延续IEEE802．11g的生命 240Mbps无线技术

现阶段，倘若你迫不及待地想体验高速无线网络带来的速度提升，那么240Mbps速率的IEEE802．11g增强型产品会是最好的选择，这项增强技术来自于Airgo的第三代True MIMO方案，它也是IEEE802．11n标准的一个有力竞逐者。[编者按]     

节能、网管是无线路由器的两大发展超势

802．11n无线路由器发展了多年,未来的路该怎么走？在探讨这个问题之前,我们需要先了解它的现状。 掐指算来,从2006年1月IEEE802．11n无线网络标准1．0版草案发布到现在已经三年多了。在这三年之中．IEEE802．11n草案标准在2007年升级为2．0版本．在2008年又升级到了3．0版本。根据最新消息．IEEE802．11n工作小组预计在今年11月对外宣布、在2010年1月批准IEEE802．11n正式标准。     

浅析无线局域网IEEE 802.11系列标准

本文主要阐述了无线局域网标准的发展历程和几个主要阶段,重点讨论了802．11g和802．11n两个标准以及其中所采用的关键技术OFDM和MIMO,最后总结了802．11n所具有的四个优势。     

Wi-Fi新规格开始讨论，带宽1000Mbps

802．11n标准仍在草案阶段,802．11r刚刚通过,一些工程师们又开始提出一种新的无线网络标准。这个标准被暂时称之为IEEE 802.11VHT（Verv High Throughput,极高吞吐量）,最低速度也有1000Mbps。目前IEEE还未对此项目进行审批。不过在IEEE802．11标准发展的前提下,这一技术得到批准并非不可能。当前该工作组正在与一些联盟合作,     

WLAN的技术发展及应用前景

本文通过IEEE802．11系列标准介绍了WLAN的技术发展，阐述了采用新的IEEE802．11系列标准后WLAN的优点及应用前景。     

续写11n的动人旋律——两款基于IEEE 802．11n草案的无线路由器

继上期IEEE 802．11n草案(以下简称11n)无线网络专题抢先发布后,第二批进入国内的11n草案产品也陆续进入我们实验室。其中包括基于Airgo第三代Ture MIMO芯片组的华硕240MIMO和基于Broadcom Intensi-fi芯片的Buffalo Nfiniti。     

无线局域网再次提速 IEEE802.11n:无线高速公路时代来临

虽然最终的标准尚未定案,但诸多厂商已经迫不及待地推出了基于IEEE 802．11n草案的产品。它们普遍标称接入速度都能够达到300Mbps,这无疑使广大用户充满了期待。IEEE 802．11n中应用了哪些最新技术?它将给未来的IT界带来怎样的变化?     

行业术语概览－移动技术术语快速指南

802．11x——定义了无线局域网技术的一系列标准。此标准由电气电子工程协会(IEEE)制定，它包括802．11a、802．11b和新兴802．1lg。802．11h和802．111标准在本文发布时仍在开发中。     

技术优势实现高吞吐

虽然802．11n标准尚未最终确定,但相比起802．11alb／g标准,802．11n标准具有明显的技术优势,能够提供高达600Mbps的传输速率,并能够减少噪音信号的干扰。作为下一代无线通迅标准,802．11n标准得到了业界众多重量级厂商的全力支持,下面将详细介绍802．11n标准和技术的优势及发展趋势。     

1920×1200震撼屏幕——惠普高性能移动工作站上市

日前，TP-Link在北京发布了全系列共11款IEEE 802．11n无线产品，无线传输速率最高可达300Mbps。其中9系列IEEE 802．11n无线产品配备了完整的3x3MIMO架构和先进的SST技术，通过发送冗余数据使错误帧大大减少，从而提高数据传输稳定性，减少掉线现象发生。     

Will the New Wi-Fi Fly?

Since the approval of the original IEEE 802.11 standard and the increased use of the resulting Wi-Fi technology over the years, interest in wireless networking has grown rapidly. As is the case with other networking technologies, Wi-Fi users have sought faster IEEE 802.11 versions with longer transmission ranges. Because of this, users have eagerly awaited IEEE 802.11n, which promises higher speeds and longer ranges than earlier Wi-Fi versions. However, the technology has had a rocky standardization process. As is so often the case, two groups of vendors squared off over whose 802.11n approach would become the standard and thereby yield revenue and potential market dominance to the winner. Recently, though, the two sides have moved toward a compromise. However, there are still some unresolved issues, and the IEEE 802.11 Wireless Local Area Networks (WLAN) Working Group still hasn't approved the new technology as a standard     

基于IEEE802.11n的无线网络及其在校园网的应用研究

该文对IEEE802.11n的标准及其核心技术进行了介绍,并就基于它的无线设备组建的校园网进行了分析,对它在校园网中的应用进行了研究。     

IEEE 802.11无线局域网标准研究*

介绍了IEEE 802.11全系列标准,研究了IEEE 802.11系列各标准的发展轨迹和相互关系,建立了该系列标准的层次模型。研究并分析了IEEE 802.11、IEEE 802.11a、IEEE 802.11b、IEEE 802.11g和IEEE 802.11n这几种常见标准,并对相应物理层和媒质访问控制层的关键技术作了重点分析。     

IEEE 802.11n MAC性能优化策略分析

伴随着各类无线产品的快速发展,传统的无线局域网已越来越不能适应这些产品的要求。IEEE 802.11n是新一代无线局域网标准。它不仅在物理层使用了如MI MO-OFDM、40 MHz信道等先进的技术,而且在MAC层也做了很大的改进,大大提高了网络的传输性能。本文将以IEEE 802.11n草案2.0协议为背景,在全面分析该协议的基础之上重点研究MAC层的帧聚合、TXOP、Block ACK、PSMP等优化策略。     

Distributed channel assignment algorithms for 802.11n WLANs with heterogeneous clients

As the latest IEEE 802.11 standard, 802.11n applies several new technologies, such as multiple input multiple output (MIMO), channel bonding, and frame aggregation to greatly improve the rate, range and reliability of wireless local area networks (WLANs). In 802.11n WLANs, access points (APs) are often densely deployed to provide satisfactory coverage. Thus nearby APs should operate at non-overlapping channels to avoid mutual interference. It is challenging to assign channels in legacy 802.11a/b/g WLANs due to the limited number of channels. Channel assignment becomes more complex in 802.11n WLANs, as the channel bonding in 802.11n allows WLAN stations (APs and clients) to combine two adjacent, non-overlapping 20MHz channels together for transmission. On the other hand, IEEE 802.11n is backward compatible, such that 802.11n clients will coexist with legacy clients in 802.11n WLANs. Legacy clients may affect the performance of nearby 802.11n clients, and reduce the effectiveness of channel bonding. Based on these observations, in this paper, we study channel assignment in 802.11n WLANs with heterogeneous clients. We first present the network model, interference model, and throughput estimation model to estimate the throughput of each client. We then formulate the channel assignment problem into an optimization problem, with the objective of maximizing overall network throughput. Since the problem is NP-hard, we give a distributed channel assignment algorithm based on the throughput estimation model. We then present another channel assignment algorithm with lower complexity, and aim at minimizing interference experienced by high-rate, 802.11n clients. We have carried out extensive simulations to evaluate the proposed algorithms. Simulation results show that our algorithms can significantly improve the network throughput of 802.11n WLANs, compared with other channel assignment algorithms.     

Runtime optimization of IEEE 802.11 wireless LANs performance

IEEE 802.11 is the standard for wireless local area networks (WLANs) promoted by the Institute of Electrical and Electronics Engineers. Wireless technologies in the LAN environment are becoming increasingly important and the IEEE 802.11 is the most mature technology to date. Previous works have pointed out that the standard protocol can be very inefficient and that an appropriate tuning of its congestion control mechanism (i.e., the backoff algorithm) can drive the IEEE 802.11 protocol close to its optimal behavior. To perform this tuning, a station must have exact knowledge of the network contention level; unfortunately, in a real case, a station cannot have exact knowledge of the network contention level (i.e., number of active stations and length of the message transmitted on the channel), but it, at most, can estimate it. We present and evaluate a distributed mechanism for contention control in IEEE 802.11 wireless LANs. Our mechanism, named asymptotically optimal backoff (AOB), dynamically adapts the backoff window size to the current network contention level and guarantees that an IEEE 802.11 WLAN asymptotically achieves its optimal channel utilization. The AOB mechanism measures the network contention level by using two simple estimates: the slot utilization and the average size of transmitted frames. These estimates are simple and can be obtained by exploiting information that is already available in the standard protocol. AOB can be used to extend the standard 802.11 access mechanism without requiring any additional hardware. The performance of the IEEE 802.11 protocol, with and without the AOB mechanism, is investigated through simulation. Simulation results indicate that our mechanism is very effective, robust, and has traffic differentiation potentialities.     

Evaluating transport protocol performance over a wireless mesh backbone

IEEE 802.11n wireless physical layer technology increases the deployment of high throughput wireless indoor mesh backbones for ubiquitous Internet connectivity at the urban and metropolitan areas. Most of the network traffic flows in today’s Internet use ‘Transmission Control Protocol’ (TCP) as the transport layer protocol. There has been extensive works that deal with TCP issues over wireless mesh networks as well as noisy wireless channels. Further, IEEE 802.11n is well known for its susceptibility to increased channel losses during high data rate communication. This paper investigates the dynamics of an end-to-end transport layer protocol like TCP in the presence of burst and correlated losses during IEEE 802.11n high data rate communication, while maintaining fairness among all the end-to-end flows. For this purpose, we evaluate four TCP variants-Loss Tolerant TCP (LT-TCP), Network Coded TCP (TCP/NC), TCP-Horizon and Wireless Control Protocol (WCP), where the first two protocols are known to perform very well in extreme lossy networks, and the last two are specifically designed for mesh networks. Our evaluation shows that WCP performs better in a IEEE 802.11n supported mesh networks compared to other three variants. However, WCP also results in negative impact at high data rates, where end-to-end goodput drops with the increase in physical data rate. The analysis of the results reveals that explicit loss notifications and flow balancing are not sufficient to improve transport protocol performance in an IEEE 802.11n supported mesh backbone, rather a specific mechanism is required to synchronize the transport queue management with lower layer scheduling that depends on IEEE 802.11n features, like channel bonding and frame aggregation. The findings of this paper give the direction to design a new transport protocol that can utilize the full capacity of IEEE 802.11n mesh backbone.     

Efficient automatic gain control algorithm and architecture for wireless LAN receivers

The performance of a receiver front-end limits the quality and range of the given communication link. An appropriate design based on well-defined system parameters and architecture can make a huge difference in the performance, cost and marketability of the entire system. In particular, there is a need for improved digital automatic gain control (AGC) for use in multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with application to wireless local area networks (WLANs), targeted for the upcoming 802.11n standard [Heejung Yu et al., IEEE 802.11 wireless LANs ETRI proposal specification for IEEE 802.11 TGn, IEEE 802.11 document, doc. No. 11-04-0923-00-000n, August, 2004; H. Yu, T. Jeon, S. Lee, Design of dual-band MIMO-OFDM system for next generation wireless LAN, in: IEEE International Conference on Communications (ICC), May, 2005]. In this paper, we propose an efficient algorithm and implementation of the digital AGC for next generation WLANs. The proposed AGC algorithm has two feedback loops for gain control to improve convergence speed, and at the same time maintains the stability of the AGC circuit. Also, a complete set of parameters for practical implementation is obtained by various experiments with fixed point constraints and accuracy requirements.     

Channel measurement-based access point selection in IEEE 802.11 WLANs

With the wide deployment of IEEE 802.11 Wireless Local Area Networks, it has become common for mobile nodes (MNs) to have multiple access points (APs) to associate with. With the Received Signal Strength Indicator (RSSI)-based AP selection algorithm, which is implemented in most commercial IEEE 802.11 clients, the AP with the best signal strength is selected regardless of the candidate AP’s available throughput, resulting in unbalanced distribution of clients among the APs in the network. Several studies have shown performance improvement in not just the new MN (nMN), but also the network as a whole when the selection process considers the current load status of candidate APs. However, the proposed algorithms in these studies assume that there are no hidden terminal problems that severely affect the performance of the network. Hidden terminal problems frequently occur in wireless networks with unlicensed frequencies, like IEEE 802.11 in the 2.4 GHz band. Moreover, none of the previous studies have considered frame aggregation, a major improvement in transmission efficiency introduced and widely deployed with the IEEE 802.11n standard. In this paper, we propose a new AP selection algorithm based on the estimation of available throughput calculated with a model based on the IEEE 802.11 distributed coordination function in consideration of hidden terminal problems and frame aggregation. The proposed algorithm is evaluated through extensive simulation, and the results show that the nMN with the proposed AP selection algorithm can achieve up to 55.84% and 22.31% higher throughput compared to the traditional RSSI-based approach and the selection algorithm solely based on the network load, respectively.     

802.11无线局域网中的智能AP切换策略

在802.11协议内,站点有权选择将要连接的接入点,因此接入点选择机制的实现就成为了负载平衡的一个关键因素.新提出的AP切换策略可应用到新的兼容802.11e的无线网络.由于无需对原有的802.11和802.11e作修改,无论从实现成本和兼容性两个方面来看,都是很实用的方案.仿真实验表明该策略既能充分利用无线通信资源,又可以实现无线局域网内的负载平衡.