Time Synchronization System Research Articles

A real-time performance improvement method for composite time scale

Abstract The composite time scale (CTS) provides a stable, accurate, and reliable time scale for modern society. The improvement of CTS’s real-time performance will improve its stability, which strengths related applications’ performance. Aiming at this goal, a method achieved by determining the optimal calculation interval and accelerating adjustment stage is proposed in this paper. The determinants of the CTS’s calculation interval (characteristics of the clock ensemble, the measurement noise, the time and frequency synchronization system’s noise and the auxiliary output generator noise floor) are studied and the optimal calculation interval is obtained. We also investigate the effect of ensemble algorithm’s initial parameters on the CTS’s adjustment stage. A strategy to get the reasonable initial parameters of ensemble algorithm is designed. The results show that the adjustment stage can be finished rapidly or even can be shorten to zero with reasonable initial parameters. On this basis, we experimentally generate a distributed CTS with a calculation interval of 500 s and its stability outperforms those of the member clocks when the averaging time is longer than ∼1700 s. The experimental result proves that the CTS’s real-time performance is significantly improved.

Hybrid fiber-based time synchronization and vibration detection system.

We propose a hybrid fiber-based time synchronization and vibration detection system. The vibration is detected by exploring the idle light of the time synchronization system, i.e., the Rayleigh backscattering of the timing pulse disseminated in the fiber link. The addition of a sensing function does not affect the performance of time synchronization. In the multiuser experimental demonstration, time deviation results are 3.6 ps at τ = 1 s and 1.4 ps at τ = 104 s on the 40-km fiber link. Meanwhile, the hybrid system can accurately detect and locate vibrations occurring on the link. This method enables multiple functions of the optical fiber network without occupying extra optical channels. Moreover, it gives a possible solution for enhancing the security of the time synchronization network through vibration detection.

Chaff Cloud Integrated Communication and TT&C: An Integrated Solution for Single-Station Emergency Communications and TT&C in a Denied Environment

In response to potential denial environments such as canyons, gullies, islands, and cities where users are located, traditional Telemetry, Tracking, and Command (TT&C) systems can still maintain core requirements such as availability, reliability, and sustainability in the face of complex electromagnetic environments and non-line-of-sight environments that may cause service degradation or even failure. This paper presents a single-station emergency solution that integrates communication and TT&C (IC&T) functions based on radar chaff cloud technology. Firstly, a suitable selection of frequency bands and modulation methods is provided for the emergency IC&T system to ensure compatibility with existing communication and TT&C systems while catering to the future needs of IC&T. Subsequently, theoretical analyses are conducted on the communication link transmission loss, data transmission, code tracking accuracy, and anti-multipath model of the emergency IC&T system based on the chosen frequency band and modulation mode. This paper proposes a dual-way asynchronous precision ranging and time synchronization (DWAPR&TS) system employing dual one-way ranging (DOWR) measurement, a dual-way asynchronous incoherent Doppler velocity measurement (DWAIDVM) system, and a single baseline angle measurement system. Next, we analyze the physical characteristics of the radar chaff and establish a dynamic model of spherical chaff cloud clusters based on free diffusion. Additionally, we provide the optimal strategy for deploying chaff cloud. Finally, the emergency IC&T application based on the radar chaff cloud relay is simulated, and the results show that for severe interference, taking drones as an example, under a measurement baseline of 100 km, the emergency IC&T solution proposed in this paper can achieve an accuracy range of approximately 100 m, a velocity accuracy of 0.1 m/s, and an angle accuracy of 0.1°. In comparison with existing TT&C system solutions, the proposed system possesses unique and potential advantages that the others do not have. It can serve as an emergency IC&T reference solution in denial environments, offering significant value for both civilian and military applications.

Research on FPGA-based dual-channel time synchronization system

As geological exploration progresses in depth and scope, the distance between transmitting and receiving systems also increases. Consequently, the synchronization of time between the two becomes an increasingly critical issue. In response, this paper presents a proposed design for a time synchronization system that is suitable for use between transmitting and receiving equipment. The system uses GPS as the main clock source. The information within the GPS system will be encoded and decoded using the FPGA. This allows us to obtain both UTC time and the time of the IRIG-B code format, enabling compatibility with the various system interfaces. Our experiments have confirmed that the system has a time error at the microsecond level, and the precision satisfies the design requirements. This verifies the validity and reliability of the system.

Controllable Asymmetric Attack Against Practical Round-Trip Fiber Time Synchronization Systems

Controllable Asymmetric Attack Against Practical Round-Trip Fiber Time Synchronization Systems

Методика формирования комплексной системы синхронизации и доставки шкалы времени для крупной распределенной системы технологического назначения

Purpose: To develop scientific and technical solutions for constructing a comprehensive synchronization system and delivery of the time scale, which includes subsystems of network clock synchronization (NCS) and unified time (UT), as a unified timekeeping system addressing the challenges of frequency, time, and phase synchronization in large-scale distributed technological purpose systems. Methods: Research methods are based on the fundamental provisions of the theory of systems and the theory of decision-making. Results: A methodology for the formation of a comprehensive synchronization system and the delivery of a time scale is proposed, which is characterized by an integrated approach to building unified time and frequency systems in the communication networks of the technological segment, the independence of the types of generator equipment used and the means of delivery of NCS and UT signals, as well as meeting the requirements of potential consumers of frequency and time services. The proposed methodology for the formation of a comprehensive synchronization system and delivery of a time scale will allow to reasonably approach building systems for delivering unified time and frequency signals in complex heterogeneous communication networks. Practical significance: Solutions based on the presented methodology will allow the provision of an infrastructure independent of external communication operators to ensure the unity of network clock synchronization and unified time. This is necessary for the correct operation of telecommunication equipment of the technological communication network. The methodology will also meet the needs for providing a full range of synchronization and unified time signal services to existing and prospective consumers. Additionally, it will enable a gradual transition of the organization of communication networks from channel-swithching to packet-oriented technologies due to a flexible approach to the routes and transmission systems used for the distribution of synchronization signals and unified time.

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.

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.

Design and Implementation of Precision Phase Measurement Module Base on Digital Dual Mixer Time Difference

Precise phase difference measurement is critical for distributed time synchronization systems. Aiming at the problem of how to realize the sub-nanosecond phase difference measurement of the time signal, the digital dual mixer time difference (DDMTD) measurement technology is used to measure the fine transmission delay and the two digital clock phase difference. Given the problem that it is difficult to generate a common clock source with fine frequency changes inside the FPGA chip, the Si5338 chip is used to generate 4 differential clocks, and the communication with the FPGA is completed through the I2C protocol, and the differential signal is converted into a single-ended clock source inside the FPGA as two The common standard frequency of clock signals with the same frequency and different phases, realize the amplification of the phase difference measurement range, making the measurement accuracy reach sub-nanosecond level.

Analysis of application of network time synchronization technology in plant and station automation system

As the inevitable result of the development of social economy and science and technology, the construction of plant and station automation system not only solves the problems existing in the traditional plant and station construction management, but also improves the fundamental requirements of the system operation. According to the accumulated experience in the construction and application of plant and station automation system in recent years, the scholars of various countries should not only ensure the accuracy and high precision of time measurement, but also scientifically control the complexity of application algorithm to reduce the amount of electric energy consumption. Therefore, on the basis of understanding the research status of plant and station automation system and network time synchronization technology, this paper mainly explores how to apply network time synchronization technology in plant and station automation system according to the structure of plant and station automation system and the key points of network time synchronization technology.

First experimental results of the cosmic time synchronizer for a wireless, precise, and perpetual time synchronization system

In 2022, the idea of the cosmic time synchronizer (CTS) was proposed for a precise wireless synchronization of local clocks (<100ns). Because CTS does not require critical timing information traffic among CTS sensors, the technique can be considered robust against jamming and spoofing. In this work, a small-scale CTS sensor network has been developed and tested for the first time. Good time synchronization performances were obtained for a short-haul configuration (30-35ns (SD, 1 σ), over 50-60m). Based on the results of this work, CTS could be potentially conceived as a 'self-adjusting' system, offering high level continuous (perpetual) performances, to be considered either as a backup chain for GPS disciplined oscillators (GPS DO), a standalone standard for frequency and time interval measurements, or as a tool for the dissemination of reference time scales to final users, with improved characteristics in terms of robustness and reliability.

Design considerations for hardware implementation of nanoseconds time synchronization low-cost system based on precise time protocol

Precise time synchronization is the key for coordinating every node of the distributed system to complete tasks. The widespread use of Field Programmable Gate Array (FPGA) in distributed nodes has a positive effect on improving time synchronization accuracy. Although the use of FPGA could significantly improve time synchronization accuracy, there is not a universal design guideline. This work has analyzed and summarized three factors that should be considered when building a low-cost clock synchronization system using FPGA: where the timestamp should be generated, the calculation and correction of time offset, and how to handle Precise Time Protocol (PTP) messages. Based on these design considerations, the time synchronization system intellectual property (IP) core was constructed. The synchronization accuracy experiments have been performed on Zynq system-on-chip (SoC) evaluation boards of different architectures. The experimental results demonstrated that the time synchronization system constructed in this article could achieve nanoseconds accuracy.

Estimating Clock Skew With One-Way Timestamps

Clock skew estimation is the principal task for time synchronization in wireless network systems. Most of the contemporary techniques require two-way exchanging timestamps, which face big challenges due to the limitation of network hierarchy and topology management. In contrast, we propose a novel optimization process based on the one-way broadcast model. Extensive simulations on various datasets demonstrate the superiority of the proposed method compared to other state-of-the-arts.

A high-precision detection method for laser time transfer based on a single-photon avalanche detector array.

Space-ground laser time transfer is of significant importance to effectively function a high-precision time synchronization system. Instead of the single-pixel single-photon avalanche detector (SPAD) commonly used in the laser time transfer system, the SPAD array device is capable of supporting the greater performance of the signal photon capture. In this paper, it is experimentally demonstrated that the detection precision and time deviation (TDEV) of the SPAD array can be extremely improved by an order of magnitude compared with those of a single-pixel SPAD. As a result, 2.4ps root mean square precision and 0.25ps over an averaging time of 1000s TDEV are achieved for the SPAD array, providing a new detection method for high-precision laser time transfer applications, such as space-ground optical clocks.

Stabilized Time Transfer via a 1000-km Optical Fiber Link Using High-Precision Delay Compensation System

Variations in optical fiber length and refractive index are induced by environmental perturbation, resulting in an additional dynamic propagation delay in fiber-based time synchronization systems, which deteriorate their transfer stability. This disadvantage can be significantly reduced by transmitting the time signal in both directions through fiber and constructing a feedback loop to compensate the propagation delay at the remote end of the link. This paper proposes an analog-digital hybrid proportional integral derivative (PID) control compensation system based on the time-frequency phase-locked loop (TF-PLL). The system is designed to keep the merits of wide servo bandwidth, servo accuracy, and a large dynamic delay compensation range up to 1 s, which is much greater than that reported in previous studies. For proving the validity of this proposed scheme, a self-developed optical fiber time synchronization equipment based on the delay compensation system is applied. The delay compensation system is used on a 1100-km long laboratory optical fiber, and the results show that the time synchronization stability in terms of time deviation (TDEV) is less than 5.92 ps/1 s and 2.56 ps/10,000 s. After successful laboratory evaluation, the proposed system is installed on a real 988.48-km line between the Xi’an Lintong branch of the National Time Service Center (NTSC) and Linfen City, Shanxi Province, realizing the time synchronization of 10 stations along the optical fiber link. The experimental results in the 988.48-km link illustrate that the measured time difference with a peak-to-peak value of 176 ps, the standard deviation of 19.3 ps, and a TDEV of less than 10.49 ps/1 s and 2.31 ps/40,000 s is achieved. The high-precision time delay compensation system proposed in this paper is simple, reliable, and accurate; has a wide range of compensation; and opens up a feasible scheme for providing synchronized time signals to multiple users over the long-distance field optical fiber networks.

Timing Synchronization System on RF-Driven Neutral Beam Injection System

The timing synchronization system (TSS) in a radio-frequency–driven negative ion–based neutral beam injection system (NNBIS) is an important part of a negative ion–based neutral beam injection control system. In order to ensure the orderly conduct of experiments and the integrity of experimental data, the TSS needs to complete the corresponding timing synchronization function. There are two aspects to control of the NNBIS: controlling the synchronization of NNBIS subsystems within a certain precision and ensuring correct timing and amplitude output during the experiment. This paper presents the design and development of the TSS in the NNBIS, aiming at the characteristics of the IEEE 1588-2019, “IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems,” clock synchronization protocol to achieve the demands of clock synchronization at a submicrosecond level, synchronously triggering other subsystems through the network trigger and hardware trigger. The TSS successfully implemented synchronization accuracy in less than 1 μs, and the network trigger is more efficient than the hardware trigger, which is about 80 μs faster. The TSS meets the requirements of timing synchronization accuracy of the NNBIS.

Опыт внедрения систем частотно-временного обеспечения сетей связи

Time synchronization systems in communication networks must be linked to the reference time scale (TS) of national standard. In most cases, receivers of global navigation satellite systems (GNSS) signals are widely used for these purposes. However, possible violations of these signals reception, as well as cases of their substitution (spoofing) force us to look for alternative options for receiving airwaves via terrestrial communication channels. One of the solutions - use of special equipment for time signals (ARSV) complete distribution with a time server that receives, stores and transmits SH signals to the consumer in any format – NTP, PTP, 1PPS + ToD, etc. The purpose of this article is to present the experience of implementing time-frequency systems using terrestrial communication channels with UTC time scale sources.

ПЕРСПЕКТИВНЫЙ ПЕРВИЧНЫЙ ЭТАЛОН ВРЕМЕНИ И ЧАСТОТЫ ДЛЯ СИСТЕМ ЧАСТОТНО-ВРЕМЕННОГО ОБЕСПЕЧЕНИЯ СЕТЕЙ СВЯЗИ

The article deals with the acquisition of primary time and frequency standards for time-frequency support systems as a reference node for the formation of the time scale for 4G and 5/6G communication networks. The basis of frequency and time synchronization systems, which together form the frequency-time support of communication networks, are the primary standards of time and frequency. For communication networks up to 4 generations in the frequency division mode (TDM, 3G, 4G FDD networks), only a network frequency synchronization system is needed, which is based on the use of primary reference generators. In fact, it is a part of the HDPE that provides the formation of the reference frequency. Taking into account the future requirements for synchronization systems of 5/6G communication networks, it is necessary to provide for the use of improved primary reference sources, as well as a secondary master oscillator with the functions of a master PTP frequency and a combiner of frequency and time signals. In the future, this will allow the transition to the introduction of improved HDPE (uHDTV). In connection with the current situation on the Russian market, the article discusses the possibility of using domestically produced equipment for time-frequency support systems.

Prospective directions for the development of microwave frequency standards for satellite navigation systems

The state of essential various quantum standards of GNSS frequencies for today are collected and presented, the results of analysis in the direction of modernization of time synchronization systems in global navigation satellite systems are presented. The most perspective directions of modernization of global navigation satellite systems are mentioned – the development of new atomic clocks on the mercury ions -199. The data on experimental satellite gives encouraging results.

Controllable Asymmetry Attack on Two-Way Fiber Time Synchronization System

Precise and secure time synchronization between two remote sites is necessary in many practical scenarios. Recently, the two-way fiber time transfer (TWFTT) system has become an attractive option for high-precision time synchronization. However, TWFTT is implemented based on symmetric link assumption, and such assumption may be maliciously utilized to cause significant time asynchronization to TWFTT. In this paper, we propose two novel controllable asymmetry attack schemes for TWFTT, namely, the link asymmetry attack and the attenuation asymmetry attack. We theoretically analyze the controllability and the effectiveness of these two attacks. Experimental results show that our link asymmetry attack can introduce 2.49 ns time offset per asymmetric link length (in meters), and our attenuation asymmetry attack can introduce at most 36.6 times time offset (compared to normal situation) when the attenuation is 45.3%. Our work can provide instructive insights for future studies of protecting TWFTT from delay asymmetry attacks.