Sub-nanosecond Synchronization Research Articles

Exploitation of an Industrial Low-Bandwidth Communication Line for Modulation-Level Synchronization of Voltage Source Converters

Parallelization of power electronic converter units is a way to meet the high current requirements of modern electrification applications. In case of voltage source converters, parallel operation can be attained only if the voltages of all the units are equal. In the current state of the art, this voltage synchronization can be achieved at the fundamental frequency, but not at modulation frequency, hence requiring bulky filters to limit circulating currents; this lowers the system performance in terms of cost, volume, weight and sustainability. In this paper, the authors propose a novel approach to synchronization, acting directly at the modulation frequency level, thus removing the need for any filter. This technique relies on the natural parasitic inductance and resistance of the wiring among parallel units. Specifically, this paper presents the first of two synchronization stages required to reach the sub-nanosecond synchronization necessary to completely remove the filters. At start-up, a low-bandwidth industrial communication line, based on the CAN protocol, is exploited to guarantee that the error in the synchronization of PWM signals among all the parallel units is lower than 0.1%. This limits the initial circulating current, supporting the subsequent control stage that achieves sub-nanosecond synchronization. The proposed concept is validated by experiments using a commercial MCU unit with an unadorned CAN peripheral.

Wireless Subnanosecond RF Synchronization for Distributed Ultrawideband Software-Defined Radar Networks

In this article, we present a distributed and decentralized synchronization algorithm for wireless sensor networks (WSNs). The proposed method achieves subnanosecond synchronization using low-cost commercial-off-the-shelf (COTS) Universal Software Radio Peripheral (USRP) software-defined radios (SDRs) and is implemented entirely in software without the need for custom hardware or atomic clocks. In an N sensor network, the proposed protocol results in each sensor having full knowledge of baseband clock offsets, RF carrier phase offsets, and pairwise RF time of flight to subnanosecond precision for the entire network after 2N total transmissions, making this method efficiently extendible to larger sensor networks. The method is decentralized and does not rely on a hierarchical master-slave structure, making it robust to sensor dropout in contested or harsh environments. The proposed methodology is validated in simulation and tested in field experiments using a three-sensor network. This work has a wide range of applications, including transmit (TX) beamforming, distributed sensor localization, and coherent multistatic/multiple-input-multiple-output (MIMO) radar imaging for autonomous sensor swarms.

IEEE 1588 High Accuracy Default Profile: Applications and Challenges

Highly accurate synchronization has become a major requirement because of the rise of distributed applications, regulatory requests and position, navigation and timing backup needs. This fact has led to the development of new technologies which fulfill the new requirements in terms of accuracy and dependability. Nevertheless, some of these novel proposals have lacked determinism, robustness, interoperability, deployability, scalability or management tools preventing them to be extensively used in real industrial scenarios. Different segments require accurate timing information over a large number of nodes. Due to the high availability and low price of global satellite-based time references, many critical distributed facilities depend on them. However, the vulnerability to jamming or spoofing represents a well-known threat and back-up systems need to be deployed to mitigate it. The recently approved draft standard IEEE 1588-2019 includes the High Accuracy Default Precision Time Protocol Profile which is intensively based on the White Rabbit protocol. White Rabbit is an extension of current IEEE 1588-2008 network synchronization protocol for sub-nanosecond synchronization. This approach has been validated and intensively used during the last years. This paper revises the pre-standard protocol to expose the challenges that the High Accuracy profile will find after its release and covers existing applications, promising deployments and the technological roadmap, providing hints and an overview of features to be studied. The authors review different issues that have prevented the industrial adoption of White Rabbit in the past and introduce the latest developments that will facilitate the next IEEE 1588 High Accuracy extensive adoption.

Sub-nanosecond synchronization node for high-energy astrophysics: The KM3NeT White Rabbit Node

The first Detection Units of the KM3NeT infrastructure, whose main goal is the detection of cosmic neutrinos, are currently being deployed on the Mediterranean Sea bed. The collaboration has chosen White Rabbit for providing sub-nanosecond synchronization between the Digital Optical Modules, the main detection component of the detector. White Rabbit functionality is provided by the main front-end electronics board, the so called Central Logic Board, that embeds both the White Rabbit firmware, as an IP core on a XILINX Kintex FPGA, and the tunable oscillators, the hardware needed to make White Rabbit to work. The present article describes the Central Logic Board of KM3NeT, focusing on how it provides White Rabbit functionalities.

Portable Calibration Node for LHAASO-KM2A Detector Array

Aiming to high sensitivity and wide spectrum of cosmic ray detection, the 1 km2 complex array of large high altitude air shower observatory (LHAASO-KM2A) project consists of over 7000 detectors of different types. To reconstruct the air shower events with high angular resolution, timestamps of all detector electronics and digitizers should be aligned better than 500 ps RMS. White Rabbit (WR) technology, a fully deterministic Ethernet-based network with subnanosecond synchronization accuracy and picoseconds precision, is applied to build the dedicated data and timing network. To guarantee the overall synchronization precision, individual calibration of each WR node is essential to compensate device deviation. This paper talks about autocalibration procedure of all nodes in the LHAASO-KM2A WR network using the portable calibration node (PCN). Usage of the PCN in deploying the detectors array and validating synchronization performance of the WR network is also discussed.

Sub-nanosecond clock synchronization and trigger management in the nuclear physics experiment AGATA

The new-generation spectrometer AGATA, the Advanced GAmma Tracking Array, requires sub-nanosecond clock synchronization among readout and front-end electronics modules that may lie hundred meters apart. We call GTS (Global Trigger and Synchronization System) the infrastructure responsible for precise clock synchronization and for the trigger management of AGATA. It is made of a central trigger processor and nodes, connected in a tree structure by means of optical fibers operated at 2Gb/s. The GTS tree handles the synchronization and the trigger data flow, whereas the trigger processor analyses and eventually validates the trigger primitives centrally. Sub-nanosecond synchronization is achieved by measuring two different types of round-trip times and by automatically correcting for phase-shift differences. For a tree of depth two, the peak-to-peak clock jitter at each leaf is 70 ps; the mean phase difference is 180 ps, while the standard deviation over such phase difference, namely the phase equalization repeatability, is 20 ps. The GTS system has run flawlessly for the two-year long AGATA campaign, held at the INFN Legnaro National Laboratories, Italy, where five triple clusters of the AGATA sub-array were coupled with a variety of ancillary detectors.

Semiconductor lasers coupled face-to-face

We show that for a large coupling time, semiconductor lasers coupled face-to-face exhibit a fast dynamics and a slow stairs-like periodic modulation. The effect can be explained by the nonlinear response of semiconductor lasers to external injection and a breakup of subnanosecond synchronization.

Optical diagnostics of a plasma-focus device

Systems for optical diagnostics of plasma created in a plasma-focus device are described, showing progress in the development and application of different optical methods used in plasma-focus research. In the experiments carried out on the plasma-focus device at the Institute of Plasma Physics and Laser Microfusion, multiframe Iser interferometry and shadow photography, the Faraday rotation method, and high-speed photography in different spectral ranges were applied. The system used for investigation of the plasma structure and dynamics is fully automatic and is able to acquire images on 10 channels with time resolution of about 1 ns and spatial resolution of about 0.1 mm. Subnanosecond synchronization between different diagnostics was achieved. Some examples of recently obtained results are given.