共查询到20条相似文献,搜索用时 171 毫秒
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本文介绍了模拟和数字示波器时基电路的原理,说明了时间因数检定方法的异同,分析了影响测量结果不确定度的因素,并对测量结果的不确定度进行了评定和比较。 相似文献
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为评定原油输送钢管Rt0.5的测量结果不确定度,以B级焊接钢管用钢L360MB为例,在WE-30液压式万能实验机上进行静载试验,得到原油输送钢管Rt0.5,然后根据实验结果分析其测量不确定度,并按照JJF 1059-1999《测量不确定度评定与表示》对原油输送钢管Rt0.5的不确定度进行评定。 相似文献
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激光多普勒测速技术被广泛应用于流体速度的测量。为减小双光束激光多普勒测速实验系统的测量误差,依据计量技术规范JJF 1059—1999 中规定测量不确定度的分析步骤和方法,针对系统的测量结果,从数学模型和测量方法2个方面,分析了流速测量中不确定度的主要来源。采用不确定度的A类评定和B类评定,对测量结果的各不确定度分量进行评定,得到了测量结果的合成标准不确定度和扩展不确定度。 相似文献
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Evaluation of Kalman filtering for network time keeping 总被引:6,自引:0,他引:6
Bletsas A 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2005,52(9):1452-1460
Time information is critical for a variety of applications in distributed environments that facilitate pervasive computing and communication. This work describes and evaluates a novel Kalman filtering algorithm for end-to-end time synchronization between a client computer and a server of "true" time [e.g., a Global Positioning System (GPS) source] using messages transmitted over packet-switched networks, such as the internet. The messages exchanged have the network time protocol (NTP) format, and the algorithm evaluated, is performed only at the client side. The Kalman filtering algorithm is compared to two other techniques widely used, based on linear programming and statistical averaging, and the experiments involve independent consecutive measurements (Gaussian case) or measurements exhibiting long-range dependence (self-similar case). Performance is evaluated according to the estimation error of frequency offset and time offset between client and server clock, the standard deviation of the estimates and the number of packets used for a specific estimation. The algorithms could exploit existing NTP infrastructure, and a specific example is presented. 相似文献
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针对公安交管部门对时间同步的需求,研究和设计了一种高精度的时间同步系统。该系统基于NIMDO进行卫星共视数据比对,实现时间标准向基准的实时溯源、实时同步,并结合光纤传输技术、精确时间协议和网络时间协议,向公安交管部门进行城域分级时间传递。通过对系统进行验证及分析,NIMDO与UTC(NIM)时间偏差测量结果中90.53%在±5ns以内,98.60%在±20ns以内;系统中时钟单元与时间标准的时间偏差在单纤双向传递时测量结果为-4.45~4.85ns,在双纤双向传递时测量结果为5.01~24.99μs,在采用网络时间协议时的测量结果为0.64~4.60ms。结果表明该系统解决了时间溯源和同步问题,可为其它领域的时间同步提供参考。 相似文献
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Florian Jarre Wolfgang Kiess Martin Mauve Magnus Roos Björn Scheuermann 《Optimization and Engineering》2010,11(1):107-123
The analysis of computer network experiments strongly relies on event log files recorded by the participating network nodes
during the experiment. Timing related issues play an important role here for a number of central parameters like, e.g., end-to-end
delay. As each node uses its local clock to timestamp the events in the log files, the large deviation of standard crystal
oscillator based clocks imposes some big problems. We look at this issue in the case of networks with local broadcast media,
where occurring transmissions can often be observed by multiple network nodes. We have developed a method to correct the timestamps
in such an environment in a previous paper. Here, we present a second solution. For this new solution, we give bounds on the
synchronization quality and compare the two approaches by means of simulation. 相似文献
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为了解决远距离光纤链路两端测量钟差限制在ps量级的问题,运用线性光学采样法测量钟差的基本理论,利用双光梳线性光学采样法完成了100 km光纤链路两端的钟差测量实验研究。通过梳齿压缩和色散补偿技术实现了光梳梳齿线宽和远距离光纤链路净色散量的优化,突破了高精度读取干涉花样中心时刻的难点,最终实现了高分辨力的钟差测量。通过时间间隔计数器与线性光学采样法测量光纤链路时延对比实验和100 km光纤链路钟差测量实验证明:基于线性光学采样法测量的钟差小于100 fs,能够有效满足高精度时间同步系统的要求。本研究为促进精密导航、高速通信和精准授时等领域的发展起到重要作用。 相似文献
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Time synchronization using the Internet 总被引:2,自引:0,他引:2
Levine J 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1998,45(2):450-460
This paper discusses a new algorithm for synchronizing the clocks of networked computers using messages transmitted over the network itself. The design is based on a statistical model of the clock and the network, and uses this model to define the parameters of a frequency-lock loop which is used to discipline the local oscillator. The design was tested by synchronizing a standard workstation to a time server located 1200 km away; the time offset between the clock synchronized in this way and UTC is 2 ms rms. This analysis also can be used to design algorithms that provide lower accuracy at lower cost. 相似文献
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为解决光纤时间传递系统中存在的远距离传递准确度低的问题,分析了环回法、双纤双向时间同步、双向波分复用、双向时分复用四种主流的高精度光纤时间传递方法的基本原理和技术特点,在此基础上研制了单信道时频传递装置。该装置采用电学相位补偿法实现频率传递同步,采用环回法与时分复用相结合的方法实现时间传递同步;使用1 秒脉冲(Pulse Per Second, PPS)和100 MHz共同标记时刻信号,其中1 PPS作为时刻粗标记,100 MHz作为时刻细标记,实现高精度时间同步。经实验证明,单信道时频传递装置的不确定度约为13 ps,能够满足现有光纤时频同步网计量校准的要求。该装置在多级时间传递同步、光纤时频同步网计量校准等领域中具有广阔的应用前景,为建设高稳定性、高可靠性和高精度的授时体系提供了重要技术支撑。 相似文献
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To cope with the arbitrariness of the network delays, a novel method, referred to as the composite particle filter approach based on variational Bayesian (VB-CPF), is proposed herein to estimate the clock skew and clock offset in wireless sensor networks. VB-CPF is an improvement of the Gaussian mixture kalman particle filter (GMKPF) algorithm. In GMKPF, Expectation-Maximization (EM) algorithm needs to determine the number of mixture components in advance, and it is easy to generate overfitting and underfitting. Variational Bayesian EM (VB-EM) algorithm is introduced in this paper to determine the number of mixture components adaptively according to the observations. Moreover, to solve the problem of data packet loss caused by unreliable links, we propose a robust time synchronization (RTS) method in this paper. RTS establishes an autoregressive model for clock skew, and calculates the clock parameters based on the established autoregressive model in case of packet loss. The final simulation results illustrate that VB-CPF yields much more accurate results relative to GMKPF when the network delays are modeled in terms of an asymmetric Gaussian distribution. Moreover, RTS shows good robustness to the continuous and random dropout of time messages. 相似文献
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Device-to-device (D2D) communication is considered as a major challenge in
the long term evolution (LTE) network wherein devices directly communicate with each
other. One of the key challenges in D2D sidelink is reliable and reduced-complexity
synchronization. To address this issue, a computationally efficient sequential detection
scheme for integer carrier frequency offset and sidelink identity is proposed in the LTED2D
system. To perform the frequency offset detection without retrieving the sidelink
identity, the conjugate relation between two primary sidelink synchronization sequences
is exploited, which facilitates the detection tasks of frequency offset and sidelink identity
to be decoupled. It is demonstrated from simulation results that the inherent property of
the sidelink synchronization sequences is effectively used for joint detection of frequency
offset and sidelink identity with significantly reduced complexity, compared to existing
estimation schemes. 相似文献
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为解决传统相位差优化方法以相邻交叉口为基础,忽略了连续交叉口对应的多个相位差之间的内在相关性的问题,以连续交叉口的多个相位差为研究对象,建立干道车辆延误与相位差关系的神经网络模型,采用遗传算法求解。首先,根据调查数据搭建仿环境获取不同相位差对应的干道延误数据,基于此采用神经网络拟合干道车辆延误与相位差之间的关系。然后通过遗传算法寻找神经网络中的最优延误对应的各个交叉口的相位差值。最后,将本文优化结果与Synchro进行比较分析。结果表明,本文模型能够有效改进相位差配时方案,方案性能提升了22.27%。 相似文献