Image: Old DHS HQ Sign – RNT Foundation
What’s new: We discovered this document from September.
Why it’s important: This is good info from DHS. Though a bit generic, it is important to “think about how to think about” this topic.
What else to know: Interesting that the document does not talk much about alternatives , perhaps because there are not a lot that are widely and easily accessible. It does say:
1.2 Transitioning from Reliance Solely on GPS
The unmatched capability of GPS has led to its widespread dependence as a PNT source in the U.S. critical infrastructure and its resulting national security. The ongoing legacy of directly consuming the GPS solution from unsophisticated user equipment (UE) creates fragile reliance, however, which motivates the need for better practices and broader sources. One such recommended practice, known as “The Flip” (5), found in competent UE, uses the GPS solution only to discipline internally integrated components at chosen intervals. A disciplined architecture logically divides PNT sources into external aiding and local reference categories, the latter of which accumulates error continuously absent the former. Notably the local frequency references, such as Cesium-beam standards, are highly immune to jamming or spoofing and can provide uninterrupted service that bridges aiding gaps during these adversities. If these local refences have been previously disciplined, the resulting holdover mode of operation can achieve a defined level of performance depending on the initial state of the reference, the duration of the event, and the quality of the local reference. Though GPS remains widely used across the nation, alternative PNT sources are available. The U.S. Department of Transportation continuously evaluates complementary PNT sources and GPS backup technologies (6) and other technologies continue to emerge. This best practices document applies to all current and emerging technologies that provide PNT solutions.
