IEEE802.11标准演进

在各种无线局域网技术交织的战国时代,WLAN、蓝牙、Home RF、UWB等竞相绽放,但IEEE802.11系列的WLAN应用最为广泛。自从1997年IEEE802.11标准实施以来,先后有802.11a、802.11b等十多个标准制定或者酝酿,这些标准的制定对无线网络技术的发展和无线网络的应用起到了重要的推动作用,也促进了不同厂家的无线网络产品的互通互联。     

无线局域网技术及组建

随着社会的进步,网络在人们生活中的地位日趋重要,人们对网络的依赖越来越强,单位、家庭、学校到处都是小型局域网,但是,建设局域网也存在一定的问题,线路的铺设既费人力也费财力,同时对建筑物的外观也会造成一定的影响,当搬迁、升级的时候又造成了一定浪费,移动办公的愿望也很难实现,传统局域网络已经越来越不能满足人们对移动办公的要求.无线局域网(WLAN)技术的出现解决了这个问题,它使网络的应用更灵活更方便.文章主要介绍无线局域网技术及其在实际中的应用.     

802.11n标准加快无线局域网的发展

做为一个旨在增加无线网络吞吐量的草案,802.11n最初被看作是一种民用技术。尽管如此,802.11n在企业级中也有很多关键应用,在下一代互联网的布设过程中也被寄予了厚望。在企业中,有很多应用对带宽很敏感,像ERP、CRM、工作组计算软件和一些无线应用对带宽的需求超过了802.11标准     

无线局域网技术刍议

文章着重介绍了802.11无线局域网的概念、关键技术及组网方式,并对其发展前景进行了展望.     

浅析无线局域网与网络安全技术

通过对目前常见的IEEE802.11、HiperLAN无线局域网技术的介绍,分析了它们各自的特点、优势所在以及局限性,并对无线局域网络安全技术作了一些分析。     

无线局域网技术探讨

在无线局域网覆盖范围内无线设备可自由移动,而且无线局域网的载频为公用频段,无需另外付费,因而使用无线局域网的成本很低。就无线局域网技术的起源、特点、优点及存在的不足做进一步探讨。     

无线局域网802．11系列标准综述

标准在工业化过程中起着重要的作用。随着宽带无线接入和无线局域网技术的发展和应用，无线局域网的标准受到工业界的高度重视。本文介绍和分析了无线局域网802．11系列标准。     

Performance analysis of IEEE 802.11e EDCA in wireless LANs

INTRODUCTION IEEE 802.11e is designed to support multimedia applications. The main and mandatory scheme of IEEE 802.11e standard is enhanced distributed channel access (EDCA), which adopts service dif-ferentiation in configuration. The performance analysis of EDCA has been extensively studied by analytical or numerical means in recent years (Kong et al., 2004; Xiao, 2005; Zhu and Chlamtac, 2005; Hui and Devetsikiotis, 2005; Zhang et al., 2006). With the help of these works, perf…     

无线局域网安全传输协议标准与安全研究

无线局域网为智能监控系统提供了便捷高速的数据传输服务,但是由于其完全暴露在外的无线传输链路,严重影响着监控系统传输数据的安全性。为解决这一问题,IEEE802.11委员会设计了一种全新的无线局域网安全协议:IEEE802.11i。以无线局域网的特性和可能存在的安全问题展开论述,着重阐明IEEE802.11i协议的安全标准以及在认证和密钥管理阶段应对安全威胁的优势。     

两种无线局域网安全标准WAPI与 IEEE802.11i的比较

本文从两个标准的技术实质与工作原理两方面来加以分析和比较，并在文末预测了它们的前景。     

Mathematical Analysis of Energy Efficiency in IEEE 802.11 DCF

The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are mobile or portable units, power consumption becomes a primary issue since terminals are usually battery driven. This paper proposes an analytical model that calculates the energy efficiency of both the basic and the RTS/CTS access mechanisms of the IEEE 802. II protocol. The model is validated with simulation results using NS-2 simulation package. The effects of the network size, the average packet length, the initial contention window and maximum backoff stages on the energy efficiency of both access mechanisms are also investigated. Results show that the basic scheme has low energy efficiency at large packet length and large network size, and depends strongly on the number of stations and the backoff procedure parameters. Conversely, the RTS/CTS mechanism provides higher energy efficiency when the network size is large, and is more robust to variations in the backoff procedure parameters.     

Finite time-horizon Markov model for IEEE 802.11e

We model wireless local area network channel utilization over a finite interval through a finite time-horizon Markov （FTHM） model. By accurately capturing time-varying utilization, the FTHM model allows for generally distributed transmission-opportunity （TXOP） duration, which most existing models do not account for. An absorbing state is introduced to limit the lifetime of the counting process, resulting in a non-ergodic Markov chain that is solved via transient analysis. The model predictions for time-varying utilization are validated by simulation with errors of no more than 0.1% after eight beacon intervals. Moreover, we show that the FTHM model prediction error is below 4% for Poisson distributed and uniformly distributed TXOP durations.     

Achieving Efficient Channel Utilization for Data Communications in IEEE 802.11 WLAN

In the IEEE g02. 11 protocol, the adoption of the exponential backoff technique leads to throughput performance strongly dependent on the initial contention window size and, most importantly, on the number of contending stations considered in the network. This paper proposes a simple but accurate method to dynamically estimate the number of contending stations in a wireless local area network （ WLAN ）. Based on estimation, all the mobile stations dynamically adjust the initial contention window in medium access control （ MAC ） layer to avoid collisions. The simulation results show that the proposed algorithm can achieve efficient channel utilization, higher system throughput, and better fairness performance.     

Performance Improvement of Distributed Coordination Function in IEEE 802.11 Wireless LAN

This paper proposes a modification to distributed coordination function (DCF) to improve the channel utilization in IEEE 802.11 wireless local area networks (WLANs). In the modified DCF, when a station has contended for the channel, it may transmit multiple data frames continuously to the same destination, which is called transmission burst(TB). When the maximum number of data packets transmitted continuously in a TB is set to be 2, the performance is expected to be the best. The theoretical analysis and simulation results show that compared with the standard DCF, the modified DCF can increase the throughput and decrease the delay of the WLAN, and the modification does not introduce any additional control overhead.     

Performance Improvement of DCF Supporting Multi-Rate in IEEE 802.11b Wireless LAN

Inrecent years ,IEEE802.11 wirelesslocal area net-work (WLAN) has emerged as a prevailing technology forthe (indoor) broadband wireless access to internet for themobile/portable devices . In IEEE 802.11 standards ,802.11b has become the most widely used v…     

一种基于802.11i的拒绝服务攻击的解决方案

文章分析了802.11i新标准下的无线局域网可能发生的分布式拒绝服务攻击,提出了一种解决方案用来检测并防御这种攻击,并且提出了惩罚不正确行为的矫正措施。在充分考虑了无线局域网中抵御拒绝服务攻击技术上和经济上的困难后,作者提出了一种利用Agent软件的解决方案,能够实现行为监视并且采取适当的措施。     

IEEE 802.11协议直扩技术的实现

802.11标准直扩技术主要是对网络的物理层(PH)和媒质访问控制层(MAC)进行了规定,其中对MAC层的规定是重点.同一物理层上可以互操作,逻辑链路控制层(LLC)是一致的,即MAC层以下对网络应用是透明的.这样就使得无线网的"(同网段内)多点接入"和"多网段互连",易于质优价廉地实现.     

Performance analysis of IEEE 802.11 DCF networks

This paper presents an analytical saturation throughput model of IEEE 802.11DCF （distributed coordination function） with basic access in ad hoc mode. The model takes into account freezing of the backofftimer when a station senses busy channel. It is shown that taking into account this feature of DCF is important in modeling saturation throughput by yielding more accurate and realistic results than models known from literature. The proposed analytical model also takes into account the effect of transmission errors. All essential features of the proposed analytical approach are illustrated with numerical results. The presen- tation of the model is proceeded by an overview of approaches to IEEE 802.11 network performance evaluation presented in the literature.     

IEEE 802.11网络中服务质量支持机制的研究

如何保证实时业务(如VoIP、AoD和VoD等多媒体业务)的服务质量是目前无线通信领域的一个重要课题。本文概述了现有的IEEE 802．11中服务质量支持机制,包括基于 MAC层的区分服务机制、基于MAC以上层的接纳控制和带宽预留机制等,对实现复杂性、兼容性和资源利用率等进行了简要分析。