PWLAN中实现有效管理的MAC层隔离方法

分析了在公共无线局域网(PWLAN)系统中为实现对用户统一有效管理而要求应用的二层隔离技术, 同时提出通过在无线接入点(AP)的媒体接入控制(MAC)层中定义一个隔离参量dot11Isolation, 并修改MAC层协议中Distribution-Service模块的运行状态图以实现二层隔离的一种方法. 同时, 介绍了一个基于MPC860处理器并以嵌入式Linux操作系统为平台来实现二层隔离功能的WLAN AP设备实现方案. 仿真结果表明, 本文提出的二层隔离实现方法是有效可行的.     

802.1x/EAP-PEAP认证方法的研究与应用

安全问题是影响无线网络发展的一个重要因素。IEEE802.1x协议的主要目的是解决无线局域网用户的接入认证问题。文章主要讨论了802.1x协议、EAP协议、PEAP协议。最后采用目前流行的一些免费软件,如MySQL,OpenSSL,FreeRadius等构建了一个简单、实效、可靠的基于802.1x/EAP-PEAP认证方案。     

Error resilient concurrent video streaming over wireless mesh networks

INTRODUCTION Wireless mesh networks (WMNs) are ad-hoc networks with full or partial mesh topologies, where nodes can automatically establish and maintain mesh connectivity among themselves. Such a mesh topol- ogy provides each node multiple communication paths to reach its peers. In the presence of link failures caused by, for example, node failures or interference, information can be rerouted through alternative paths to the destination. WMNs have no fixed infrastructure and are easily…     

一种基于CDMA的多信道自组网MAC协议

This paper proposes a novel multichannel medium access control(MAC)protocol based on CDMA that improves network performance and reduces collision probability in wireless ad hoc networks.In the scheme,the code channel is divided into common channel,broadcast channel and several data channels.Simulation results show that the proposed protocol can achieve significantly better performance than the IEEE 802.11 standard.     

Achieving Efficient Channel Utilization for Data Communications in IEEE 802.11 WLAN

In the IEEE g02. 11 protocol, the adoption of the exponential backoff technique leads to throughput performance strongly dependent on the initial contention window size and, most importantly, on the number of contending stations considered in the network. This paper proposes a simple but accurate method to dynamically estimate the number of contending stations in a wireless local area network （ WLAN ）. Based on estimation, all the mobile stations dynamically adjust the initial contention window in medium access control （ MAC ） layer to avoid collisions. The simulation results show that the proposed algorithm can achieve efficient channel utilization, higher system throughput, and better fairness performance.     

A cross-layer approach to enable multipacket transmission in MIMO-SDMA based WLAN

We propose a medium access control （MAC） protocol for uplink transmissions in wireless local area networks （WLANs）, where both stations and access points （APs） are equipped with multiple antennas. The protocol solves some common problems in utilizing multiple input multiple output （MIMO） under the 802.11 protocol, e.g., how to deploy preamble （training sequence） used for channel estimation and how to enable simultaneous data transmissions, and facilitates two simultaneous uplink data transmissions via a cross-layer approach. Furthermore, we develop a 3D discrete-time Markov model to analyze the performance of the proposed WLAN scheme. The analytical results are verified by simulation, and numerical results show that the system throughput can be significantly improved by our proposed scheme as compared with conventional schemes.     

An embedded packet train and adaptive FEC scheme for effective video adaptation over wireless broadband networks

INTRODUCTION With the emergence of wireless technology, various multimedia services, e.g., audio and/or video, are reaching us today through portable devices any- time, anywhere and even more increasingly accessi- ble in the near future. High quality video streaming over wireless IP is one of the most attractive applica- tions by ongoing deployment of wireless local area network (WLAN) hotspots and even powerful Wi- MAX mobile coverage. However, the present Internet is not providing a…     

一种基于IEEE 802.11ac协议标准的帧聚合实现算法

如何提升IEEE 802.11ac无线局域网协议标准中的MAC层效率,进而提高无线局域网传输速率,是当前研究热点。提出一种基于IEEE 802.11ac协议标准新的帧聚合实现算法,该算法一方面根据系统动态速率算法选择的速率自适应地选取媒体访问控制服务数据单元聚合中的聚合帧个数,另一方面提出一种媒体访问控制协议数据单元聚合机制,该机制规定了聚合时机和聚合长度等;同时,针对由无线信道环境嘈杂性引起带宽下降导致丢包率上升的现象,引入AMPDU聚合情况下的带宽自适应机制。与现有IEEE 802.11ac聚合机制相比,该算法可提高数据帧发送吞吐率,同时又能在带宽下降时减少丢包率,增强数据发送鲁棒性。     

Performance Improvement of DCF Supporting Multi-Rate in IEEE 802.11b Wireless LAN

Inrecent years ,IEEE802.11 wirelesslocal area net-work (WLAN) has emerged as a prevailing technology forthe (indoor) broadband wireless access to internet for themobile/portable devices . In IEEE 802.11 standards ,802.11b has become the most widely used v…     

Unequal Forced-Intra-Refresh for robust video streaming

INTRODUCTION In the encoding or transcoding of video stream- ing, intra refresh is introduced as a non-normative error-resilience tool. Although the intra-refresh schemes based on the rate-distortion optimization (C?té et al., 2000; Stockhammer et al., 2002) are superior to the early heuristic intra-refresh strategies, these new schemes cannot yet accurately estimate the video distortion due to time-varying packet losses, and usually ignore the inter-frame error-propagation effect. Chiou…     

无线网络中信道基本接入机制研究探讨

IEEE 802．11标准的制定解决了无线网络中信道接入控制的问题,介绍了IEEE 802．11 MAC层完成的主要功能,详细讨论MAC层的基本接入机制DCF,介绍了另一个可选的接入机制PCF工作原理,简述了DCF机制存在的问题以及目前相关研究的进展情况。     

无线网状网组建及应用

无线网状网是近年来无线网络研究的热点之一,它融合了无线局域网和Ad hoc网络的优势,支持节点多跳路由和转发功能,并有自组网、自修复、移动宽带、Internet接入等特点.该网络以Linux为操作系统,使用XSBase270硬件平台和AODV路由协议实现网络的搭建,用BOA服务器软件实现网络服务器、视频服务器,并实现互联网接入.     

一种基于最小均方误差的无线局域网信道估计算法

在基于IEEE 802．11b标准的无线局域网中,提出了一种基于最小均方误差的自适应信道估计算法。通过已知码片的训练,可快速准确地估计出系统信道参数。仿真结果表明,在典型的JTC—OfficeA多径信道模型下,该算法可保证良好的系统误码率性能,在信噪比为8dB时,误码率就已经小于10^-4;此外,算法的估计误差仅需20-30个码片的训练就快速收敛,从而大幅降低了算法复杂度,是一种简单实用的算法,便于硬件实现。     

一种车联网多跳视频传输实验系统的设计与实现(英文)

提出一种在车辆自组织网络(VANET)中应用的无线多跳视频传输实验系统的设计和实现方案及其对应的传输控制和路由选择协议.该系统将嵌入式Linux与IEEE 802.11n传输协议集成到ARM内核,由S3C6410主控模块、无线局域网网卡及LCD屏等构成.针对VANET的无线多跳视频传输场景,对视频编译码分别采用H.264和JPEG两种标准实现并对它们的压缩比、时延、传输丢包率等性能进行了理论分析和实验比较,进行了室内室外多种不同场景的实际测试.结果表明:所设计的多跳视频传输实验系统方案能够适应VANET等多种场景的应用,所提出的传输控制和路由选择协议能够保证视频传输的多跳和实时性要求.     

基于巴克码自相关特性的无线局域网同步算法

在基于IEEE802．11b标准的无线局域网中,提出一种简单的同步算法．该算法根据帧头数据的巴克码自相关特性,通过能量累加和峰值位置比较找到帧头,实现粗同步;然后对帧头数据解调并找到SFD字段,从而实现系统的精确同步．仿真结果表明,算法在信噪比较差的情况下也能精确实现系统同步,且便于硬件实现．     

WLAN安全方案探析

无线局域网(WLAN)技术的发展使人们摆脱了传统线缆的束缚,可以更加方便、灵活、快捷地访问网络资源.但空间的开放性使无线局域网的安全受到来自外部入侵的威胁,安全方案已经成为无线网络发展的瓶颈.802.11i标准中采用的核心的加密方案WPA是无线网络发展的主要安全方案.     

Rate-distortion optimized bitstream switching for peer-to-peer live streaming

Peer-to-peer （P2P） technology provides a cost-effective and scalable way to distribute video data. However, high heterogeneity of the P2P network, which rises not only from heterogeneous link capacity between peers but also from dynamic variation of available bandwidth, brings forward great challenge to video streaming. To attack this problem, an adaptive scheme based on rate-distortion optimization （RDO） is proposed in this paper. While low complexity RDO based frame dropping is exploited to shape bitrate into available bandwidth in peers, the streamed bitstream is dynamically switched among multiple available versions in an RDO way by the streaming server. Simulation results show that the proposed scheme based on RDO achieves great gain in overall perceived quality over simple heuristic schemes.     

基于站的IEEE 802．11b／g无线局域网快速切换方案

由于实时应用对传输时延和抖动相对敏感,为减小WLAN切换过程对实时应用的影响,研究了WLAN切换过程的3个方面：触发切换,AP选择和快速切换算法．充分考虑到方案的可部署性和可扩展性,提出了一个以终端站为中心的快速切换方案．设计实现了基于动态阈值的切换触发机制、基于探寻时延的AP选择机制和信道区分选择结合动态缓存的快速切换算法．该方案完全在站上实现,不需要AP的配合或者对协议进行修改,因而具有良好的鲁棒性和可部署性．通过在实际的hotspot WLAN环境下测试和分析,该快速切换方案有效地减小了切换时延,同时使用户获得的实时应用网络性能有所增强．     

带鳍片的热交换管道检测机器人的研制

This paper introduces a novel robot for outer surface inspection of boiler tubes.The paper describes the hardware system,wireless communication strategy,communication procedure and system software of the robot.The WLAN technology is used in the robot.It solves the problem of shielding generated by iron boiler and 11Mbps bahdwidth made it possible for video and control steam real-time transmit within the same channel.Though TCP/IP protocol is tobust,serial server is a transparent channel but cannot detect error and retansmit the data.In order to improve the reliability of srial communication,a new communication protocol is proposed.     

高职院校数字校园无线视频监控系统设计

分析了高职院校校园中进行视频监控的必要性,对整个视频监控系统的关键技术包括H。264/AVC视频编解码、移动流媒体技术等进行研究,设计了一种应用于手持智能终端的视频监控系统,详细阐述了其体系结构和客户端实现,为高职院校建设数字化校园视频监控提供了一种新的方案。