朔黄铁路隧道防灾监控及应急通信系统的应用

为保证铁路安全运输,有必要进行沿线隧道特别是长大隧道的防灾监控及应急通信系统的建设。以朔黄铁路长梁山隧道为例,介绍隧道防灾监控及应急通信系统的结构、组成及应用。     

Instantaneous communication throughputs of vehicular ad hoc networks

Vehicular ad hoc networks (VANETs) formed by connected vehicles in a traffic stream could be applied to improve safety, mobility, and environmental impacts of a transportation system. In this paper, we present analytical models for the instantaneous communication throughputs of VANETs to measure the efficiency of information propagation under various traffic conditions at a time instant. In particular, we define broadcast and unicast communication throughputs by the wireless channel bandwith multiplied by the average probabilities that one vehicle is a successful receiver and sender in a VAENT, respectively. With a protocol communication model, we derive formulas to determine the probabilities for an equipped vehicle to be a successful broadcast receiver and a successful unicast receiver/sender, and obtain broadcast and unicast throughputs along discrete and continuous traffic streams. We further examine the impacts on communication throughputs of the transmission range and the interference range of dedicated short range communication devices as well as the market penetration rate of equipped vehicles and the percentage of senders. Finally, we investigate the influence of shock waves on communication throughputs.     

Scheduling for Uncertain Data Broadcast in Mobile Networks

With the increasing popularity of wireless sensor network and GPS (global positioning system) , uncertain data as a new type of data brings a new challenge for the traditional data processing methods. Data broadcast is an effective means for data dissemination in mobile networks. In this paper, the definition of the mean uncertainty ratio of data is presented and a broadcasting scheme is proposed for uncertain data dissemination. Simulation results show that the scheme can reduce the uncertainty of the broadcasted uncertain data effectively at the cost of a minor increase in data access time, in the case of no transmission error and presence of transmission errors. As a result, lower uncertainty of data benefits the qualities of the query results based on the data.     

网络中的VLAN技术

VLAN有效控制了整个网络中广播信息的流量，简化网络设备的变更。合理划分VLAN会使网络变得简单，介绍3种常用划分方法。结合VLAN在以太网中的实际应用，阐述不同VLAN间互相通信的数据流程。     

系统功能语法在英国女王演讲语篇中的应用分析

本文在系统功能语法的框架下,从概念功能和人际功能两方面对2010年圣诞节英国女王的圣诞演讲进行了分析,阐述了系统功能语法在演讲中的作用。本文还就系统功能语法在语篇分析过程中的可操作性和实用性进行了论述。     

舰载GPS航姿测量中卫星位置的计算与最优星座的选取

该文给出了在GPS航姿测量算法研究中的卫星位置计算的整个过程,数据处理采用RINEX标准输入格式,所得结果形象直观,便于分析。在此基础上提出了一种选择最优星座的方法。作为试验算例,最后给出了以广播星历参数为基础的GPS航姿测量中最优星座的选取结果。     

用模拟示波器测试接口性能的探讨

分析了常规示波器的工作原理,探讨了用模拟示波器测试两种接口性能的方法。结果表明测试方法简洁、可靠,拓展了示波器的应用范围。     

Optimization models to characterize the broadcast capacity of vehicular ad hoc networks

Broadcast capacity of the entire network is one of the fundamental properties of vehicular ad hoc networks (VANETs). It measures how efficiently the information can be transmitted in the network and usually it is limited by the interference between the concurrent transmissions in the physical layer of the network. This study defines the broadcast capacity of vehicular ad hoc network as the maximum successful concurrent transmissions. In other words, we measure the maximum number of packets which can be transmitted in a VANET simultaneously, which characterizes how fast a new message such as a traffic incident can be transmitted in a VANET. Integer programming (IP) models are first developed to explore the maximum number of successful receiving nodes as well as the maximum number of transmitting nodes in a VANET. The models embed an traffic flow model in the optimization problem. Since IP model cannot be efficiently solved as the network size increases, this study develops a statistical model to predict the network capacity based on the significant parameters in the transportation and communication networks. MITSIMLab is used to generate the necessary traffic flow data. Response surface method and linear regression technologies are applied to build the statistical models. Thus, this paper brings together an array of tools to solve the broadcast capacity problem in VANETs. The proposed methodology provides an efficient approach to estimate the performance of a VANET in real-time, which will impact the efficacy of travel decision making.     

天津地铁1号线车站乘客向导系统的设计与实现

作为城市轨道交通建设重要组成部分的乘客向导系统,是一套面向乘客的数字媒体信息综合发布和管理平台。主要说明天津地铁1号线乘客向导系统的设计与实现。