A resilient architecture for the realization and distribution of coordinated universal time to critical infrastructure systems in the United States :

Abstract

The Time and Frequency Division of the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce (DOC), was tasked with fulfilling Section 4, Part (i) of the Position, Navigation and Timing (PNT) Executive Order that was signed by the President on February 12, 2020. The Executive Order states that Within 180 days of the date of this order, the Secretary of Commerce shall make available a GNSS-independent source of Coordinated Universal Time, to support the needs of critical infrastructure owners and operators, for the public and private sectors to access. Although the Executive Order does not specifically provide an accuracy requirement, this report assumes an accuracy requirement of 1 ?s with respect to Coordinated Universal Time (UTC). This specification is assumed because numerous critical infrastructure timing systems in the United States are now heavily dependent on signals received from the Global Positioning System (GPS) satellites that routinely provide sub-microsecond accuracy, and other UTC sources that deliver time at comparable accuracy levels are needed to alleviate or reduce these dependencies. This report was written to describe, propose, and recommend technical methods that NIST has already implemented, or can potentially implement, to fulfill Section 4, Part (i) of the PNT Executive Order.

Achieving traceability to UTC through GNSS measurements

“…The free availability of GNSS signals of excellent quality and reliability has spurred the extensive reliance on GNSS as a single source of time and the neglect of other sources. In recent years the proliferation of equipment to disrupt reception of GNSS signals and concern about the vulnerability of services has led to a re-think, with requests from users for assured access to accurate time based on more than one source [22]. Furthermore, legal requirements or regulations issued by many user communities specify traceability to national or international standards when measurements are made and time stamps are issued.…”

“…The widespread use of GNSS in many user communities has spurred concerns about the vulnerability of a GNSS-based service because of the weakness of the received signals and the proliferation of electronic equipment suitable for jamming and spoofing GNSS signals [22]. From a practical point of view, jamming and spoofing present different problems.…”

Picosecond programmable delay line using commercial components for precision timing signal alignment

“…This product provides additional steerable frequency and phase outputs with similar quality as the original frequency source. The AOG is widely used within the coordinated universal time system of the United States which is established and serviced by the National Institute of Standards and Technology (NIST) [15] and used in the time system maintained by the United States Naval Observatory (USNO). Beyond the U.S.A., it is used in universal time systems in Taiwan [16] and studies of time systems in Japan [17].…”

The Formation of a Chip Scale Atomic Clock Ensemble Using Software Defined Radios

“…The repeated adjustment of oscillator frequency is known as clock steering. Clock steering techniques are used in the realization of timescales in order to take advantage of the best clock stability across different averaging intervals [17]. In initial steering tests we steer a simulated OCXO to simulated CSAC 01 from Fig.…”