Comparative performance evaluation of IEEE 802.11v for positioning with time of arrival

Time of Arrival (TOA) based techniques are expected to overcome performance limitations of existing WLAN positioning approaches. The upcoming IEEE 802.11v standard is expected to play a key role because it will include new specific mechanisms for TOA-based positioning with WLAN. This article analyzes some of these new capabilities and evaluates the performance enhancement that they can provide in practice. To this end, a comparative assessment between an existing WLAN TOA-based approach that uses IEEE 802.11 b/g and an analogous solution employing IEEE 802.11v is performed.     

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。     

蓝牙微微网对WLAN网络同频干扰的建模

由于同在2.4 GHz的ISM频段下工作,IEEE 802.11b局域网和蓝牙微微网不可避免地产生相互干扰,严重影响各自的网络性能。通过对基于CSMA/CA和RTS/CTS机制的IEEE 802.11b协议进行数学分析,剖析了其吞吐量降低与发送不同蓝牙数据包之间的内在关系,建立了一个蓝牙微微网对IEEE 802.11b局域网干扰影响的数学模型。仿真结果表明：该模型能较好地逼近IEEE 802.11b局域网在蓝牙微微网干扰下的吞吐量仿真曲线,在蓝牙DH1、DH3、DH5数据包干扰的情况下,平均相对误差分别为17.86%、10.39%和6.64%。根据该数学模型,提出了一个降低蓝牙微微网干扰的有效方案。该方案能快速、低成本、自适应地调整IEEE 802.11b发送帧长,有效提高其在蓝牙微微网干扰下的吞吐量。     

校园无线局域网性能优化途径之初探

系统吞吐率是衡量网络性能的最重要的指标之一。无线局域网不同标准的选择、无线网络标准的单一IEEE802．11g模式和IEEE802．11g／b双模式、接入点AP设备的数量以及定位原则直接影响吞吐率的提高，围绕上述三个因素概括性的阐述了校园无线网络性能优化的措施。     

校园无线局域网性能优化途径之初探

系统吞吐率是衡量网络性能的最重要的指标之一。无线局域网不同标准的选择、无线网络标准的单一IEEE802.11g模式和IEEE802.11g/b双模式、接入点AP设备的数量以及定位原则直接影响吞吐率的提高,围绕上述三个因素概括性的阐述了校园无线网络性能优化的措施。     

NDIS-based virtual polling algorithm for IEEE 802.11b for guaranteeing the real-time requirements

This paper focuses on the feasibility of IEEE 802.11b wireless LAN for real-time wireless industrial network. In general, it has been known that IEEE 802.11b is not suitable for industrial networking because its medium access control method is the contention-based CSMA/CA (Carrier Sensing Multiple Access with Collision Avoidance) that exhibits unstable performance under heavy traffic and unbounded delay distribution. As an attempt to circumvent the probabilistic nature of IEEE 802.11b, this paper presents an enhanced four-layer architecture using the Network Driver Interface Specification (NDIS) and a virtual polling algorithm. Also, the enhanced four-layer architecture's performance is compared with that of conventional IEEE 802.11b. Based on the experimental results, it is found that the enhanced four-layer architecture for IEEE 802.11b is a very promising alternative for wireless industrial networking.     

Mutual interference analysis of IEEE 802.15.4 and IEEE 802.11b

IEEE 802.15.4 and IEEE 802.11b, operating in the 2.4 GHz unlicensed industrial scientific medical (ISM) frequency band, may lead to signal interference and result in significant performance degradation when devices are collocated in the same environment. The main goal of this paper is to evaluate the effect of mutual interference on the performance of IEEE 802.15.4 and IEEE 802.11b systems. An analytic model for interference between IEEE 802.15.4 and IEEE 802.11b is suggested. The packet error rate (PER), transmission delay, and throughput are evaluated for IEEE 802.15.4 and IEEE 802.11b. The power spectral density of the IEEE 802.11b is considered in order to determine in-band interference power of the IEEE 802.11b to the IEEE 802.15.4. The simulation results by OPNET are shown to validate the numerical analysis.     

IEEE802.11MAC层性能分析及仿真

无线网络通信作为新兴的通信技术已备受人们关注。无线局域网使用无线传输媒体,可以覆盖有线网络难于涉及的范围,成为传统有线网的必要补充。IEEE802.11b是当前无线局域网的主流标准,对其性能仿真和结果分析已做了大量工作,而对尚未普及的802.11a却没有太多的性能分析。论文利用文献眼1演算法得出802.11吞吐量理论极限值,并通过ns-2软件对802.11a进行仿真。     

802.11a. More bandwidth without the wires

802.11a represents the third generation of wireless networking standards and technology (behind 802.11 and .11b). It was actually approved as a standard earlier than 802.11b, but it presented a greater engineering challenge, and was delayed. Advances in technology (Moore's Law continues to prove true) helped Internet engineers overcome those challenges in a cost-effective manner and prepare the specification for market introduction. The result is the further extension of 802.11 networking capabilities. My previous article, "802.11: Leaving the Wire Behind," (Kapp, 2002) focused on 802.11b wireless networking and the various 802.11 task groups that will directly affect the future of 802.11 networking. In this article, I examine 802.11a networking in depth and compare it to 802.11b and the upcoming 802.11g networking.     

QoS provisioning in IEEE 802.11-compliant networks: Past,present, and future

Proliferation of portable, wireless-enabled laptop computers and PDAs, cost-effective deployment of access points, and availability of the license-exempt bands and appropriate networking standards contribute to the conspicuous success of IEEE 802.11 WLANs. In the article, we provide a comprehensive overview of techniques for capacity improvement and QoS provisioning in the IEEE 802.11 protocol family. These techniques represent the R&D efforts both in the research community and the IEEE 802.11 Working Groups. Specifically, we summarize the operations of IEEE 802.11 legacy as well as its extension, introduce several protocol modeling techniques, and categorize the various approaches to improve protocol capacity, to provide QoS (by either devising new MAC protocol components or fine-tuning protocol parameters in IEEE 802.11), and to judiciously arbitrate radio resources (e.g., transmission rate and power). To demonstrate how to adapt QoS provisioning in newly emerging areas, we use the wireless mesh network as an example, discuss the role IEEE 802.11 plays in such a network, and outline research issues that arise.     

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.     

Enhancing IEEE 802.11a/n with dynamic single-user OFDM adaptation

Earlier paper have demonstrated that the achievable throughput of OFDM systems can benefit significantly from individual modulation/transmit power selection on a per sub-carrier basis according to the actual gain of individual sub-carriers (so called dynamic OFDM scheme). Usage of such an approach requires, however, providing support for additional functionalities such as: acquisition of the sub-carrier gains, signaling of the modulation types used between sender and receiver, etc. Therefore dynamic OFDM is actively pursued for future radio interfaces, rather than considered as extension of existing OFDM based standards. In this paper we introduce a proposal on how the widely accepted IEEE 802.11a/g systems as well as the emerging IEEE 802.11n system might be extended to support the dynamic OFDM in a single-user (point-to-point) setting. The presented approach guarantees backward compatibility to legacy devices. We address these issues by presenting (a) a set of protocol modifications required to incorporate dynamic OFDM in 802.11a/g/n; and (b) a performance evaluation of the suggested extension (referred to further on as single-user 802.11 DYN mode). Although 802.11n already includes advanced MAC and PHY features, i.e., frame aggregation and MIMO transmissions, our performance evaluation demonstrates that a further improvement is achievable by incorporating dynamic OFDM.     

Throughput analysis of IEEE 802.11 multirate WLANs with collision aware rate adaptation algorithm

This paper presents a mathematical model that analyzes the throughput of the IEEE 802.11b distributed coordination function (DCF) with the collision aware rate adaptation (CARA) algorithm. IEEE 802.11 WLANs provide multiple transmission rates to improve system throughput by adapting the transmission rate to the current channel conditions. The system throughput is determined by some stations using low transmission rates due to bad channel conditions. CARA algorithm does not disturb the existing IEEE 802.11b formats and it can be easily incorporated into the commercial wireless local area networks (WLAN) devices. Finally, we verify our findings with simulation.     

非理想信道下无线局域网的性能分析

提出了一种在非理想信道下分析IEEE 802.11无线局域网的饱和吞吐量的方法。分析的过程中考虑到信道“捕获”和退避“冻结”的问题，采用条件概率建立了数学模型。在IEEE 802.11b无线局域网定义的不同数据速率下，利用该方法对基本访问机制和RTS/CTS访问机制进行了分析。仿真表明，分析结果与DCF模式下的饱和吞吐量是吻合的。     

IEEE 802.11无线局域网OPNET建模与性能测试

讨论了IEEE802．11无线局域网的建模和性能问题。基于对IEEE802．11协议和目前功能最强大的网络仿真工具OPNET软件的研究。首先分析了无线局域网的各种行为，分别对这些行为单独建模后，通过有线状态机将它们集成而形成IEEE802．11协议支持模块。给出了模型输入输出接口的详细说明。并对网络的性能进行了分析比较。     

Design and implementation of a dual‐band concurrent fully‐integrated LNA for WLAN IEEE 802.11a/b/g applications

This article presents a dual‐band concurrent fully‐integrated low‐noise amplifier (LNA) targeted to WLAN IEEE 802.11a/b/g standards. The use of a concurrent topology enables saving die area and power consumption compared with the parallel solution that employs two separated LNAs. An original design methodology that helps in the selection of input/output matching network element values is also presented. The LNA die area is 1.0 × 0.9 mm² and it consumes 9 mW (5 mA at 1.8 V). © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

The challenge of Wi-Fi roaming

Wi-Fi, consisting of the IEEE 802.11a, 802.11b, and 802.11g technologies, has proven to be a fast wireless networking approach that is relatively easy and inexpensive to implement. Companies are working on a variety of approaches to extend Wi-Fi's capabilities, appeal, and potential for generating income. Industry observers say more people would use the technology more often if they could roam among networks, working with one carrier in numerous locations. Carriers would also support Wi-Fi roaming because it would extend the reach of their service and attract more customers.     

基于IEEE802.11b WLAN安全技术研究

随着无线局域网（WLAN）技术的迅速发展,其安全问题日益受到人们的关注。由于传输的特殊性,WLAN始终面临严峻的安全考验。无线网络攻击技术的不断翻新,基于IEE802.11b的攻击技术会越来越多,复杂性将越来越高。所以与有线网路相比,保护WLAN安全的难度要远大于保护有线网络。文中介绍了基于IEEE802.11b协议下的WLAN可能面临的非法登录、拒接服务、字典攻击等安全威胁,分析了如何提高WLAN下的几种安全机制及802.11协议下的802.11i安全标准。提出了现有无线设备使用中一些可提高WLAN安全性的解决措施,在一定程度上提高了WLAN的安全性。     

基于WiFi的移动IP安全研究

文章简要介绍了WiFi(IEEE802.11b)技术及移动IP的基本概念,然后着重对基于WiFi的移动IP的安全性进行分析,并提出了相应的解决方案。     

无线局域网在医疗中的应用

作为个人通信的一个重要组成部分，无线局域网已经掀起移动计算的新浪潮。无线技术在传榆速率、安全性方面不断改进，它不仅是有线网络的无线延伸，也可以作为LAN的无线替代。通过分析3种不同的IEEE802.11扩展标准的调制方式、工作频段等，突出说明了IEEE802.llg标准的优越性。根据医疗领域的特殊性，在基于IEEE802.11g基础上，初步构建了一个可扩展的无线医疗网络。