First Fix: GPS can stay first

This month’s cover story focuses on jamming and spoofing in the military domain, but this is also a big challenge for users of civilian GNSS applications, such as airline pilots. Our July cover story will focus on complementary PNT — that is, non-GNSS sources of positioning, navigation and timing data that can complement GNSS and help make up for its inherent shortcomings, such as weak signals that are easily blocked by thick foliage and roofs, multipath and few satellites in view from natural and urban canyons.

Matteo Luccio

In the coming months, we will steadily increase our coverage of complementary PNT companies, products and services, including those based on low Earth-orbiting (LEO) satellites, because they are an increasingly important component of the PNT industry. We will start by expanding our coverage of this area on our website and in our digital newsletters, then increase coverage in our print editions.

One proposal that has received scant attention, including from this magazine, is to set up a ground-based, cryptographically protected GPS High Accuracy and Robustness Service (HARS) using the internet to distribute data already being produced by the U.S. government and government-sponsored organizations. This was the subject of a white paper released in May 2023 by the National Space-Based Positioning, Navigation, and Timing Advisory Board.

The paper argued that GPS is “falling behind” other GNSS because it relies on augmentation by third-party systems rather than providing such specialized advanced services itself, as BeiDou and Galileo do. While nearly all GNSS chips currently acquire first GPS signals, then those from other systems, deployment by BeiDou and Galileo of sub-meter accuracy services may lead chip manufacturers to reverse this order. If they do, the paper argued, it will cause the U.S. government to lose its strategic advantage in this area and put it in the same position that led the Chinese and European governments to launch their own GNSS programs.

The paper proposed a HARS that would remove satellite orbit and clock errors, ionospheric errors, and tropospheric errors and enhance the ability of GNSS receivers to operate in challenging conditions. This approach, the paper says, could allow Precise Point Positioning (PPP), authentication, and more. It would be “secure and less sensitive to radio noise and disruptions,” protect critical infrastructure, and enable new applications, such as “lane-dependent route guidance in automobile navigation and emergency vehicle guidance.” Additionally, by delivering, along with the corrections, cryptographically signed ephemeris on the same channel, the system would solve the problem of spoofed navigation data.

All of this could be done “without adding cost and complexity to GPS itself” resulting in “a world-class HARS at a small fraction of the cost or time, compared to implementing it on new GPS satellites.” The paper asked for funding for this new service and an agency to operate it, such as the U.S. Space Force or the federal Department of Transportation.

I thank John Betz, Ph.D., of MITRE, for bringing the PNT Advisory Board’s white paper on HARS to my attention. It can be found here.