共查询到20条相似文献,搜索用时 46 毫秒
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James Aweya Delfin Y. Montuno Michel Ouellette Kent Felske 《International Journal of Network Management》2006,16(1):3-28
In this paper, we present a clock synchronization scheme based on a simple linear process model which describes the behaviors of clocks at a transmitter and a receiver. In the clock synchronization scheme, a transmitter sends explicit time indications or timestamps to a receiver, which uses them to synchronize its local clock to that of the transmitter. Here, it is assumed that there is no common network clock available to the transmitter and the receiver and, instead, the receiver relies on locking its clock to the arrival of the timestamps sent by the transmitter. The clock synchronization algorithm used by the receiver is based on a weighted least‐squares criterion. Using this algorithm, the receiver observes and processes several consecutive clock samples (timestamps) to generate accurate timing signals. This algorithm is very efficient computationally, and requires the storage of only a small number of clock samples in order to generate accurate timing signals. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Timing recovery for OFDM transmission 总被引:29,自引:0,他引:29
Baoguo Yang Letaief K.B. Cheng R.S. Zhigang Cao 《Selected Areas in Communications, IEEE Journal on》2000,18(11):2278-2291
Orthogonal frequency division multiplexing (OFDM) is an effective modulation technique for high-rate and high-speed transmission over frequency selective fading channels. However, OFDM systems can be extremely sensitive and vulnerable to synchronization errors. In this paper, we present a scheme for performing timing recovery that includes symbol synchronization and sampling clock synchronization in OFDM systems. The scheme is based on pilot subcarriers. In the scheme, we use a path time delay estimation method to improve the accuracy of the correlation-based symbol synchronization methods, and use a delay-locked loop (DLL) to do the sampling clock synchronization. It is shown that by using this scheme, the mean square values of the symbol timing estimation error can be decreased by several orders of magnitude compared to the common correlation methods in both the AWGN and multipath fading channels. In addition, the scheme can track the symbol timing drift caused by the sampling clock frequency offsets 相似文献
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陈东 《信息安全与通信保密》2011,9(7):54-56
下一代网络(NGN)是一种融合了IP技术和多媒体通信技术的全新网络,然而当涉及到传统TDM业务应用及需要进行时钟同步分配时,基于IP技术的全新网络则需要具备完善的时钟同步能力来满足相关业务的同步需求。IEEE1588协议标准的出现正好解决了在新一代路由交换平台中的时钟同步问题。这里分析了IEEE1588协议的偏移测量和延时测量时钟同步过程,并给出了IEEE1588协议在路由交换平台中的具体实现过程。 相似文献
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James Aweya Delfin Y. Montuno Michel Ouellette Kent Felske 《International Journal of Communication Systems》2007,20(6):669-694
Circuit emulation service (CES) allows time‐division multiplexing (TDM) services (T1/E1 and T3/E3 circuits) to be transparently extended across a packet network. With circuit emulation over IP, for instance, TDM data received from an external device at the edge of an IP network is converted to IP packets, sent through the IP network, passed out of the IP network to its destination, and reassembled into TDM bit stream. Clock synchronization is very important for CES. This paper presents a clock synchronization scheme based on a double exponential filtering technique and a linear process model. The linear process model is used to describe the behaviour of clock synchronization errors between a transmitter and a receiver. In the clock synchronization scheme, the transmitter periodically sends explicit time indications or timestamps to a receiver to enable the receiver to synchronize its local clock to the transmitter's clock. A phase‐locked loop (PLL) at the receiver processes the transmitted timestamps to generate timing signal for the receiver. The PLL has a simple implementation and provides both fast responsiveness (i.e. fast acquisition of transmitter frequency at a receiver) and significant jitter reduction in the locked state. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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IEEE 1588标准的基本功能是使分布式网络内的各个时钟与最精确的时钟保持同步,目前主要用于以太网中,无线分组网中尚未移植该协议.本文旨在研究无线分组通信网精确定时技术,分析IEEE 1588定义的PTP(Precision Time Protocol)体系结构和时钟同步原理,提出能在无线分组网络中通过IEEE 15... 相似文献
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In this letter, we propose a one‐way ranging algorithm that is based on wireless synchronization with measured timestamps and clock frequency offsets. In our proposed algorithm, an active mobile node initiates a ranging procedure by transmitting a ranging frame, and the anchor nodes report their timestamps for the received ranging frame to a reference anchor node. The synchronization of a pair of nodes is provided with instantaneous time information, and the corresponding difference of distances can be calculated. 相似文献
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GPS-Based Satellite Tracking System for Precise Positioning 总被引:1,自引:0,他引:1
Yunck T.P. Melbourne W.G. Thoenton C.L. 《Geoscience and Remote Sensing, IEEE Transactions on》1985,(4):450-457
NASA is developing a Global Positioning System (GPS) based measurement system to provide precise determination of Earth satellite orbits, geodetic baselines, ionospheric electron content, and clock offsets between worldwide tracking sites. The system will employ variations on the differential GPS observing technique and will use a network of nine fixed ground terminals. Satellite applications will require either a GPS flight receiver or an on-board GPS beacon. Operation of the system for all but satellite tracking will begin by 1988. The first major satellite application will be a demonstration of decimeter accuracy in determining the altitude of TOPEX in the early 1990's. By then the system is expected to yield long-baseline accuracies of a few centimeters and instantaneous time synchronization to 1 ns. 相似文献
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One‐way delay variation (OWDV) has become increasingly of interest to researchers as a way to evaluate network state and service quality, especially for real‐time and streaming services such as voice‐over‐Internet‐protocol (VoIP) and video. Many schemes for OWDV measurement require clock synchronization through the global‐positioning system (GPS) or network time protocol. In clock‐synchronized approaches, the accuracy of OWDV measurement depends on the accuracy of the clock synchronization. GPS provides highly accurate clock synchronization. However, the deployment of GPS on legacy network equipment might be slow and costly. This paper proposes a method for measuring OWDV that dispenses with clock synchronization. The clock synchronization problem is mainly caused by clock skew. The proposed approach is based on the measurement of inter‐packet delay and accumulated OWDV. This paper shows the performance of the proposed scheme via simulations and through experiments in a VoIP network. The presented simulation and measurement results indicate that clock skew can be efficiently measured and removed and that OWDV can be measured without requiring clock synchronization. 相似文献
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Arthur A. Zopellaro Soares Juan Lucas Vieira Silvio E. Quincozes Vinicius C. Ferreira Luana M. Uchôa Yona Lopes Diego Passos Natalia C. Fernandes Igor Monteiro Moraes Débora Muchaluat-Saade Célio Albuquerque 《International Journal of Network Management》2021,31(3):e2112
With the popularization of the smart grid paradigm, substation automation technology has gradually been upgraded with additional processing and communication capabilities within control and protection devices. Hence, the research community is pressured to find new, efficient, and reliable communication solutions for such a scenario. That task is complicated by the stringent temporal requirements defined by the International Electrotechnical Commission (IEC) 61850 standard for power system communication comprising teleprotection schemes. Further compounding the issue is the critical nature of the power grid, in which availability is definitely a strong requirement. Software-defined networking (SDN) may provide powerful tools to fulfill those requirements at acceptable costs. As such, this paper surveys and compares several available SDN controllers and their applicability to the teleprotection scenario. It further evaluates controllers in terms of capacity and resilience through experiments in an emulated environment. 相似文献
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介绍了GPS接收原理及模块化接收机的组成,分析了NMEA-0183协议及其解码过程,设计了基于GPS卫星授时时钟,其具有实时性、同步性以及高精度的特点,是无线电波授时所无法比拟的,模块化GPS接收机使GPS接收设备设计更简单、成本更低。 相似文献
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Time synchronization is critical in distributed environments. A variety of network protocols, middleware and business applications rely on proper time synchronization across the computational infrastructure and depend on the clock accuracy. The Network Time Protocol (NTP) is the current widely accepted standard for synchronizing clocks over the Internet. NTP uses a hierarchical scheme in order to synchronize the clocks in the network. In this paper we present a novel non-hierarchical peer-to-peer approach for time synchronization termed CTP-Classless Time Protocol. This approach exploits convex optimization theory in order to evaluate the impact of each clock offset on the overall objective function. We define the clock offset problem as an optimization problem and derive its optimal solution. Based on the solution we develop a distributed protocol that can be implemented over a communication network, prove its convergence to the optimal clock offsets and show its properties. For compatibility, CTP may use the packet format and number of measurements used by NTP. We also present methodology and numerical results for evaluating and comparing the accuracy of time synchronization schemes. We show that the CTP outperforms hierarchical schemes such as NTP in the sense of clock accuracy with respect to a universal clock. 相似文献
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在数字化变电站自动化进程中应用IEC61850标准成为现实。随着对IEC61850标准研究和应用的不断深入,各厂家生产的变电站智能化电气设备会逐步满足这一标准,尤其是生产消弧设备、电源设备等厂家将不再依赖变电站内的规约转换装置,直接使用IEC61850标准进行生产。IEC61850标准的实施,将使数字化变电站的发展进入一个崭新的阶段。文中提出了IEC61850标准及其在220 kV三乡数字化变电站的实际应用,浅释了IEC61850标准在变电站内设备间信息共享以及站内与远端信息的交互问题。同时验证了应用IEC61850标准建立开放式变电站自动化系统通信平台的可行性。 相似文献
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在基于网络的测量与控制系统中,对分散节点间的时钟同步有很高的要求.IEEE 1588标准的精确时钟协议为测控系统的时钟同步提供了一种简单可行的途径.分析了精确时钟协议实现的原理和算法,针对测控系统中对时钟同步精度的需求,研究了系统内选择最优主时钟的算法和实现,以及硬件辅助检测时间戳的方法和应用.最后以以太网为例,对设计... 相似文献
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The key synchronization aspects in the system design of a QQPSK (quadrature-quadrature phase-shift-keying) modem are addressed. The sensitivity of the data demodulator to synchronization errors is discussed, and contextually the performances of some IF and baseband carrier phase and symbol timing recovery schemes are evaluated both theoretically and by computer simulations. In particular, a fourth-power IF carrier/clock regenerator and two baseband clock recovery schemes, with and without the aid of data decisions, respectively, are taken into account. The analysis shows on the one hand the substantial robustness of QQPSK to carrier phase errors and the adequacy of the examined carrier extraction scheme. On the other hand, the remarkable sensitivity of QQPSK to symbol timing inaccuracy is stressed and the need to resort to the newly proposed decision-aided baseband clock recovery scheme is pointed out 相似文献
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IEEEl588在工业以太网交换机中的关键应用 总被引:2,自引:2,他引:0
随着智能变电站技术的发展,数字信号的采集与传输必须基于统一的时序和时钟标准,才能保证数据的准确性、实时性和有效性,IEEEl588技术在新一代智能变电站中发挥着重要作用。系统地分析了IEEEl588协议的系统结构、报文类型以及PTP透明时钟工作原理。突出介绍了P2P和E2E的两种对时方案的异同点,并总结了IEEEl588工业以太网交换机报文处理流程。该文设计的1588交换机具有精度高、易配置、经济实用等优点,可以满足电力系统对时同步的技术要求。 相似文献