Circular polarized dual‐band antenna for WLAN/Wi‐MAX application

A novel square ring printed antenna has been suggested for dual‐band circular polarization (CP). The geometry contains a square patch and a square ring structure for dual‐band operation. Circular polarization is achieved using triangular cut at the boundary and right angle bend with inner perturbation. The suggested antenna is excited from the lower layer through electromagnetic (EM) coupling technique. The antenna shows good impedance bandwidths of 90 MHz (2.43‐2.52 GHz) and 800 MHz (5.7‐6.5 GHz, respectively. The antenna shows 3 dB axial ratio bandwidth of 20 MHz at lower band and 120 MHz at upper band with improved gain > 6 dBi. The simulated and measured results are well agreed with each other. The antenna is promising wideband operation at the upper band. This antenna was implemented on fiberglass reinforcement laminated Arlon substrate with dielectric constant (?_r = 2.55), and the overall physical dimension of 30 × 30 × 3.048 mm³. The designed antenna can be extensibly applicable in WLAN/Wi‐MAX communication. The presented antenna is designed using hyperlynx IE3D and the simulated results are presented.     

面向安全关键嵌入式系统的时钟同步设计

为了满足安全关键性实时嵌入式系统对实时行为正确性和确定性的要求,本文应用ETSEC网络控制器的硬件时间戳特性, ReWorks嵌入式实时操作系统的实时特性,结合IEEE 1588精密度时钟同步协议,设计并实现了一个面向安全关键性领域的时钟同步系统原型.其同步精度达到100纳秒以内,并通过软件插桩测试和验证了该时钟同步系统的正确性和精度.     

IEEE1451智能传感器多传感信息自校正方法研究

针对多传感信息耦合问题,基于IEEE1451标准,提出了一种通用的多传感信息自校正模型。模型根据传感元件输出信号额定特征,从信号幅度、变化趋势等方面,实现对传感器的故障判断和自免疫处理;然后基于多传感信息插值解耦数学原理,建立了基于特定TEDS格式的校正引擎,通过将标定点数据以矩阵表格形式输入TEDS中来实现解耦校正。试验研究表明:通过TEDS解耦校正引擎,可实现对多传感耦合信息的良好校正补偿,提高检测准确度,在解耦校正的前端引入传感元件的自评估技术,可有效提高智能传感器自校正的可靠性。     

基于PTPd改进的高精密时钟同步实现

IEEE1588定义了一种精密时钟同步(PTP)协议,广泛应用于分布式测控系统中。PTP协议可以通过纯软件或者纯硬件的方式实现。纯软件方式可采用开源的PTPd代码,开发简单,协议实现完整,但只能达到毫秒级同步精度;纯硬件方式通过硬件编程实现,同步精度可达纳秒量级,但是开发难度大。在开源的PTPd的基础上,保留协议上层部分,底层则采用DP83640硬件代替原有的软件捕获时间戳,经过测试,大大提高了PTPd的同步精度,达到了20ns以内。     

基于IEEE 802.15.4协议的物联网节点通信编程

在基于物联网的高校后勤数字化建设项目中,对点到点节点的无线数据传输进行了设计。设计包括协议选取,硬件设计、软件设计、具体设计及最终的编程实现。完成了TinyOS系统中的程序编写,实现了项目建设中的点到点节点无线数据传输的设计要求。     

An overview of vertical handover techniques: Algorithms, protocols and tools

Wireless technologies, under the “Anywhere, Anytime” paradigm, offer users the promise of being always attached to the network. Mobile devices enabled with multiple wireless technologies make possible to maintain seamless connectivity in highly dynamic scenarios such as vehicular networks (VNs), switching from one wireless network to another by using vertical handover techniques (VHO). In this paper we present an overview of VHO techniques, along with the main algorithms, protocols and tools proposed in the literature. In addition we suggest the most appropriate VHO techniques to efficiently communicate in VN environments considering the particular characteristics of this type of networks.     

Effective-capacity-based stochastic delay guarantees for systems with time-varying servers, with an application to IEEE 802.11 WLANs

Many network applications rely on stochastic QoS guarantees. With respect to loss-related performance, the effective bandwidth/capacity theory has proved useful for calculating loss probabilities in queues with complex input and server processes and for formulating simple admission control tests to ensure associated QoS guarantees. This success has motivated the application of the theory for delay-related QoS too. However, up until now this application has been justified only heuristically for queues with variable service rate. The paper fills this gap by establishing rigorously that the effective bandwidth/capacity theory may be used for the asymptotically correct calculation and enforcement of delay tail-probabilities in systems with variable rate servers too. Subsequently, the paper applies the general results to IEEE 802.11 WLANs, by representing each IEEE 802.11 station as an On/Off server and employing the effective capacity function for this model. Comparison of analytical results with simulation validates the effectiveness of the On/Off IEEE 802.11 model for delay-related QoS, complementing earlier results on loss-related performance.     

面向高速工业无线网络的TDMA MAC协议设计与实现

随着无线技术的发展,在工业自动化中引入无线技术已经成为一种潮流,同时TDMA机制由于可以完全避免冲突,因此在大规模高实时要求的面向车间的无线技术研究中受到了广泛关注,但现在面向车间的高速实时无线技术的研究大都局限于软件仿真。通过在商用802.11硬件上设计并实现面向车间级工业应用的高速工业无线TDMAMAC层协议,建立了一个基于TDMA的面向工业应用的高速无线网络原型系统,实验结果表明实验平台完全能够支撑毫秒级时隙调度的TDMA应用。     

对校园网中千兆位以太网的QoS分析

在以千兆位以太网为技术的校园主干网中,它的ＱｏＳ是如何保证的,达到了一个什么样的水平？这是讨论的中心议题,在这种前提下,分析了千兆位以太网的ＱｏＳ所采用的几种结合技术,并与ＡＴＭ的ＱｏＳ进行了比较。     

基于Freescale SMAC的无线连接组建研究

本文介绍了Freescale公司的简单媒体访问控制器(SMAC)协议栈软件的结构,在其基础上开发了一个自定义的主从式网络,给出了具体的实现方案,并编写了中心节点和终端设备节点的程序,最后把程序下载到基于Freescale MC13213芯片的实验板上,演示了自定义网络的数据收发流程.