无线局域网的媒体访问探讨协议

本文主要围绕ＩＥＥＥ８０２．１１ＤＦＷＭＡＣ建议并结合无线局域网研究实实践，讨论应用于无线局域网的媒体访问控制技术。     

无线局域网的两大主要标准

无线局域网是一种能支持较高数据速率（２～１１Ｍｂｉｔ／ｓ）、采用微蜂窝、微微蜂窝结构的自主管理的计算机局部网络。它可采用扩展频谱技术,以无线电或红外线作为传输媒质,其移动的终端可通过无线接入点来实现对Ｉｎｔｅｒｎｅｔ的访问。在无线局域网这个领域中有两个主要标准：ＩＥＥＥ８０２．１１和ＨＩＰＥＲＬＡＮ Ｈｉｇｈ Ｐｅｒｆｏｒｍａｃｅ Ｒａｄｉｏ Ｌｏｃａｌ Ａｒｅａ Ｎｅｔｗｏｒｋ。ＩＥＥＥ８０２．１１只规定了开放式系统互联参考模型（ＯＳＩ／ＲＭ）的物理层和ＭＡＣ（介质访问控制）层,它的主要特点如下…     

无线调制解调器

８０２．１１为无线局域网标准，本文描述了采用Ｈａｒｒｉｓ半导体公司ＰＲＩＳＭ＾ＴＭ２．４ＧＨ，ＤＳＳＳ芯片组，加上媒体访问控制器，构成符合ＩＥＥＥ８０２．１１标准的直接序列扩展频谱的无线调制解调器系统。     

无线局域网（WLAN）的新标准——802.11

本文对无线局域网的标准－－８０２．１１做了一个总体的介绍，包括其传输媒体、三扑结构、媒体访问控制等。ＩＥＥＥ８０２．１１是无线局域网的一个新标准，需要经过实践检验并在实践中逐步改进和完善。     

遵循IEEE802.11a的无线技术亮相

在美国亚特兰大市所召开的“Ｎｅｔｗｏｒｌｄ＋Ｉｎｔｅｒｏｐ ２０００”上,无线ＬＡＮ半导体芯片制造商美国Ａｔｔｅｌｏｓｓ ｃｏｍｍｕｎｉｃａｔｉｏｎｓ公开演示了遵循ＩＥＥＥ８０２．１１ａ的无线技术。ＩＥＥＥ８０２．１１ａ是在５ ＧＨｚ频带上实现最大５４ Ｍｂｐｓ传送速度的无线通信规格,其最大特点在于其可实现高速数据通信。通过与ＩＥＥＥ８０２．１１ｂ的无线通信系统作比较,发现使用遵循ＩＥＥＥ８０２．１１ａ的系统所发送的ＨＤＴＶ高清淅度电视动态图像,其画面平稳流畅得多。ＩＥＥＥ８０２．１１ａ规格将５．１…     

计算机无线局域网发展趋势

计算机通信的广泛应用促使无线局域网的迅速发展，论文介绍了无中域网特点及其拓扑结构，介绍其产品及特点，追踪无线局域网的标准化进程，介绍了ＩＥＥＥ８０２．１１和ＨＥＰＥＲＬＡＮ两种最流行的物理层和数据链路层标准，得出无线局域网系统未来发展趋势。     

计算机局域网组网技术浅析

一、概述８０年代,美国ＩＥＥＥ制定了８０２系列ＬＡＮ标准,其中的ＩＥＥＥ８０２．３（ＣＳＭＡ／ＣＤ）标准由物理层和ＭＡＣ层规范构成,著名的以太网就是ＩＥＥＥ８０２．３标准的代表产品。由ＸＥＲＯＸ、ＤＥＣ和Ｉｎｔｅｌ三家公司首先推出的标准以太网是１０Ｍｂｐｓ基带网标准,属于公共总线型（ＣｏｍｍｏｎＢｕｓ）网络。当网上某工作站发布信息时,网上所有站点都可以通过公共总线接收,这种工作方式类似无线广播。以前以太网为了提高兼容性,涵盖了不同技术规格和传输介质。同时,为了适应通信技术宽带化、智能化、光纤化的…     

标准与规范

无线局域网新标准８０２．１１ｇ通过批准　　　　新一代无线局域网标准８０２．１１ｇ已经通过批准。这种新标准可以和过去的网络技术同时运行，即无需对现有设备升级换代，同时使家用和商用的电脑无线连接数量的激增成为可能。　　　　这种新标准由美国工业标准组织──电子工程研究所（Ｉｎｓｔｉｔｕｔｅ　ｏｆ　Ｅｌｅｃｔｒｉｃａｌ　ａｎｄ　Ｅｌｅｃｔｒｏｎｉｃｓ　Ｅｎｇｉｎｅｅｒｓ（ＩＥＥＥ．））投票决定，并且仍然处于试验性阶段。据悉，该系统标准的传输速度从现有的　８０２．１１ｂ的１１Ｍｂｉｔ／Ｓ提高到　５４Ｍｂｉ…     

无线局域网技术探讨

无线局域网（ＷＬＡＮ）不使用电缆或光缆,特别适用于移动用户与临时性用户访问现有的网络资源。本文主要讨论由ＩＥＥＥ工作组制定的ＩＥＥＥ８０２．１１标准和欧洲电信标准协会（ＥＴＳＩ）提出的高性能无线局域网（ＨＩＰＥＲＬＡＮ）标准,最后对移动ＩＰ技术作了简单介绍。     

国外无线红外数字通信的研究

介绍了国外兴起的一种通信技术－红外无线数字通信的工作原理，组成结构及该技术中已有的两个标准：ＩｒＤＡ及ＩＥＥＥ８０２．１１，并就国外的一些研究与开发成果作了简要综述。     

Wireless LAN security and IEEE 802.11i

This article reviews wireless LAN security with a focus on the evolving new IEEE 802.11i standard. The major security enhancements in encryption and authentication defined by 802.11i are illustrated. In addition, the newly introduced key management in 802.11i is discussed. Because 802.11i incorporates IEEE 802.1X as its authentication enhancement, 802.1X with consideration of roaming users is depicted. Both intrasubnet and intersubnet roaming are illustrated.     

New high-rate wireless LAN standards

After the IEEE 802.11 standardization group established the first wireless LAN, several efforts were started to increase data rates and also to use other bands. This article describes the new wireless LAN standards developed by IEEE 802.11, ETSI BRAN, and MMAC. The new standards are targeting data rates up to 11 Mb/s in the 2.4 GHz band and up to 54 Mb/s in the 5 GHz band     

The 802.11n MIMO-OFDM Standard for Wireless LAN and Beyond

An overview is given of the new IEEE 802.11n standard. This is the first wireless LAN standard based on MIMO-OFDM, a technique pioneered by Airgo Networks to give a significant performance increase in both range and rate relative to conventional wireless LAN. Performance results show that net user throughputs over 100 Mbps are achievable, which is about four times larger than the maximum achievable throughput using IEEE 802.11a/g. For the same throughput, MIMO-OFDM achieves a range that is about 3 times larger than non-MIMO systems. This significant improvement in range-rate performance makes MIMO-OFDM the ideal solution not only for wireless LAN, but also for home entertainment networks and 4G networks. Richard van Nee received the M.Sc. degree in Electrical Engineering from Twente University in Enschede, the Netherlands, in 1990. In May 1995, he received the PhD degree from Delft University of Technology. From 1995 to 2000, he worked for Lucent Technologies Bell Labs on wireless LAN transmission techniques. He was one of the original proposers of the CCK and OFDM modulation techniques which were adopted by the IEEE 802.11b and IEEE802.11a wireless LAN standards. In 2001, he cofounded Airgo Networks that developed the first MIMO-OFDM modem for wireless LAN and which techniques form the basis of the IEEE 802.11n standard. Together with Ramjee Prasad, he wrote a book on OFDM, entitled ‘OFDM for Mobile Multimedia Communications.’ In 2002 he received the Dutch Veder award for his contributions to standardization of wireless communications.     

IEEE802.11无线局域网EDCF接入研究与仿真

分析了现有IEEE 802.11无线局域网的基本接入机制DCF(Distributed Coordination Function)对QoS(Quality of Service)技术支持的局限性,介绍了未来具有QoS保证的IEEE 802.11e标准采用的一种新的MAC层接入机制EDCF(Enhanced DCF).对EDCF的性能进行了仿真,并对比原有DCF的性能对仿真结果进行了分析.     

下一代WLAN技术IEEE 802.11ac

IEEE 802.11ac是继802.11n的下一代无线局域网新技术标准,本文主要介绍了802.11ac在新技术方面的特性,重点介绍了MU-MIMO系统在802.11ac中的应用,包括MU-MIMO中多用户调度公平性问题的解决及目前最新的SLNR波束成形技术对多用户间干扰问题的解决方案。     

A novel performance analysis model for an IEEE 802.11 wireless LAN

This letter presents a novel analytic model that accurately evaluates the performance of a single-hop IEEE 802.11 wireless LAN (WLAN). By using a closed queuing network, we model an IEEE 802.11 WLAN system that consists of a fixed number of stations and derive the saturated throughput of the IEEE 802.11 distributed coordination function (DCF). The ns-2 simulation results show that our new analysis model is very accurate in evaluating the performance of the IEEE 802.11 DCF.     

一种新型提供服务质量保证的自适应无线局域网媒体接入协议

在无线局域网中提供QoS保证近年来日益成为研究热点.本文基于自适应无线局域网MAC协议在一种新的建模分析的基础上提出了一种提供QoS的新算法QoS-NSAD.QoS-NSAD赋予高优先级站点和低优先级站点不同的自适应特性从而很好地保证高负载环境高优先级用户的QoS特性.同时由于继承了以前算法的自适应机制,系统吞吐量能够逼近最优.大量仿真结果验证了算法的有效性.     

基于OFDM的高速无线局域网标准IEEE 802.11a的同步和信道估计方法

介绍了基于OFDM的无线局域网标准IEEE802．11a的物理层相关OFDM参数和其基带IFFT实现原理,结合具体的分组结构,给出了其符号定时、载波频率偏移估计和信道估计方法,这也是一般OFDM系统的关键问题。     

Use of Different Acknowledgement Policies for Burst Transmission in Fiber-fed Wireless LANs

The IEEE 802.11 e medium access control (MAC) for quality-of-service (QoS) support in 802.11 networks defines burst transmission and new acknowledgment (ACK) operations as optional mechanisms for increasing channel utilization. In this paper, we investigate how the performance of these new features is affected by the presence of fiber delay in high speed Wireless LAN (WLAN) over fiber networks. It is shown that the negative effect of the fiber delay on the throughput performance of the 802.11 MAC protocol can be significantly reduced when burst transmission is used with the block or the no ACK policies.     

WLAN安全机制

随着无线局域网技术的广泛应用,新的无线局域网安全标准被提出以增强无线局域网的安全性能.本文介绍了IEEE 802.11i和WAPI两个无线网络安全技术标准的实现机理和具体流程,重点分析了我国自主研发的WAPI的技术特征和应用状况,并将其与IEEE 802.11i技术标准做了分析对比.