无线局域网 IEEE802.11 高性能局域网统一信息系统

无线局域网标准 IEEE802.11是第一代无线局域网标准之一。 1990年 IEEE802标准化委员会成立 802.11无线局域网 (WLAN)标准工作组。 802.11无线局域网标准工作组任务为研究 1Mbit/s和 2Mbit/s数据速率、工作在 2.4GHz开放频段的无线设备和网络发展的全球标准,并于 1997年 6月公布了该标准。该标准定义物理层和媒体访问控制 (MAC)规范,允许无线局域网及无线设备制造商建立互操作网络设备。 　　IEEE 802.11标准中物理层定义了数据传输的信号特征和调制。在物理层中,定义了两种 RF传输方法和一种红外线传输方法。在该标准中, RF传输采用扩频方法,即采用了跳频扩频 (FHSS)和直接序列扩频 (DSSS)两种方法,工作在 2.4000GHz～ 2.4835GHz频段。     

IEEE802.11无线局域网标准

介绍了IEEE802.11无线局域网技术规范.给出了ISM频段、扩频技术的背景及各国相应的标准、规范.描述了允许可证2.4GHzISM频段的直接序列扩频技术及IEEE802.11协议规范。     

Effects on IEEE 802.11 MAC Throughput in Wireless LAN Over Fiber Systems

An experimental investigation of the influence of the fiber distribution of wireless LAN (WLAN) signals on throughput performance is presented. Transmission using different medium-access-control mechanisms and IEEE 802.11b and 802.11g physical layers is considered, and results are compared with those from the corresponding simulations in a commercial event-driven network simulator (OPNET). Performance of the WLAN-over-fiber network in the presence of multiple clients is also analyzed. This paper confirms that a fiber delay does not significantly affect the performance obtained by fragmentation mechanism. Furthermore, when multiple antenna units are fed by a single access point, it is demonstrated that the presence of hidden nodes can cause the performance of WLAN-over-fiber networks to deteriorate. Finally, it is shown that the request-to-send/clear-to-send mechanism can be utilized to mitigate the negative effects associated with the hidden node problem.     

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.     

可用于无线局域网802.11a标准的5-GHz CMOS功率放大器设计

介绍了TSMC0．18μm CMOS工艺的功率放大器的设计,给出了仿真结果,版图照片和芯片键合测试方案。该电路采用三级差分放大结构,在其工作频段内满足绝对稳定条件,在3．3V电源电压下,增益为27．3dB,输入1dB压缩点为-7dBm,最大输出功率为19．3dBm,输入端反射系数S11=-30dB,可用于无线局域网802．11a标准的系统中。     

IEEE802.11无线局域网视频流传输综述

With relatively high transmission capacity and usually unconstrained connections, IEEE802.11 WLANs provide the ideal infrastructure for pervasive video content sharing and communications. However, the delivery of high-performance video streams over 802.11 WLANs remains a challenging task due to the inherent characteristics of compressed video and dynamic channels. In this paper, we present a brief survey of various recent innovations that have been developed to enhance the Quality of Service (QoS) performance for video over WLANs. Based on the application scenarios, the solutions have focused mainly on three network layers, that is, Application layer (APP), Media Access Control layer (MAC), and Physical layer (PHY). After reviewing the video compression technology, we first examine various single-layer solutions for video over WLANs. We then discuss several cross-layer solutions that take advantage of mutual interactions between different network layers. Finally, several technical issues beyond QoS performance, including energy and security, are also addressed. We conclude that the application of video over WLANs will continue to increase in future.     

IEEE 802.11 Wireless LAN: can we use it for multimedia?

The IEEE P802.11 committee developed the 802.11 Wireless LAN standard to cover wireless networks for fixed, portable, and moving stations within a local area. This standard addresses the need for wireless connectivity to stations, equipment, or automatic machinery that requires rapid deployment and may be portable, handheld, or mounted on moving vehicles. It can function totally wireless or connected to a wired network. Most people familiar with the standard expect to use it in providing wireless networks for personal computers or stations connected to the global wired infrastructure through access points. Now that the 802.11 standard is finally here, it will energize the wireless LAN market and result in the proliferation of low cost wireless connectivity in the office and home. Study groups are working on higher rates at 2.4 GHz and at 5 GHz for future inclusion into the standard. These higher rates will make it even more practical to employ this standard for multimedia traffic     

OFDM技术在无线局域网中的应用研究及最新发展

本文全面详述了第四代移动通信的关键技术0FDM及其特点，分析了OFDM技术在无线局域网中的应用，探讨了OFDM最新发展MIMO OFDM技术及其在下一代无线局域网标准：IEEE802．11n。     

The Effect of Terminal Movement on the Performance of IEEE 802.11 g Wireless LAN Systems in Simulated Radio Channels

The effect of terminal movement on the performance of the IEEE 802.11 g wireless LAN (WLAN) system is evaluated using a measurement set-up including a radio channel simulator. The evaluation is based on laboratory measurements of WLAN PC cards in different simulated radio environments. In the measurements, two different radio channel models are used; the exponential channel model and the UMTS vehicular channel model. The measurement results indicate promising operation of IEEE 802.11 g WLAN systems as such. However, the use of different packet sizes has a significant effect on the system behaviour. With large packets the terminal is more likely to experience channel estimation errors than with small packets. This is due to the fact that the IEEE 802.11 g receiver estimates the channel only once per frame, and uses this estimation over the entire frame. Based on the measurement results we suggest a modification to the medium access control (MAC) layer operation that overcomes this problem: the use of optimized fragmentation.     

基于IEEE 802.11的多信道多址接入协议性能分析

 本文对一种基于IEEE 802.11 DCF协议多信道多址接入方案的性能进行了分析,在该接入方案中,节点在公共的控制信道上预约数据信道,随后在预约成功的数据信道上,进行数据分组的传输.本文采用马尔科夫链构建了控制信道的预约模型,给出了多信道吞吐量的理论分析算法.最后,通过仿真验证了理论分析结果与仿真结果的一致性,并给出了信道吞吐量与信道数、数据分组长度、节点密度、信道切换时延等参数之间的数值关系.     

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.     

FHCF: A Simple and Efficient Scheduling Scheme for IEEE 802.11e Wireless LAN

The IEEE 802.11e medium access control (MAC) layer protocol is an emerging standard to support quality of service (QoS) in 802.11 wireless networks. Some recent work shows that the 802.11e hybrid coordination function (HCF) can improve significantly the QoS support in 802.11 networks. A simple HCF referenced scheduler has been proposed in the 802.11e which takes into account the QoS requirements of flows and allocates time to stations on the basis of the mean sending rate. As we show in this paper, this HCF referenced scheduling algorithm is only efficient and works well for flows with strict constant bit rate (CBR) characteristics. However, a lot of real-time applications, such as videoconferencing, have some variations in their packet sizes, sending rates or even have variable bit rate (VBR) characteristics. In this paper we propose FHCF, a simple and efficient scheduling algorithm for 802.11e that aims to be fair for both CBR and VBR flows. FHCF uses queue length estimations to tune its time allocation to mobile stations. We present analytical model evaluations and a set of simulations results, and provide performance comparisons with the 802.11e HCF referenced scheduler. Our performance study indicates that FHCF provides good fairness while supporting bandwidth and delay requirements for a large range of network loads. Pierre Ansel received a multidisciplinary in-depth scientific training in different fields such as Pure and Applied Mathematics, Physics, Mechanics, Computer Science and Economics from the Ecole Polytechnique, Palaiseau, France. Then, he joined the Ecole Nationale Superieure des Telecommunications, Paris, France in 2005 where he went further into electronics, databases, computer network security and high speed networks. He received a multidisciplinary master of sciences degree and an additional master of sciences degree in telecommunications in 2005. He did a summer internship in 2003 in INRIA, Sophia Antipolis, France where he worked on the Quality of Service in 802.11 networks at Planete Group, France. Then in 2004, he joined France Telecom R&D, Issy-les-Moulineaux, France to work on Intranet Security issues. He designed a WiFi security supervision architecture based on WiFi Intrusion Detection Sensors. He is currently a French civil servant and belongs to the French Telecommunications Corps. Qiang Ni received the B.Eng., M.Sc. and Ph.D. degrees from Hua Zhong University of Science and Technology (HUST), Wuhan City, China in 1993, 1996 and 1999 respectively. He is currently a faculty member in the Electronic and Computer Engineering Division,School of Engineering and Design, Brunel University, West London, U.K. Between 2004 and 2005 he was a Senior Researcher at the Hamilton Institute, National University of Ireland, Maynooth. From 1999 to 2001, he was a post-doctoral research fellow in the multimedia and wireless communication laboratory, HUST, China. He visited and conducted research at the wireless and networking group of Microsoft Research Asia Lab during the year of 2000. From Sept. 2001 until may 2004, he was a research staff member at the Planète group of INRIA Sophia Antipolis France. Since 2002, he has been active as a voting member at the IEEE 802.11 wireless LAN standard working group. His current research interests include communication protocol design and performance analysis for wireless networks, cross-layer optimizations, vertical handover and mobility management in mobile wireless networks, and adaptive multimedia transmission over hybrid wired/wireless networks. He has authored /co-authored over 40 international journal/conference papers, book chapters, and standard drafts in this field. He is a member of IEEE. E-mail: Qiang.Ni@ieee.org Thierry Turletti received the M.S. (1990) and the Ph.D. (1995) degrees in computer science both from the University of Nice – Sophia Antipolis, France. He has done his PhD studies in the RODEO group at INRIA Sophia Antipolis. During the year 1995–96, he was a postdoctoral fellow in the Telemedia, Networks and Systems group at LCS, MIT. He is currently a research scientist at the Planete group at INRIA Sophia Antipolis. His research interests include multimedia applications, congestion control and wireless networking. Dr. Turletti currently serves on the Editorial Board of Wireless Communications and Mobile Computing.     

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。     

基于分组到达率的IEEE802.11无线局域网区分服务方法

本文针对IEEE 802.11无线局域网提出了一种基于分组到达率的区分服务实现方法,建立了一种基于二维马尔可夫链的分析模型,结果表明,在控制网络总的负荷的情况下,该方法可有效实现吞吐量的区分并且能够为各个业务流提供统计意义上的吞吐量保证.另外,该方法易于实现而且不需要对IEEE 802.11硬件做任何改动.仿真实验结果表明分析模型相当准确.     

基于802.11a标准的CMOS正交调制器和上变频器

采用0.18μm CMOS工艺,设计并实现了应用于WLAN IEEE 802.11a的正交调制器和上变频器.正交调制器在传统的Gilbert单元基础上,采用负反馈跨导放大器来提高线性度;上变频器采用LC谐振网络作混频器负载来提高增益和电压输出摆幅.测试结果表明,在1.8V电源电压下,谐振频率点的1dB压缩点P1dB为-3.6dBm,功率转换增益为-3.6dB,电流消耗大约45.8mA.     

Packet telephony support for the IEEE 802.11 wireless LAN

Packet telephony is one of the most promising applications in the Internet. In this paper, we propose a modified MAC protocol supporting voice traffic over the IEEE 802.11 WLAN. The proposed scheme adapts the power-saved mode of the IEEE 802.11 specifications in such a way that it approaches the TDM access mode carrying voice traffic, and is compatible with the IEEE 802.11 standard. Simulation results show that the proposed scheme does not degrade the performance of the IEEE 802.11 WLAN using the DCF and also provides good voice quality     

IEEE 802.11 Wireless Local Area Networks

The draft IEEE 802.11 wireless local area network (WLAN) specification is approaching completion. In this article, the IEEE 802.11 protocol is explained, with particular emphasis on the medium access control sublayer. Performance results are provided for packetized data and a combination of packetized data and voice over the WLAN. Our performance investigation reveals that an IEEE 802.11 network may be able to carry traffic with time-bounded requirements using the point coordination function. However, our findings suggest that packetized voice traffic must be handled in conjunction with an echo canceler     

多用户MIMO系统TH预编码

传统TH预编码方案将所有的均衡工作放在发射端完成,没有充分发挥MIMO技术的优势。该文提出一种针对移动端多天线的TH预编码方案,用户之间的干扰消除由发射端完成,而用户之间多个流之间的干扰消除由各个用户自行完成。通过对信道矩阵进行块下三角分解并按速率最大准则进行功率注水,所提方案比传统单天线TH预编码方案有更高的速率。     

Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems

Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and data symbols encoded by space–time codes can be steered to these eigenmodes similar to MIMO wireless communication systems with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G TDD.