的消息交互机制.在OPNET仿真平台上与AODV/802.11和G...     

移动代理在MANET路由协议中的应用研究

移动Ad Hoc网络(MANET)是由移动节点组成的分布式异构网络,其路由协议的研究是该领域的焦点之一。本文分析了现有移动Ad Hoc网络两类路由协议的优缺点,接着提出将移动代理应用于AODV路山协议的方案,最后给出了初步的仿真结果。仿真结果表明,通过移动代理的漫游更新途经节点路由表,可以在网络负载增加不人的情况下,减少路由发起数,降低端到端的数据传输延迟。     

多速率移动Ad hoc网络路由策略研究

在多速率Ad hoc网络中，要充分利用多速率的优势，提高网络的整体性能，妊须设计一种适合网络特点以及满足用户需要的多速率路由策略。文中简要分析了多速率路由策略对网络性能的影响，重点介绍了现有的多速率路由策略。论文还给出了后续的工作——对在多频段和多模式的无线网络中采用改进的多速率路由算法的研究。     

TCP Performance in IEEE 802.11-Based Ad Hoc Networks with Multiple Wireless Lossy Links

We propose a packet-level model to investigate the impact of channel error on the transmission control protocol (TCP) performance over IEEE-802.11-based multihop wireless networks. A Markov renewal approach is used to analyze the behavior of TCP Reno and TCP Impatient NewReno. Compared to previous work, our main contributions are listed as follows: 1) modeling multiple lossy links, 2) investigating the interactions among TCP, Internet Protocol (IP), and media access control (MAC) protocol layers, specifically the impact of 802.11 MAC protocol and dynamic source routing (DSR) protocol on TCP throughput performance, 3) considering the spatial reuse property of the wireless channel, the model takes into account the different proportions between the interference range and transmission range, and 4) adopting more accurate and realistic analysis to the fast recovery process and showing the dependency of throughput and the risk of experiencing successive fast retransmits and timeouts on the packet error probability. The analytical results are validated against simulation results by using GloMoSim. The results show that the impact of the channel error is reduced significantly due to the packet retransmissions on a per-hop basis and a small bandwidth delay product of ad hoc networks. The TCP throughput always deteriorates less than ~ 10 percent, with a packet error rate ranging from 0 to 0.1. Our model also provides a theoretical basis for designing an optimum long retry limit for IEEE 802.11 in ad hoc networks.     

Cross-Layer Interaction of TCP and Ad Hoc Routing Protocols in Multihop IEEE 802.11 Networks

In this research, we first investigate the cross-layer interaction between TCP and routing protocols in the IEEE 802.11 ad hoc network. On-demand ad hoc routing protocols respond to network events such as channel noise, mobility, and congestion in the same manner, which, in association with TCP, deteriorates the quality of an existing end-to-end connection. The poor end-to-end connectivity deteriorates TCP's performance in turn. Based on the well-known TCP-friendly equation, we conduct a quantitative study on the TCP operation range using static routing and long-lived TCP flows and show that the additive-increase, multiplicative-decrease (AIMD) behavior of the TCP window mechanism is aggressive for a typical multihop IEEE 802.11 network with a low-bandwidth-delay product. Then, to address these problems, we propose two complementary mechanisms, that is, the TCP fractional window increment (FeW) scheme and the Route-failure notification using BUIk-losS Trigger (ROBUST) policy. The TCP FeW scheme is a preventive solution used to reduce the congestion-driven wireless link loss. The ROBUST policy is a corrective solution that enables on-demand routing protocols to suppress overreactions induced by the aggressive TCP behavior. It is shown by computer simulation that these two mechanisms result in a significant improvement of TCP throughput without modifying the basic TCP window or the wireless MAC mechanisms.     

AdHoc多跳网络在EDCA机制下对实时音／视频业务的仿真分析

在AdHoc多跳网络中,IEEE802.11e协议采用了增强型分布信道接入机制（Enhanced Distributed Channel Access,EDCA）,用于为实时多媒体业务提供有效的QOS保证机制。本文简单介绍和对比了802.11分布式协调功能（DCF）和802.11e EDCA两种信道接入机制,并通过使用网络仿真软件OPNET,模拟了实时的视／音频业务在802.11DCF和802.11e EDCA信道接入机制下在不同网络负载下的性能并进行了仿真分析。     

Ad Hoc网络可靠性评估

针对一种特殊的通信网Ad Hoc网络,提出了一种可靠性评估算法,首先根据物理拓扑抽象出Ad Hoc网络模型,并充分分析Ad Hoc网络特点确定失效判据,依据失效判据进行可靠性建模,选择合适的可靠性模型。将Ad Hoc网络模型划分为逻辑上的一个个子区域,采用层次分析法确定各个子区域的权重系数,在各子区域内,利用最小定点割集确定Ad Hoc网络中的重要节点,同时根据生成树算法确定重要节点的权重系数,从而可以计算出Ad Hoc网络的可靠度。最后通过实例说明某Ad Hoc网络的可靠性评估。     

Structured Peer-to-Peer Real Time Video Transmission over Vehicular Ad Hoc Networks

Video communication over Vehicular Ad Hoc Networks (VANET) has several applications such as road safety, commercial advertisements and on-road entertainment. In this paper we present a structured peer-to-peer (P2P) network designed for the distribution of live-content, with low bandwidth consumption, within a VANET. This P2P network is modelled using a media distribution graph. The implementation of a structured network allows a peer to schedule consecutive data chunks produced by the media source by means of a scheduling algorithm. In our analysis we obtain a bound for the maximum delay between the media source and any of the peers of the network and the buffer size needed to allow consecutive scheduling. We study a type of media distribution graph and we calculate its order and diameter, which means that under stable conditions we can ensure certain quality-of-service parameters. The results of simulation over NS2 show the fitness of the mathematical analysis.     

移动Ad Hoc网络中的安全问题

移动自组网(Mobile Ad HoC Network)是一种无基础设施的无线网络由于它具有开放的媒质、分布式的合作、动态的拓扑结构和受限的网络能力等特点,所以特别容易受到攻击.为此文章结合移动Ad Hoc网络的特点分析了移动Ad Hoc网络面临的安全威胁,并对移动Ad Hoc网络的安全路由和安全报文传送问题进行了详细讨论.