In our increasingly connected society, our dependence on the Global Positioning System for critical applications and services including the electric grid, financial networks, and aviation, has never been greater. To protect those capabilities, there has been recent focus on GPS backup technologies. For critical technologies where failure is not an option, redundancy makes sense.
Responding to this need, in 2017 Congress required the Secretary of Defense, the Secretary of Transportation, and the Secretary of Homeland Security, to develop a joint plan for demonstrating various GPS backup technologies developed by the private sector. A year later, Congress instructed the Department of Transportation (DOT) to establish the requirements for a land-based system to complement and backup the timing component of GPS. In January of this year, the agency issued a comprehensive report detailing its findings from the 11 technologies tested during the Congressionally-mandated demonstrations.
The results of the DOT’s study show that no single technology is capable of replacing GPS as the gold-standard for positioning, navigation, and timing services. With more than 900 million GPS receivers in the United States, and billions more devices worldwide, GPS delivers unprecedented reliability and global coverage that a terrestrial-based technology simply cannot match. Instead, as the report outlines, “the best strategy for achieving resilient PNT service is to pursue multiple technologies to promote diversity in the PNT functions that support transportation and other critical infrastructure sectors.” The GPS Innovation Alliance agrees.
While GPSIA maintains a technology-neutral stance when it comes to the solutions chosen as backups, it is essential they be able to offer equivalent capabilities, a level of performance on par with GPS technologies; and are driven by the PNT requirements of each industry sector, not government mandates. Similarly, there should be an eye towards cost-effective solutions that afford the appropriate level of capability to the greatest number of users, without diverting funding from the GPS program.
Increasing PNT resiliency though is not just about investing in alternative technologies – it’s also about modernization. The GPS industry is innovating at a rapid pace, developing solutions that make GPS receivers, the satellites that deliver these GPS signals, and the ground control segment that tracks and monitors GPS performance even more precise and more resilient. These efforts include a major modernization of the GPS constellation, which when completed, will deliver dozens of new satellites providing greater accuracy and increased anti-jamming capabilities for the military. Modernization also includes the completed roll out of M-code, an advanced, new signal designed to improve anti-jamming and anti-spoofing, as well as to increase secure access to military GPS signals for U.S. and allied armed forces.
Select classes of GPS receivers operating in areas with a high likelihood of experiencing jamming or spoofing can also be made more resilient through certain regulated techniques and technologies. Unfortunately, U.S. restrictions, such as the current ITAR regulations, prevent GPS receiver manufacturers from selling certain solutions that would drive greater resiliency. At present, U.S. regulation limits domestic commercial use of technologies like beamforming and/or nulling as applied to open service GPS signals. However, overseas vendors are already providing these technologies with varying levels of capabilities. To increase U.S. competitiveness, and enable more resilient solutions, Congress should enact legislation requiring the examination of this issue and ultimately removing current restrictions on using these “hardening” capabilities outside of the Department of Defense (DoD). Some advocates of PNT alternatives have used Armageddon-like scenarios to depict GPS as vulnerable to solar flares and other natural disturbances. The GPS constellation was built to withstand these occurrences, and it is why the U.S. Space Force consistently maintains more GPS satellites than are actually needed at any one time.
These claims are a distraction from the real risks to GPS, which at one time had no competition. Today, other international Global Navigation Satellite Systems (GNSS) – like Galileo, GLONASS and BeiDou have entered the GPS ecosystem. They don’t necessarily have better signals, but have benefitted by modeling their signals after GPS signal development, and ultimately have launched their constellations more quickly. In order to maintain our competitive edge, we must step up GPS modernization to ensure that technology and system resilience refreshes are injected as technology and threats evolve. This mean changing our mindset of how we address technology and resiliency lags -- moving away from a historical pattern of just launching to replace satellites, which are finally fading after operating more than twice their design life -- to a plan that prioritizes launching and fielding new capabilities more quickly.
Locally we have threats too, like allowing a terrestrial-based service, to operate in spectrum adjacent to the GPS band. GPS has thrived because of its placement in spectrum zoned for satellite-based services. GPSIA has long advocated for application of a 1 dB standard to measure and prevent interference that could render GPS receivers less reliable, accurate, and resilient, removing the benefits that they provide to critical sectors of our economy.
To ensure GPS remains the gold-standard for PNT, Congress should continue investing in new satellites, a modern ground control, and eliminate restrictions on the commercial use of more resilient GPS receivers. It is also essential that Congress and the Biden Administration remain committed to protecting the GPS spectrum from adjacent band interference. Taken together, the GPS industry is committed to making GPS even more resilient, with greater capabilities through continued modernization of space and ground segment, while simultaneously supporting complementary backup technologies.
J. David Grossman is executive director of the GPS Innovation Alliance.
