The operational performance of hydrogen masers in the deep space network: The performance of laboratory reference frequency standards in an operational environment

Hydrogen masers used as aids in meeting the routine frequency and time operational requirements within the 64 m antenna Deep Space Network. Both the operational syntonation (frequency synchronization) and the the clock (epoch) synchronization requirements were established through the use of specifically calibrated H-P E215061A flying clock. The sync/synt to UTC was maintained using LORAN and TV in simultaneous reception mode. The sync/synt within the 64 m net was maintained through the use of very long base interferometry. Results indicate that the hydrogen masers perform well within the required specifications

Precision packet-based frequency transfer based on oversampling

Frequency synchronization of a distributed measurement system requires the transfer of an accurate frequency reference to all nodes. The use of a general-purpose packet-based network for this aim is analyzed in this paper, where oversampling is considered as a means to counter the effects of packet delay variation on time accuracy. A comprehensive analysis that includes the stability of the local clock is presented and shows that frequency transfer through a packet network of this kind is feasible, with an accuracy level that can be of interest to a number of distributed measurement applications

Distributed clock generator for synchronous SoC using ADPLL network

International audienceThis paper presents a novel architecture of on-chip clock generation employing a network of oscillators synchronized by the distributed all-digital PLLs (ADPLLs). The implemented prototype has 16 clocking domains operating synchronously in a frequency range of 1.1-2.4 GHz. The synchronization error between the neighboring clock domains is less than 60 ps. The fully digital architecture of the generation offers flexibility and efficient synchronization control suitable for use in synchronous SoCs

Distributed synchronization algorithms for wireless sensor networks

The ability to distribute time and frequency among a large population of interacting agents is of interest for diverse disciplines, inasmuch as it enables to carry out complex cooperative tasks. In a wireless sensor network (WSN), time/frequency synchronization allows the implementation of distributed signal processing and coding techniques, and the realization of coordinated access to the shared wireless medium. Large multi-hop WSN\u27s constitute a new regime for network synchronization, as they call for the development of scalable, fully distributed synchronization algorithms. While most of previous research focused on synchronization at the application layer, this thesis considers synchronization at the lowest layers of the communication protocol stack of a WSN, namely the physical and the medium access control (MAC) layer. At the physical layer, the focus is on the compensation of carrier frequency offsets (CFO), while time synchronization is studied for application at the MAC layer. In both cases, the problem of realizing network-wide synchronization is approached by employing distributed clock control algorithms based on the classical concept of coupled phase and frequency locked loops (PLL and FLL). The analysis takes into account communication, signaling and energy consumption constraints arising in the novel context of multi-hop WSN\u27s. In particular, the robustness of the algorithms is checked against packet collision events, infrequent sync updates, and errors introduced by different noise sources, such as transmission delays and clock frequency instabilities. By observing that WSN\u27s allow for greater flexibility in the design of the synchronization network architecture, this work examines also the relative merits of both peer-to-peer (mutually coupled - MC) and hierarchical (master-slave - MS) architectures. With both MC and MS architectures, synchronization accuracy degrades smoothly with the network size, provided that loop parameters are conveniently chosen. In particular, MS topologies guarantee faster synchronization, but they are hindered by higher noise accumulation, while MC topologies allow for an almost uniform error distribution at the price of much slower convergence. For all the considered cases, synchronization algorithms based on adaptive PLL and FLL designs are shown to provide robust and scalable network-wide time and frequency distribution in a WSN

Two-Way Quantum Time Transfer: A Method for Daytime Space-Earth Links

Remote clock synchronization is crucial for many classical and quantum network applications. Current state-of-the-art remote clock synchronization techniques achieve femtosecond-scale clock stability utilizing frequency combs, which are supplementary to quantum-networking hardware. Demonstrating an alternative, we synchronize two remote clocks across our freespace testbed using a method called two-way quantum time transfer (QTT). In one second we reach picosecond-scale timing precision under very lossy and noisy channel conditions representative of daytime space-Earth links with commercial off-the-shelf quantum-photon sources and detection equipment. This work demonstrates how QTT is potentially relevant for daytime space-Earth quantum networking and/or providing high-precision secure timing in GPS-denied environments.Comment: arXiv admin note: text overlap with arXiv:2211.0073

Synchronized State in Networks of Digital Phase-Locked Loops

International audienceClock distribution networks of synchronized oscillators are an alternative approach to classical tree-like clock distribution methods. Each node of the network may consist of a phase-locked loop (PLL) trying to match the phase of its neighbors. Then a network of independent oscillators takes the place of the centralized clock source, providing separate clock signals to the physically distant parts of the system. In the discrete case, the digital filter is necessarily operated asynchronously: each operation is triggered by a rising edge of the locally-generated clock, the frequency and phase of which vary as the whole system tries to synchronize. The locking behavior, the synchronous state and the stability conditions of such a system are analyzed. Similarly, the synchronization of an autonomous network of two self-sampled PLLs is studied. Surprisingly, its analysis is much simpler than that of the single PLL

Intelligent and Low Overhead Network Synchronization over Large-Scale Industrial Internet of Things Systems

With the extensive development of information and communication technologies and vertical industry applications, industrial IoT (IIoT) systems are expected to enable a wide variety of applications, including advanced manufacturing, networked control, and smart supply chain, which all exclusively hinge on the efficient cooperation and coordination among the involved IIoT machines and infrastructures. The ubiquitous connection among IIoT entities and the associated exchange of collaborative information necessitate the achievement of accurate network synchronization, which can guarantee the temporal alignment of the critical information. To enhance the temporal correlation of heterogeneous devices in large-scale IIoT systems, this thesis aims at designing industry-oriented network synchronization protocols in terms of accuracy improvement, resource-saving, and security enhancement with the assistance of learning-based methods. Initially, the real-time timestamps and historical information of each IIoT devices are collected and analyzed to explore the varying rate of the skew (VRS) at each enclosed clock. K-means clustering algorithm is adopted to organize the distributed devices into a few groups, and each of them is assigned with an optimized synchronization frequency to avoid potential resource waste while ensuring synchronization accuracy. Historical VRS values are further utilized as the identification of each clock for providing verification information so that the security against message manipulation attacks during network synchronization can be enhanced. Moreover, a digital twin-enabled clock model is established by comprehensively investigating the characteristics of each clock with diversified operating environments. A cloud-edge-collaborative system architecture is orchestrated to enhance the efficiency of data gathering and processing. With the assistance of the accurate estimation generated by the digital twin model for each clock, the situation-awareness of network synchronization is enhanced in terms of a better understanding of the clock feature and necessary synchronization frequency. Meanwhile, since temporal information generated at each local IIoT devices are efficiently gathered at the edge devices, the effect of packet delay variation is significantly reduced while the synchronization performance under various network conditions can be guaranteed. To further reduce the network resource consumption and improvement the performance under abnormal behaviors during network synchronization, a passive network synchronization protocol based on concurrent observations is proposed, where timestamps are exchanged without occupying dedicated network resources during synchronization. The proposed scheme is established based on the fact that a group of IIoT devices close to each other can observe the same physical phenomena, e.g., electromagnetic signal radiation, almost simultaneously. Moreover, multiple relay nodes are coordinated by the cloud center to disseminate the reference time information throughout the IIoT system in accomplishing global network synchronization. Additionally, a principal component analysis-assisted outlier detection mechanism is designed to tackle untrustworthy timestamps in the network according to the historical observation instants recorded in the cloud center. Simulation results indicate that accurate network synchronization can be achieved with significantly reduced explicit interactions