GPS time transfer

The authors describe the use of GPS (Global Positioning System) for time coordination. When GPS first became available, it provided a quantum leap in time coordination with little or no effort on the part of the user. However, workers realized that with more sophisticated analysis techniques even greater accuracy could be wrung from GPS. The authors describe the level of time coordination these more sophisticated techniques have affected. The principles of GPS time transfer are described with emphasis on the so-called common view method. The sources of error during GPS time transfer are discussed and the various possibilities of reducing them are investigated. Some possibilities for overcoming SA (selective availability of GPS) are also discussed. GPS is additionally shown to be an outstanding tool for the dissemination of Coordinated Universal Time (UTC)     

一种光纤双向时间比对时间码的设计与验证

提出了一种适用于通过光纤链路实现高精度双向时间比对的时间编码方案.在保留IRIG-B(DC)码型格式的基础上,通过压缩码元宽度实现时间编码信号在光纤链路中的高精度传输.给出了基于FPGA的时间编解码实现方案,在1m电缆和室内50km光纤传输链路上进行了双向时间比对的实验.实验结果表明,该方案可稳定精确地实现时间传递,1m电缆的传输精度优于33ps,50km光纤传输精度优于55ps.     

双向时分复用光纤时间传递链路噪声分析

研究分析了双向时分复用(BTDM)光纤时间传递链路 的主要噪声及产生机理,建立了基于BTDM光纤时间传递 的链路噪声模型。仿真分析了激光器强度噪声、光放大器增益与个数、接收机带宽等对BTDM 光纤时间传 递接收信噪比(SNR)的影响。结果表明,BTDM光纤时间传递 接收SNR在光放大器达到最优增益时最大,且最 大SNR随光放大器个数的增加而增加并趋于稳定;相同长度光纤链路,光放大器个数越多 ,在一定范围 内,激光器相对强度噪声对BTDM光纤时间传递链路接收SNR 影响更大,接收机带宽对BTDM光纤时 间传递接收信号抖动的影响越小;BTDM光纤时间传递接收SNR随定时信号前 光持续时间的增加而减小,并趋于WDM方案的SNR。     

基于差分GPS的战术数据链高精度时间同步

精确协同作战作为信息化条件下作战形态的必然发展趋势,其对作战平台间高精度时间同步提出了较高的要求。针对该要求,在分析了战术数据链往返计时（ RTT)时间同步算法的基础上,提出了卫星导航载波相位差分GPS（ DGPS)技术与数据链高精度时间同步算法,利用卡尔曼滤波构建时间同步计算算法模型,实现高精度的时间同步。仿真结果表明该算法可提高时间同步精度到3 ns。     

基于ARM的GPS同步授时系统设计

基于国际航海标准NMEA-0183为数据协议,以保证电力系统精准授时为目的,通过ARM微控制器STM32f103rbt6和高精度GPS接收模块NEO-5Q为核心控制数据采集和传输,实现了GPS同步授时的设计方案。系统采用GPS接收模块接收卫星发送的标准数据串,通过微控制器对GPRMC最小定位信息中的时间数据进行筛选和处理,最后经上位机授时软件对本地计算机进行成功校时,保证了系统的可行性。     

Bidirectional optical amplifier for time transfer using bidirectional WDM transmission

In this letter, we propose a bidirectional optical amplification scheme for fiber-optic time transfer based on bidirectional wavelength-division multiplexing (WDM) transmission. The proposed scheme employs single unidirectional erbium-doped fiber amplifier (Uni-EDFA) for commercial optical networks to implement bidirectional optical amplification. Since including isolators, the effect of backscattering due to the accumulated amplification can be efficiently suppressed by the proposed amplifier. The proposed scheme is validated over different length fiber links in laboratory. Experimental results show that the proposed amplifier can support fiber-optic time transfer over several thousands of kilometers with an additional bidirectional delay difference fluctuation at picosecond magnitude.     

GPS接收机空域和空时滤波性能研究

提出了空域滤波和空时滤波的优缺点,研究了他们的抗干扰性能,并在圆阵中进行了仿真.仿真结果表明这两种方法都可以用于GPS接收机抗干扰.其中,空时滤波结构相对于空域滤波能增加系统的自由度,对于宽带信号能提供更佳的抗干扰性能;价格相对较低的空域滤波结构在普通干扰环境中(干扰数目较少)也是一种合适的选择.     

Two-way time transfer via communication satellites

The history of two-way satellite time transfer is provided and developments in satellite communications technology conducive to this time transfer technique are briefly reviewed. The difference between one-way and two-way satellite time transfer is explained, and the advantages and disadvantages of the two-way method are pointed out. The theory of the two-way technique using geostationary communication satellites is presented showing the high accuracy potential of the method. The advantages of the use of spread spectrum techniques are outlined. The implementation of the two-way method using communication satellites and small Earth stations using pseudonoise (PN) modems is described. Methods for signal delay calibration are dealt with. Existing links are listed and their performances are given. The future use of the two-way technique using communication satellites is discussed     

Frequency and time stability of GPS and glonass clocks

The frequency stability and reliability of the clocks are critical to the success of the GPS and GLONASS programs. We will show some of the similarities and differences between the clocks involved in these two systems. Because both systems plan to be operational in the next few years, the data leading up to this operational stage is of significant interest. On-board clocks and the stability of the master control clocks for these systems are analysed. We will discuss the attributes of these two systems as time and frequency references. Their relationship to UTC will also be illustrated. More data over a longer period of time was available for the authors from GPS than from GLONASS. Even so it is obvious that both systems have matured. Though the GLONASS system was developed later, its overall clock performance has improved more rapidly. Some of the more recent GLONASS clock performance is at about the same level as that of the GPS clocks. The analysis has yielded some very interesting contrasts, comparisons and changes in these systems that should be of great interest for time and frequency users, as well as for clock vendors and receiver vendors.     

一种四通道GPS信号模拟器相对时延的测量方法

本文提出了一种四通道信号源相对时延的测量方法,基于通用数字存储示波器,能在测量四通道信号源相对时延的同时,获得示波器通道之间以及不同连接电缆之间的时延校正参数。该方法特别适合应用于输入不可见的多通道数模混合系统,可扩展适应任意数目的多通道信号源系统,无需使用任何标准测试件,弥补了网络分析仪测量时延的局限性,方便非专业用户使用。     

一种基于特征向量法的高分辨率GPS多路径信号延迟估计方法

多路径原理和干扰抑制是在GPS信号捕获、跟踪和高精度定位中的一个研究热点.延迟时间是多路径信号分析中的一个重要参数,相关延迟估计法是一种基本的估计方法,但是对于GPS多路径信号,它的分辨率有限.在对相关延迟估计方法分析的基础上,给出了一种基于特征向量分解的高分辨率延迟估计方法.首先利用互功率谱把时域的延迟变换到频域的频移,然后把求得的功率谱等效为一个时间序列,再利用特征向量法对该时间序列求功率谱.该功率谱估计方法是一种基于信号子空间和噪声子空间的估计方法,具有高的频率分辨率,从而可以实现对延迟时间的高分辨率估计.     

Automatic video object generation tool: segmentation and tracking of persons in real time

In the field of the multimedia applications, future standards as mpeg4 or mpeg7 allow new image content representation that goes far from the basic compression. This way, the objects of interest become entities that the user can manipulate. Nevertheless, the norm does not specify how objects have to be segmented, even if in some cases this is a complex task. In the framework of the European project m4m (mpeg fo(u)r Mobiles, Medea project Al 16), we have in charge the development of a demonstrator able to segment and track a speaker in videophone and vidéoconférence applications.     

VCSEL-based Raman technology for extended reach time and reference frequency transfer systems

This paper experimentally demonstrates a low-cost energy efficient alternative technique for long reach transfer of accurate reference frequency (RF) clock signals for extended reach RF distribution systems. This is achieved by adopting distributed forward Raman amplification and vertical cavity surface emitting laser (VCSEL) technology. A class 10G VCSEL is directly modulated with a 2 GHz RF clock signal. By exploiting a forward Raman pump with the flat gain of 8.6 dB, a 100.8-km-long standard single mode fiber (SMF) RF clock distribution is experimentally achieved. A maximum phase noise of ?117.66 dBc/Hz at offset frequency of 100 kHz and an RF clock jitter (RMS) of 5.36 ps is experimentally measured for 100.8-km-long fiber transmission without forward Raman amplification. However, with the adoption of forward Raman amplification, the measured phase noise and RMS improves to ?86.59 dBc/Hz and 1.7 ps, respectively. Forward Raman pumping offers distributed high flat gain over a wide spectra range (over 35.5 nm), while VCSELs offer cost effective broadband signal distribution, therefore keeping the network optics investment low.     

Plasma impedance monitoring for real time endpoint detection of bulk materials etched in ICP tool

Plasma impedance monitoring (PIM) based on electrical measurements is successfully used as an alternative to determine real time detection endpoint during plasma etching of structured bulk materials. In this paper we present the results with this technique for the endpoint detection during the etching of various materials.The endpoint conditions are tested in the sixth harmonic components of the electrical plasma parameters with an RF sensor. The endpoint is determined when an electrical parameter transition is observed. This transition corresponds to the change of the total reactor impedance, and allows the etching of the doped layer to stop on the bulk substrate.Using a Smith chart we determine the best harmonics/electrical monitoring couple parameters for processes on various materials. Resistivity measurements are used before and after etching in order to confirm the usefulness of the PIM method.In this paper, we also demonstrate how to monitor a real time control of non-uniformity during the reactive ion etching (RIE) process in the case of gallium arsenide etching.     

用于卫星双向时间传递系统的调制器设计

设计开发了一种用于卫星双向时间传递(TWSTT) 系统的调制器,详细介绍了该调制器 的内部结构和相关算法。采用FPGA和DDS进行硬件实现,并完成系统的仿真测试。该调制器 的中频输出频率为70 MHz,峰值输出功率为-15 dBm。     

用于降低高速CMOS图像传感器电荷转移时间的工艺技术

This paper proposes pixel process techniques to reduce the charge transfer time in high speed CMOS image sensors.These techniques increase the lateral conductivity of the photo-generated carriers in a pinned photodiode(PPD) and the voltage difference between the PPD and the floating diffusion(FD) node by controlling and optimizing the N doping concentration in the PPD and the threshold voltage of the reset transistor,respectively.The techniques shorten the charge transfer time from the PPD diode to the FD node effectively.The proposed process techniques do not need extra masks and do not cause harm to the fill factor.A sub array of 3264 pixels was designed and implemented in the 0.18 m CIS process with five implantation conditions splitting the N region in the PPD.The simulation and measured results demonstrate that the charge transfer time can be decreased by using the proposed techniques.Comparing the charge transfer time of the pixel with the different implantation conditions of the N region,the charge transfer time of 0.32 s is achieved and 31% of image lag was reduced by using the proposed process techniques.     

PLANET: a tool for telecommunication network

PLANET is an integrated software package aiding several steps of the transmission network planning, as well as the traffic simulation. The database of PLANET consists of the structural and the cost models of the transmission systems, the topological alternatives, the circuit routing and grouping rules, etc. The topological and transmission plans of the networks are obtained based on the traffic planning results checked by simulation and they are stored systematically with the input data in the database of plans. The results describe the network topology, the circuit routes meeting different kinds of routing conditions, the grouping solutions and the equipment assignments to the circuit demands of different services. The users of PLANET are provided with lists and graphical documentation that can be directly used in the development of the network. The global structure of the software package as well as the algorithms of specific phases are discussed and the results obtained by the application of PLANET are demonstrated     

GaN based transfer electron and avalanche transit time devices

A new model is developed to study the microwave/mm wave characteristics of two-terminal GaN-based transfer electron devices (TEDs), namely a Gunn diode and an impact avalanche transit time (IMPATT) device. Microwave characteristics such as device efficiency and the microwave power generated are computed and compared at D-band (140 GHz center frequency) to see the potentiality of each device under the same operating conditions. It is seen that GaN-based IMPATT devices surpass the Gunn diode in the said frequency region.     

基于单向传输的光纤时延波动测量

为了与现有光纤通信网络兼容,研究了一种基于单纤单向传输的光纤时延波动测量方法。基于色散温变效应和Sellmeier等式,建立了利用温度的准确测量和双波长光信号传输时延差波动反推单向时延波动的比例模型。令模型中的比例系数是单波长时延波动和双波长时延差波动的比,仿真研究了温度和波长差对比例系数的影响。搭建了75 km光纤单向时延波动测量实验平台,实验结果表明:实测比例系数?258.4接近于理论比例系数?277.3,对应单向传输时延波动误差为660 ps,实验结果验证了模型的正确性和基于单向传输的光纤时延波动测量的可能性。     

数码玩家的GPS指南 行走天地间

GPS很有用，天上飞的，地上跑的，路上走着的，都需要它。 可GPS是一套庞大复杂的系统，你不是大地测量员，那些艰深枯燥的地理知识，太难理解。[编者按]