Time Synchronization for Distributed Measurement and Control Systems
University of Trento, Trento, Italy
Distributed and networked measurement systems, both wired and wireless, usually require a tight synchronization of different nodes, e.g. to coordinate and to schedule tasks performed by different systems or simply to align and to aggregate the measurement data on a common timescale. Unfortunately, achieving accurate time synchronization is a challenging measurement problem per se, which has been deeply studied over the last few years. In this general context, the goal of the tutorial is threefold, i.e. i) explaining the importance and the role of time synchronization in different kinds of industrial applications; ii) presenting the main sources of uncertainty affecting time synchronization and iii) showing the principle of operation as well as the limits of some state-of-the-art solutions. In order to address these objectives, after a general introduction on the definition and on the meaning of time synchronization, the tutorial will be structured into three parts.
Part 1 will be fully devoted to understand the physical phenomena limiting time synchronization accuracy. These include both intrinsic nonidealities of local oscillators (e.g. because of tolerances, aging and power-law noises in frequency and phase) and synchronization-related uncertainty contributions such as time-stamping resolution and communication latencies.
Part 2 will be focused on the techniques that can be used to estimate the time and frequency offsets as well as the communication delays between pairs of systems over a single-hop link. Different classic estimators and point-to-point synchronization mechanisms will be proposed to this purpose. In addition, it will be shown how such estimated quantities can be used to discipline local clocks in real-time through a so-called servo clock.
Part 3 will merge part of the technical contents of parts 1 and 2 in the case of a networked system. In particular, an overview of one of the most important synchronization protocols for measurement and control applications will be provided, namely the Precision Time Protocol (PTP), also standardized as IEEE 1588. In this respect, some of the general techniques described in the previous parts 1 and 2 will be contextualized in the specific framework of IEEE 1588 with the help of some examples.
The tutorial will be concluded with a performance comparison of different solutions for time synchronization and with a quick overview of some ongoing research activities on this topic.
David Macii received the M.S. degree in Electronic Engineering and the Ph.D. degree in Information Engineering from the University of Perugia, Perugia, Italy in 2000 and 2003, respectively. After an internship at the German Aerospace Centre - DLR in Germany, in 2000, he was a visiting researcher at the Department of Electronic Systems of the University of Westminster, London, UK in 2002, and at the Advanced Learning and Research Institute (ALARI) in Lugano, Switzerland between 2003 and 2005. Also, he was a Fulbright Research Scholar at the Berkeley Wireless Research Center (BWRC) of the University of California, Berkeley, USA between 2009 and 2010. From 2005 to 2012 he was an Assistant Professor at the University of Trento, Trento, Italy, with the Department of Information Engineering. Currently, he is an Associate Professor with the Department of Industrial Engineering of the same University.
David Macii received the best student paper award during the IMEKO International workshop on ADC Modeling and Testing in 2003, the national Doctoral Prize “C. Offelli” in 2005 and the Best Academic Paper Award as a co-author of the paper titled "A Clock State Estimator for PTP Time Synchronization in Harsh Environmental Conditions" presented at the IEEE International Symposium on Precision Clock Synchronization in 2011.
He is author and co-author of more than 100 papers published in Proceedings of international conferences, scientific journals and books. David Macii has been an IEEE Senior Member since 2014.
His research interests comprise the design, implementation and characterization of embedded systems as well as digital signal processing and estimation techniques for a variety of measurement applications, with a special emphasis on localization problems, smart grids and time synchronization.