移动定位业务概述

车辆监控、调度系统利用公用移动通信网的数据承载通道（SMS、GPRS、CDMA 1X）作为监控中心与移动目标之间的信息传输媒介，利用各种通信平台（Internet、DDN专线、帧中继、VPN、ISDN、PSTN等）作为监控中心与远程工作站之间的通信方式，综合运用全球定位系统（GPS）和基于电子地图的地理信息系统（GIS）相关技术，实现对移动目标位置的跟踪、调度／指挥、监控、报警求助和信息咨询等服务。     

多目标安全监控系统的组成及实现

介绍了多目标安全监控系统的结构及组成，给出了基于ＧＰＳ的移动目标的硬件及软件的结构，介绍了移动目标与监控中心的通信方案。     

基于GPS/BDS的移动目标定位追踪系统设计

利用GPS(全球卫星定位系统)和BDS(北斗卫星导航系统)联合定位技术,设计了一款针对移动目标的高精度定位与跟踪系统。系统主要包括移动目标通信终端、GSM网络、GIS电子地图等。其中,核心部分——移动目标通信终端硬件由ATGM331C单元、TC35I单元和STC12C5A60S2微处理器单元等构成;其软件设计主要包括:微处理器初始化、GPS/BDS解码、短信命令解码和AT命令控制等。实践测试结果表明:该系统运行稳定,且移动目标通信终端具有定位精度高、体积小、功耗低、操作简单方便等特点,应用前景广阔。     

基于GPS／GSM短消息车载终端的设计与实现

基于XT55 GPS/GSM模块,设计实现了GPS车载移动终端,该终端利用GPS获取用户当前位置和时间信息,以短消息(SMS)的形式通过GSM网络发往监控中心,同时该终端也可接收来自监控中心的控制指令,从而实现对车辆的自动报警、自动控制、自动信息查询等功能.详细介绍了终端设备的硬件设计和软件流程图.     

移动GIS应用中的通信技术探讨

移动GIS的载体是互联网,借助智能终端实现了准确的定位,提供多样化的服务业务。移动GIS的应用越来越广泛,需要考虑通信技术的应用,通过提高通信水平,满足移动GIS的需求,支持移动GIS的积极性发展。移动GIS中的通信技术,负责了移动化的通信,属于一项关键技术,文章结合移动GIS,重点分析应用中的通信技术。     

快速发展的移动通信

所谓移动通信是指通信双方(甚至多方)或至少一方在进行信息交换时是运动的。也就是说，移动体(如车辆、船舶、飞行器)或移动人与固定点，或者移动体(或人)与移动体(或人)之间的通信都属于移动通信。移动通信包括对讲机、无绳电话、无线寻呼、集群、无线移动数据、移动卫星通信和蜂窝系统等。目前人们通常所说的移动通信是指蜂窝系统。     

移动IP中的几个热点问题

当前 ,移动通信和Ｉｎｔｅｒｎｅｔ技术迅速发展并且相互渗透 ,各种功能强大的便携式终端不断涌现 ,使得人们对移动ＩＰ技术的需求也日益增强。移动ＩＰ技术是由ＩＥＴＦ制定的用于解决移动主机在不中断通信的情况下接入网络的一种技术。１移动ＩＰ的设计要求和目标移动ＩＰ协议应满足以下设计要求。(１)移动节点改变其链路层连接点后 ,能够保持ＩＰ地址不变 ,从而可以继续和其他节点通信 ,同时移动节点还能够和其他没有采用移动ＩＰ协议的节点进行通信。(２)移动ＩＰ应与现存的ＩＰ协议兼容 ,不需要对当前的网络连接、用户设施和路由器的配…     

GPS车辆管理和监控系统中快速通信的实现

GPS定位技术在车辆管理和监控系统中已经得到广泛地应用。系统利用GPS技术,GIS技术和通信技术对移动车辆进行实时监控和管理。整个系统由监控中心和多个移动车载台组成,监控中心通过无线通信与各移动车辆相互联络。目前,由于通信系统和手段的限制,中心采用轮询的方法对各移动车辆的位置、状态等信息进行查询。根据时分制的原理,将一个轮询周期分为若干个时间段,每个移动车载台占用其中的一个时间段,移动车载台只有在自己的时间段里才向监控中心回传车辆信息。     

GPS车辆管理和监控系统中快速通信的实现

GPS定位技术在车辆管理和监控系统中已经得到广泛地应用。系统利用GPS技术 GIS技术和通信技术对移动车辆进行实时监控和管理。整个系统由监控中心和多个移动车载台组成,监控中心通过无线通信与各移动车辆相互联络。目前,由于通信系统和手段的限制,中心采用轮询的方法对各移动车辆的位置、状态等信息进行查询。根据时分制的原理,将一个轮询周期分为若干个时间段,每个移动车载台占用其中的一个时间段,移动车载台只有在自己的时间段里才向监控中心回传车辆信息。     

移动IPv6切换时延优化新方法

移动IPv6中,移动节点(MN)在不同子网间移动时,既不中断与通信对端(CN)的通信,也不用改变其本身的IP地址.但是当MN与其家乡代理(HA)之间相距较远时,移动IPv6切换时延较大,对于实时性要求较高的业务无法适用.本文分析比较了目前移动IPv6常用的切换时延优化方法,提出了一种自适应快速层次移动IPv6切换时延优化方法,减小了移动IPv6切换时延,提高了网络的性能.     

Performance improvement in tensile-strained In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As metamorphic HEMT

This paper proposes a In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As (x=0.3-0.5-0.3) metamorphic high-electron mobility transistor with tensile-strained channel. The tensile-strained channel structure exhibits significant improvements in dc and RF characteristics, including extrinsic transconductance, current driving capability, thermal stability, unity-gain cutoff frequency, maximum oscillation frequency, output power, power gain, and power added efficiency.     

Very low-noise Al/sub 0.3/Ga/sub 0.7/As/Ga/sub 0.65/In/sub 0.35/As/GaAs single quantum-well pseudomorphic HEMTs

AlGaAs/GaInAs/GaAs pseudomorphic HEMTs with an InAs mole fraction as high as 35% in the channel has been successfully fabricated. The device exhibits a maximum extrinsic transconductance of 700 mS/mm. At 18 GHz, a minimum noise figure of 0.55 dB with 15.0 dB associated gain was measured. At 60 GHz, a minimum noise figure as low as 1.6 dB with 7.6 dB associated gain was also obtained. This is the best noise performance yet reported for GaAs-based HEMTs.<>     

A 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode array

We report a 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode (APD) array. The mean breakdown voltage of the APD was 57.9 V and the standard deviation was less than 0.1 V. The mean dark current was /spl sim/2 and /spl sim/300 nA, and the standard deviation was /spl sim/0.19 and /spl sim/60 nA at unity gain (V/sub bias/ = 13.5 V) and at 90% of the breakdown voltage, respectively. External quantum efficiency was above 40% in the wavelength range from 1.0 to 1.6 /spl mu/m. It was /spl sim/57% and /spl sim/45% at 1.3 and 1.55 /spl mu/m, respectively. A bandwidth of 13 GHz was achieved at low gain.     

Al/sub 0.3/Ga/sub 0.7/As/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) doped-channel field-effect transistors (DCFET's)

The properties of both lattice-matched and strained doped-channel field-effect transistors (DCFET's) have been investigated in AlGaAs/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) heterostructures with various indium mole fractions. Through electrical characterization of grown layers in conjunction with the dc and microwave device characteristics, we observed that the introduction of a 150-/spl Aring/ thick strained In/sub 0.15/Ga/sub 0.85/As channel can enhance device performance, compared to the lattice-matched one. However, a degradation of device performance was observed for larger indium mole fractions, up to x=0.25, which is associated with strain relaxation in this highly strained channel. DCFET's also preserved a more reliable performance after biased-stress testings.<>     

Morphological and electrical characterization of SixCryCzBv thin films

Si_xCr_yC_zB_v thin films with several compositions have been studied for integration of high precision resistors in 0.8 μm BICMOS technology. These resistors, integrated in the back-end of line, have the advantage to provide high level of integration and attractive electrical behavior in temperature, for analog devices. The film morphology and the structure have been investigated through transmission electron microscopy analysis and have been then related to the electrical properties on the base of the percolation theory. According to this theory, and in agreement with experimental results, negative thermal coefficient of resistance (TCR) has been obtained for samples with low Cr content, corresponding to a crystalline volume fraction below the percolation threshold.Samples with higher Cr content exhibit, instead, a variation of the TCR as a function of film thickness: negative TCR values are obtained for thickness lower than 5 nm, corresponding to a crystalline volume fraction below the percolation threshold; positive TCR are obtained for larger thickness, indicating the establishment of a continuous conductive path between the Cr rich grains. This property seems to be determinant in order to assure the possibility to obtain thin film resistors almost independent on the temperature.     

Highly linear Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMTs

We report an Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMT with enhanced linearity. By engineering the channel region, i.e., inserting a 6-nm-thick AlGaN layer with 5% Al composition in the channel region, a composite-channel HEMT was demonstrated. Transconductance and cutoff frequencies of a 1 /spl times/100 /spl mu/m HEMT are kept near their peak values throughout the low- and high-current operating levels, a desirable feature for linear power amplifiers. The composite-channel HEMT exhibits a peak transconductance of 150 mS/mm, a peak current gain cutoff frequency (f/sub T/) of 12 GHz and a peak power gain cutoff frequency (f/sub max/) of 30 GHz. For devices grown on sapphire substrate, maximum power density of 3.38 W/mm, power-added efficiency of 45% are obtained at 2 GHz. The output third-order intercept point (OIP3) is 33.2 dBm from two-tone measurement at 2 GHz.     

Comparison between Pt/TiO2/Pt and Pt/TaOX/TaOY/Pt based bipolar resistive switching devices

Nonvolatile memories have emerged in recent years and have become a leading candidate towards replacing dynamic and static random-access memory devices. In this article, the performances of TiO₂ and TaO₂ nonvolatile memristive devices were compared and the factors that make TaO₂ memristive devices better than TiO₂ memristive devices were studied. TaO₂ memristive devices have shown better endurance performances (10⁸ times more switching cycles) and faster switching speed (5 times) than TiO₂ memristive devices. Electroforming of TaO₂ memristive devices requires~4.5 times less energy than TiO₂ memristive devices of a similar size. The retention period of TaO₂ memristive devices is expected to exceed 10 years with sufficient experimental evidence. In addition to comparing device performances, this article also explains the differences in physical device structure, switching mechanism, and resistance switching performances of TiO₂ and TaO₂ memristive devices. This article summarizes the reasons that give TaO₂ memristive devices the advantage over TiO₂ memristive devices, in terms of electroformation, switching speed, and endurance.     

Electrooptic ferroelectric Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films

We report on waveguiding and electrooptic properties of epitaxial Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films grown by radio-frequency magnetron sputtering on Al/sub 2/O/sub 3/(11_02) single crystal substrates. High optical waveguiding performance has been demonstrated in infrared and visible light. The in-plane electrooptic effect has been recorded in transmission using a transverse geometry. At dc fields, the effective linear electrooptic coefficient was determined to 28 pm/V, which is promising for modulator applications.