Mathematical Analysis of Energy Efficiency in IEEE 802.11 DCF

The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are mobile or portable units, power consumption becomes a primary issue since terminals are usually battery driven. This paper proposes an analytical model that calculates the energy efficiency of both the basic and the RTS/CTS access mechanisms of the IEEE 802. II protocol. The model is validated with simulation results using NS-2 simulation package. The effects of the network size, the average packet length, the initial contention window and maximum backoff stages on the energy efficiency of both access mechanisms are also investigated. Results show that the basic scheme has low energy efficiency at large packet length and large network size, and depends strongly on the number of stations and the backoff procedure parameters. Conversely, the RTS/CTS mechanism provides higher energy efficiency when the network size is large, and is more robust to variations in the backoff procedure parameters.     

谈无线局域网的应用

简要介绍了WLAN的定义、特点,讨论了802．11协议族主要内容．重点论述了无线局域网在网络安全方面的发展及应用．通过对无线局域网的应用分析,探讨了它在电信级的运营思路．     

Performance analysis of IEEE 802.11 DCF networks

This paper presents an analytical saturation throughput model of IEEE 802.11DCF （distributed coordination function） with basic access in ad hoc mode. The model takes into account freezing of the backofftimer when a station senses busy channel. It is shown that taking into account this feature of DCF is important in modeling saturation throughput by yielding more accurate and realistic results than models known from literature. The proposed analytical model also takes into account the effect of transmission errors. All essential features of the proposed analytical approach are illustrated with numerical results. The presen- tation of the model is proceeded by an overview of approaches to IEEE 802.11 network performance evaluation presented in the literature.     

Performance Improvement of Distributed Coordination Function in IEEE 802.11 Wireless LAN

This paper proposes a modification to distributed coordination function (DCF) to improve the channel utilization in IEEE 802.11 wireless local area networks (WLANs). In the modified DCF, when a station has contended for the channel, it may transmit multiple data frames continuously to the same destination, which is called transmission burst(TB). When the maximum number of data packets transmitted continuously in a TB is set to be 2, the performance is expected to be the best. The theoretical analysis and simulation results show that compared with the standard DCF, the modified DCF can increase the throughput and decrease the delay of the WLAN, and the modification does not introduce any additional control overhead.     

Finite time-horizon Markov model for IEEE 802.11e

We model wireless local area network channel utilization over a finite interval through a finite time-horizon Markov （FTHM） model. By accurately capturing time-varying utilization, the FTHM model allows for generally distributed transmission-opportunity （TXOP） duration, which most existing models do not account for. An absorbing state is introduced to limit the lifetime of the counting process, resulting in a non-ergodic Markov chain that is solved via transient analysis. The model predictions for time-varying utilization are validated by simulation with errors of no more than 0.1% after eight beacon intervals. Moreover, we show that the FTHM model prediction error is below 4% for Poisson distributed and uniformly distributed TXOP durations.     

IEEE 802.11分布式协调功能在MANET网络中的性能改善

研究了移动Ad Hoc网络中的媒体接入控制问题. 首先, 基于IEEE 802. 11媒体接入控制协议, 提出了应用于MANET网络媒体接入控制的2个机制: 自适应回退窗转发优先机制(FPF)和多跳链邀请发送机制(MFCTI). FPF机制根据业务优先级自适应调整竞争窗大小, 而MFCTI机制则充分利用了网络层路由信息和无线传播的广播特性. 在此基础上对所提出的机制进行了仿真研究并与原IEEE 802. 11媒体接入控制进行了比较. 结果表明, 所提机制可以有效地提高网络吞吐率, 降低端对端迟延, 缓解网络局部拥塞, 从而提高了MANET网络的性能. 其另一优点是只需对IEEE 802. 11媒体接入控制作少量的补充和改动.     

无线局域网认证计费研究与设计

无线局域网由于其通信信道的开放性,决定了无线局域网比有线局域网面临着更多、更严重的安全威胁；采用合适的认证计费方案,来加强无线局域网的安全,有着十分重要的意义。本文比较有线局域网和无线局域网,分析了现有的的各种认证方法,结合无线局域网的特点,设计了无线局域网的认证计费方案,对方案的工作过程进行了阐述,并对其特点进行了分析。     

新完善的WAPI协议安全性分析

在深入研究中国无线局域网安全标准WAPI接入鉴别过程的基础上,利用CK模型并结合BAN逻辑,对其认证和密钥协商过程安全性进行了形式化分析,证明其能够实现所声称的各种认证及密钥协商目标.进一步的分析结果表明,WAPI不仅具有所声称的各种安全属性,同时还能够有效地实现实体间相互认证、密钥的相互控制、密钥确认、消息完整性校验等安全属性.如果协议中所采用的椭圆曲线加密算法和杂凑算法足够安全,则该协议能够实现STA和AP之间的相互身份认证,可以用于替代原来的无线局域网国际标准中的安全机制,以增强无线局域网的安全性.     

An adaptive joint source and channel coding scheme for H.264 video multicasting over wireless LAN

INTRODUCTION Video multicasting over wireless local area net- work (WLAN) (IEEE Standard 802.11, 1997) enables the distribution of live or pre-recorded programs to many receivers efficiently. An example application is to redistribute TV programs or location-specific in- formation in hot spots such as airport. Users can watch their favorite TV programs on mobile devices while browsing the Internet. For enterprise applica- tions, an example is multicasting video of a lecture or trainin…     

无线网络在win7中的运用

无线网络已经融入了现代人生活、工作中,成为必不可少的网络工具。网络是信息化的基础,网络设施的完善和网络技术的进步,对信息网络化起到积极的推动作用。随着Internet应用的迅猛发展,以及笔记本电脑、个人数据助理（PDA）等移动智能终端的日益增长,人们对无线局域网（WLAN）的需求也急剧增加。以无线局域网的现状、特点为研究对象,探讨win7系统下如何设置无线网络连接及局域网连接、WLAN安全,使无线网络在学习、生活中得到更广泛的应用。     

VoWLAN中的接纳控制策略研究

本文分析了连接接纳控制策略的相关内容并重点介绍了基于测量的接纳控制算法,提出了新的接纳控制算法来改善VoWLAN的QoS(Quality of Service)性能。该算法对应于不同的业务类型采用不同的时间窗阀值测量机制,根据负载的实时情况动态调整时间窗大小,从而可以改变系统的接纳性能,并提供相应的动态带宽分配机制,有效地保障VoWLAN系统的QoS需求。最后通过仿真实验对该算法进行了验证。     

无线网络在校园中的构建与应用

讨论校园无线网络的特点、组建方案及安全性分析 ,介绍无线网络在校园中的相关应用。