IEEE802.11b与蓝牙系统的共存

该文重点讨论了IEEE802.11b无线局域网(Wireless Local Area Network WLAN)与蓝牙(Bluetooth,BT)通信系统之间共存的问题，归纳了一些减小或消除这两个系统之间互扰的方法并加以比较     

蓝牙与802.11共存技术及干扰阻塞测试方法与规格

本文主要讨论802．11与蓝牙共存的一些技术应用，以及蓝牙信号在其他干扰信号源，如PCS、GSM、CDMA等的环境下，如何做阻塞测试以验证蓝牙的抗干扰能力。一般而言，当802．11无线局域网装置与蓝牙装置相距2米以上时，不会有共存干扰的问题。文章先介绍802、11b／g及蓝牙的基本原理，然后再介绍目前业界所提出的共存(Coexistence)技术，最后再阐述测试的方法以验证各种共存技术的性能优劣。     

一种克服蓝牙和802.11b相互干扰的共存机制

由于使用相同频段,使得蓝牙技术和IEEE802.11b无线局域网之间存在干扰,严重影响系统的正常工作.本文首先介绍了传统解决办法,分析了其优缺点,在此基础上,详细介绍了一种新机制--OLA机制.     

蓝牙技术与红外、IEEE802.11b和HomeRF的比较

本文从介绍蓝牙技术特点入手，将蓝牙技术与红外、IEEE802．11b、HomeRF进行比较，使大家对蓝牙这一新技术能有进一步的了解。     

802.11b无线LAN功率放大器设计

随着无线局域网(WLAN)在办公室、家庭和公共场所（如：机场、宾馆、会议中心等)的广泛应用，同时．在基于802.11b无线通信网络标准元器件的支持下．这种网络正逐步成为企业通信的酋选择方案、IEEE802.11b为手提电脑或其它手持终端提供了一条接入网络资源的便利途径，从而增强了现有无线装置的功能，新一代WLAN无线收发装置将安装在与高密度     

两种提高IEEE802.11b WLAN 物理层数据传输速率的编码技术

本文提出两种将IEEE802.11bWLAN物理层数据速率提高到16.5Mbps的编码和译码方法。这两个方案都继续采用原IEEE802.11b中对于5.5和11Mbps速率所采用的CCK编码方法。两个方案的编码过程变化不大，第一方案的译码还是采用对5.5和11Mbps数据率所使用的快速WALSH变换（FWT），第二个方案的译码被修改成适合16.5Mbps数据率的快速WALSH变换（FWT）。最后通过仿真比较了这两个方案在无多径干扰的AWGN信道上的性能，结果表明第二个方案优于第一个。     

IEEE802.11g的推出及其影响

1引言从办公室应用起家的无线局域网(WLAN)技术正在向Hotspot、小型机及AV机等用途扩展。同时它的最大传输速率已由11Mbps提升到54Mbps,而所用频带也由2.4GHz增加为2.4GHz及5GHz两种。进入2003年后,IEEE802.11g又迅速受到PC业界的支持,开始在WLAN市场增强起来。继美国苹果计算机公司于2003年1月发售其笔记本电脑“PowerBook”的新型号后,尽管IEEE802.11g的正式标准尚未完成,但各制造厂商都在相继发售IEEE802.11g对应的路由器及WLAN卡等等。该新格式一方面使用2.4GHz频带,另一方面又把最大传输速率提高到54Mbps,这就打破了…     

无线局域网标准802.11b与802.11a的物理层比较

无线局域网(WLAN)已经存在10多年了,但由于原来一直把它单纯定位于有线LAN的延伸,加上无统一标准以及传输速率低,其应用难以推广.到上世纪末,随着自身技术的进步和标准的统一,WLAN被重新定位作为因特网高速无线接入技术,之后便开始被广泛应用于办公室、机场、酒店、商场、咖啡屋等公共热点场所(hotspots).因此,2000年WLAN被评为美国通信技术十大发展趋势之一.     

蓝牙与IEEE802.11g系统的共存

蓝牙与IEEE802.11g无线局域网(Wireless Local Area Network,WLAN)都工作在2.4GHz频段上,因此它们之间存在一定的干扰。分析了蓝牙与IEEE802.11g通信系统之间的干扰,并提出了解决这一问题的两种方法:自适应跳频和删除标记法,并对两种方法的性能做了比较。     

802.11b无线局域网信道间干扰的研究

无线局域网技术已经广泛的应用于我们的生活之中。由于它只有三个互不重叠的信道，频带资源非常有限，而许多应用场景都需要三个以上的信道，怎样使用相互重叠的信道、重叠信道间的相互干扰如何将成为802．11b的一个主要课题。现对802．11b协议相邻信道的频谱进行了分析，并对信道间干扰进行测试，对重叠信道的使用具有指导意义。     

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。     

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。     

Interference Evaluation of Bluetooth and IEEE 802.11b Systems

The emergence of several radio technologies, such as Bluetooth and IEEE 802.11, operating in the 2.4 GHz unlicensed ISM frequency band, may lead to signal interference and result in significant performance degradation when devices are colocated in the same environment. The main goal of this paper is to evaluate the effect of mutual interference on the performance of Bluetooth and IEEE 802.11b systems. We develop a simulation framework for modeling interference based on detailed MAC and PHY models. First, we use a simple simulation scenario to highlight the effects of parameters, such as transmission power, offered load, and traffic type. We then turn to more complex scenarios involving multiple Bluetooth piconets and WLAN devices.     

应用于802.11b无线局域网的低噪声高线性度的CMOS射频接收机

实现了一个单片集成、直接转换结构的2.4GHz CMOS接收机. 这个正交接收机作为低成本方案应用于802.11b无线局域网系统,所处理的数据传输率为该系统的最大速率--11Mbps. 基于系统设计以及低噪声高线性度考虑,设计了低噪声放大器、直接转换混频器、增益可变放大器、低通滤波器、直流失调抵消电路及其他辅助电路. 该芯片采用中芯国际0.18μm 1p6m RF CMOS工艺流片,所测的接收机性能如下：噪声系数为4.1dB,高增益设置下低噪声放大器与混频器的输入三阶交调点为-7.5dBm,整个接收机的输入三阶交调点为-14dBm,相邻信道干扰抑制能力在距中心频率30MHz处达到53dBc,输出直流失调电压小于5mV. 该接收机采用1.8V电源电压,I, Q两路消耗的总电流为44mA.     

Fair and efficient Transmission Control Protocol access in the IEEE 802.11 infrastructure basic service set

When the stations in an IEEE 802.11 infrastructure basic service set employ Transmission Control Protocol (TCP), this exacerbates per‐flow unfair access problem. We propose a novel analytical model to approximately calculate the maximum per‐flow TCP congestion window limit that prevents packet losses at the access point buffer and therefore provides fair TCP access both in the downlink and uplink. The proposed analysis is unique in considering the effects of varying number of uplink and downlink TCP flows, differing round trip times among TCP connections and the use of delayed TCP acknowledgment (ACK) mechanism. Motivated by the findings of this theoretical analysis and simulations, we design a link layer access control block to be employed only at the access point in order to resolve the unfair access problem. The proposed link layer access control block uses congestion control and ACK filtering approach by prioritizing the access of TCP data packets of downlink flows over TCP ACK packets of uplink flows. Via simulations, we show that the proposed algorithm can provide both short‐term and long‐term fair accesses while improving channel utilization and access delay. Copyright © 2013 John Wiley & Sons, Ltd.     

Throughput Analysis and Admission Control for IEEE 802.11a

We propose a new Markov model for the distributed coordination function (DCF) of IEEE 802.11. The model incorporates carrier sense, non-saturated traffic and SNR, for both basic and RTS/CTS access mechanisms. Analysis of the model shows that the throughput first increases, and then decreases with the number of active stations, suggesting the need for an admission control mechanism.We introduce such a mechanism, which tries to maximize the throughput while maintaining a fair allocation. The maximum achievable throughput is tracked by the mechanism as the number of active stations increases. An extensive performance analysis shows that the mechanism provides significant improvements.Mustafa Ergen received the B.S. degree in electrical engineering from Middle East Technical University (METU) and was the METU Valedictorian in 2000. He received the M.S. and Ph.D. degrees in electrical engineering in 2002 and 2004, the MOT certificate of HAAS Business School in 2003, and the M.A. degree in International and Area Studies in 2004 from the University of California, Berkeley.Dr. Ergen has been conducting research in wireless communication networks with an emphasis on sensor networks, wireless LAN and OFDM systems and is the author of many works in the field, including the book (with A.R.S. Bahai and B.R. Saltzberg) Multi-Carrier Digital Communications: Theory and Applications of OFDM (New York: Springer, 2004).He is National Semiconductor Post Doctoral Fellow and was awarded eight times Bulent Kerim Altay Award by department of electrical engineering in METU and received Best Student Paper Award in IEEE ISCC 2003 and has an invited paper in IEEE GLOBECOM CAMAD 200.Pravin Varaiya is Nortel Networks Distinguished Professor in the Department of Electrical Engineering and Computer Sciences at the University of California, Berkeley. From 1975 to 1992, he was also Professor of Economics at Berkeley. His research is concerned with communication networks, transportation, and hybrid systems. He has taught at MIT and the Federal University of Rio de Janeiro, Varaiya has held a Guggenheim Fellowship and a Miller Research Professorship. He received an Honorary Doctorate from L’Institut National Polytechnique de Toulouse, and the Field Medal of the IEEE Control Systems Society. He is a Fellow of IEEE and a member of the National Academy of Engineering. He is on the editorial board of several journals, including “Discrete Event Dynamical Systems” and “Transportation Research-C.” He has co-authored three books and more than 250 technical papers. The second edition of “High-Performance Communication Networks” (with Jean Walrand) was published by Morgan-Kaufmann in 2000. “Structure and interpretation of signals and systems” (with Edward Lee) was published in 2002 by Addison-Wesley.     

IEEE 802.11在无线自组网中的应用研究

深入分析了IEEE 802.11 DCF机制应用于无线自组网存在的固有缺陷及潜在原因,并阐明了数据流竞争、物理层机制对MAC协议性能的影响。IEEE 802.11 DCF是针对全连通adhoc网络结构设计的,分析表明,要在实际的多跳无线自组网中应用还存在很多问题需要解决。在此基础上提出了将IEEE 802.11有效应用于多跳无线自组网的进一步研究方向。     

Estimation Algorithm of Contending Stations Based on Improved DCF Model in IEEE 802.11

The fundamental access method of IEEE 802.11 is a DCF known as carrier sense multiple access with collision avoidance (CSMA/CA) scheme with exponential back-off. RTS_threshold is used to determine whether to deploy RTS/CTS access method. This threshold should vary with the number of contending stations which contend wireless media to get better throughput. The paper proposes an algorithm which estimates the number of contending stations in BSS. The algorithm is shown to be accurate which is verified by elaborate simulations.