Synchronization Accuracy Research Articles

Mathematical Morphology-Based Fault Data Self-Synchronization Method for Differential Protection in Distribution Networks

Conventional overcurrent protection is hard to apply to modern distribution networks with high penetration of distributed generations and flexible operation modes. Current differential protection (CDP) is considered to be a good solution, but the expensive cost of data synchronization equipment limits its application. Fault data self-synchronization (FDSS) methods realize the approximate data synchronization according to the features of measured currents at both terminals, which makes it possible to achieve the low-cost CDP. However, the existing FDSS methods still have shortcomings such as low accuracy or complicated steps. In this paper, the principles and defects of existing FDSS methods are first analyzed, and then an improved FDSS method based on mathematical morphology (MM) is proposed. This method is realized by MM filter and MM-based peak-valley detection algorithm, which has higher synchronization accuracy and anti-noise ability. More importantly, in this method, the reference time required for synchronization can be obtained in the pre-communication process, which is easily implemented. The simulation based on PSCAD-MATLAB verifies the effectiveness of the proposed method under different fault conditions and its improvement compared with the existing method. Finally, the RTDS-based hardware test platform is used to verify the differential relay prototypes developed based on the proposed method.

Ethernet-based timing system for accelerator facilities: The IFMIF-DONES case

This article presents the design of a timing system for accelerator facilities, which relies on a general networking approach based on standard Ethernet protocols that keeps all the devices synchronized to a common time reference. The case of the IFMIF-DONES infrastructure is studied in detail, providing a framework for the implementation of the timing system. The network time protocol (NTP) with software timestamping and the precision time protocol (PTP) with hardware timestamping are used to synchronize devices with sub-millisecond and sub-microsecond accuracy requirements, respectively. The design also considers the utilization of IEEE 1588 high accuracy default PTP profile (PTP-HA) to provide sub-nanosecond accuracy for the most demanding components. Three different solutions for the design of the timing system are discussed in detail. The first solution considers the deployment of one time-dedicated network for each synchronization protocol, while the second one proposes the integration of the synchronization data of NTP and PTP into the networks of the facility. The third solution relies on the single distribution of PTP-HA to all the systems. The final design aims to be fully based on standard technologies and to be cost-efficient, seeking for interoperability and scalability, and minimizing the impact on other systems in the facility. An experimental setup has been implemented to evaluate and discuss the suitability of the solutions for the timing system by studying the synchronization accuracy obtained with NTP, PTP and PTP-HA under different network conditions. It includes a timing evaluation platform that tries to resemble the network architecture foreseen in the facility. The measured results revealed that PTP is the most limiting protocol for the second solution. Using the default PTP configuration, it tolerates less than 20% of maximum bandwidth utilization for symmetric bidirectional flows, and around 30% in the case of unidirectional flows (server to client or client to server), with the current setup and using switches without enabled timing support. This case study provides a better understanding of the trade-off between bandwidth utilization, synchronization accuracy and cost in these kinds of facilities.

AUV-Aided joint time synchronization and localization of underwater target with propagation speed uncertainties

The accurate sensor localization is one of the most basic requirements for the Underwater Acoustic Sensor Networks (UASNs) in many applications. However, in harsh underwater environment, the existence of propagation speed variation with depth (i.e., stratification effect) and asynchronous clock generally affects the ranging estimation, and in turn significantly decreases localization accuracy. Taking into account these specific characteristics of UASNs, we first propose an efficient Autonomous Underwater Vehicle (AUV) aided joint localization and time synchronization solution for UASNs, subjected to stratification effect constraint, in which AUV acts as a mobile anchor and broadcasts beacon signals periodically to provide localization reference for unknown target sensors. Next, since the estimation accuracy of localization and synchronization is very sensitive to the accuracy of the AUV locations, the joint localization and synchronization method in the case of inaccurate AVU locations is considered. Then, Cramer Rao Lower Bound (CRLB) analyses are presented for both accurate and inaccurate AVU locations cases. Finally, numerical simulation results show that the proposed method in this paper outperforms the existing ones in terms of estimation errors.

Analysis on BDS-3 Autonomous Navigation Performance Based on the LEO Constellation and Regional Stations

The global navigation satellite system (GNSS) is developing rapidly, and the related market applications and scientific research are increasing. Studies based on large low Earth orbit (LEO) satellite constellations have become research hotspots. The global coverage of the LEO constellation can reduce the dependence of navigation satellites on ground-monitoring stations and improve the precise orbit determination (POD) accuracy of navigation satellites. In this paper, we simulate various LEO satellite constellations (with 12, 30, and 60 satellites), along with ground stations’ observation data, to examine the impact of LEO satellites on the precision of the BeiDou-3 Global Navigation Satellite System (BDS-3) in terms of its POD accuracy. Using the simulated observation data of both LEO satellites and ground-monitoring stations, we analyze the integrated orbit determination for the LEO and BDS-3 satellites. The findings reveal that the 3D orbital accuracy of BDS-3 is 9.51 dm by using only seven ground-monitoring stations, and it is improved to a centimeter level after adding the LEO constellations. As the number of LEO constellation satellites increases, the impact on improving accuracy gradually diminishes. In terms of time synchronization accuracy in the BDS-3, compared to the results of clock offset using only ground stations, the addition of 12 LEO satellites resulted in an improvement of 49% for RMS1(root mean square) and 52% for RMS2 (standard deviation), the addition of 30 LEO satellites resulted in an improvement of 66% for RMS1 and 70% for RMS2, and the addition of 60 LEO satellites resulted in an improvement of 87% for RMS1 and 90% for RMS2. The integrated orbit determination of the LEO and BDS-3 satellites constellation greatly improves the accuracy of time synchronization. In addition, we also use simulated inter-satellite link (ISL) data to perform enhanced BDS-3 satellites POD and time synchronization experiments. The experiments showed that the orbit determination accuracy of the seven sta (seven stations) and ISL scheme is comparable to that of the seven sta and LEO12 scheme, and that the time synchronization accuracy of the seven sta and ISL scheme is slightly worse. The preliminary experiments showed that the LEO satellite could enhance the orbit determination accuracy of BDS-3 and obtain a higher time synchronization accuracy.

BMAR

A requirement of cross-modal signal processing is accurate signal alignment. Though simple on a single device, accurate signal synchronization becomes challenging as soon as multiple devices are involved, such as during activity monitoring, health tracking, or motion capture---particularly outside controlled scenarios where data collection must be standalone, low-power, and support long runtimes. In this paper, we present BMAR, a novel synchronization method that operates purely based on recorded signals and is thus suitable for offline processing. BMAR needs no wireless communication between devices during runtime and does not require any specific user input, action, or behavior. BMAR operates on the data from devices worn by the same person that record barometric pressure and acceleration---inexpensive, low-power, and thus commonly included sensors in today's wearable devices. In its first stage, BMAR verifies that two recordings were acquired simultaneously and pre-aligns all data traces. In a second stage, BMAR refines the alignment using acceleration measurements while accounting for clock skew between devices. In our evaluation, three to five body-worn devices recorded signals from the wearer for up to ten hours during a series of activities. BMAR synchronized all signal recordings with a median error of 33.4 ms and reliably rejected non-overlapping signal traces. The worst-case activity was sleeping, where BMAR's second stage could not exploit motion for refinement and, thus, aligned traces with a median error of 3.06 s.

Low-power time synchronization algorithm for wireless sensor networks

Time synchronization technology is very significant for wireless sensor networks. A typical time synchronization algorithm is applied to the multi-hop topology network, which has the problems of poor time synchronization accuracy, slow convergence speed, and high power consumption. In this paper, a low-power time synchronization algorithm (LPTSA) is proposed. It is based on clustering in a multi-hop environment and adopts a node hierarchy strategy to reduce the synchronous communication overhead. The synchronization error compensation mechanism is adopted to reduce the impact of algorithm synchronization errors. The clustering algorithm divides the whole network into a primary network and a secondary network. By using different time synchronization algorithms in the primary and secondary networks respectively, unnecessary message overhead is reduced. Simulation shows that the algorithm effectively reduces energy consumption and improves synchronization accuracy.

Toward Low-Latency and Accurate State Synchronization for Programmable Networks

Programmable switches empower stateful packet processing, in which incoming packets continuously update states in the data plane, while applications in the control plane read and write states. However, since the data plane and control plane are separated, a consistent view of states in both planes is required for stateful packet processing. Existing approaches suffer from either high latency or low accuracy. In this paper, we propose, a framework that offers approximate state synchronization with low latency and high accuracy. To achieve low latency, directly transfers states between switch ASICs and the control plane by bypassing switch operating systems. To achieve high accuracy, utilizes the resources in the switch ASIC to realize rate control in state synchronization, such that it avoids potential state loss. It also bounds the divergence between the states in the data plane and that in the control plane under limited link capacity. We prototype on Barefoot Tofino switches. The experimental results indicate that compared to existing approaches, achieves order-of-magnitude latency reduction while maintaining high accuracy of state synchronization. Also, our experiments demonstrate that provides significant latency benefits to existing network management applications and well preserves high application-level accuracy.

Study of Methods and Techniques for Manipulating the Time Synchronization Component of NTP Servers in Computer Networks

Abstract In computer networks as well as in many other domains, time synchronization is carried out by some dedicated devices called time servers that uses network protocols, such as NTP (Network Time Protocol), PTP (Precision Time Protocol) or SNTP (Simple Network Time Protocol). Many domains and applications, such as, computer networks, security protocols, telecommunications, network services, and many others, depend on accurate time synchronization. According to the CVE (Common Vulnerabilities and Exposures) databases, between 2001-2022, more than 150 time synchronization protocols vulnerabilities have been reported. One of the most dangerous threats is the manipulation of the time synchronization information. Thus, the existence of such a vulnerability can generate serious security problems. Considering these aspects, in this article we aim to use some methods and techniques for the manipulation of the time component and use them to test some synchronization systems. This will require real-life scenarios of the use of time synchronization systems in which some methods and techniques are applied to exploit their vulnerabilities. Following these scenarios, we will be able to assess the risk to which these systems are exposed.

Accurate time synchronization of power reference station based on BD3 system

A Beidou 3 (BD3) system-based power reference station can provide high-precision time synchronization for power distribution systems by sending synchronization data packets to devices in a multi-hop routing fashion. However, optimizing route selection to reduce both time synchronization error and delay is a challenging problem. In this paper, we establish a software-defined network-enabled power reference station time synchronization framework based on BD3. Then, we formulate the joint problem to minimize cumulative synchronization error and delay through multi-hop route selection optimization. A back propagation (BP) neural network-improved intelligent time synchronization route selection algorithm named BP-RS is proposed to learn the optimal route selection, which uses a BP neural network to dynamically adjust the exploration factor to achieve rapid convergence. Simulation results show the superior performance of BP-RS in synchronization delay, synchronization error, and adaptability with changing routing topologies.

Implementation on SDR platform of algorithms for noncoherent reception of optimal signals built on the basis of eigenfunctions

Formulation of the problem. When transmitting data at speeds above the Nyquist barrier, the algorithmic and computational complexity of radio modems increases significantly, especially with incoherent signal reception. Non-coherent reception algorithms can be implemented on a software-defined radio platform, on which optimal signals are formed and received. The ability to programmatically change the radio frequency parameters of signals without making structural changes to the transmit-receive path can significantly reduce the computing resources of radio modems. The goal is to determine the possibility of practical implementation on the SDR platform (Software Defined Radio) of noncoherent processing algorithms with decision feedback with the choice of optimal values of the observation interval for symbol rates R>1/T using optimal signals built on the basis of eigenfunctions. Results. The possibility of using differential modulation of optimal signals, the forms of which are obtained as a result of solving an optimization problem in accordance with the criterion of the maximum decay rate of the spectrum level outside the occupied frequency band, is shown for packet data transmission protocols and the use of an incoherent processing algorithm in channels with additive Gaussian noise. It is shown that when using algorithms of incoherent element-by-element processing with optimization of the observation interval, it is possible to ensure stable reception of binary optimal signals up to transmission rates exceeding the Nyquist barrier by 1.66 times and for an error probability of 10–3, the energy loss is about 18 dB relative to potential noise immunity. The digital modem of optimal spectrally efficient signals, built on the basis of the SDR platform, makes it possible to conduct spectral and energy efficiency studies in real time in the presence of additive channel noise, and the influence of clock synchronization inaccuracies during packet messaging leads to energy losses of no more than 1 dB. Practical significance. The use of differential modulation of optimal signals can be used in digital television and radio broadcasting systems in the European digital television standards DVB-S2 (Digital Video Broadcasting Satellite Second Generation), DVB-T2 (Digital Video Broadcasting Terrestrial Second Generation).

A High Precision Joint Time Synchronization and Location Algorithm for Moving Target

Time synchronization is the guarantee of normal operation of wireless sensor networks, and it is the premise of ranging and location. At present, most researches focus on joint time synchronization and location of non-moving targets, while there are few types of research on joint time synchronization and location of moving targets. Therefore in this paper, under the condition that the time synchronization of the moving target is not carried out, and the information measurement means such as the speed and position of the moving target are not available. We established the system model of joint time synchronization and location with the help of the anchor nodes whose clock has been synchronized and location is known, and derived the Cramer-Rao lower bound (CRLB) of the system. Then we proposed the two-step least square method and iterative method. The former has lower computation and suboptimal performance, while the latter has higher time synchronization accuracy and positioning accuracy, which can attain CRLB. The results are verified by simulation.

Enabling Time-Synchronized Hybrid Networks With Low-Cost IoT Modules

Precisely synchronized communication is a major precondition for many industrial applications. At the same time, hardware cost and power consumption need to be kept as low as possible in the Internet-of-Things (IoT) paradigm. While many wired solutions on the market achieve these requirements, wireless alternatives are an interesting field for research and development. This paper presents a novel IEEE802.11n/ac wireless solution, exhibiting several advantages over state-of-the-art competitors. It is based on a market-available wireless System on a Chip with modified low-level communication firmware combined with a low-cost field-programmable gate array. By achieving sub-microsecond synchronization accuracy, our solution outperforms the precision of low-cost products by almost four orders of magnitude. Based on inexpensive hardware, the presented wireless module is up to 20 times cheaper than Software-Defined-Radio solutions with comparable timing accuracy. Moreover, it consumes three to five times less power. To back up our claims, we report data that we collected with a high sampling rate (2000 samples per second) during an extended measurement campaign of more than 120 hours, which makes our experimental results far more representative than others reported in the literature. Additional support is provided by the size of the testbed we used during the experiments, composed of a hybrid network with nine nodes divided into two independent wireless segments connected by a wired backbone. In conclusion, we believe that our novel Industrial IoT module architecture will have a significant impact on the future technological development of high-precision time-synchronized communication for the cost-sensitive industrial IoT market.

Consensus-Based Time Synchronization Using Bayesian Estimation in Wireless Sensor Networks Under Communication Delays

Time synchronization is crucial for various applications in wireless sensor networks. Consensus-based time synchronization is an essential distributed strategy for its high precision, robustness, and scalability. In practical networks, however, communication delays are not ignorable and make time messages received inaccurate, which is the fundamental limitation for time synchronization. It was pointed out that if a consensus-based time synchronization algorithm does not consider the influence of delays, it may be divergent under the scenario with delays. Making use of the knowledge of statistical signal processing to develop an efficient relative skew estimator is a viable method to restrain communication delays. In this article, we propose a relative skew estimator based on Bayesian estimation theory to counteract the impact of time delays, which improves the estimation accuracy while reducing the memory requirement. By applying the presented estimator to average consensus protocol, precise network-wide synchronization is achieved in the presence of delays. In addition, the proof of convergence of the proposed scheme is given by theoretical analysis. Simulation results demonstrate the effectiveness of the proposed scheme and show that our algorithm outperforms other similar algorithms in terms of synchronization accuracy under random delays.

A Study Regarding the Impact of Navigation Data Manipulation on Unmanned Aerial Vehicle GNSS Sensors

Abstract Nowadays, Unmanned Aerial Vehicle systems have proven to be very useful in a variety of applications, such as monitoring and surveying an area of interest, mapping inaccessible terrain, real-time traffic monitoring, reconnaissance missions, transport of loads, and also for military purposes. The movement and stability in the air of these systems is dependent on the on-board sensors such as GNSS sensors, proximity sensors, accelerometer, gyroscope, light and temperature sensors. GNSS sensors are vital devices capable of processing navigation signals to determine the position, orientation and speed of the UAV system during operation. GNSS sensors are also used in many applications that require navigation data as well as highly accurate synchronization data. Both GNSS systems and the sensors that process their data have been shown to be vulnerable to jamming and spoofing attacks. GNSS sensors are of particular importance and the information provided by them requires protection. Considering these things, this paper aims to carry out a study in which several UAV systems will be exposed to signal samples with manipulated navigation data. This study will help us to assess the impact of exploiting GNSS sensor vulnerabilities and the effects it can have during the operation of UAV systems.

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.

Development Board Implementation and Chip Design of IEEE 1588 Clock Synchronization System Applied to Computer Networking

With the vigorous development of industrial automation and the Internet of things, the transmission of data is more dependent on immediacy, so network devices have higher and higher requirements for time synchronization accuracy. The clock source of common network devices is provided by the transistor oscillator in the server, but the oscillator will change with factors such as aging and temperature, and it cannot be guaranteed that the oscillator in the server will work at the same frequency. Time synchronization can be achieved by technologies such as IRIG-B, NTP, or IEEE 1588 (PTP), but the hardware cost of building IRIG-B is high, and NTP has the lowest cost, but it can only provide time accuracy from milliseconds to microseconds. PTP can provide sub-microsecond or even nanosecond time precision. It is a system of time synchronization mechanisms through Ethernet transmission. In this article, we first propose a time synchronization system using the development board and PDP protocol. On the Xilinx Zynq-7000 SOC platform of Petalinux, we implement the hardware solution of Linux PTP. The hardware time stamp is 20 ns. To improve the accuracy, the congenital frequency error between the oscillators must be considered. Therefore, a PTP auxiliary time stamp with dynamic frequency compensation is proposed and designed into a chip. Experimental results show that at 45 nm (TN40G) it can operate at 370 MHz and achieve 2.7 ns resolution, which can be applied to more demands.

Throughput analysis of frequency-domain contention under realistic conditions for hyperautomation

ABSTRACT Internet of Things (IoT) has widely been deployed in various industrial fields. To achieve hyperautomation in IoT-based applications, it calls for high-efficient wireless transmission technologies to improve the response speed of IoT nodes. Frequency-domain contention (FDC) is a promising contention-based channel access mechanism to meet this requirement. However, the nature of FDC’s multiple-transmission-multiple-reception and the limit of IoT chip’s synchronization accuracy will lead to carrier frequency offset (CFO) and hence frequent transmission collisions and null transmissions. Considering integer and fractional CFO, this paper theoretically analyzes the FDC throughput and verifies the accuracy of our model via extensive simulations.

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.

Intelligent and Low Overhead Network Synchronization for Large-Scale Industrial IoT Systems in the 6G Era

Holistic temporal coherence among distributed industrial infrastructures enabled by accurate network synchronization is essential for achieving tight orchestration of large-scale industrial Internet of Things (IIoT) systems. However, the low efficiency and situation agnosticism of conventional synchronization techniques using an inflexible "observing-andcalibrating" approach for clock offset correction are inevitably hindering the performance of many IIoT applications with increasing scale and heterogeneity. In this article, we provide an in-depth analysis of the challenges associated with conventional synchronization schemes over large-scale IIoT systems and then present three promising research directions for achieving intelligent and low overhead IIoT synchronization. Particularly, we first propose a new modelbased network synchronization scheme that can proactively enable low overhead clock calibration by leveraging the inherent characteristics of heterogeneous clocks to avoid frequent timestamp exchange. We then design an intelligent device clustering mechanism with a specifically designed synchronization strategy for each group of IIoT devices by jointly exploiting their distinctive synchronization requirements and multi-dimensional device attributes. To leverage the unique characteristics of each oscillator, we analyze historical timestamps to reject unreliable timestamps and identify unreliable devices. Finally, we envision an edge-cloud collaborative network synchronization paradigm to implement the proposed schemes and demonstrate their efficacy in large-scale IIoT systems.

Angular Dependent Auto-Oscillations by Spin-Transfer and Spin-Orbit Torques in Three-Terminal Magnetic Tunnel Junctions

Spintronic oscillators are promising candidates for neuromorphic computing due to their true miniaturization, non-linearity and synchronization properties. However, spin torque nano-oscillators are excited by current-induced spin-transfer torque which may cause high power consumption and reliability problems. Spin Hall nano-oscillators can realize higher energy efficiency, while their relatively low power emission limits their further applications. Here, we demonstrate three-terminal magnetic tunnel junction based spin torque nano-oscillators excited by the combination of spin-transfer and spin-orbit torques under different angle configurations. Thanks to the large spin Hall angle (-0.278) of W, the ratio between threshold current density of spin-transfer and spin-orbit torques for auto-oscillations can reach 0.6, indicating their high energy efficiency. Furthermore, we observe that the ratio has a sine function dependence on the angle between the spin-polarization directions of spin-transfer and spin-orbit torques. Our work could benefit the development of high-efficiency spintronic oscillators and their large network designs.