High-precision Synchronization Research Articles

Quantum clock synchronization protocol based on microwave-optical entanglement

The cavity electro-opto-mechanical converter serves as a meticulously designed platform where hybrid entanglement, including microwave-optical entanglement, can be efficiently prepared. Leveraging microwave-optical entanglement, we propose a quantum synchronization protocol in this paper. This protocol utilizes the second-order coherence function of entanglement signals to determine the propagation time interval and time offset between two parties. Our results demonstrate that the entanglement feature is well-preserved throughout the entire process. Despite the transformation from microwave photodetection to convenient optical photodetection, the transmission superiority of microwaves in free-space is preserved. Under experimentally accessible parameter settings, we achieve a high synchronization precision of Δτ=±2.704ps. It is theoretically proven that our quantum synchronization protocol holds promise as a viable candidate for future navigation synchronization systems.

Picometer-Sensitivity Surface Profile Measurement Using Swept-Source Phase Microscopy

In recent years, the Swept-Source Phase Microscope (SS-PM) has gained more attention due to its greater robustness to sample motion and lower signal decay with depth. However, the mechanical wavelength tuning of the swept source creates small variations in the wavenumber sampling of spectra that introduce serious phase noise. We present a software post-processing method to eliminate phase noise in SS-PM. This method does not require high-quality swept light sources or high-precision synchronization devices and achieves ~72 pm displacement sensitivity using a conventional SS-PM system. We compare the performance of this method with traditional software-based methods by measuring phase fluctuations. The phase fluctuations in the traditional software-based method are five times those of the proposed method, which means the proposed method has better sensitivity. Using this method, we reconstructed phase images of air wedges and resolution plates to demonstrate the SS-PM’s potential for high-sensitivity surface profiling measurement. Finally, we discuss the advantages of SS-PM over traditional Spectral-Domain PM techniques.

Advancing Convergence Speed of Distributed Consensus Time Synchronization Algorithms in Unmanned Aerial Vehicle Ad Hoc Networks

Time synchronization is a critical prerequisite for unmanned aerial vehicle ad hoc networks (UANETs) to facilitate navigation and positioning, formation control, and data fusion. However, given the dynamic changes in UANETs, improving the convergence speeds of distributed consensus time synchronization algorithms with only local information poses a major challenge. To address this challenge, this study first establishes a convex model on the basis of graph theory and relevant theories of random matrices to approximate the original problem. Subsequently, three acceleration schemes for consensus algorithms are derived by minimizing the Frobenius norm of the iteration matrix. Additionally, this study provides a new upper bound for constant communication weights and discusses the limitations of existing metrics used to measure the convergence speeds of consensus algorithms. Finally, the proposed schemes are compared with existing ones through simulation. Our results indicate that the three proposed schemes can achieve faster convergence while maintaining high-precision synchronization in scenarios with static or known topological structures of networks. In scenarios where the topological structure of a UANET is time-varying and unknown, the scheme proposed in this paper achieves the fastest convergence speed.

Research on Clock Synchronization of Data Acquisition Based on NoC

Data acquisition based on network-on-chip (NoC) technology is a high-sampling-rate data acquisition scheme using low-sampling-rate analog–digital conversion (ADC) chips. It has the characteristics of multi-task parallel communication, being global asynchronous, local synchronous clock distribution, high throughput, low transmission latency, and strong scalability. High-speed data acquisition is realized through the combination of an on-chip network and time-interleaved data acquisition technology. In the time-interleaved sampling technique, the precision of clock synchronization directly affects the precision of sampling. Based on the proposed NOC data acquisition scheme, an improved White Rabbit clock synchronization protocol is applied to high-speed data acquisition to achieve high-precision synchronization of multi-channel time-interleaved sampling clocks. Firstly, the offset of the master clock and slave clock is determined by the PTP protocol, and the offset is corrected to achieve rough synchronization between the master clock and slave clock. Secondly, a digital dual-mixer time difference (DDMTD) is used to measure the phases of the master and slave clocks. After that, the phase of the slave clock is corrected through the dynamic phase-shift function of the clock’s phase-locked loop (PLL). Finally, according to the simulation results in Modelsim, the average absolute error of a TI-ADC sampling clock can be less than 20 ps.

Trajectory planning and control strategy optimization design of double electric cylinder erecting device

The transition of the rocket from a horizontal to an erect state before its launch on the offshore platform is a crucial stage. Compared with erecting the rocket on the ground, higher servo control and synchronization accuracy are required for erecting it on the offshore platform. Most rocket erecting devices on offshore platforms rely on hydraulic drive systems, posing challenges due to their lower servo control accuracy and difficulties in achieving high-precision synchronization. The erecting process, trajectory planning, control system, and control strategies of rockets driven by a double electric cylinder erecting device are studied, aiming at the requirement of erecting rocket devices on offshore platforms. This paper commences by establishing the kinematic model of erecting the rocket with a double electric cylinder erecting device. It delves into the process and trajectory of the erection rocket with a double electric cylinder erecting device. Subsequently, the focus shifts toward designing the control system, while inclination and angular velocity sensors monitor the erection process. Finally, designing and demonstrating control strategies for a double electric cylinder erecting device, three different control strategies, master control, master-slave control, and cross-coupling control, are analyzed, and the cross-coupling control strategy is selected as the control strategy of the double electric cylinder offshore platform rocket erecting device.

Microwave frequency transfer over 3000-km fiber based on optical frequency combs and active noise cancellation

Time and frequency transfer plays an important role in the fields of navigation and positioning, remote sensing, and fundamental physics. The performance of long-haul frequency transfer is ultimately limited by accumulated phase and amplitude noise in fiber propagation. In this work we overcome these limitations and demonstrate a frequency transfer system over 3000 km of indoor spooled fibers via repetition-frequency-locked frequency combs, which benefit from the extremely high signal-to-noise ratio. With the help of the digital phase discrimination and compensation method and active power stabilization, the dramatic phase and amplitude variations are sufficiently suppressed, respectively, which results in the residual instability 7.5×10−14 at 1 s and 1.0×10−16 at 10 000 s, without optical-electrical-optical recovery by the regeneration system. Our results mark a breakthrough in building large-scale, high-precision synchronization networks. Published by the American Physical Society 2024

An adaptive kernel correlation filter algorithm and synchronization error correction method for 3D motion reconstruction of flexible flapping wings using binocular vision

In order to measure the kinematic parameters and deformation of flapping wings precisely, this paper presents a wing motion reconstruction method utilizing a binocular vision system (BVS) comprising two action cameras. We designed an Adaptive Kernel Correlation Filter algorithm based on target scaling prediction for wing reconstruction to improve target tracking accuracy and robustness. A binocular error correction method with a startup time difference-induced error model was proposed, which helps the action cameras achieve the same high-precision synchronization as the industrial cameras with external trigger mode. Moreover, an infrared motion capture system is applied to assess and compensate for errors in the BVS. The experimental results show that the maximum value of the average errors of the BVS is 1.352 mm, and the minimum similarity value of the two wings is 0.996. The results contribute to the deformation measurement and optimization of soft materials such as the flapping wings.

Design of a high-precision clock distribution and synchronization system

In large-scale nuclear and particle physics experiments, there is a high demand for high precision clock distribution and synchronization. In this paper, the design and testing of a high precision clock distribution and synchronization system for the CSR External Target Experiment (CEE) is presented. To achieve high synchronization precision, a dedicated high-quality clock distribution network is designed, while the timestamp synchronization is achieved over the existing trigger link in CEE with a customized protocol in order to simplify the system structure. Automatic metastability elimination and real-time monitoring of both the timestamps on the front end nodes and the clock electronics status are also implemented. The test results indicate that the period jitter of the clock network is better than 4 ps rms, and all the expected functionalities have been achieved successfully.

5G Physical Layer-Based Procedure to Support Time-Sensitive Networking

Deploying 5G in new and diverse use cases, such as Industry 4.0 and factory automation, requires 5G systems to harmonize with the communication technologies used in these industries. To this end, 3GPP Release 16 and Release 17 have made significant progress in integrating 5G systems with the IEEE 802.1 working group specifications on Time-Sensitive Networking (TSN). This paper explains a method and architecture for supporting TSN over a wireless channel in a 5G network that adds the TSN synchronization function in a Small Cell gNB implementing the TSN Translator function (SC-TT). This TSN-capable small cell provides TSN over the wireless network to synchronize UEs with the Grand Master (GM) using the physical layer signal of the 5G radio frame and the transmission of the GM reference time to provide high-precision synchronization. This paper explores the pivotal role of a Slot Indicator Signal in enhancing synchronization precision, ensuring that the UE-GM synchronization occurs within an exceptionally narrow timeframe as small as 10 ns.

Attosecond delay locking of large arm pump-probe system

With the development of ultrafast science and attosecond laser technology, the pump-probe system based on isolated attosecond laser pulses is a key to attosecond science, which will be used to study electronic dynamics on an attosecond time-scale. To obtain stable and reliable signals, it is necessary to ensure ultra-stable and ultra-accurate synchronization. Any timing jitter can cause signal to disperse or get buryied in noise, making it impossible to obtain the true physical mechanism. Based on the above, the delay between pump laser pulse and probe laser pulse must be controlled with an attosecond time resolution. In this work, a dual-layer system is developed to achieve high-precision synchronization locking. To ensure that both layers have the same time jitter, we design an adapter to secure the elements placed during installation. Timing jitter is obtained by shaking interference fringes through fast Fourier transformation, and can be calculated in several ms. Then error signals are fed back to the PZT stage in order to compensate for real-time optical path drift. Through such a design, a time-delay accuracy of 7.64 as to 15.53 as is realized, which is linearly related to the interferometer arm length ranging from 1 m to 5 m, with an <i>R</i><sup>2</sup> of 0.96. Moreover, the error between the experimental result of arm length of 8 m and 10 m and the result fitted with the above data is less than 3 as. These results show that using a small interferometer can achieve the fast detection of the time-delay accuracy of long-arm attosecond pump-probe detection system in large scientific instrument, which is of great significance in guiding ther applications such as in non-collinear attosecond streaking spectroscopy, time-resolved photoelectron spectroscopy, and coherent synthesis.

External Synchronization of Distributed Redundant Flight Control Computers

<div>This work introduces a practical approach to external synchronization for flight control computers (FCCs) deployed in a decentralized fashion. The internal synchronization among the FCCs in distributed flight control systems needs to be extended for specific applications, necessitating an urgent need for an external synchronization mechanism. For instance, when the air data and attitude reference system (ADAHRS) and the flight control computer (FCC) are not synchronized, a dead time or time offset occurs between the time the ADAHRS transmits data and the time the FCC begins executing its control functions, which can impair flight control system performance or even cause system instability, particularly for the system with incremental control approaches, such as incremental nonlinear dynamic inversion (INDI). Therefore, an external synchronization technique that does not rely on establishing a global view of time that is accurately synchronized with an external reference device has been proposed and implemented for distributed flight control systems. The findings of the implemented system demonstrate that the suggested approach can synchronize the distributed FCCs to an external reference device with high synchronization precision and deal with varying clock drift rates.</div>

Голографическая фотонная система фазовой синхронизации в спутниковом радиоканале

A necessary condition for the qualitative solution of telecommunication, infocommunication and navigation tasks in satellite communication systems is the presence of a high-precision synchronization system in satellite radio channels. It is indicated that the operation of the data exchange synchronization system in satellite radio channels is adversely affected by a number of external factors, such as, for example, the presence of the Doppler effect, errors in determining the relative speeds and directions of movement of artificial Earth satellites (ISS), the presence of a delay time of the transmitted signal due to significant distances between the nodes of the satellite communication network. The main disadvantages of modern synchronization systems used in satellite radio channels are given, and it is concluded that there is a relatively high probability of synchronism failure. It is indicated that the primary type of synchronization in a satellite radio channel is phase synchronization, the errors of which affect all subsequent types of synchronization (clock, frame and cycle). Analysis of the technical characteristics of modern phase synchronization systems in satellite radio channels allowed us to conclude that it is urgent to search for a new approach to the construction of these systems, which provides an increase in the speed and accuracy of their works. A possible way to solve this problem is the use of holographic photonics elements based on holographic sensing elements in measuring equipment that ensures the functioning and synchronization of satellite radio channels. The article solves the problem of constructing a holographic photonic phase synchronization system in a satellite radio channel. A technical solution is proposed to increase the speed, sensitivity and accuracy of the phase synchronization system by using a volumetric reflective Fourier hologram in the design of this system. A variant of the block diagram of the holographic photonic phase synchronization system is developed and the operation of this scheme is described. The constructive construction of optical elements of the developed block diagram in the form of electro-optical modulators and deflector optical systems is proposed. The individual features of the construction of these structural elements are indicated. The functional purpose of a volumetric reflective Fourier hologram in the design of a holographic photonic phase synchronization system is formulated. The regularities of changes in the parameters of optical fields in the holographic photonic elements of the phase synchronization system of a satellite radio channel are investigated. Concrete numerical examples demonstrate the possibility of providing high sensitivity and accuracy of a holographic photonic phase synchronization system.

A high-precision synchronization system based on custom benchmarks

In order to meet the requirements of high synchronization of information flow for the cooperation among subsystems of spacecraft and of autonomous operation and management of spacecraft, this article proposes a synchronization system design based on a custom synchronization benchmark. This plan provides a custom synchronization benchmark design method and design constraints and proposes synchronization strategies for different system requirements. On this basis, a high-precision synchronization system design scheme is proposed. By conducting tests, the synchronization error compliance of the synchronization system is verified based on custom benchmarks. This design does not rely on the availability of GPS signals, and the synchronization system design is triggered by the requirement for synchronization accuracy. This method can be applied to spacecraft onboard systems and ground testing systems with extensive application value.

Multi-nodes dissemination of stable radio frequency with 10-17 instability over 2000 km optical fiber.

To meet the demand of flexible access for high-precision synchronization frequency, we demonstrate multi-node stable radio frequency (RF) dissemination over a long-distance optical fiber. Stable radio frequency signals can be extracted at any node along the optical fiber, not just at the endpoint. The differential mixing structure (DMS) is employed to avoid the frequency harmonic leakage and enhance the precision. The phase-locked loop (PLL) provides frequency reference for the DMS while improving the signal to noise ratio (SNR) of dissemination signal. We measure the frequency instability of multi-node stable frequency dissemination system (MFDS) at different locations along the 2,000 km optical fiber. The measured short-term instability with average time of 1 s are 1.90 × 10-14 @ 500 km, 2.81 × 10-14 @ 1,000 km, 3.46 × 10-14 @ 1,500 km, and 3.84 × 10-14 @ 2,000 km respectively. The long-term instability with average time of 10,000 s are basically the same at any position of the optical fiber, which is about (6.24 ± 0.05) × 10-17. The resulting instability is sufficient for the propagation of precision active hydrogen masers.

Learning-Enabled Output-Feedback-MPC-Based Synchronization Tracking Control of Multiaxis Motion Systems

The unknown and time-varying model parameters and measurement noises impose great influence on the highprecision synchronization tracking control performance of multiaxis motion systems (MAMSs). To deal with the influence of the factors on the high-precision synchronization tracking control performance in MAMSs, a learning-enabled output feedback model predictive control (MPC) strategy for MAMSs is proposed. Firstly, an efficient learning mechanism is introduced to capture the unknown and slow time-varying behavior of the system parameters. Then, considering both the existence of the measurement noises and the unavailability of the velocity signals in system and synchronization coupling errors, the learning-enabled output feedback MPC based synchronization tracking controller is designed to achieve the high-precision synchronization tracking control of the MAMSs. The stability of overall synchronization tracking system with proposed learning procedure is analyzed. Finally, simulations and experiments are performed on fourmotor motion system to demonstrate the practicability and effectiveness of the proposed control strategy.

Multi-motor position synchronization control method based on non-singular fast terminal sliding mode control.

In order to improve the position high-precision synchronization performance of multi-motor synchronous control, a multi-motor position synchronization control method based on non-singular fast terminal sliding mode control (NFTSMC) combined with an improved deviation coupling control structure (Improved Deviation Coupling Control(IDCC), NFTSMC+IDCC). Firstly, this paper designs a sliding mode controller using a non-singular fast terminal sliding mode surface with a Permanent Magnet Synchronous Motor (PMSM) as the control object. Secondly, the deviation coupling is improved to enhance the coupling between multiple motors and achieve position synchronization. Finally, the simulation results show that the total error of multi-motor position synchronization under NFTSMC control is 0.553r in the simulation of multi-motor synchronization control under the same working conditions, which is 2.873r and 1.772r less than that of SMC and FTSMC in terms of speed error, and the anti-disturbance performance is 83.68% and 76.22% higher than that of both of them, respectively. In the subsequent simulation of the improved multi-motor position synchronization structure, the total error of the multi-motor position is in the range of 0.56r-0.58r at three speeds, which is much smaller than the synchronization error under the Ring Coupling Control (RCC) structure and Deviation Coupling Control (DCC) structure, showing a better The synchronization error is much smaller than that of the RCC structure and DCC structure, which shows better position synchronization performance. Therefore, the multi-motor position synchronization control method proposed in this paper has a good position synchronization effect and achieves the control effect of small displacement error and fast convergence of the multi-motor position synchronization control system after being disturbed, the control performance is significantly improved.

MPC-based time synchronization method for V2V (vehicle-to-vehicle) communication

PurposeAs the strategy of 5G new infrastructure is deployed and advanced, 5G-R becomes the primary technical system for future mobile communication of China’s railway. V2V communication is also an important application scenario of 5G communication systems on high-speed railways, so time synchronization between vehicles is critical for train control systems to be real-time and safe. How to improve the time synchronization performance in V2V communication is crucial to ensure the operational safety and efficiency of high-speed railways.Design/methodology/approachThis paper proposed a time synchronization method based on model predictive control (MPC) for V2V communication. Firstly, a synchronous clock for V2V communication was modeled based on the fifth generation mobile communication-railway (5G-R) system. Secondly, an observation equation was introduced according to the phase and frequency offsets between synchronous clocks of two adjacent vehicles to construct an MPC-based space model of clock states of the adjacent vehicles. Finally, the optimal clock offset was solved through multistep prediction, rolling optimization and other control methods, and time synchronization in different V2V communication scenarios based on the 5G-R system was realized through negative feedback correction.FindingsThe results of simulation tests conducted with and without a repeater, respectively, show that the proposed method can realize time synchronization of V2V communication in both scenarios. Compared with other methods, the proposed method has faster convergence speed and higher synchronization precision regardless of whether there is a repeater or not.Originality/valueThis paper proposed an MPC-based time synchronization method for V2V communication under 5G-R. Through the construction of MPC controllers for clocks of adjacent vehicles, time synchronization was realized for V2V communication under 5G-R by using control means such as multistep prediction, rolling optimization, and feedback correction. In view of the problems of low synchronization precision and slow convergence speed caused by packet loss with existing synchronization methods, the observer equation was introduced to estimate the clock state of the adjacent vehicles in case of packet loss, which reduces the impact of clock error caused by packet loss in the synchronization process and improves the synchronization precision of V2V communication. The research results provide some theoretical references for V2V synchronous wireless communication under 5G-R technology.

Fine Timing and Frequency Synchronization for MIMO-OFDM: An Extreme Learning Approach

Multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) is a key technology component in the evolution towards cognitive radio (CR) in next-generation communication in which the accuracy of timing and frequency synchronization significantly impacts the overall system performance. In this paper, we propose a novel scheme leveraging extreme learning machine (ELM) to achieve high-precision synchronization. Specifically, exploiting the preamble signals with synchronization offsets, two ELMs are incorporated into a traditional MIMO-OFDM system to estimate both the residual symbol timing offset (RSTO) and the residual carrier frequency offset (RCFO). The simulation results show that the performance of the proposed ELM-based synchronization scheme is superior to the traditional method under both additive white Gaussian noise (AWGN) and frequency selective fading channels. Furthermore, comparing with the existing machine learning based techniques, the proposed method shows outstanding performance without the requirement of perfect channel state information (CSI) and prohibitive computational complexity. Finally, the proposed method is robust in terms of the choice of channel parameters (e.g., number of paths) and also in terms of “generalization ability” from a machine learning standpoint.

Principle of Distributed Bus Protection Based on Directional Impedance Component Comparison

Distributed bus protection is one of the main tasks of smart substation construction to improve the secondary system because it is economical, simple, easy to layout, and easy to realize double. This paper mainly considers that distributed current differential protection is limited by high precision synchronization and high bandwidth and a distributed bus protection based on the directional impedance element comparison principle is proposed. The bus impedance protection constructed by reverse current calculation is proposed, which the impedance protection with positive sequence polarization and the impedance protection with memory polarization are the main components. Further considering the influence of system oscillation, the power frequency variable distance protection is introduced to form a distributed bus protection system, and the setting and time setting principles are given. The principle of the protection system is simple and the action is reliable. The effectiveness of the protection system is verified based on PSCAD simulation software.

Investigation of active pump-signal synchronization technique for a ps-pulse pumped OPCPA

High-precision synchronization between pump and signal is one of the key issues that should be solved in picosecond short pulse pumped optical parametric chirped pulse amplification (ps-OPCPA). Based on the all-OPCPA laser facility in Research Center of Laser Fusion, China Academy of Engineering Physics, the high-precision active pump-signal synchronization technique used in its ps-OPCPA frontend is studied in detail in this paper. The synchronization is actively controlled by an amplified narrowband spectrum from the short ps-pulse pumped optical parametric amplification of a large chirped signal. By reasonably designing the time-domain broadening chirped coefficient of the signal in the feedback optical path, relative timing jitter between pump and signal of the ps-OPCPA frontend decreases from ps to one hundred fs, which greatly improves its energy and spectral stability. The root mean square (RMS) value of the relative timing jitter decreases from 458 to 93 fs, which improves the RMS instability of the output energy from 30.3% to 3.15%, and a stable wide spectrum with width greater than 100 nm is obtained in 7-min measurement.