A novel precise and accurate clock synchronization algorithm

Execution of a task in a synchronized manner in a distributed setting, one needs the common idea of time. To accomplish this task, clock synchronization is conceptualized. Clock drifting is an intrinsic property of a clock, which necessitates the synchronization and resynchronization. A network consists of nodes, which may behave appropriately or behave badly. The mischievous node may pose difficulty in clock synchronization. We require a method to overcome the effect of mischievous nodes. Synchronization can be achieved in two ways namely accuracy and precision. In this paper, we present an accurate weighted average clock synchronization algorithm to execute a coordinated activity in a fault-tolerant manner. We use trusted clock value from GPS/GLONASS/IRNSS as a reference clock to achieve better accuracy. We also use behavior of the node to compute normalized weight in a localized manner, which lies between unit intervals. This weight assignment enables us to contain the effect of misbehavior up to some extent. This algorithm offers better accuracy and precision while tolerating mischievous nodes. The upper bound of tolerance boundary is one-third of the network size.

Time consistency of each node and each core is one of the kernel problems that must be addressed to promote the development of many-core cluster system that keeps the distributed system in step, and it is the basis of performance evaluation. In this study, a new model of hybrid time synchronization architecture was established to improve the precision of internal clock synchronization of a many-core cluster and the accuracy of time. First, some clock synchronization method was compared for clock synchronization model decision. Second, a high precision time acquire method based on was explored. Third, a hybrid clock synchronization and time acquire architecture on cluster system was designed to enhance the time precision and internal clock consistency. Finally, the architecture was implemented on a Zynq SoC and Epiphany many-core processor combined platform. An experiment was conducted to evaluate the precision and accuracy of this architecture. The result shows that the hybrid architecture achieved a higher level time precision and internal clock consistency than common clock synchronization method like NTP. And result demonstrates the promising application of the proposed architecture in study many-core cluster system and in supplying reliable time reference for the evaluation of distributed system performance.

SpaceWire fiber-optic Bus is a development of the SpaceWire ECSS-E-50-12C standard. Its transmission rate can reach 2 Gbps. However, it suffers from the problems of imprecise clock synchronization and link blocking in networks. Therefore, we analysis the problems and propose following methods. Firstly, we design clock synchronization algorithms to guarantee the precision of clock synchronization. Furthermore, we design static time distribution scheduling table which takes time-triggered traffic for real-time messages. Through simulation verification, the time precision can be within 58 ns while using clock synchronization algorithm. The use of scheduling table can effectively avoid network conflicts and reduce the delay of data transmission. The improved scheduling method can meet the real-time requirements of SpaceWire fiber-optic Bus systems, and will effectively promote the space application of fiber-optic technology.

The global clock synchronization problem in distributed multi-hop wireless networks is studied in this paper. A fully distributed synchronization solution based on mean field is proposed. A neighbor system and a label problem are defined to describe clock synchronization problem. The clock offset and skew are mapped to clique potential, and an energy function is established based on clique potential. Then the clock synchronization is transformed to finding the minimum of the energy function. By minimizing the energy function, clock synchronization is reached. A distributed energy minimization algorithm is also proposed. The simulation results show the proposed solution achieves high precise global clock synchronization and has the virtue of low overhead, robustness and scalability.

年图灵奖获得 者 Lamport 教授就指出时钟同步是分布式系统的关键依赖性条件 [4] .随着 21 世纪科学技术的高速发 展, 人们对网络化系统中分散时钟的有效同步提出了更高要求, 这正是因为网络化系统日益渗透到不 同行业

Fault-tolerant clock synchronization is the foundation of synchronous architectures such as the Time-Triggered Architecture (TTA) for dependable cyber-physical systems. Clocks are typically local counters that are increased with a given rate according to real time, and clock synchronization algorithms ensure that any two clocks in the system read about the same value at about the same point in real time. This is achieved by a clock synchronization algorithm that changes the current values of the clocks, the clocks' rate, or both. This paper presents a diagnosis algorithm and a clock-rate correction algorithm as layered services on top of the TTEthernet clock synchronization algorithm, which itself is a clock-state correction algorithm. We analyze the algorithms' properties and explore and understand their behavior using a bounded model checker for infinite data types. We use our formal framework for both simulation and formal proof. To the best knowledge of the authors this has been the first time that formal methods, should they be theorem provers or model checkers, have been applied to the problem of rate-correction for fault-tolerant clock synchronization. Furthermore, the formal development process itself demonstrates how easily existing models can be utilized in the development of new algorithms and their formal verification.

<h3>Abstract</h3> Clock synchronization is critical for synchronous pseudolite systems. Wireless synchronization methods are desirable for their flexibility in system deployment, and most of them build a tree topology of time information flow based on master-slave synchronization between pseudolites. A slave pseudolite can receive signals broadcast by multiple pseudolites; however, existing methods usually utilize one signal and ignore others in which the time information could improve synchronization precision and reliability. We present a mesh topology based clock synchronization (MTCS) technique by utilizing all received signals. MTCS builds a mesh topology of time information flow, which can keep synchronization in case of link interruption or pseudolite failure. The coupling relationship of slave clocks is derived, and the influence of measurement biases is analyzed. As shown by both analysis and simulations, MTCS has better clock synchronization precision. When link interruption or pseudolite failures occur, MTCS is more robust than tree topology based methods.

Synchronization of the clocks is one of the essential thing for many applications in distributed systems. Clock synchronization is very important because they improve the performance and reliability of distributed systems. The main purpose of clock synchronization algorithms is to provide the common time to essential parts of the distributed systems. In this paper the problem considered is synchronization of clock with bounded clock drift and proposing a two level synchronization algorithm which synchronizes the processors local clocks by combining both internal and external clock synchronization.

The high popularity of ultra-wideband technology for accurate indoor positioning in industrial and public spaces has led to a large amount of research in recent years. The focus has mostly been on localization accuracy in small-scale setups with a single localization zone. However, solutions designed for line-of-sight environments are not suitable for many large-scale applications. To overcome this lack of research, we propose novel concepts for precise wireless multi-hop clock synchronization and localization zone selection. By integration into a time-difference-of-arrival-based ultra-wideband localization scheme, continuous cross-spatial positioning in large-scale scenarios is enabled. Validation is carried out in an unprecedented testbed with multiple rooms. We could show that positioning accuracy in multi-room scenarios is up to three times higher when exploiting the proposed concepts compared to the initial accuracy achieved with existing approaches. In addition, we provide an open-source implementation of our real-time localization system.

Sensor localization in wireless sensor networks is an important component of many applications. Previous work has demonstrated how localization can be achieved using various methods. In this paper we focus on achieving fine-grained localization that does not require external infrastructure, specialized hardware support, or excessive sensor resources. We use a real sensor network and provide measurements on the actual system. We adopt a localization approach that relies on acoustic sounds and clock synchronization. The contribution of our work is achieving consistent sound pulse detection at each sensor and precise range estimation using a high-precision clock synchronization implementation. We first describe our technique and then we evaluate our approach using a real setup. Our results show that our approach achieves an average clock synchronization accuracy of 5μs. We verify this accuracy using an external global clock via an interrupt mechanism. Our sound detection technique is able to consistently identify sound pulses up to 10m distances in indoor environments. Combining the two techniques, we find that our localization method results in accurate range estimation with an average error of 11cm in distances up to 7m and in consistent range estimation up to 10m in various indoor environments.

Existing response time analysis and optimization techniques for real-time distributed systems show that EDF schedulers feature better scheduling capabilities when a global clock reference can be used; this form of scheduling is known as global-clock EDF. In this context, precise clock synchronization is an enabling technology for future distributed real-time systems that want to leverage EDF scheduling. The IEEE 802.1AS protocol can be considered a stable technology for this purpose, as it is part of the Time-Sensitive Networking (TSN) family of standards to provide real-time communication over Ethernet. This paper presents a system architecture for applying global-clock EDF scheduling in distributed systems with soft real-time requirements. It also presents experiments to (1) assess the synchronization capabilities of the clock synchronization mechanism in the proposed architecture, (2) evaluate the performance of different scheduling deadline assignment techniques, and (3) contrast the theoretical results obtained by the schedulability analysis against those obtained through the execution of these experiments.

This paper proposes an extension of the precision time protocol (IEEE 802.1AS) to improve clock synchronization in hybrid networks including both wireless and wire-bound segments. This extension targets systems based on Time Sensitive Networking (TSN) such as industrial applications and vehicular systems. By considering the deterministic delays and the clock drift, the precision of the clock synchronization of the standard 802.1AS scheme can be significantly improved. Furthermore, in order to support dynamic communication environments with mobile nodes, the problem of asymmetric delays in the transmission of the timing packets of the synchronization protocol is also considered. Therefore, a Path Deviation Delay (PDD) filter is introduced to monitor the traffic behavior of timing packets as well as to exclude outlier values which can occur as a result of dynamic and asymmetric scenarios. The paper presents a simulation framework for the proposed protocol to evaluate it with TSN-based systems that support the TSN features (e.g. IEEE 802.1Qci and IEEE 802.1Qbv sub-standards). The simulation results show that the proposed protocol improves the synchronization precision compared with the standard 802.1AS protocol. It shows that the proposed protocol enhances the synchronization precision to less than 1 microsecond. In contrast, the synchronization error increases significantly with the standard protocol in the presence of different asymmetric ratios and in mobile node scenarios.

In order to reduce accumulation errors in the time synchronization for higher required systems,in this paper,the source of residual in clock synchronization and the working principle of transparent clock were in-depth analyzed.Combined with the delay request-response mechanism and the peer delay mechanism of IEEE 1588v2,a precise clock synchronization protocol applied to networked measurement and control systems,a set of high precision simultaneous algorithm based on transparent clock was summarized in detail.According to the test results,synchronization accuracy and precision in the sub-microsecond range can be perfectly reached by drift adjustment and offset adjustment,which can fully comply with the required precision requirments.

In order to solve the problem about the clock synchronization and high precision in the TDOA location system, a clock synchronization scheme was designed. In the article, the GPS+TCXO clock module was used as the front end of the reference clock source, and the PLL + clock buffer solution was used in the back end. The effect of the clock and ADC was analyzed on the TDOA location system; the system hardware designs were analyzed, such as the selection principle of the reference clock source and the PLL clock hardware circuit design and the parameter selection basis; the synchronous sampling method of the system clock and the register allocation process through the FPGA logic were introduced. The experimental result showed that the proposed scheme can reduce the clock jitter and improve the accuracy and stability of the input clock.

IP networks allow constructing versatile device configurations for multimedia streaming. However, the stochastic nature of the packet-switched data transmission may complicate IP-based implementations of some conventional applications such as analog wired transmission of synchronized multi-channel audio. This paper introduces a multimedia streaming system based on the synchronization of multiple playback clients as a ‘swarm’. The proposed ‘swarm synchronization’ mechanism is based on precise clock synchronization with the PTP protocol and adjusting the client-specific sampling rates according to the true playback rates of other clients. A streamlined version of the RTP protocol is employed to minimize playout delay. The proposed system is empirically evaluated in wired Ethernet LAN and in wireless IEEE 802.11g LAN. The experimental results show that in the Ethernet network the proposed streaming system is able to achieve very precise synchronization.