Accurate Clock Synchronization Research Articles

A distributed PD detection method for high voltage cables based on high precision clock synchronization

Partial discharge (PD) is a crucial cause of high voltage (HV) cable failures. Detecting and locating PD efficiently and effectively is paramount for HV cable maintenance. However, the attenuation of the PD signal after long-distance propagation makes it challenging to identify. This paper presents a distributed PD detection method that significantly reduces the propagation distance of PD signals before the sensor captures them. The technique uses the time-of-arrival to locate PD, whose localization accuracy is directly linked to the clock synchronization (CS) accuracy. CS between different sensors is achieved through three times interactions of the CS signal. The linear frequency modulation (LFM) signal is selected as the CS signal, which can generate a significant gain after pulse compression. It ensures that the CS signal can be effectively recognized after the attenuation of long-distance propagation. The paper also introduces a signal discrimination method based on the short-time Fourier transform that eliminates the influence of the LFM signal on PD identification. The cableless CS method makes it easier to set up before the onsite test. A prototype was implemented and tested. The CS accuracy was measured within 4 ns in the laboratory. An onsite test was carried out to evaluate the performance of the distributed PD detection system. A defect was found at a joint location, which was also confirmed by an additional ultrasonic PD test.

CRT-Based Clock Synchronization for Millimeter-Wave Communication with Asymmetric Propagation Delays

The rapid advancement of millimeter-wave communication technology has presented new challenges for time synchronization, driven by the need for high-speed and low-latency data transmission. Ethernet synchronization technologies, such as Precise Time Protocol (PTP), have emerged to overcome the limitations of point-to-point architecture and enable precise synchronization across multiple devices. A key drawback of conventional PTP is its reliance on symmetric packet exchange delays, which may not hold in real-world scenarios where there is relative mobility between master and slave nodes, leading to asymmetric propagation delays and clock offset errors. To address this issue, a novel clock synchronization protocol that integrates Chinese Remainder Theory (CRT) has been proposed. This protocol enhances conventional PTP by incorporating distance estimation based on CRT using multi-carrier phase measurement. By combining a coarse estimation of one-way propagation delay from conventional PTP with a fine estimation of remainder distance from CRT, the protocol accurately determines the distance between master and slave nodes, reducing motion errors and enhancing clock synchronization accuracy. Simulation results indicate that the Root Mean Square Error (RMSE) of distance estimation remains below 10−5 m, with a corresponding motion time error of approximately 0.01 picosecond.

A clock synchronization and trigger distribution scheme for China Spallation Neutron Source

China Spallation Neutron Source (CSNS) is a complex system engineering composed of particle accelerators, a target station, and neutron spectrometers with various equipment types and distribution. The collaborative operation of the equipment requires accurate clock synchronization and trigger distribution. Currently, to meet the requirements of different system devices, clock synchronization and trigger distribution in CSNS are implemented based on different methods, resulting in complex clock and trigger networks, demanding upgrades, and a lack of unified timestamps. This paper proposes a clock synchronization and trigger distribution scheme based on the field-programmable gate array (FPGA) and single-mode dual-core fiber link. The decoupling of clock phase synchronization and time base synchronization improves the frequency of phase compensation. Benefiting from the phase interpolator (PI) in the FPGA transceivers, high-precision phase compensation and phase deterministic control are realized, achieving picoseconds synchronization precision and stability in the four-level network. Based on the custom lightweight link layer protocol, by optimizing the routing method of data frames and adopting priority control, the transmission of multiple data is realized, and the hardware delay of the critical data, such as interlock, is guaranteed to be less than 1.5 μs in the four-level system. The scheme provides a general precise clock synchronization and distributed trigger method for CSNS devices, simplifies the system complexity, and is conducive to the system upgrade in the second stage.

Predictable Timestamping for the Controller Area Network: Evaluation and Effect on Clock Synchronization Accuracy

Predictable Timestamping for the Controller Area Network: Evaluation and Effect on Clock Synchronization Accuracy

Design of Light, Small, and High-precision Digital Servo Clock for LEO Constellation

Modern low earth orbit (LEO) satellite systems have placed increasingly stringent requirements on spaceborne time-frequency systems in the fields of constellation autonomous management, distributed synthetic aperture radar (SAR) imaging, and navigation time service. Admittedly, the original high-stability constant-temperature crystal oscillator and high-stability temperature-compensated crystal oscillator can no longer comply with the indicator requirements of clock source frequency characteristics and clock synchronization accuracy. Likewise, traditional satellites use atomic clocks (rubidium atomic clocks and cesium atomic clocks). On account of their inherent characteristics, the ground receiving system needs to observe and count the clock parameter characteristics for a long time after the satellite enters orbit and frequently modify the future working state parameters. The features of being expensive and bulky increase the operation and maintenance costs of the ground system and the complexity of engineering implementation. In this paper, a kind of light and small high-precision digital servo clock based on the deep coupling of the global navigation satellite system (GNSS) is designed for the LEO satellite constellation. The tame clock is deeply coupled with the GNSS navigation receiver, and the high precision time-frequency difference between the local clock frequency source and GNSS is obtained by using the carrier and pseudo-range measurement information of visible satellite and carrier phase measurement information of the receiver. It not only utilizes the short-term high stability of OCXO but also employs the long-term time-frequency maintenance ability of GNSS so that the tamed OCXO is locked in GNSS for a long time, which can achieve frequency calibration of local clock sources and long-term output to various space-borne systems. The system is small in size and low in power consumption, with output frequency stability better than 3E-13 (10000 s), accuracy better than ±2E-13, and timing accuracy better than ±10 ns, which is comparable to the key technical indexes of spaceborne miniaturized rubidium clocks, in line with the current demand of miniaturization, low power consumption, and low cost of LEO constellations.

Fast Kalman filter synchronization algorithm for cooperative synchronization in time sensitive networks

Clock synchronization is crucial in time-sensitive networks (TSN) to ensure the normal operation of devices. However, traditional synchronization techniques face challenges such as the accumulation of synchronization errors over multiple hops and slow synchronization speed, which hinder the development of large-scale and multi-hop TSN. In this paper, we propose a cooperative synchronization scheme based on two-way timestamp exchange to reduce error accumulation and enable synchronization information exchange between any node in the network and the reference node. Moreover, we develop a fast Kalman filter (FKF) algorithm to estimate clock offset and clock skew. To reduce time complexity, we replace the calculation of gain matrices with extremely high dimension with a small matrix based on the randomization matrix approximation in the updating phase of the Kalman Filter. Simulation results show that the proposed method significantly reduces synchronization complexity without sacrificing clock synchronization accuracy, making it highly promising for future TSN deployments.

Joint Synchronization and Range Estimation With Correlated Arrival Times in Molecular Communication Networks

Time synchronization is needed in information exchange and collaboration among nanomachines for molecular communication networks. The time of arrival-based synchronization method requires the range information between the transmitter nanomachine (TN) and the receiver nanomachine (RN) in order to improve the accuracy of clock synchronization. The range information between the nanomachines helps to choose the optimal transmission rate. In contrast to the existing methods, this article proposes a joint clock offset and range estimation with correlated arrival times based on the maximum likelihood estimator. The RN uses the molecules' transmission and correlated arrival times to estimate the clock offset and range between the TN and RN. Even with correlated arrival times, the individual clock offset estimation performance is comparable to independent arrival times performance. Notably, the joint estimation problem with correlated arrival times is generic and realistic for molecular applications.

Precise Clock Synchronization Strategy of Power Distribution Field Network Based on HPLC Communication

In order to improve clock synchronization precision of the power distribution field network, a power distribution field network with high‐speed power line broadband carrier communication is designed, and a step‐by‐step precision clock synchronization strategy is developed based on modified timing‐sync protocol for sensor networks. In the strategy, the clock of the central node is calibrated in real‐time as the master clock of the field network by the communication master station through the long‐distance communication network, the time and frequency deviations of the clocks of each node in the network are accurately monitored using the broadcast mechanism and the network time base of the carrier communication, and the clock frequency is gradually amended by re‐calibrating the clock temperature compensation coefficient of the node so that the clock of the node is synchronized step‐by‐step within a clock synchronization cycle. The clock synchronization performances of the field network are tested in the laboratory and jobsite, and test results show that the clock synchronization accuracy of the field network is within ± 0.23 s/24 h, which is 28% higher than that of the power distribution field network based on narrowband power line carrier, and these phenomena of time gap or time repetition are avoided in the clock synchronization process. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Bi-directional PRN laser ranging and clock synchronization for TianQin mission

Laser frequency coupling noise due to unbalanced arm lengths is the dominant noise source for space-based gravitational wave detection. Time-delay interferometry is a proposed technique to eliminate the coupling noise by constructing a virtual equal-arm-length interferometer, where the real-time information of both absolute inter-satellite distance and clock synchronization is required. Inter-satellite laser ranging based on pseudo-random noise (PRN) sequence modulation has become the main technical means for extraction of the inter-satellite distance and clock difference information. This paper shows a bi-directional laser ranging scheme based on PRN code modulation and experimentally demonstrates its function by using an optical fiber of 10 km long. The measured results of the transmission time duration and the clock difference are compared with independent methods of pulse laser ranging and 1PPS signal measurement, respectively, both of which coincide well. It is also evaluated that the laser ranging accuracy is 1.2 m, and the clock synchronization accuracy reaches 6.7 ns, applicable to TianQin with the preliminarily determined requirement of 3 m and 10 ns. This laser ranging scheme can be applied to satellite navigation and space-based gravitational wave detection.

Design of Medium and Long Distance Satellite Signal Transmission Scheme Based on Baseband Resource Pool

In order to solve the problems such as the delay and jitter in the transmission of medium and long distance satellite signals, as well as the transmission capacity, switching capacity, number of ports and optical crossover capability caused by multiple high rate channels, a signal transmission scheme based on baseband resource pool was proposed in this paper. Firstly, through OTN device, intelligent switching function is introduced to increase optical crossover capability to reduce the long distance transmission delay. On this basis, the baseband resource pool technology was used to construct large-scale optical cross network, and then realized the dynamic sharing and allocation of baseband processing resources. Experimental results show that the proposed scheme can provide deterministic low time delay, and the clock synchronization accuracy can reach less than 50PPB.

Performance Investigation on a Clock Distribution and Synchronization Scheme Over DWDM Optical Links

For most large-scale physics experiments, it is desirable that the clock distribution and data transmission are unified on a single optical network. To meet the requirement of current large-scale physics experiments for clock synchronization accuracy in the range of tens of picoseconds, and adapt to the increasingly widespread use of dense wavelength division multiplexing (DWDM) optics, this paper investigates the performance of clock distribution and synchronization scheme based on DWDM optics and high-speed serializer-deserializer (SerDes) transceivers embedded in field programmable gate arrays (FPGAs). By extending our previously proposed simplified calibration procedure based on the White Rabbit protocol to the present asymmetric link, all possible errors, especially the new factors brought about by the asymmetric link, are investigated so that the time uncertainty on the link can be minimized. Using the built test system to carry out multiple Reset and long-term operation tests, the measured clock synchronization accuracy over a 5km optical fiber connection is better than 20ps, and the RMS jitter of the recovered clock is less than 10ps. The test results show that the combination of White Rabbit with DWDM optics can have both high-bandwidth data transmission and high-performance clock synchronization at the same time.

Highly Accurate Clock Synchronization With Drift Correction for the Controller Area Network

Modern vehicles, that have to be considered as safety-critical cyber-physical systems, require highly accurate <i>clock synchronization</i> (CS) among their distributed computing devices. Since Controller Area Network (CAN) is the predominant in-vehicle communication bus, it is highly relevant to support CS for CAN. This article proposes an original CS method for distributed in-vehicle networks based on CAN with both <i>offset</i> and <i>drift correction</i> . While offset correction is performed based on timestamps in periodic reference messages (RMs), our new method benefits from the re-synchronization mechanism of the CAN bit timing to apply highly accurate drift correction. Our algorithm does not make any modifications to the CAN protocol but requires the measurement of the phase error from the CAN controller. We derive analytical bounds for the expected clock differences and further validate the practicability of the proposed method by comprehensive experiments. As the main result, our method achieves a clock accuracy below <inline-formula><tex-math notation="LaTeX">$2\;\mu$</tex-math></inline-formula> s independent of important parameters such as the bit rate, RM period, bus utilization and time-varying clock drifts.

Research on Global Clock Synchronization Mechanism in Software‐Defined Control Architecture

Adopt software-definition technology to decouple the functional components of the industrial control system (ICS) in a service-oriented and distributed form is an important way for the industrial Internet of things to integrate information technology, communication technology, and operation technology. Therefore, this paper presents the concept of software-defined control architecture and describes the time consistency requirements under the paradigm shift of ICS architecture. By analyzing the physical clock and virtual clock mechanism models, the global clock synchronization space is logically divided into the physical and virtual clock synchronization domains, and a formal description of the global clock synchronization space is proposed. According to the fundamental analysis of the clock state model, the physical clock linear filtering synchronization model is derived, and a distributed observation fusion filtering model is constructed by considering the two observation modes of the virtual clock to realize the time synchronization of the global clock space by way of timestamp layer-by-layer transfer and fusion estimation. Finally, the simulation results show that the proposed model can significantly improve the accuracy and stability of clock synchronization.

Continuous-Variable Quantum Key Distribution Without Synchronized Clocks

It is well known that accurate clock synchronization is the backbone of quantum information processing tasks. Continuous-variable quantum key distribution (CV QKD), when proposed, benefited from its natural synchronization signals, i.e., local oscillator (LO), which provides a precise and automatic clock synchronization without a special clock board. The application of LO, however, incurs security loopholes, exposing the system to the risk of being attacked. We resolve this unsafe synchronization by proposing a virtual clock synchronization method for the CV QKD protocol without sending a real LO. The proposed method, which is based on the interpolation algorithm, extracts the clock information from the measured quadrature of the quantum signal rather than the classical LO. By formulating the measured quadrature as the synchronization signal, Bob recovers the clock information without both security loopholes and a specific clock board. Numerical results test the robustness of our method and show its potential in a real CV QKD implementation.

Clock Synchronization for Wireless Time-Sensitive Networking: A March From Microsecond to Nanosecond

Industrial control systems in the era of Industry 4.0 present significant challenges from a communication perspective, that is, low latency, ultrahigh reliability, and accurate synchronization. Time-sensitive networking (TSN) has emerged as the main solver of these challenges. As a research trend, TSN and wireless technologies are expected to converge in the wireless TSN paradigm. This convergence starts with the adoption of accurate clock synchronization over wireless systems. In this article, we review the existing wireless clock-synchronization approaches and their attainable performances, and we discuss their feasibility to enable wireless TSN. We conclude that the existing clock-synchronization techniques are enough to enable wireless TSN, although significant implementation efforts are required to incorporate accurate clock synchronization over wireless systems.

Hardware Efficient Clock Synchronization Across Wi-Fi and Ethernet-Based Network Using PTP

Precision time protocol (PTP), a state-of-the-art clock synchronization protocol primarily designed for wired networks, has recently gained attention in the wireless community, due to the increased use of the IEEE 802.11 wireless local area networks (WLAN) in real-time distributed systems. However, all the existing WLAN-based PTP designs either incorporate software timestamping (TS) delivering poor clock synchronization accuracy, or hardware (HW) TS providing better synchronization accuracy at the cost of a significant amount of HW overhead. Moreover, the performance of the existing PTP solutions is mostly evaluated in single-hop wireless networks, while the performance across wired and wireless networks is taken for granted. In this article, a new software-defined-radio-based approach to implement PTP is introduced and validated for the IEEE 802.11 WLAN. Instead of using a dedicated HW clock, the solution utilizes the timing synchronization function clock, an existing clock in the IEEE802.11 standard for synchronization between access point and WLAN stations. The performance of the proposed solution is first investigated within a single-hop WLAN and then across wired–wireless networks. Experimental results unveil that 90% of the absolute clock synchronization error falls within 1.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu \mathrm{s}$</tex-math></inline-formula> .

UNDERWATER ACOUSTIC MODEM WITH HIGH PRECISION RANGING CAPABILITY BASED ON SECOND-LEVEL CESIUM ATOMIC CLOCK

Abstract. Equipped with a high-precision atomic clock can significantly improve the ranging accuracy of the underwater acoustic ranging system. However, the adverse characteristic of underwater acoustic channel (UAC) seriously deteriorates the ranging accuracy. In addition, as a timing device typically commercial cesium atomic clock is only designed to output second-level time reference, which cannot be applied to underwater ranging systems directly. To overcome this limitation, a new underwater acoustic modem with high precision ranging capability based on second-level cesium atomic clock is developed in this paper. The spread spectrum technology is chosen for highly reliable communication and the second-level commercial cesium atomic clock is used to ensure accurate clock synchronization. The proposed modem executes a predetermined ranging scheme based on spread spectrum technology. Specifically, at a certain specified second-level, the transmitter modem sends the ranging signal, and the receiver modem starts timing. Until the receiving modem detects the ranging signal, the propagation time is obtained and the single-item ranging capability is realized. The pool experiment shows the effectiveness of the modem, its ranging accuracy can reach cm level, and the average absolute error of ranging is 8 cm.

Implementation of White Rabbit Time Synchronization System in State Acquisition System of High-energy Physics Experimental Device

Abstract The state acquisition system of high energy physics experimental device has very high requirements for the clock synchronization accuracy of each node. The White Rabbit (WR) distributed synchronous timing technology can realize multi node sub nanosecond clock distribution within several kilometers, and meet the requirements of clock synchronization accuracy of the system. This paper presents an implementation of WR timing system with ZYNQ 7045 as the core in the state acquisition system. This paper introduces the hardware design and implementation scheme of collector node, the implementation scheme of WR node, and the statistical data of WR-PTP time synchronization experiment results. The test results show that this method can realize the time synchronization between the nodes of the state collector, and the accuracy is better than 1 nanosecond. It can provide high-precision time synchronization function for the multi node signal acquisition system of high-energy physics experiment.

An anti-outlier robust clock compensated algorithm for wireless network

Clock synchronization technology plays an important role in wireless networks, and the improvement of clock synchronization precision has always been the goal pursued by research. This paper introduces a clock compensation technology in wireless networks, which solves two main problems influencing clock accuracy in current clock synchronization technology: time-varying clock frequency deviation and interference from outliers. In this paper, the linear regression algorithm with local weighting and least square sum estimation is used to solve the above problems. Simulation results show that the algorithm has higher clock synchronization accuracy than other algorithms, and the clock synchronization error is significantly lower than the non-robust regression algorithm when there are outliers, proving that this method can effectively resist the influence of outliers on clock synchronization accuracy.

Wicsync: A wireless multi-node clock synchronization solution based on optimized UWB two-way clock synchronization protocol

The clock synchronization accuracy directly determines the performance of wireless distributed cooperative systems. However, the mature high accuracy wireless clock synchronization schemes are generally based on GNSS or other auxiliary sources to complete the synchronization process, which cannot be applied to GNSS degraded and denied environments. In this paper, a wireless high-accuracy clock synchronization solution for multi-node distributed cooperative systems – Wicsync – is proposed, which contains an optimized wireless two-way clock synchronization and mutual calibration protocol to support wireless multi-node clock synchronization. Based on the UWB synchronization hardware architecture with local clock phase adjustment we designed, Wicsync implements a non GNSS-aided, high-accuracy, multi-node, low cost wireless clock synchronization performance through the protocol. Experiments shows that the Wicsync can support the instantaneous clock synchronization accuracy of less than 3 ns (@75 m at least) for 10 nodes (more than 100 nodes theoretically).