Time Synchronization Method Research Articles

High-precision time synchronization of kinematic navigation system using GNSS RTK differential carrier phase time transfer

Time synchronization is a fundamental requirement of radio navigation systems, and it is essential for real-time high-precision positioning in emergency applications such as fire scenes and military operations. For urgent positioning requirements without effective positioning means, a radio kinematic navigation system, which can be quickly deployed, is designed based on the Global Navigation Satellite System (GNSS) space–time reference. Firstly, aiming at the time difference between system stations, a Real Time Kinematic-Differential Carrier Phase Time Transfer (RTK-DCPTT) method based on Global Positioning System (GPS) common view principle is proposed. This method can solve the interstation time difference in real time with high precision by using sequential least squares recursion technique. Secondly, interstation time synchronization method based on RTK-DCPTT is proposed by using Pulse Per Second (PPS) signal trigger and clock correction. Thirdly, PPS signal stability and availability are evaluated. Fourthly, clock difference consistency between PPS signal acquisition and RTK-DCPTT approach is analyzed. Finally, a signal synchronization measurement system of kinematic navigation system is designed and time synchronization performance is evaluated. Experimental results demonstrate the feasibility of real-time high-precision signal synchronization method based on RTK-DCPTT technique for kinematic navigation system.

Precision and Characteristics Analysis of Precise Satellite Clock Bias Data of BDS

High-precision satellite clock bias (SCB) data is a critical product for satellite navigation systems to realize accurate navigation, positioning and timing. Unlike other satellite navigation systems, the precise SCB data for the BeiDou Navigation Satellite System (BDS) are mainly determined by two methods, the Two-Way Time Transfer (TWTT) method and the Orbit Determination and Time Synchronization (ODTS) method. Awareness of the data variations obtained from different methods can be used to improve clock modeling performance, and be beneficial to higher-rate GNSS positioning and for predictions in real-time applications. We describe a comprehensive method to analyze the systematic and random characteristics of BDS SCB data obtained from TWTT and ODTS and discuss possible causes of observed variations. Some new conclusions are drawn: the data continuity of TWTT is highly related to satellite orbit types; affected by orbit error and other factors, the fitting residuals (RMS) of ODTS is 0.2 ns worse than that of TWTT on average, while the fitting precision of TWTT is 0.49 ns. There are up to 8ns periodic fluctuations in the mutual agreement between TWTT and ODTS data. The stability result shows a remarkable effect of flicker phase modulation (FLPM) noise can be seen in the period of 300-1000 s in TWTT data. All the BDS satellites display more complex, nonpower law behavior due to the effects of periodic clock variations.

Research on Green Habitat Design Based on Field Wireless Sensing Hazardous Substance Detection

Field wireless sensor network is the current global engineering field research hotspot for structural health monitoring wireless sensor network that is one of the important branches to real‐time monitoring of the safety status of the upper wood engineering structure to avoid the occurrence of many safety accidents caused by major structural and equipment damage and to guide the maintenance of major structures; the establishment of a wireless sensor network system is one of the current research priorities. This paper researches and designs a wireless sensor network system level scheme for structural health monitoring that is divided into two parts based on the hardware platform design and software development based on the system that focuses on the time synchronization protocol and synchronous acquisition method featuring synchronous acquisition start time scheme, time separation method, and flexible optimization model of time information. The method applies to high‐frequency acquisition to guarantee the time of sampling points in structural environmental measurement. The accuracy of the information and the reliability of the field diagnosis, for the detection of harmful substances, as well as leading to the construction of green habitat environment have a qualitative leap, for the design of green habitat environment that has enough progress.

Development of Self-Synchronized Drones’ Network Using Cluster-Based Swarm Intelligence Approach

Timing synchronization has a vital role in swarm drones' network (SDN) or a swarm of unmanned aerial vehicle (UAV) network. Current timing synchronization methods focus on enhancing single-hop skews which remarkably improve timing synchronization precision at this level. The improper clock of the drone system can cause interference, affect spectrum precision and interrupt the operation of the transceiver. In the drones' network, master drones' (MD) neighbor drone's timing synchronization approaches like Reference Broadcast System (RBS) realize a good performance. However, the requirement of one super drone with a large number of broadcasts for RBS makes it unrealistic to use in some situations like SDN network situation. Appropriate study and adjustments are needed to have real timing synchronization by eliminating the clocks drift and enhancing the timing synchronization precision. Therefore, a new self-timing synchronization approach is proposed in this paper where several MD drones can autonomously generate swarm clusters. The cluster head (CH) instigates a timing synchronization procedure starting with intra-Swarm cluster timing synchronization. The intermediate drones (ID) are elected between two swarm clusters to synchronize all drones in line with the inter-swarm cluster timing synchronization approach. The proposed approach is distributed and flexible to achieve high timing synchronization precision. The paper proposes a novel self-timing synchronization approach for in large scale semi-flat SND network architecture. Self-timing synchronization is swarm cluster-based and applicable for a huge number of master drones in SDN. One is the intra-Swarm cluster where the timing synchronization procedure starts with the CH to synchronize all CM. Secondly, in the inter-swarm cluster timing synchronization, two clusters are synchronized via intermediate drone (ID). However, the simulations demonstrated that in many cases all CHs are synchronized by the synchronized CHs from intra-swarm cluster timing synchronizations; this increased the system throughput and synchronization delay to about 75% compared to what we planned to achieve. Moreover, the simulation results also proved that the achieved synchronization precision can be used for position estimation and prediction with high accuracy.

Efficient Geometrical Clock Synchronization for Pairwise Sensor Systems

Numerous time synchronization methods have been proposed during the last decades targeted at devices transmitting in general-topology networks, e.g. wireless sensor networks. Interestingly enough, there are still sensorics applications that, from the data flow point of view, just consist of pairs of devices —typically, being one of them a central controller shared among all pairs—; this is common in embedded systems, mobile robots, factory cells, domotic installations, etc. In these cases, time synchronization takes the form of the estimation of the relative drifts and offsets of these pairs of clocks, thus the quality, guarantees and computational cost of the methods become crucial. Under that specific perspective, it is still possible to propose novel approaches that are computationally efficient while providing guarantees on the resulting estimates for the relative clocks relation. In particular, solving the synchronization problem through a geometrical interpretation is specially suitable, since it provides both efficiency and sound estimates with hard bounds. In this article we analyze a direct geometrical approach for pairwise systems that, through a more direct formulation of the common geometrical setting, improves efficiency and adapts better to diverse stochastic transmissions, while providing good estimates. We demonstrate its advantages with a real low-cost, embedded test bed that can be appropriately instrumented for measuring times, comparing its performance against previous synchronization approaches suitable for pairwise systems.

WUR-TS: Semi-Passive Wake-Up Radio Receiver Based Time Synchronization Method for Energy Harvesting Wireless Networks

WUR-TS: Semi-Passive Wake-Up Radio Receiver Based Time Synchronization Method for Energy Harvesting Wireless Networks

Research on Evaluation Method of Time Transfer Performance Between Ground Stations in Two-Way Satellite Comparison Network

High-precision time synchronization between ground stations is essential for the precise measurement and determination of satellite orbits. Among the numerous time synchronization methods available, two-way satellite time and frequency transfer (TWSTFT) technology is widely used because of the approximate symmetry of its signal transmission path, such that most of the error terms can be offset to obtain subnanosecond time transmission accuracy. A C-band two-way satellite comparison network has been constructed at National Time Service Center (NTSC), Chinese Academy of Sciences for orbit determination and to compare the times between ground stations. The gradual increase in the number of ground stations has created a problem in need of urgent resolution: the facile and rapid evaluation of the time transfer performance between ground stations by a two-way satellite comparison network without the use of additional equipment. We solve this problem by applying the TWSTFT triangle closure method and the precise point positioning time transfer method to the NTSC two-way satellite comparison network and conduct joint observations between terrestrial stations to evaluate the network time transfer performance. We select the Xi'an, Kashi and Sanya stations of the NTSC two-way satellite comparison network to carry out verification tests. The results show that the NTSC two-way satellite comparison network can achieve subnanosecond time synchronization accuracy. The accuracy of time synchronization between stations can be checked conveniently and quickly without the use of additional equipment. This study presents the most recent developments for the NTSC two-way satellite comparison network and serves as a reference for evaluating the time transfer performance of similar networks.

Sub‐10‐fs Timing for Ultrafast Electron Diffraction with THz‐Driven Streak Camera

AbstractUltrafast electron diffraction (UED) has evolved to be a powerful tool for the study of structural dynamics with subpicosecond temporal resolution and subatomic spatial resolution. Recently, there have been intense research efforts toward femtosecond timing jitter and stability for improving the temporal resolution of UEDs, however, so far there has been no work showing long‐term (e.g., >1 h) stable timing for MeV‐level UED systems. In this article, a comprehensive timing synchronization method, based on optical‐radiofrequency synchronization and THz streaking, is demonstrated to maintain sub‐10‐fs long‐term timing stability for radiofrequency‐gun‐based MeV‐level UED, which results in 5.5 fs root‐mean‐square timing drift maintained over 4600 s. With high electron energy and low timing drift, the demonstrated capability is an important step toward studying ultrafast phenomena in samples with low scattering power, such as volatile gases and 2D materials.

Achieving Millimetre Wave Seeker Performance Evaluation Based on the Real-Time Kinematic

The millimetre wave (MMW) seeker can realize target detection under all weather conditions, the performance of which directly determines the design of the control algorithms. To guarantee the hitting accuracy and damaging effect of the expensive MMW guidance missile, assessing the performance of the seeker is indispensable before the launching of the missile. Real tactical environment of the seeker cannot be simulated comprehensively by indoor laboratories, and high-precision evaluation method outdoor is desperately needed. Focusing on the problem, a method for outdoor MMW seeker performance evaluation is proposed via the real-time kinematic (RTK) technology in this paper, which has the advantages of high-precision orientation and working ability under all climates. Firstly, the geometry of the seeker performance evaluation system is constructed, guaranteeing the effective working of the RTK. And then, the key parameters associated with the guidance control are calculated on the basis of the global position system (GPS) measurements. Finally, comparisons are made between the parameters obtained based on the RTK and the seeker outputs. Besides, for the performance assessment of the MMW seeker towards moving targets, a time synchronization method for different GPS carrier platforms is presented. The effectiveness of the proposed method is validated by the mooring test-fly experiments. Experimental results demonstrate that the performance of the MMW seeker can be evaluated effectively by using the proposed RTK-based method.

Cooperative time synchronization via laser/radio inter-satellite links in navigation constellations

Time synchronization is vital in positioning, navigation, and time services in satellite navigation systems. Under the autonomous operation mode, time synchronization of the entire constellation is realized via inter-satellite links to support normal navigation and positioning services. Compared with radio inter-satellite links, continuous laser links are able to provide clock deviation measurements with the same time tag and higher accuracy. In this paper, cooperative time synchronization via laser/radio inter-satellite links is proposed. First, a time comparison network based on the continuous laser inter-satellite link is established, and an inter-satellite time reference is generated using the weighted average algorithm. Then, through radio inter-satellite links, clocks of satellites outside the laser inter-satellite link network are traced to the time reference by using the distributed Kalman filter algorithm, thereby realizing time synchronization of the entire constellation. Finally, a simulation based on the new generation of BeiDou constellation is performed. Results show that the stability in the short and medium terms of the time reference generated via the cooperative time synchronization method is significantly improved compared with that generated via radio inter-satellite links. The standard deviation of the time synchronization error in the constellation is better than 0.05 ns.

High-precision dual-wavelength time transfer via1085-km telecommunication fiber link

To reduce the influence of fiber dispersion on accuracy of fiber-based time synchronization, a method of dispersion-error corrected dual-wavelength time synchronization is proposed in this paper. Specificlly, the method is to measure the dispersion coefficient of the fiber link, and then input it to each remote terminal, the time delay error caused by the fiber dispersion is eliminated through the delay phase controller. With the self-developed engineering prototypes, the experimental verifications are subsequently made both in laboratory and real field. Before the test, 16 devices of time synchronization are connected in series for calibration. The time synchronization system is able to keep delay difference within ± 15 ps after being calibrated. In the laboratory, the experimental setup is built by cascading 16 rolls of 50km-long fiber coils, and the total length of the fiber link is 800 km. The experimental results show that the dispersion coefficient of 800 km fiber link is 13.36 ps/(km·nm), and the delay error caused by dispersion is maintained within 10 ps after correction. The stability of the time transfer is 5.7 ps in standard deviation and the time deviation is 1.12 ps at an averaging time of 100000 s. In the real field test, a 1085-km-long field fiber link is utilized, along which 16 self-developed time-frequency transceiversare set at the cascaded fiber-optic stations. After being corrected with a dispersion coefficient of 16.67 ps/(km·nm) for 1085 km urban fiber link, the time transfer is demonstrated to have a dispersion-caused delay error of 60 ps. The experimental results show that the time standard deviation is 18 ps and the time transfer instability is 9.2 ps at an averaging time of 1 s and 5.4 ps at an averaging time of 40000 s. Finally, the time uncertainty of 800-km-long laboratory optical fiber link and 1085-km-long urban optical fiber link are evaluated, and the time uncertainty is 18.4 ps and 63.5 ps, respectively. This work paves the way for constructing the time synchronization fiber network in China. To further reduce the delay error caused by dispersion in a long-distance time transfer link, the more accurate thermal control of the lasers should be adopted to reduce the shifts of forward and backward wavelengths.

A Study of Time Synchronization Methods for IoT Network Nodes

Many devices are connected on the internet to give functionalities for interconnected services. In 2020', The number of devices connected to the internet will be reached 5.8 billion. Moreover, many connected service provider such as Google and Amazon, suggests edge computing and mesh networks to cope with this situation which the many devices completely connected on their networks. This paper introduces the current state of the introduction of the wireless mesh network and edge cloud in order to efficiently manage a large number of nodes in the exploding Internet of Things (IoT) network and introduces the existing Network Time Protocol (NTP). On the basis of this, we propose a relatively accurate time synchronization method, especially in heterogeneous mesh networks. Using this NTP, multiple time coordinators can be placed in a mesh network to find the delay error using the average delay time and the delay time of the time coordinator. Therefore, accurate time can be synchronized when implementing IoT, remote metering, and real-time media streaming using IoT mesh network.

Overview of Time Synchronization for IoT Deployments: Clock Discipline Algorithms and Protocols.

Internet of Things (IoT) is expected to change the everyday life of its users by enabling data exchanges among pervasive things through the Internet. Such a broad aim, however, puts prohibitive constraints on applications demanding time-synchronized operation for the chronological ordering of information or synchronous execution of some tasks, since in general the networks are formed by entities of widely varying resources. On one hand, the existing contemporary solutions for time synchronization, such as Network Time Protocol, do not easily tailor to resource-constrained devices, and on the other, the available solutions for constrained systems do not extend well to heterogeneous deployments. In this article, the time synchronization problems for IoT deployments for applications requiring a coherent notion of time are studied. Detailed derivations of the clock model and various clock relation models are provided. The clock synchronization methods are also presented for different models, and their expected performance are derived and illustrated. A survey of time synchronization protocols is provided to aid the IoT practitioners to select appropriate components for a deployment. The clock discipline algorithms are presented in a tutorial format, while the time synchronization methods are summarized as a survey. Therefore, this paper is a holistic overview of the available time synchronization methods for IoT deployments.

Time Synchronization Between EtherCAT Network and External Processor

We employ an external processor to distribute the master computing load in the EtherCAT networked control system and develop a method for time synchronization between the Linux on the external processor and EtherCAT network. The synchronization between the Linux on the external processor and EtherCAT master is performed by using general-purpose input/output and shared memory, and the synchronization accuracy is significantly improved by compensating for the system time setting latency and general-purpose input detection latency in the EtherCAT master. The developed method is implemented as part of the master application without modifying the EtherCAT protocol or requiring an excessive computational load. By performing extensive experiments and analyzing the results, we demonstrate that the developed method achieves the synchronization error means less than 1 μs with standard deviations less than 5 μs between the external processor and EtherCAT network. This synchronization accuracy can be acceptable for various networked control applications based on Linux.

Vibration analysis of planet gear bore-rim failure using enhanced planet time synchronous averaging

It is a worldwide challenge to detect planet gear bore-rim cracking using vibration data analytics, especially for large helicopters like the Airbus Super Puma that has experienced two fatal accidents since 2009 due to planet gear bore-rim cracking. For helicopter safety, it is of vital importance to equip helicopter vibration health monitoring systems with the capability of detecting and monitoring the progression of planet gear bore-rim cracking. When a crack reaches sufficient size in the rim of the gear, the weakening stiffness caused by the crack allows the planet gear teeth near the crack to distort as they come into and out of mesh, resulting in vibration impacts. A key challenge for detecting a planet gear bore-rim crack lies in isolating these impacts from the dominating gear mesh harmonics. In this paper, we propose a method of vibration data analytics based on enhanced planet gear time synchronous averaging (EP-TSA). The method takes advantage of visualizing the impacts from planet-ring and planet-sun gear meshes over the planet-ring hunting tooth period of the planetary gear system. We firstly process the raw vibration signal using time-synchronous averaging with respect to the relative rotation of the planet gear over a number of hunting tooth periods. The method employs a novel resampling scheme, termed boosted synchronous resampling scheme (BSRS), which facilitates simultaneous removal of multiple shaft and gear mesh harmonics and their intermodulation components using the spectrum of the averaged signal in order to derive a residual signal. By construction, the BSRS facilitates three-dimensional (3-D) plotting of the squared envelope of the residual signal, comprising multiple individual revolutions of the planet gear over the hunting tooth period. With crack-induced impacts visualized in 3-D, we can identify those planet gear revolutions where the crack-induced impacts are in close proximity to the vibration transducer to obtain a final feature signal reflecting the characteristics of the bore-rim cracking. We call the final feature signal the enhanced planet residual signals (EPRS), which is those individual residual signals at the selected planet gear revolutions with the largest kurtoses above a certain threshold. Where possible we should look at multiple planet gear revolutions to reinforce the detection of vibration impacts. Lastly, we confirm the detection of planet gear bore-rim cracking by the consistent pattern of two spikes in each planet revolution that are associated with the planet-ring and planet-sun gear meshes. The method is validated using vibration data generated from a small industrial planetary gearbox with simulated cracks inserted in the bore-rim from one side of a planet gear. The results show that the BSRS can be very effective in removing multiple sets of shaft harmonics and their intermodulation sidebands. We have demonstrated that the visualization tool can provide strong evidence of the crack-induced impacts. In comparison to other methods our results have shown that we can detect the planet gear bore-rim crack more effectively using the enhanced planet time synchronous averaging method.

Efficient Time Synchronization Method With Adaptive Resource Configuration for FBMC Systems

We propose a time synchronization method which is applicable to both offset quadrature amplitude modulation based filter-bank multicarrier (FBMC-OQAM) system and quadrature amplitude modulation based filter-bank multicarrier (FBMC-QAM) system. Based on the relation between the transmitted data symbols and FBMC signal, we design the scattered symbols to make a specific time domain region empty. Then, we insert the preamble in that region so as to transmit it perfectly. The performance of the proposed synchronization method is compared with the conventional time synchronization methods for the FBMC systems in terms of root mean square error (RMSE) of symbol timing offset (STO), bit error ratio (BER) and correctly detected data bit ratio per frame. Since the proposed method can reduce the resource usage for the synchronization, the resources for data transmission can be increased, thereby improving the spectral efficiency of the FBMC systems.

Time synchronization and data transfer method for towed electromagnetic receiver.

Deep marine controlled-source electromagnetic (CSEM) prospecting has attracted extensive interest because it enables high efficiency and high horizontal-resolution prospecting of gas hydrate and oil. However, the elimination of time errors between the transmitter and the receiver and realization of long-distance high-speed real-time data transmission (submarine towed body status information and raw electromagnetic field data stream) are worthwhile challenges that require continuous effort. We developed a novel towed CSEM system using double-vessels that have high time synchronization accuracy and real-time data transmission. The near-seafloor-towed CSEM receiver contains a deck user terminal, master node, slave nodes, tail buoy, and neutrally buoyant towed cable. The deck user terminal generated and transmitted a pulse per second to the master node through a fiber converter and optical fiber. The RS-485 transceiver then turned the pulse signal into a differential signal and transmitted it to each slave node for error-free synchronization. The time information was also transmitted from the deck user terminal to various nodes through ethernet switches, optical fibers, and serial to ethernet converters. The deck user terminal can conveniently communicate with each node cascaded by the ethernet switch through ethernet and fiber optic communication technology. During an offshore experiment involving oil and gas exploration in the South China Sea, the towed CSEM receiver continuously acquired all electromagnetic components and status information, which achieved a preliminary prospecting result. The maximum transfer rate of real-time data can reach 10 Mbps with 300 m distance between each slave node, and the time synchronization error between transmitter and receiver is less than ±3 µs.

Characterization, Statistical Analysis and Method Selection in the Two-Clocks Synchronization Problem for Pairwise Interconnected Sensors.

Time synchronization among sensor devices connected through non-deterministic media is a fundamental requirement for sensor fusion and other distributed tasks that need a common time reference. In many of the time synchronization methods existing in literature, the estimation of the relation between pairs of clocks is a core concept; moreover, in applications that do not have general connectivity among its devices but a simple pairwise topology, such as embedded systems, mobile robots or home automation, two-clock synchronization is actually the basic form of the time estimation problem. In these kinds of applications, especially for critical ones, not only the quality of the estimation of the relation between two clocks is important, but also the bounds the methods provide for the estimated values, and their computational effort (since many are small systems). In this paper, we characterize, with a thorough parameterization, the possible scenarios where two-clock synchronization is to be solved, and then conduct a rigorous statistical study of both scenarios and methods. The study is based on exhaustive simulations run in a super-computer. Our aim is to provide a sound basis to select the best clock synchronization algorithm depending on the application requirements and characteristics, and also to deduce which ones of these characteristics are most relevant, in general, when solving the problem. For our comparisons we have considered several representative methods for clock synchronization according to a novel taxonomy that we also propose in the paper, and in particular, a few geometrical ones that have special desirable characteristics for the two-clock problem. We illustrate the method selection procedure with practical use-cases of sensory systems where two-clock synchronization is essential.

Time Synchronization Method of Distributed System Considering Local Area Network

Time Synchronization Method of Distributed System Considering Local Area Network

A High-Precision Energy-Efficient GPS Time-Sync Method for High-Density Seismic Surveys

Large numbers of seismic channels and high-density energy-efficient acquisition systems are the development trend of seismic instruments and have attracted high R&D interests in recent years. The combination of remote sensing and wireless sensor network technology provides superior observation capabilities for high-density seismic exploration. However, large-scale and multi-node acquisition methods place higher requirements on time synchronization performance. Seismic data with poor time synchronization will cause considerable errors in the interpretation of seismic data and even have no practical significance. Thus, the strict time synchronization performance is the prerequisite and basis for the application of cable-less storage seismograph in high-density seismic array applications. The existing time synchronization methods have high power consumption and poor time synchronization accuracy, which is not suitable for the long-time task. In addition, these methods are affected by the number of nodes and the distance. This paper presents an energy-efficient time-sharing indexed interpolation intercept method for the seismic data synchronization. The time synchronization method uses the high-precision TCXO as the main clock and records GPS time in the SD card at intervals to achieve the high-precision time-stamp for the seismic data. Then the seismic data is intercepted intermittently based on precise time stamps, which achieves the strict seismic data synchronization. Performance analysis shows that the time synchronization accuracy of the proposed method is 0.6 μs and saves 73% energy of the time-sync periods compared to the common GPS timing method. The field measurement results indicate that the time synchronization accuracy is not associated with the working time and the distance between nodes so that the proposed synchronization method is suitable for the high-density seismic survey.