IEEE 802.11 5GHz标准物理层研究

IEEE 802.115GHz技术标准及相关设备的逐步成熟,使得5GHz WLAN网络建设成为可能.文章研究并分析了IEEE 802.11a、IEEE 802.11n、IEEE 802.11ac等5GHz WLAN标准的技术发展路径,并对其物理层关键技术及各标准所支持的最高数据速率作了重点分析.     

无线局域网IEEE802.11n标准分析

802.11n是制定中的最新的无线局域网标准.首先介绍了无线局域网以及802.11标准系列的发展历史.然后介绍了802.11n标准的特点和发展现状.通过对WWiSE和TGnSynch两大技术阵营的对比.对802.11n的核心技术进行了分析介绍.最后对未来的802.11n标准做出了预测.     

WLAN热点建设方案探讨

1 WLAN概况 WLAN的标准是IEEE 802.11系列协议,包括IEEE 802.11a/b/g/n,另外还有基于QoS的IEEE 802.11e,用于安全协议的IEEE 802.11i等.     

WLAN标准及技术最新进展

继1999年IEEE批准802．11b和802．11a标准以来，基于802．11系列标准的产品已经在全球逐渐普及，其低廉的价格和开放的频谱为企业、家庭和个人用户带来了方便。据Infoneties研究公司的报告，2004年第二季度全球无线局域网(WLAN)硬件收入达到7．195亿美元，比第一季度增长3％，预计2005年第二季度将增长9％，达到7．862亿美元。但IEEE在WLAN方面的工作并未止步，802．11系列标准仍在紧锣密鼓地制定当中，新的技术也给WLAN带来了动力，提高带宽和传输性能成为下一代WLAN发展的目标。     

IEEE 802.11系列标准

介绍了无线局域网(WLAN)的802．11系列标准，描述了WLAN的工作频段，除了论述窄带微波(Narrowband Microwave)技术、红外线(Infrared)技术及扩展频谱技术，还讨论了介质访问控制和802．1l的安全机制和发展。     

无线局域网标准 IEEE802.11g的技术优势

本文详细介绍了无线局域网标准IEEE802.11g的发展历程及其技术优势。     

WLAN接入控制技术

WLAN因其应用日益广泛而备受关注。作为未来核心网的一种重要的接入形式，WLAN需要满足现在和未来网络对高服务质量的要求和多样化的要求，高质量要求做好底层传输和设计合适的接入控制协议，多样化要求在对用户的接入控制的优先级和资源分配上结合用户的服务质量要求。本文概述了WLAN的接入控制，描述了结合服务质量的接入控制思想，分析了现有技术存在的问题，提出了以后的改进方向。     

基于WLAN技术的无线校园网组网研究

无线局域网(WLAN)使用无线多址信道方法来支持计算机间通信。本简要介绍了IEEE802．110标准协议以及无线局域网基本原理和拓扑结构，并结合无线局域网组网特点，详细阐述无线校园网设计规划的原则、方法和步骤。最后介绍一个可行的802．11g无线校园网设计方案。     

基于多跳路由技术的WLAN研究

本文首先研究了IEEE802．11b无线局域网的工作原理及相关协议，然后对多跳路由协议的性能进行了仿真分析。在此基础上，充分研究了WWAN与WLAN的特点，对二者进行融合，建立仿真模型，分析比较模型的容量。实验结果表明，WWAN与WLAN融合有效提高业务移动性和覆盖面。     

基于IEEE 802．11协议的WLAN无线资源管理浅析

1、前言 近年来，随着数据业务需求的不断增加，以IEEE 802．11协议为基础的无线局域网（WLAN）的研究正逐渐成为人们研究的热点。最初开发WLAN的目的是对有线LAN进行无线扩展，通过无线通信的方式实现有线LAN的功能，并以比有线网络更加低廉的价格和更加方便、灵活的方式进行网络安装和维护，主要用于企业和家庭网络。但是，随着蜂窝移动通信产业的成功和WLAN技术的发展，     

一种IEEE 802.11中慢启动递减的竞争窗口控制算法

本文在研究现有的无线局域网802.11 MAC层拥塞控制的基础上,提出了一种增强的拥塞控制性能的算法,称为"慢启动递减算法"(SSDS:Slow-Start Decrease Scheme).该算法通过修改802.11的MAC层中的DCF(Distributed Coordination Function)子协议,改善了IEEE802.11无线局域网在拥塞情况下的性能,提高了网络吞吐量.文中通过仿真对算法进行了分析和研究.     

Analytical Study of TCP Performance over IEEE 802.11e WLANs

IEEE 802.11 Wireless LAN (WLAN) has become a prevailing solution for broadband wireless Internet access while the Transport Control Protocol (TCP) is the dominant transport-layer protocol in the Internet. Therefore, it is critical to have a good understanding of the TCP dynamics over WLANs. In this paper, we conduct rigorous and comprehensive modeling and analysis of the TCP performance over the emerging 802.11e WLANs, or more specifically, the 802.11e Enhanced Distributed Channel Access (EDCA) WLANs. We investigate the effects of minimum contention window sizes and transmission opportunity (TXOP) limits (of both the AP and stations) on the aggregate TCP throughput via analytical and simulation studies. We show that the best aggregate TCP throughput performance can be achieved via AP’s contention-free access for downlink packet transmissions and the TXOP mechanism. We also study the effects of some simplifying assumptions used in our analytical model, and simulation results show that our model is reasonably accurate, particularly, when the wireline delay is small and/or the packet loss rate is low.

IEEE802．11a无线局域网性能分析

IEEE802．11系列标准是无线局域WLAN（Wireless Local Area Network）中应用最广的标准。其中IEEE802．11a工作在5．8GHz频段,除了不受向下兼容性的限制外,同频段系统之间的干扰也很小,因而比较适合高密度、高容量的网络。IEEE802．11a采用正交频分复用（OFDM）调制方式,理论最高传输速率可达54Mbit／s,但在实际应用中,其传输净数据率均远低于此。为了评估其数据业务支持能力,指导网络容量规划,文章主要从MAC层协议性能方面对IEEE802．11a WLAN网络的性能进行了分析,并给出了其实际吞吐量。     

WLAN中IEEE802.11n标准及关键技术研究

对WLAN中最新的802.11n标准进行探讨,从MIMO-OFDM结合的相容性及技术原理分析IEEE802.11n标准中的关键技术MIMO-OFDM,分析MIMO-OFDM中同步,信道估计、MIMO检测等关键技术,从IEEE802.11g/a产品的实践应用及对IEEE802.11n传输速率实验,指出该标准能有效解决WLAN应用中的传榆瓶颈问题,在未来WLAN的应用中将会起到主导作用.     

一种基于预测式公平队列调度算法的802.11e MAC层机制

在共享媒体的通信系统中,队列调度的公平性是很重要的。该文在研究了IEEE WLAN已有的各种队列调度算法的基础上,提出了一种预测式公平队列调度算法 (Predict Fair Queuing, PFQ),并结合IEEE 802.11e的EDCF(Enhanced Distributed Coordination Function)机制提出一种基于PFQ的新的MAC层协议P-EDCF(PFQ-based EDCF)。该协议通过引进PFQ算法来修改EDCF的优先级控制方式,提供一种公平、高效的接入机制。仿真结果表明,该机制很好地改善了EDCF的性能,为各种类型业务提供了公平的服务。     

Towards providing optimal energy‐efficiency and throughput for IEEE 802.11 WLANs

IEEE 802.11 wireless network standard has become one of the most used wireless networking technologies for smart devices as it offers mobility support and low cost deployment. However, these devices deeply rely on the energy provided by their batteries, which results in limited running time. IEEE 802.11 network standard provides stations with carrier sense multiple access with collision avoidance for the medium access. Yet it results in stations to consume an important amount of power. Therefore, minimizing WiFi‐based energy consumption in smart devices has been received substantial attention in both academia and industry. Accordingly, this paper * proposes a novel beacon‐based energy‐efficient collision‐free medium access control protocol for any type of IEEE 802.11 stations, regardless of being stationary or mobile, or having different amount of traffic flow, transmission rates, or traffic types. The proposed scheme is valid for all types of low or wide bandwidth, single or multiuser multiple‐input multiple‐output WLAN channels, such as IEEE 802.11a\b\g\n\ac. In the proposed scheme, energy saving is achieved, enabling stations to transmit on the right time and maintaining stations in the doze state during a predetermined sleep_time interval after each successful frame transmission, by making use of modified control and management frames of the standard IEEE 802.11 protocol. The proposed scheme reduces the probability of collisions and may allow stations to enter the collision‐free state, regardless of the number of stations on the channel and their traffic types. Widespread simulations have been executed to validate the efficiency of the proposed method. The results demonstrate that the proposed method significantly increases overall throughput and reduces power consumption of stations over IEEE 802.11 WLANs.     

IEEE 802.11无线局域网标准发展历程及其发展方向

本详细介绍了IEEE802．11标准组成，标准发展历程和发展方向。     

Frequency assignments in IEEE 802.11 WLANs with efficient spectrum sharing

As the number of WLAN users grows, the need to perform efficient radio resource management strategies becomes essential due to the fact that most popular technologies, those based on IEEE 802.11 standards, use unlicensed frequency bands. A good channel assignment improves the network performance, producing benefits that are perceived by the users and also by the network administrators. In this paper, we present a new frequency management scheme for IEEE 802.11 WLANs in the 2.4 GHz ISM band that minimizes interference to increase the throughput available to client stations by adapting a weighted DSATUR algorithm for graph coloring. The algorithm takes both co‐channel and adjacent channel interference into account, and makes use of all available channels instead of the traditional non‐overlapping three. In this way, collisions as well as transmission errors are minimized, thus improving the network capacity and the user experience. Different architectures are discussed for the implementation of our approach, including the possibility to incorporate client stations into the management system. Copyright © 2008 John Wiley & Sons, Ltd.     

WLAN中基于IEEE802.11u协议的终端节能功耗管理方案

支持IEEE 802.11u标准的移动终端在无线局域网提供的网络服务覆盖范围内可自动接入无线局域网。针对IEEE 802.11u无线局域网的特点,提出了一种基于时间序列感知的PSM（S-PSM）方案。采用IEEE 802.11u标准中定义的公共广播服务（GAS）来广播传输序列信息,所有终端根据该序列信息相应地控制自身的工作状态。为了降低竞争信道的碰撞概率,引入了响应竞争窗口。当接入点（AP）中没有数据分组时,AP 广播GAS帧并激活空闲计时器。所有终端进入睡眠状态直到空闲计时器到期。仿真结果表明,与传统的PSM相比,该方案能显著降低功耗,提升终端能效。