By Duke Buckner, Microchip Technology
The world’s Global Navigation Satellite System (GNSS) has never been more integral to daily lives than it is now. It is like an invisible utility, as vital as power or water. The position, navigation, and time (PNT) information it provides is crucial to the reliable functioning of critical infrastructure such as energy, telecommunications, transportation, emergency services and financial transaction networks. Yet never has the system been more vulnerable to interference from threats including jamming and an attack called spoofing, when a radio transmitter located near a target receiver feeds it false information.
The sources of spoofing range from malevolent nation-states to delivery drivers who, trying to disguise their location and long lunch breaks from their bosses with do-it-yourself jamming devices, have inadvertently disrupted local air traffic control operations. Governments and the private sector are all rallying around the development and deployment of backup strategies and solutions, but until they are available on a nationwide scale wherever critical infrastructures operate, the industry faces serious challenges. Infrastructure operators have backup generators, but they do not have backup PNT sources. Many of the critical infrastructure operators provide safety-of-life services and demand to be available 100 percent of the time, 24 hours a day, 7 days a week, 365 days a year.
Special Timing Needs of the Electric Grid
Electric power utilities use space-based timing signals in PNT solutions that monitor, protect, and operate grid assets that are often separated across large geographic areas. The timing clocks in these dispersed systems must share and be precisely synchronized with a common global reference for timekeeping. The common time source is coordinated Universal Time, or U.T.C., which is beamed down from extremely precise atomic clocks aboard satellites like GPS. This time source can also be used to fuel solutions for dynamic situational awareness and enable utilities to identify and understand specific incidents such as lightning strikes, the progression of a system collapse, and other transient grid events.
The impact of timing signal outages on power utilities has been studied by the North American SynchroPhasor Initiative (NASPI), a voluntary group of representatives from the utility industry, manufacturers and vendors, academia, national laboratories, government experts and standards-making bodies. Funded by the U.S. Department of Energy (DOE), this collaborative looked specifically at synchrophasor technology used by utilities to enhance power system reliability and visibility through precise, time-stamped measurements of instantaneous voltage, current and frequency at specific locations on the grid. Initially deployed primarily in transmission and bulk power systems, the technology is increasingly attractive at the grid edge where it can also be used to help monitor distributed energy resources (DERs), analyze grid imbalances, and detect instabilities caused by the growth in electric vehicle (EV) charging stations and more customer-initiated demand response.
In its 2017 technical report, NASPI said most phasor measurement units (PMUs) in North America acquire timing data from GPS. This is the GNSS service operated by the U.S. Air Force. According to the report, GPS disruption “will complicate grid operations by raising false alarms, increasing cost, delaying operational actions, and lowering system efficiency.” The report also warned grid operators that they must start implementing measures “to assure that PMU data receives accurate, reliable time-stamps despite multiple time signal delivery failure modes.” It also recommended that PMUs not be used in automated control and other mission-critical purposes “until timing challenges have been resolved and time and measurement integrity can be assured.”
Public and Private Sectors Collaborate on Solutions
Only a handful of countries including China and Russia have terrestrial GPS backup systems. Other countries are considering them and/or have approved but not yet funded them. For instance, the European Commission, assisted by its Directorate General for Defence Industry and Space, recently awarded seven contracts to six different companies for demonstration of alternative PNT solutions that could provide backup during a GNSS outage.
In the U.S., nearly two dozen U.S. government reports, guidance, and policy directives issued since 2001 have recommended, at a minimum, the deployment of a wireless, nationwide, terrestrial based back-up system to the nation’s GPS service. The Bush administration in 2004 ordered that a backup system be added to GPS, and in 2008 and 2015 the government announced the establishment of a system of complementary high-powered terrestrial signals that would be more difficult to disrupt than space-based GPS. Nothing was done until a bipartisan effort by senior leaders of Congress led to passage of the National Timing Resilience and Security Act (NTRSA) of 2018.
The NTRSA promised that an affordable, wireless, and nationwide GPS backup system would be available to all Americans, everywhere. While this continues to be its standing recommendation, some are under the misconception that NTRSA mandates a single GPS backup system. On the contrary, resiliency requires an ecosystem of diverse technologies, a true “system of systems” methodology, based on the deployment of foundational technology that delivers what lawmakers and government agencies agree are critical attributes: terrestrial deployment with high enough power and wide enough reach, that is affordable for commercial customers and has no common failure modes to GPS
The NTRSA also recommends that the GPS backup system be implemented through a public/private partnership (PPP) to fund the construction and deployment of the system at no risk or cost for the taxpayer, and ensure it is brought to market and made available to all users and the PNT resiliency ecosystem. The NTRSA will not limit the use of existing commercial PNT products that provide GPS resiliency for critical infrastructures, nor mandate adoption of the recommended technology or make strategy or architecture recommendations to any one entity.
The private sector supports these recommendations and has been actively developing solutions. Organizations including the Alliance for Telecommunications Industry Solutions (ATIS) and the Resilient Navigation and Timing Foundation (RNTF) have endorsed the findings of the US DOT’s Complementary Positioning, Navigation, and Timing (PNT) and GPS Backup Technologies Demonstration Report. It included the pilot test results of 11 candidate technologies for complementary positioning or timing functions in the event of GPS service disruptions. Multiple scenarios were created to assess the time transfer capability and positioning performance of participating vendor systems to a static location.
The eLORAN Reference Station Offset scenario may be the most interesting to the power industry, as it was designed to demonstrate timing error characteristics and short-term stability of specific eLORAN vendor technologies at locations with progressively larger, 15- to 60-mile baseline distances between the user equipment (UE) and reference stations antennae locations, consistent with the typical grid layout. The objective was to verify the availability and to assess the uniformity of the coverage of each of the participating eLORAN systems. The eLORAN system uses a network of terrestrial antennae and high-power radio frequency (RF) transmitters to distribute time and position information over very large geographical areas without the same threat vectors as GNSS. To further improve accuracy, an underlying network of reference stations are used to provide corrections for RF interference caused by weather, atmospheric and topographical anomalies and changes.
The DOT report’s conclusion was that the best strategy for achieving resilient PNT service is to pursue multiple technologies, and there is a diverse enough universe of technologies to meet the varied function, application and end-user specific positioning and navigation needs of each type of critical infrastructure. Among these technologies are those that solve the GPS spoofing and jamming challenge. One is a type of mitigation equipment that performs a finite period of timekeeping “holdover” during shorter GNSS lapses of a few hours. A second is the use of cesium-based atomic clocks that can replace GNSS as the primary reference clock right at the location where time is needed. The third is equipment that is installed between an existing GNSS antenna and the GNSS receiver system and operates like a network firewall to defend against unwanted, potentially jammed or spoofed, signals coming into the firewall mitigating the threat.
The private sector must continue to innovate while the public sector works to fund and deliver GNSS backup systems, worldwide. In the U.S., this includes fulfilling the NTRSA’s original intent to protect America using proven, widely adopted technologies. Similar initiatives are underway worldwide. Putting terrestrial backup systems in place will enable electric utility operators across the globe to continue relying on their nation’s GNSS services as PNT sources for existing applications while expanding their use to solve the difficult challenges of predicting failures and maintaining reliable service in an increasingly complex and dynamic grid.
About the Author
Duke Buckner leads business operations and strategy for Microchip’s Frequency and Time Systems business unit. With more than 30 years experience, Mr. Buckner has held successive management and executive roles in network operations and engineering, as well as global sales and marketing. In addition, as an expert in frequency and timing for critical infrastructure networks, he currently serves as Vice Chairperson for the International Time and Synchronization Forum (ITSF) in Europe.
