Time Synchronization Scheme Research Articles

Finite-time H∞ synchronization of semi-Markov jump neural networks with two delay components with stochastic sampled-data control

This article investigates the finite-time H∞ synchronization for semi-Markov jump neural networks with two delay components based on stochastic sampled data control. Additionally, the parametric uncertainties are randomly varying which follows the Bernoulli distributed sequences. In the stochastic sampled data control, the sampling interval ′m′ is supposed to be two different values in the time-varying component with given probability conditions. By constructing triple and quadruple integral term in the Lyapunov-Krasovskii functional (LKF) a new integral inequality technique is addressed to derive the main results. Dissimilar from previous literature, involving the new integral inequality, a delay dependent finite-time H∞ synchronization requirements are acquired with regard to linear matrix inequalities (LMIs). In the end, the effectiveness of the considered stochastic sampled data control finite time synchronization scheme is highlighted by numerical examples.

Time transfer over 113 km free space laser communication channel.

The space time frequency transfer plays a crucial role in applications such as space optical clock networks, navigation, satellite ranging, and space quantum communication. Here, we propose a high-precision space time frequency transfer and time synchronization scheme based on a simple intensity modulation/direct detection (IM/DD) laser communication system, which occupies a communication bandwidth of approximately 0.2%. Furthermore, utilizing an optical-frequency comb time frequency transfer system as an out-of-loop reference, experimental verification was conducted on a 113 km horizontal atmospheric link, with a long-term stability approximately 8.3 × 10-16 over a duration of 7800 seconds. Over an 11-hour period, the peak-to-peak wander is approximately 100 ps. Our work establishes the foundation of the time frequency transfer, based on the space laser communication channel, for future ground-to-space and inter-satellite links.

Trajectory Generation Method for Serial Robots in Hybrid Space Operations

The hybrid space of robots is divided into task space and joint space, with task space focused on trajectory-tracking accuracy, while joint space considers dynamic responsiveness and synchronization. Therefore, the robot-motion control systems need to effectively integrate both aspects, ensuring precision in task trajectory while promptly responding to unforeseen environmental events. Hence, this paper proposes an online trajectory-generation method for robots in both joint and task spaces. In task space, a planning approach is presented for high-precision NURBS curves. The global NURBS curve is segmented into several rational Bezier curves, establishing local coordinate systems for control points. This ensures that all local control points meet the chord error constraint, guaranteeing trajectory accuracy. To address the feed rate dynamic planning issue for segmented curves, an improved online S-shape feed-rate scheduling framework is introduced. This framework dynamically adjusts the current execution speed to meet task requirements. In joint space, an offline velocity planning based on a time synchronization scheme and a multi-dimensional synchronization technique based on the principle of spatial-coordinate system projection are proposed. Building upon the offline scheme, it allows for the modification of the target state for any sub-dimension during the motion process, with the remaining dimensions adapting accordingly. Simulation and experimentation demonstrate that the two proposed online trajectory generations for robot motion spaces, while ensuring task trajectory accuracy, effectively handle external unexpected events. They ensure joint synchronization and smoothness, carrying significant practical implications and application value for the stability of robot systems.

Large-aperture Telescope Tracking Control Based on Time-synchronization Strategy

A time-synchronization strategy for packetized transmission of target position about a large-aperture telescope observation control system has been proposed in this study. Compared with the existing telescope tracking strategy, the target position packing and sending strategy based on the time synchronization method proposed in this paper has the advantages of high stability and reliability. First, the telescope tracking observation control method was elaborated in this paper, including the motion pattern during telescope tracking. Then, the strategy for packetizes transmission of target positions based on time-synchronization is established and lists the detailed steps. Finally, the performance of the tracking strategy is verified using the 2.5 m telescope for the simulated uniform speed star and the blind-tracking fixed star HIP 31216, respectively. The test results show that the accuracy root mean square of the tracking strategy proposed in this paper is less than 0.″02 at 30 minutes, and the performance is much better than the design requirement of 0.″3. The most important advantage of this tracking strategy is that the telescope can guarantee normal tracking for a certain period of time even if the hardware or software of the host computer is abnormal.

A Novel Parallel Timing Synchronization Scheme for High-Speed Receivers

A Novel Parallel Timing Synchronization Scheme for High-Speed Receivers

Frequency-Offset Information Aided Self Time Synchronization Scheme for High-Dynamic Multi-UAV Networks

Due to the unique merits of unmanned aerial vehicle (UAV) systems, they have already been harnessed for military, public, and civil applications. Time synchronization is a significant premise of formatting and applying UAV networks. However, the irregular high-speed mobile UAVs pose new challenges to time synchronization, especially when external time references are unavailable in some rigid scenarios. Therefore, in these harsh cases, self-time-synchronization (STS) without any external assistance should be concerned to overcome the relative velocity between UAVs caused by irregular high-speed motion. In this paper, a realistic timestamps model for the multi-UAV networks is established, and then a dynamic topology-based maximum likelihood estimator will be developed to carry out the STS. Furthermore, by introducing the information on frequency offset, a new estimator with the closed-form expression is proposed based on a two-way message exchange framework. After that, a tracking algorithm with the assistance of estimation results will be introduced to compensate for the time-varying change of the clock parameters for the dynamic topology UAV networks. To evaluate the performance of the estimator, both the estimation error and Cramér-Rao lower bound are analyzed. Numerical results show that the proposed algorithm exhibits its superiority in STS performance and computational complexity compared to the existing two-way message exchange algorithm using timestamps only.

Time Synchronization Based on Cross-Technology Communication for IoT Networks

Time synchronization is a fundamental requirement for wireless communication systems to work properly. Most of the existing studies focus on time synchronization among homogeneous devices. This work investigates time synchronization with heterogeneous technologies (e.g., WiFi, ZigBee and Bluetooth) which is important for the rising Internet of Thing (IoT) scenarios where heterogeneous devices coexist. Recent advances in Cross-Technology Communication (CTC) break the wall between heterogeneous wireless devices. In this work, we propose a new time synchronization strategy based on the CTC technique and provide a technique called TimeBee, which takes the advantage of coordination from a WiFi device to assist ZigBee devices for time synchronization. An effective method is employed so that ZigBee nodes are coordinated for time synchronization based on the received timestamps from WiFi devices. The experimental results show that TimeBee achieves global time synchronization with low time errors.

Robust Symbol Timing Synchronization for Initial Access under LEO Satellite Channel.

This paper proposes a robust symbol timing synchronization scheme for return link initial access based on the Digital Video Broadcasting-Return Channel via Satellite 2nd generation (DVB-RCS2) system for the Low Earth Orbit (LEO) satellite channel. In most cases, the feedforward estimator structure is considered for implementing Time Division Multiple Access (TDMA) packet demodulators such as the DVB-RCS2 system. More specifically, the Non-Data-Aided (NDA) approach, without using any kind of preamble, pilot, and postamble symbols, is applicable for fine symbol timing synchronization. However, it hinders the improvement in estimation accuracy, especially when dealing with short packet lengths during the initial access from the User Terminal (UT) to the Gateway (GW). Moreover, when a UT sends a short random access packet for initial access or resource request to the LEO satellite channel, the conventional schemes suffer from a large Doppler error depending on UT's location in a beam and satellite velocity. To ameliorate these problems, we propose a novel symbol timing synchronization algorithm for GW, and its advantage is confirmed through computer simulation.

Real-time estimate and control contour errors for five-axis local smoothed toolpaths based on airthoid splines

Five-axis linear commands are blended as the local smoothed toolpaths by inserting clothoid and airthoid splines at corners in five-axis CNC machining. The contour error is the bottleneck to achieve the precise dimension of the machined parts, when following the local smoothed toolpaths. This paper presents a contour error estimation and control method for the five-axis smoothed toolpaths with airthoid splines, according to the geometric characteristics of the toolpaths. The tool-tip contour error is analytically calculated based on the expression of the smoothed toolpaths. Consequently, the tool-orientation contour error is obtained by synchronizing the tool-orientation contour point with the tool-tip item based on the motion time through the designed time scale coefficient, when the toolpaths are scheduled by the time-synchronization scheme. Furthermore, a contour error compensation strategy is constructed to adaptively determine the compensator gain. It can be qualified to maximally eliminate the contour errors and steadily hold the control stability of the feed drives, in spite of the modeling error between the nominal and actual control models. The simulation and experiment results show that the estimation algorithm has higher accuracy than traditional methods, and the compensation strategy effectively eliminates the five-axis contour error.

Complex Dynamic Analysis, Circuit Design and Simplified Predefined Time Synchronization for a Jerk Absolute Memristor Chaotic System

In this parper, a 4D absolute memristor Jerk chaotic system is proposed. Firstly, complex dynamics are studied by phase diagram, Poincaré section, power spectrum, bifurcation diagram, 0-1 test, and Lyapunov exponent spectrum. Then, the period doubling bifurcation, degradation, and offset boosting are revealed. For the feasibility of practical application, the analog circuit and FPGA digital circuit are designed. Finally, a simplified predefined time synchronization scheme is proposed; comparing with the full control input synchronization scheme, the simplified predefined time synchronization scheme can not only reduce the controller inputs but also predefine the synchronization time.

Novel Control Theoretic Consensus-Based Time Synchronization Algorithm for WSN in Industrial Applications: Convergence Analysis and Performance Characterization

Fourth Industrial Revolution (IR4.0) depends heavily on the Internet of Things (IoT) and wireless sensor networks (WSNs). Through WSN, data in an industrial environment can be captured. Time synchronization is an important issue in WSN to ensure the correct sequence of the data collected. Besides, gauging on a common perceived time reference, local clocks on each node within any interconnected WSN should be able to initiate message exchanges. Referencing to an unsynchronized value of virtual global reference clock will render the nodes’ communication and applications in WSN useless. In this work, a newly improved control theoretic consensus-based time synchronization algorithm for WSN known as time synchronization using sliding-mode control and proportional, integral, and derivative (TSMPID) is proposed. The novel algorithm uses an augmented sliding-mode control (SMC) in the skew and relative skew estimation schemes, which is a useful switching action, to provide a salient feature in guaranteeing finite-time convergence in synchronized virtual time clock estimation. A proportional, integral, and derivative (PID) term has been introduced in the offset estimation to improve the estimation performance. The main purpose is to achieve global clock synchronization with lower computational effort and reduced synchronization error. TSMPID has the characteristics of being totally distributed, asynchronous, scalable across different network topological structures and robust to ad hoc nodes deployment. Ad hoc communication link node deployment scenarios are simulated comprising five, seven, and nine WSN nodes. TSMPID requires low energy and exhibits a much lesser consensus error spike in comparison to other recent prior-art time synchronization schemes.

An Energy-Efficient MAC Protocol for Three-Dimensional Underwater Acoustic Sensor Networks With Time Synchronization and Power Control

In recent years, Underwater Acoustic Sensor Networks (UASNs) have gained considerable attention for their unique role in detecting and monitoring the underwater environment. However, due to the long propagation time, high bit error rate, and limited bandwidth of underwater acoustic systems, the design of media access control (MAC) protocols is extremely complex, especially for the power consumption of UASNs. Therefore, this paper proposes an energy-efficient MAC protocol for three-dimensional UASNs with time synchronization and power control (TDTSPC-MAC). The proposed protocol is a hybrid access scheme for three-dimensional UASN using techniques such as time synchronization, power control, clustering, layering, and sleep mechanisms. Moreover, the TDTSPC-MAC protocol uses the hierarchical concept and distributed clustering algorithm to divide the three-dimensional space, and combines time synchronization and power control strategies to avoid collisions. Besides, energy consumption is reduced through monitoring and sleep mode. Simulation results demonstrate that the proposed TDTSPC-MAC protocol has reasonable data transmission delay time, throughput, energy consumption, and other performance.

Robust End Hopping for Secure Satellite Communication in Moving Target Defense

Satellite communication contributes tremendously to the Industrial Internet of Things (IIoT) with telecommunication efficiency and data accessibility at global-scale coverage. However, realizing proactive defense for satellite communication remains a challenge. In order to address such an issue, we first explore state-of-the-art proactive defense methods and, following next, a step forward on proposing an end hopping scheme based on fixed hopping timeslot and strict time synchronization strategy by utilizing moving target defense (MTD). In addition, we worked on a Proof of Concept (PoC) to evaluate the scheme’s theoretical protection performance for Distributed Denial of Service (DDoS). Experimental evaluation and analysis of the proposed scheme show that it is efficient and secure, as seen when the attack rate is 100 times/s, the response time of the hopping state is 69.98% shorter than that of the normal state, and when the attack rate is 1000 times/s, the response time of the hopping state is 90.15% shorter.

A Timestamp-Free Time Synchronization Scheme Based on Reverse Asymmetric Framework for Practical Resource-Constrained Wireless Sensor Networks

Energy-efficient time synchronizations for wireless sensor networks (WSNs) have been put under the spotlight for years. A promising technique among which is the timestamp-free approach where no timestamps are required to establish the synchronization, thereby sparing the transmissions of the timing messages for conserving significant transmission energy. In this paper, we first investigate the feasibility of adopting timestamp-free time synchronization in practical resource-constrained WSNs; we then identify the issue of inaccuracy in maintaining the pre-defined response interval which affects the foundations of most existing timestamp-free schemes. Based on the investigation and our previously proposed reverse asymmetric time synchronization framework, we further propose an asymmetric timestamp-free time synchronization scheme with two estimation methods tailored for resource-constrained WSNs. We as well introduce the centralized and distributed multi-hop extension methods for the proposed scheme to cover diverse multi-hop scenarios. Experimental results on a real WSN testbed consisting of TelosB motes running TinyOS demonstrate that the proposed scheme achieves high energy efficiency while maintaining microsecond-level time synchronization accuracy compared to three other conventional schemes.

A Distributed Formation Joint Network Navigation and Positioning Algorithm

In view of the problem that the leader-follower joint navigation scheme relies too much on the absolute navigation and positioning accuracy of the leader node, under the conditions of distributed network-centric warfare (NCW) and to meet the location service accuracy, reliability, and synergy efficiency of the future integrated communication, navigation (ICN), we built a joint navigation and positioning system with low Earth orbit (LEO), airborne data link, and inertial navigation system (INS) as the core; designed a ranging and time-synchronization scheme of the joint navigation and positioning system; and established a joint navigation and positioning method for formation and networking based on mutual ranging and velocity measurement information between aircrafts. Finally, based on the designed LEO constellation, the universality, effectiveness, superiority, and potential superiority of algorithm are verified, respectively. The simulation results show that the scheme can meet the requirements of joint location services in challenging environments, and could be used as a reference scheme for future ICN integration.

Configuration strategy and application for distribution network protection based on standalone 5G

The 5G network, with its characteristics of wide coverage, high reliability and low delay communication, has a high application value in solving the “last kilometer” problem in interconnection between the terminal equipment of a distribution network. To improve the practical level of distribution network protection based on standalone 5G, we analyze the requirements of communication resource for distribution network protection firstly. Then, given the overall structure of 5G distribution network protection, a time synchronization scheme with higher reliability is proposed by means of homologous transmission of clock signal and data signal. At the same time, differential protection and regional protection are applied in an urban distribution network. The differences between the two protection methods in overhead lines and cables are analyzed. The results show that overhead lines are recommended for regional protection, and cables can be compatible with differential protection and regional protection.

Improving Multi-Hop Time Synchronization Performance in Wireless Sensor Networks Based on Packet-Relaying Gateways With Per-Hop Delay Compensation

Based on the reverse asymmetric time synchronization framework, we have proposed several schemes with a major focus on the energy efficiency and computational complexity of a large number of battery-powered, low-cost sensor nodes in wireless sensor networks (WSNs). To address the cumulative end-to-end synchronization error, we have also introduced an idea of compensating for the processing delays at packet-relaying gateways as an energy-efficient way of multi-hop extension of WSN time synchronization schemes. In this paper, we present a comprehensive analysis of the multi-hop extension of WSN time synchronization schemes based on packet-relaying gateways with the per-hop delay compensation and the results of extensive experiments for the energy-efficient time synchronization schemes based on the reverse asymmetric time synchronization framework together with the flooding time synchronization protocol as a representative of existing schemes. Experimental results based on a real testbed demonstrate that the multi-hop extension based on packet-relaying gateways with the per-hop delay compensation greatly improves the performance of time synchronization of all the schemes considered compared to the multi-hop extension based on the conventional time-translating gateways.

Distributed event-triggered multi-timer synchronization scheme for secondary control in islanded microgrids

Consensus-based distributed control has been widely applied in the secondary control for microgrids (MGs) with the assumption that the control actions of each distributed generations (DGs) are triggered at the same time as others in the state-of-art literature. However, in the absence of centralized timer synchronization, the asynchrony resulting from the independent timer localized in each DG would inevitably undermine the system performance or even cause instability. This paper proposes a distributed time synchronization strategy to guarantee the update actions of individual DGs to be triggered at the same discrete instants. First, the asynchrony problem in the distributed secondary control due to the essential distributed characteristic is elaborated and the resultant convergence deviation is deduced. Then, the distributed time synchronization strategy based on pinning consensus is described, with the optimal pinning timer selected to achieve superior propagation performance. Further, the event-triggered mechanism is introduced, which reduces the communication burden significantly compared to the time-driven mode and maintains the global clock synchronization efficiently. The selection of event triggering threshold is formulated for the tradeoff between the trigger frequency and convergence accuracy. The effectiveness as well as flexibility of the proposed control strategy is demonstrated by simulations.

Implementation of Embedded Testbeds Using USRP and GNU-Radio for Performance Measurement and Analysis of PPS and PCO-Based Time Synchronizations

In wireless networks, time synchronization is one of the key functions for the MAC and the physical layer because it is important to accurately transmit data by maintaining the order and consistency of transmission between nodes. The time synchronization can be divided into centralized and distributed methods and there are many synchronization schemes. However, there are little testbeds for comparing and analyzing various time synchronization schemes in a real environment. Most papers analyze the proposed time synchronization algorithm by simulation, and some testbeds are also configured for the proposed scheme only. In this paper, the authors build embedded testbeds using USRP and GNU-Radio. The two typical methods of the centralized and decentralized time synchronizations, PPS, and PCO-based schemes, respectively, are implemented on the testbeds and their performances are measured and analyzed in the real environment.

Multiple-Node Time Synchronization Over Hybrid Star and Bus Fiber Network Without Requiring Link Calibration

In this article, a multiple-node fiber-optic time synchronization scheme is proposed over a hybrid star and bus-shaped optical fiber network based on the bidirectional wavelength division multiplexing (BWDM) transmission. Time signals can be obtained at arbitrary access and remote nodes, which are accurately synchronized with the one at the local node by compensating for the transmission delay of corresponding fiber link. By utilizing the optimized wavelengths configuration, in addition to eliminating the impact of single Rayleigh backscattering of the optical fiber, the effect of bidirectional wavelengths asymmetry on the accuracy of time synchronization is also effectively suppressed. Therefore, link calibrations are not required in the proposed scheme. Experimentally, a multiple-node time synchronization system is demonstrated over a hybrid star and bus fiber network with three branches. The results show that the stabilities in terms of time deviation (TDEV) of less than 30 ps at 1 s and 5 ps at 10000 s can be obtained for all of the access and remote nodes, and the clock difference of less than 25 ps can be achieved.