Analysis and Throughput Performance of IEEE 802.11 DCF in Multi-hop Wireless Networks

This paper presents a simple and more accurate linear approximation model to compute the throughput for a saturated IEEE 802.11 distributed coordination function using the Request to Send/Clear to Send mechanism for multi-hop wireless networks. The linear approximation model is closer to reality since it takes a majority of the factors that are neglected in previous works. Most of the previous works provide complex nonlinear system equations that are difficult to set their parameters in simulation or experiments. In addition, analytical results for these nonlinear models are difficult to verify and some equations are given without clear proof. Some other works also attempt to provide approximate solutions to the nonlinear system. This paper introduces a new linear approximation model that reduces the complexity of the nonlinear analytical model. We investigate the linear approximation model with different values of the maximum backoff stage and number of nodes. Analytical results show that the linear approximation model outperforms the renowned non-linear approximation model.     

路由特性对IEEE802．11 DCF多跳网络容量的影响

使用数学分析方法研究基于IEEE 802.11 DCF的Ad Hoc网络中节点传输半径和路由策略选择问题.在节点均匀分布的多跳网络中,使用四种路由策略以及不同的节点传榆半径设王,试图找出能够使网络容量最大化的方案组合.计算结果表明,在节点密度一定的情况下,减小网络节点的传输距离有利于增加网络的容量,而在传输半径一定的条件下,使用能够导致长跳路由的策略,有利于提高网络容量.     

802.11a/g相对于802.11b的低功耗优势

引言 802.11无线局域网(WLAN)技术正在全球范围内的企业与家庭中得到应用.随着Wi-Fi的实施不断发展,基于其上运行的新型应用数量也不断上升.起初,人们认为Wi-Fi只是家庭与商业网络中以太网以及工业移动计算的简单替代,但过去一年以来已显现了新的趋势.     

802.11网络中Eifel算法性能的探讨

相对于有线网络来说,无线局域网的无线链路具有带宽低、误码率高、易受影响和电磁波能量容易被吸收等特点。因此,用户数据分组在无线链路上的传输具有传输时延高、传输时延变化大、链路突发中断的特点。这可能会引起错误的超时,触发TCP重传。分析了传统TCP触发无用重发的原因,介绍了Eifel算法消除错误重传的原理,并在NS-2环境下对Eifel和其他版本的TCP进行了仿真和比较。     

802.11 a/b/g和4.9GHz频段设备的SAR测试方法

在分析802.11和4.9 GHz频段设备技术特点和现有SAR测量系统的基础上,介绍了测试模式的要求、测量信道的选择和数据传输速率的要求。为减小测量误差,对不同占空比和功率下的线性缩放原则,以及使用分集技术、MIMO和波束成形天线技术的设备的SAR测量方法也进行了分析和说明。     

Dynamic Multi-hop Clustering in a Wireless Sensor Network: Performance Improvement

A cluster-based model is preferable in wireless sensor network due to its ability to reduce energy consumption. However, managing the nodes inside the cluster in a dynamic environment is an open challenge. Selecting the cluster heads (CHs) is a cumbersome process that greatly affects the network performance. Although there are several studies that propose CH selection methods, most of them are not appropriate for a dynamic clustering environment. To avoid this problem, several methods were proposed based on intelligent algorithms such as fuzzy logic, genetic algorithm (GA), and neural networks. However, these algorithms work better within a single-hop clustering model framework, and the network lifetime constitutes a big issue in case of multi-hop clustering environments. This paper introduces a new CH selection method based on GA for both single-hop and the multi-hop cluster models. The proposed method is designed to meet the requirements of dynamic environments by electing the CH based on six main features, namely, (1) the remaining energy, (2) the consumed energy, (3) the number of nearby neighbors, (4) the energy aware distance, (5) the node vulnerability, and (6) the degree of mobility. We shall see how the corresponding results show that the proposed algorithm greatly extends the network lifetime.     

IEEE802.11b协议在户外无线网络传输的应用与改进

文章针对IEEE802．11b协议在户外传输中存在的问题进行研究,通过对CSMA／CA协议的访问流程进行修改,利用时间片选择的随机性,降低不同站点发送数据的冲突概率,有效解决了“隐藏结点”和“低数据吞吐量”等问题。从而提高了在户外现场监控设备图象传输的效率,系统已经成功应用于油田的无人值守监控系统。     

高速铁路移动网络覆盖方案的研究

对GSM高速铁路覆盖所涉及的技术原理进行研究,主要包括小区切换带选取、多普勒频移克服、切换关系设置、容量估算、建设覆盖方案等,为在建300 km级高速铁路的无线网络规划和优化提供参考.     

Improve Performance of Wireless Sensor Network Clustering Using Mobile Relay

Wireless Personal Communications - Wireless sensor networks sense events, collect data and forward it to the infrastructural node, called sink, for further processing and assessment. The...     

IEEE 802.11a中同步性能的研究

针对IEEE802.11a协议中的同步问题进行了研究和分析。在不同的使用环境、不同的信道特性以及不同信噪比的情况下对同步性能进行了仿真,结果表明采用了OFDM调制技术的IEEE802.11a协议可以较好地克服多径衰落。同时由于是在5GHz频段的无线信道中传输信号,协议对帧结构进行精心设计以保证在高速率的情况下能有较好的同步性能。     

使用EHN-HP机制提高移动切换中TCP性能

移动通讯技术的发展促使传统有线互联网向无线移动网络延伸.TCP协议是现在互联网上使用最为广泛的端到端可靠传输协议,但TCP协议是在有线链路基础上设计的,直接在无线移动网络上使用TCP协议会造成TCP性能的下降.本文详细分析了移动切换对TCP协议造成的影响,比较并分析现有的几种解决方案,针对切换对TCP造成的影响提出了EHN-HP机制.EHN-HP机制在现有的TCP协议上进行改进,增加了切换处理机制(Handoff Process),通过网络模拟器的模拟结果表明,EHN-HP机制有效的改善了TCP协议在切换过程中的性能.     

支持WAPI协议的802.11a/b/g WLAN芯片

本文介绍了中国国家无线局域网标准中的WAPI安全体系结构,同时介绍了支持该标准的USB2.0接口无线局域网网卡芯片设计,特别是其中安全协议部分.测试结果表明,该芯片可以实现中国国家无线局域网标准规定的各项要求,性能优异.     

802.11b DCF协议和802.11e EDCA协议性能仿真与分析

使用NS-2(Network Simulator Version 2)仿真软件,选取平均峰值信噪比、封包平均时延和封包最大时延3个指标对802.11b DCF和802.11e EDCA协议的流媒体通信性能进行仿真,通过改变最大封包长度分析比较该参数对2个协议性能的影响,研究结果表明了802.11e EDCA协议在多媒体通信业务中的优越性。     

Mobile Hotspot Network System for High‐Speed Railway Communications Using Millimeter Waves

We propose a millimeter wave (MMW)‐based mobile hotspot network (MHN) system for application in high‐speed railways that is capable of supporting a peak backhaul link throughput of 1 Gbps per train at 400 km/h. The MHN system can be implemented in subways and high‐speed trains to support passengers with smart devices and provide access to the Internet. The proposed system can overcome the inherent high path loss in MMW through system designs and high antenna gains. We present a simulation of the system performance that shows that a fixed beamforming strategy can provide high signal‐to‐interference‐plus‐noise‐ratio similar to those of an adaptive beamforming strategy, with the exception of 15% of the train path in which the network can use link adaptation with low‐order modulation formats or trigger a handover to maintain the connection. We also demonstrate the feasibility of the MHN system using a test bed deployed in Seoul subway line 8. The backhaul link throughput varies instantaneously between 200 Mbps and 500 Mbps depending on the SNR variations while the train is running. During the field trial, the smartphones used could make connections through offloading.     

移动代理在网络性能管理中的应用研究

将移动代理技术应用到网络性能管理中,可以在增强性能管理功能的同时提高网络性能和准确性.文章给出了一个基于移动代理的网络性能管理系统Perma,并对该系统进行分析.     

Coexistence Performance of IEEE 802.15.4 Wireless Sensor Networks Under IEEE 802.11b/g Interference

IEEE 802.15.4 Wireless Sensor Networks (WSNs) and IEEE 802.11b/g Wireless Local Area Networks (WLANs) are often collocated, causing a coexistence issue since these networks share the same 2.4GHz Industrial, Scientific, and Medical band. In our previous work, we built a coexistence model of IEEE 802.15.4 WSNs and IEEE 802.11b/g WLANs. By identifying three distinct coexistence regions, the model explained the coexistence behavior of IEEE 802.15.4 WSNs and IEEE 802.11b/g WLANs, and the model was experimentally validated. In this paper, we improve the model by introducing two important implementation factors: the transceiver’s Rx-to-Tx turnaround time and the Clear Channel Assessment partial detection effect. The enhanced model significantly improves the accuracy on explaining and predicting the coexistence performance of IEEE 802.15.4 WSNs in the real-life environment. Furthermore, under the guidance of the model, the coexistence performance of IEEE 802.15.4 WSNs is extensively investigated in various coexistence scenarios by analysis, simulation and experiments, respectively. The simulation and experimental results agree with our analysis. The coexistence model is believed to be helpful in resolving the coexistence issue.     

Modeling a Mobile Cellular Network Using a Discrete-Event Simulator

In this paper we introduce a discrete-event-based simulation technology suitable to model cellular mobile radio systems with respect to their dynamic behavior. The latter results in the need for simulation tools which support mutable system configurations. The problems encountered when modeling mutable system configurations using conventional discrete-event simulators are discussed. In order to show a possible solution to this problem we introduce configuration events and configuration objects into the theory of discrete-event simulations. We demonstrate how configuration objects can be implemented in a discrete-event simulator using a dynamic map-function, hereby extending a definition of higher order functions. We apply the configuration objects in a Multiple Layer Model for modeling an entire mobile cellular radio network in a discrete-event simulator as an application for the extended theory. In this model we use the configuration objects to change the network's configuration during runtime. We show that this solution—combined with an object-oriented software design and, possibly, a visual programming language—is a powerful tool for the simulation of the dynamic aspects of mobile cellular radio networks. The software technology presented will be applied by the German cellular network operator Mannesmann Mobilfunk to model dynamic features applicable to the radio resource management of mobile radio networks and to access their performance by simulation.     

Passive Online Detection of 802.11 Traffic Using Sequential Hypothesis Testing with TCP ACK-Pairs

In this paper, we propose two online algorithms to detect 802.11 traffic from packet-header data collected passively at a monitoring point. These algorithms have a number of applications in real-time wireless LAN management, for instance, in detecting unauthorized access points and detecting/predicting performance degradations. Both algorithms use sequential hypothesis tests and exploit fundamental properties of the 802.11 CSMA/CA MAC protocol and the half-duplex nature of wireless channels. They differ in that one requires training sets, while the other does not. We have built a system for online wireless traffic detection using these algorithms and deployed it at a university gateway router. Extensive experiments have demonstrated the effectiveness of our approach: the algorithm that requires training provides rapid detection and is extremely accurate (the detection is mostly within 10 seconds, with very low false-positive and false-negative ratios), the algorithm that does not require training detects 60 percent to 76 percent of the wireless hosts without any false positives, and both algorithms are lightweight, with computation and storage overhead well within the capability of commodity equipment.     

网络端到端性能测量方式

首先阐述当今网络发展面临的挑战和网络测量的重要意义,之后阐述了网络测量的国内外现状和基本概念,详细分析各种网络测量方式的特点及这些测量方式所存在的问题.