移动运营商WLAN的用户认证

运营商无线局域网系统电信运营商组网建设的无线局域网，叫做运营商无线局域网（OWLAN，OPERATOR WLAN）。OWLAN包括四个关键物理实体：认证服务器、接入控制器、接入节点和移动终端（图1）。移动终端通过IEEE 802.11b无线协议与接入节点（AP）建立无线链路。移动终端的工作频率一般为2.4G，采用DSSS或FHSS扩频，采取64/128位WEP加密方式，支持11M、5.5M、2M、1M自适应功能。移动终端可采用WLAN单模卡或WLAN/GPRS双模卡方式。AP（接入节点）是WLAN网络中的小型无线基站设备，AP的一端通过802.11b无线协议与移动终…     

精品出版快讯

构建无线局域网人民邮电出版社书号：10816定价：21.00元本书共分9章，综述了无线网络与通信的基本原理、技术以及无线局域网的调制方式，全面系统地阐述了无线局域网通信系统的一系列扩频技术：跳频扩频（FHSS）、直接序列扩频（DSSS）、编码正交频分复用（COFDM）；介绍了无线局域网的系列标准：IEEE802.11、IEEE802.11b、IEEE802.11a的调制方式，帧格式以及MAC层规范。本书还结合无线局域网的适配器（网卡）、接入点、网桥和路由器等硬件以及工具软件，讲述了安装无线局域网的过程：组网、配置、安全、测试与分析，最后还展…     

无线局域网的安全策略

阐述了无线局域网的安全标准与方案,对IEEE802.11,IEEE802.11i和GB15629.11等3种方案进行了比较,并对无线局域网安全方案的发展方向提出了见解.     

IEEE802.11e EDCA和CFB下饱和吞吐量分析

IEEE802.11eMAC草案规范对IEEE802.11无线局域网标准在QOS方面加以了补充。IEEE802.11e采用2种协调机制基于控制的综合协调可控信道接入方式HCCA和基于竞争的增强型分布式信道接入方式EDCA。主要评估EDCA和竞争空闲脉冲(contention-freeburst)CFB相结合时,在系统负载过载的情况下,改变性能参数后系统饱和吞吐量的变化,并分析系统性能参数对饱和吞吐量的影响,从而达到系统参数优化的作用。     

IEEE 802.11s网络及其性能评估

无线局域网标准IEEE 802.11是一种较低成本的无线数据传输方案。无线网状网的产生解决了无线局域网覆盖范围小的问题。IEEE Task Group S早在2004年就开始策划制定关于无线网状网多跳通信,MAC层路由转发以及安全的标准——IEEE 802.11s。介绍了IEEE 802.11s最新的草案标准,并通过试验床的设计与试验评估了当前基于IEEE 802.11s无线网状网网络的整体性能。最后探讨了视频应用在IEEE 802.11s中的可行性。     

Wi-Fi热的冷思考

Wi-Fi是Wireless Fidelity（无线保真）的缩写，由产业标准组织Wi-Fi联盟（Wi-Fi Alliance）代指无线局域网协议IEEE 802.11b，在IEEE802.11a出现并获得批准后，Wi-Fi联盟曾一度想将其命名为“Wi-Fi5”，但为了防止引起消费者混乱，IEEE802.11a标准和即将获得批准的IEEE802.11g标准都将被冠以Wi-Fi的通俗代名。因此，Wi-Fi可以看作是用于无线局域互联的包括802.11b、802.11a和802.11g等标准的IEEE 802.11技术的代称。经过几番严酷的市场竞争后，Wi-Fi已经成为无线局域网事实上的标准，2002年如果要评选热门通信词汇，非Wi-…     

展望无线技术走近无线局域网

无线局域网技术（包括IEEE802.11、蓝牙技术、HomeRF等）将是新世纪无线通信领域最有良好发展前景的重大技术之一，本文着重介绍了无线局域网标准的进展，IEEE802.11、蓝牙技术、HomeRF等几种主流标准的比较，分析了无线局域网技术，市场，发展与应用前景。     

无线局域网中的OFDM技术

802.11是IEEE最初制定的一个无线局域网(WLAN)标准,主要用于解决办公室局域网和校园网中用户与用户终端的无线接入,业务主要限于数据存取,速率最高只能达到2Mbit/s。由于它在速率和传输距离上都不能满足人们的需要,因此,IEEE小组又相继推出了新的标准。目前802.11b实际上已成为无线局域网     

基于WLAN网络的视频流组播传输机制研究

本文针对基于IEEE802.11的无线局域网上组播视频流时终端异构问题,提出一种对客户端分组要：组播传输机制。该机制中,AP根据不同终端的接收能力和实时视频流的码率,将组播组内的站点进行分组,对划分的子组采用不同速率进行组播,以此来提高IEEE802.11无线局域网的传输性能,降低差站点对好站点视频接收效果的限制。NS-2仿真实验结果表明,分组组播机制有效地提高了无线局域网和好站点的性能。     

基于IEEE802．11b无线局域网支持QoS的盲检测算法

这里提出了一种基于IEEE802.11b无线局域网(WLANs)的MAC层的终端盲检测算法.和以往的算法相比,该算法通过对连接接入点AP(Access Point)的所有活动终端进行盲检测,可以非常有效的增加每个AP点所支持的语音通信终端数量,从而增加了信道的带宽,提高语音服务质量QoS.而且算法只执行在接入点的点协调功能上(PCF),因此不需要对当前的IEEE802.11MAC层的协议做任何修改.仿真结果表明了本算法对WLANs语音服务质量的有效支持.     

A dynamic location management service for group applications in cellular networks

To cope with the increasing demand of multimedia applications, new IEEE 802.11 wireless local area networks devices have been defined such as IEEE 802.11aa and IEEE 802.11ac. The former proposes new intra-access categories (AC) differentiation based on stream classification service (SCS) scheme. The latter standard allows simultaneous downlink transmissions thanks to downlink multi-user MIMO technology and sharing transmission opportunity (TXOP) period scheme. In this paper, we focus on the basis of this technique and the behavior of the access point (AP) to manage the multi-user access. Then, we propose a hybrid access mechanism entitled multi-user multi-cast access mechanism (MUMAM) that supports downlink multi-user transmissions while considering intra-AC differentiation. MUMAN considers SCS scheme to prioritize between multicast and unicast flows of an AC and follows transmissions based on IEEE 802.11ac TXOP sharing technique. Extensive simulation and analysis show that MUMAM has a significant positive impact on delay and throughput performance of different AC(s).     

Pre-scan based fast handoff scheme for enterprise IEEE 802.11 networks

In IEEE 802.11 networks, many access points (APs) are required to cover a large area due to the limited coverage range of APs, and frequent handoffs may occur while a station (STA) is moving in an area covered by several APs. However, traditional handoff mechanisms employed at STAs introduce a few hundred milliseconds delay, which is far longer than what can be tolerated by some multimedia streams such as voice over Internet protocol (VoIP), it is a challenging issue for supporting seamless handoff service in IEEE 802.11 networks. In this paper, we propose a pre-scan based fast handoff scheme within an IEEE 802.11 enterprise wireless local area network (EWLAN) environment. The proposed scheme can help STA obtain the best alternative AP in advance after the pre-scan process, and when the handoff is actually triggered, STA can perform the authentication and reassociation process toward the alternative AP directly. Furthermore, we adopt Kalman filter to minimize the fluctuation of received signal strength (RSS), thus reducing the unnecessary pre-scan process and handoffs. We performed simulations to evaluate performance, and the simulation results show that the proposed scheme can effectively reduce the handoff delay.     

Quality-of-service provisioning system for multimedia transmission in IEEE 802.11 wireless LANs

IEEE 802.11, the standard of wireless local area networks (WLANs), allows the coexistence of asynchronous and time-bounded traffic using the distributed coordination function (DCF) and point coordination function (PCF) modes of operations, respectively. In spite of its increasing popularity in real-world applications, the protocol suffers from the lack of any priority and access control policy to cope with various types of multimedia traffic, as well as user mobility. To expand support for applications with quality-of-service (QoS) requirements, the 802.11E task group was formed to enhance the original IEEE 802.11 medium access control (MAC) protocol. However, the problem of choosing the right set of MAC parameters and QoS mechanism to provide predictable QoS in IEEE 802.11 networks remains unsolved. In this paper, we propose a polling with nonpreemptive priority-based access control scheme for the IEEE 802.11 protocol. Under such a scheme, modifying the DCF access method in the contention period supports multiple levels of priorities such that user handoff calls can be supported in wireless LANs. The proposed transmit-permission policy and adaptive bandwidth allocation scheme derive sufficient conditions such that all the time-bounded traffic sources satisfy their time constraints to provide various QoS guarantees in the contention free period, while maintaining efficient bandwidth utilization at the same time. In addition, our proposed scheme is provably optimal for voice traffic in that it gives minimum average waiting time for voice packets. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design indeed provides a good performance in the IEEE 802.11 WLAN's environment, and can be easily incorporated into the hybrid coordination function (HCF) access scheme in the IEEE 802.11e standard.     

An energy-efficient MAC protocol based on IEEE 802.11 in wireless ad hoc networks

Energy efficiency is a measure of the performance of IEEE 802.11 wireless multihop ad hoc networks. The IEEE 802.11 standard, currently used in wireless multihop ad hoc networks, wastes bandwidth capacity and energy resources because of many collisions. Therefore, controlling the contention window size at a given node will increase not only the operating life of the battery but also the overall system capacity. It is essential to develop effective backoff schemes for saving power in IEEE 802.11 wireless multihop ad hoc networks. In this paper, we propose an energy-efficient backoff scheme and evaluate its performance in an ad hoc network. Our contention window mechanism devised by us grants a node access to a channel on the basis of the node’s percentage of residual energy. We use both an analytical model and simulation experiments to evaluate the effective performance of our scheme in an ad hoc network. Our extensive ns-2-based simulation results have shown that the proposed scheme provides excellent performance in terms of energy goodput, end-to-end goodput, and packet delivery ratio, as well as the end-to-end delay.     

Supporting multimedia streaming and best‐effort data transmission over IEEE 802.11e EDCA

As demand for broadband multimedia wireless services increases, improving quality of service (QoS) of the widely deployed IEEE 802.11 wireless LAN (WLAN) has become crucial. To support the QoS required by a wide range of applications, the IEEE 802.11 working group has defined a new standard: IEEE 802.11e. In this paper, we propose a measurement‐based dynamic media time allocation (MBDMTA) scheme combined with a concatenating window scheme to support real‐time variable bit rate (rt‐VBR) video and best‐effort (BE) data transmission using IEEE 802.11e enhanced distributed channel access (EDCA). To provide the QoS guarantee for rt‐VBR video, the proposed MBDMTA scheme dynamically assigns channel time to the rt‐VBR video based on the estimate of the required network resources. On the other hand, the concatenating window scheme controls the contention window (CW) ranges of different priority flows such that real‐time services always have higher channel access probability, thus achieving the capability of preemptive priorities. In addition, the concatenating window scheme preserves fairness among flows of the same class and attains high channel utilization under different network conditions. Simulation results demonstrate that the throughput and delay performance improve significantly for the transmission of rt‐VBR video and BE traffic as compared to those for the 802.11e EDCA specification. It is also revealed that combining the two proposed schemes provides seamless integration and reliable transmission of digital video and data service within the 802.11e EDCA framework. Copyright © 2007 John Wiley & Sons, Ltd.     

Carrier sense multiple access with improvised collision avoidance and short-term fairness

In this paper, we present a simple method to simultaneously enhance collision avoidance efficiency and short-term fairness of a most popular contention based medium access control protocol, carrier sense multiple access with collision avoidance. The key idea here is to adaptively tune the shape of contention slot selection distribution over the temporal contention window during ongoing collision resolution process which, in the legacy scheme, used to be flat throughout. The tuning mechanism is such designed that it not only maximizes the selection likelihood of relatively less collision prone contention slots over the contention window but also compensates the idle delay that the contending stations have suffered in their recent access attempt. Through rigorous numerical and simulation based analysis, the proposed scheme is shown to enhance the performance of a IEEE 802.11 based distributed wireless network in terms of network throughput efficiency and packet transmission delay while allowing individual stations to share the channel fairly even in short time scale.     

Variable Beam Width Selection for Improving the Throughput of IEEE 802.11ad Wireless LAN in the Contention Based Access Period

The hybrid MAC protocol specified by IEEE 802.11ad for millimeter wave wireless LANs consist of carrier sense multiple access/collision avoidance (CSMA/CA) during the contention based access periods (CBAPs) and TDMA during the service periods. To provide channel access during CBAP, the coverage area around the access point (AP) can be divided into several quasi omni (QO) beam levels. When uplink channel access during CBAP is considered, every directional multigigabit station residing within a QO level uses CSMA/CA protocol for getting the transmission opportunity. With equal beam width receive QO levels at the AP, we present an analytical model to compute the uplink throughput of the network in the CBAP, by closely following the 802.11ad MAC protocol specifications. We demonstrate that PHY layer MCS (modulation and coding scheme) dependent adaptive selection of QO levels can improve the throughput performance. In the second part of the paper, we consider that PCP/AP can have at most three radios, each tuned to operate in non-overlapping frequency bands as specified by 802.11ad PHY. We establish that such an arrangement can lead to concurrent transmissions in the network and improve the uplink throughput performance.     

WLAN层间服务接口设计与FPGA实现

提出一种无线局域网中物理层与媒体访问控制(MAC)层的层间接口设计方案。该方案分别从硬件连线规划、地址分配、层间原语交互操作和层间数据收发等几个方面进行设计,并在FPGA上实现。通过一套完整的无线传输实验平台进行实验验证,结果表明,此接口功能符合IEEE 802.11a协议要求,物理实现简单,可扩展性好。     

Model-based admission control for IEEE 802.11e enhanced distributed channel access

IEEE 802.11e enhanced distributed channel access (EDCA) is a distributed medium access scheme based on carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this paper, a model-based admission control (MBAC) scheme that performs real-timely at medium access control (MAC) layer is proposed for the decision of accepting or rejecting requests for adding traffic streams to an IEEE 802.11e EDCA wireless local area network (WLAN). The admission control strategy is implemented in access point (AP), which employs collision probability and access delay measures from active flows to estimate throughput and packet delay of each traffic class by the proposed unsaturation analytical model. Simulation results prove accuracy of the proposed analytical model and effectiveness of MBAC scheme.     

基于IEEE802.11协议的WLAN节省能耗的策略

在WLAN中移动终端设备的电池寿命是一个关键问题.文章概述了基于IEEE802.11协议的WLAN节省能耗的策略,并通过对IEEE802.11MAC协议层节能机制的分析提出一种改进的轮询方案.该方案能克服IEEE802.11在PSM工作模式下,当无线网络流量负载较重时不能显著降低能耗的缺点.