浅析WIFI技术的应用与发展

随着网络以及通信技术的快速发展,由于WIFI具有接入速率高、覆盖范围广、具有极大的应用前景等多种优势,WIFI已经发展成为一种比较常见的宽带无线技术.本文对WIFI技术的应用以及发展趋势进行了详细的分析.     

基于白频谱的超级WIFI技术研究及实地测试验证

近几年来,随着世界范围内通信业务的增长,频谱资源日渐紧张。认知无线电技术的提出为人们利用电视广播“白频谱”进行通讯提供了可能。IEEE 802.22工作组颁布的802.22标准对认知无线电技术进行了规范,在此标准上设计的超级WIFI设备理论上能够对低人口密度地区实现良好的网络覆盖。本文介绍了IEEE 802.22标准提出的背景和主要技术内容,阐述了Carlson RuralConnect 超级WIFI设备的工作原理,并利用该设备进行了实验室和场地数据测试和整理,给出超级WIFI和白频谱设备在不同环境不同模式下的数据率、接收灵敏度和邻道干扰等信息,为我国开展超级WIFI和白频谱通讯应用提供技术参考。     

千兆比以太网及其应用

千兆比以太网是一种新型高速局域网 ,它可以提供 1Gbit的通信带宽 ,采用和传统 10兆比、10 0兆比以太网同样的CSMA/CD协议、帧格式和帧尺寸 ,因此可以实现在原有低速以太网基础上平滑、连续的网络升级 ,从而能最大限度的保护用户以前的投资。文章简要介绍了千兆比以太网出现的背景 ,然后详细阐述了与其相关的实现技术及其特性 ,最后介绍了其应用和发展前景。     

基于WIFI的低能耗建筑监测系统的设计与应用

现代建筑与智能技术的结合是建筑科技水平创新发展和综合效益优化提高的最好表现.本文在满足现有通信方式的基础上,增加了WIFI的数据传输方式,使低能耗监测系统的远传能力更加完善,增强了低能耗建筑的网络化节能控制方式.同时实现能耗在线的综合管理,并对用户能源利用效率、消耗水平、能源经济与环境效果进行监测、诊断.     

IEEE802.15.4MAC协议研究现状

无线传感器网络(Wireless Sensor Networks,WSNs)是一门新兴的无线网络技术。IEEE802.15.4标准作为一种新兴的无线通信协议,以其低功耗、低速率传输和低成本的设计宗旨为无线传感器网络提供了一种很好的解决方案。对IEEE802.15.4标准的相关规定和特点进行了简要介绍,在该标准的基础上针对当前关于能量消耗、GTS调度机制和CSMA/CA协议等方面的研究现状进行了介绍,并做了总结。     

基于WIFI技术的矿用机车无线通信系统的应用

我国是一个煤矿资源非常丰富的国家,全国各地拥有大量的煤矿开采基地。针对我国当前对煤矿进行开采和运输的过程中,所使用的矿用机车通信系统中存在的具体问题进行探索和分析。在当前矿用机车的运输和操作中采用先进的WIFI无线通信技术进行传输,并针对这一过程中遇到的具体问题,进行对该技术手段和设备进行探究,希望能够为我国煤矿产业中实现无线通信技术的指挥和规范发挥重要的指导性意义。     

基于WiMAX技术的边防路口自动监控系统研究

针对边防哨所无人监控的系统,分析其监控信号的传输与边防偏远地区网络的实际需求,研究利用WiMAX（IEEE802．16）优越的无线网络接入技术,实现边防哨所重要路口的无人监控系统构建,网络覆盖,信号传输,提高边防哨所监控预警的能力,具有一定实用性,可推广到民用监控。     

基于WIFI的无缝定位技术在网络安全中的应用

介绍了无线局域网技术、网络安全及传统的网络安全问题的解决方案,分析了基于WIFI的无缝定位技术,针对企业的无线局域网使用牦最,提出了一种基于WIFI的无缝定位技术网络安全问题解决方案及技术架构。     

IEEE 802.11 MAC层中参数τ的算法

IEEE 802．11在MAC子屡使用CSMMCA技术。很多文章就此技术展开研究，并培出了不同算法。在应用非常广泛的二堆马尔可夫链模型中，参数τ的取值直接影响到系统吞吐量的理论值。本文对τ的计算方法进行了讨论。并给出一种简单可行的计算方法。经过与化简结果及二分法比较，此方法简化了运算过程，且具有相当的可行性。     

Estimation Algorithm of Contending Stations Based on Improved DCF Model in IEEE 802.11

The fundamental access method of IEEE 802.11 is a DCF known as carrier sense multiple access with collision avoidance (CSMA/CA) scheme with exponential back-off. RTS_threshold is used to determine whether to deploy RTS/CTS access method. This threshold should vary with the number of contending stations which contend wireless media to get better throughput. The paper proposes an algorithm which estimates the number of contending stations in BSS. The algorithm is shown to be accurate which is verified by elaborate simulations.     

基于FPGA无线传感器网络MAC控制器的设计

给出了一种由FPGA实现的无线传感器网络MAC控制器的设计方法,采用自顶向下的方法设计各个模块,并在QuartusⅡ 8.0完成了仿真,该控制器主要支持IEEE802.15.4协议.测试结果表明,该MAC控制器支持20～250 kb·s<'-1>数据传输速率,适应IEEE802.15.4协议要求.     

Performance and fairness enhancement in IEEE 802.11 WLAN networks

The multi-rate transmission mechanism in IEEE 802.11 can improve its reliability and robustness. However, it causes a performance anomaly. After analyzing the reasons for the performance anomaly in multi-rate mechanism, we propose a new scheme to solve the performance anomaly. By adjusting packet size according to the transmission rate, this scheme guarantees that these nodes with different transmit rates can access wireless channel fairly. Theoretical analysis and performance evaluation show that the proposed scheme can well solve the performance anomaly problem.     

Enhancing channel utilization by improving media access coordination in wireless local area networks

Distributed coordination function (DCF) is the basis protocol for IEEE 802.11 standard wireless local area networks. It is based on carrier sense multiple access with collision avoidance (CSMA/CA) mechanism. DCF uses backoff process to avoid collisions on the wireless channel. The main drawback with this process is that packets have to spend time in the backoff process which is an additional overhead in their transmission time. The channel is rendered idle when all the stations defer their transmissions due to their backoff process. Therefore, the channel utilization and the total throughput on the channel can be improved by reducing the average time spent by the packets in the backoff process. In this paper, we propose a new media access coordination function called proposed media access protocol (PMAP) that will improve the channel utilization for successful packet transmission and therefore, the total achievable throughput. In addition, we propose an analytical model for PMAP under saturated conditions. We use this model to analyze the performance of PMAP under saturated conditions. To substantiate the effectiveness of our model, we have verified the model by simulating PMAP in NS‐2. Simulation and analytical results show that under saturated conditions, PMAP shows profound improvement in the throughput performance compared to DCF. In addition, the throughput performance of PMAP under unsaturated conditions is presented. We have also presented the delay performance of PMAP and DCF through simulation in both saturated and unsaturated conditions. Simulation results show that the average delay experienced by the packets is less in PMAP compared to DCF. Further, the variance in the packet delay is same for both PMAP and DCF protocols under unsaturated conditions. From the performance results obtained for PMAP under both saturated and unsaturated conditions, it can be concluded that PMAP is superior in performance compared to DCF. Copyright © 2006 John Wiley & Sons, Ltd.     

IEEE802.11与高级红外无线AIr MAC协议的性能比较

红外线作为室内通信无线传输媒质,具有低成本、低功耗等特点.本文描述 了IEEE 802.11红外局域网媒质访问控制协议（MAC）和红外数据协会（IrDA）提出的高级红外媒质访问控制层协议（AIr MAC）;研究了两种协议性能估计模型并利用OPNET仿真工具对IEEE 802.11 MAC与高级红外AIr MAC接入性能进行了仿真验证.通过对两种MAC协议接入方式、吞吐量性能估计模型以及吞吐量性能仿真结果进行比较分析,总结了IEEE 802.11红外局域网媒质接入协议和高级红外媒质接入协议之间的不同之处.     

Adaptive coordination function for IEEE 802.11 wireless LANs

Multiple access control (MAC) protocols play a significant role in wireless LANs. The IEEE 802.11 MAC protocol specifies two coordination functions that are Distributed Coordination Function (DCF) and Point Coordination Function (PCF). While both DCF and PCF are available in a wireless cell, we propose a novel access mechanism called Adaptive Coordination Function (ACF) to support various classes of traffic. The ACF superframe comprises two periods, one TDMA period designed for real-time traffic and followed by an adaptive period which adaptively employs DCF or PCF to support non-real-time traffic. In this paper, we apply the theory of M/G/1 queues to analyze the performance of adaptive period in terms of queuing delay, end-to-end delay, and saturation throughput. With our analytic model, DCF or PCF can be invoked appropriately according to the number of stations, packet arrival rate, packet payload size, and effective channel bit rate. Analytical results are derived for an extensive throughput and delay performance evaluation of both DCF and PCF.     

无线局域网MAC层信道利用效率分析

基于IEEE802·11g的WLAN的标称速率高达54Mb/s,而实际数据传输速率只有20Mb/s左右。从成帧效率、信道共享效率和冲突避免效率的角度对IEEE802·11g的MAC层信道利用效率进行了分析,得出这种基于CSMA/CA机制的MAC层信道利用效率较低。实测结果验证了分析结论的有效性。     

无线MESH网络拓扑控制研究

作为下一代无线网络中的一种新型网络结构,无线MESH网受到了广泛关注。MESH网络节点间的自组织组网方式,使得网络具有良好的灵活性、鲁棒性,同时也使得MESH网络的性能称为研究的重点。从功率控制和信道分配等方面研究了MESH网络的虚拟骨干结构的拓扑优化,功率控制通过调节节点发射功率来改变其对邻居节点的影响;信道分配利用正交信道的相互不连通性质改变节点对于邻居节点的影响,以降低链路间的干扰、维护网络连通性、提高系统容量。     

无线传感器网络MAC协议的实现与分析

介绍了无线传感器网络中2种重要的基于竞争的MAC协议(IEEE802.11和S-MAC)原理。从平台的整体架构和运行环境2个方面对无线传感器网络测试平台的设计进行了详细介绍。对于IEEE802.11和S-MAC协议的实现,具体描述了通信接口的定义和组件重用技术,从状态机的角度阐述了协议的运行流程。根据测试数据从不同方面对IEEE802.11和S-MAC协议进行了对比分析。实验结果真实地反映了协议的性能,对无线传感器网络MAC协议的研究有着积极的推动作用。