Following is a guest editorial by GPS World’s contributing editor for Defense, Don Jewell.
Advanced low-frequency (LF) signals are back on the air in North America, with live testing of a wide-area precise-timing solution. Initial tests include a comprehensive pallet of signals, including eLoran, that are being evaluated for their ability to provide a robust, wide-area, wireless precise-timing alternative that can operate cooperatively with GPS, or during periods of GPS unavailability.
The high-power, virtually jam-proof and spoof-proof LF signals operate independently of GPS and GNSS, and provide a Universal Coordinated Time reference, critical to many aspects of U.S. national infrastructure, on the order of tens of nanoseconds.
Not only is this an independent timing backup, but the LF signals can also be used as pseudoranges mixed with GPS, or if enough transmitters are available, as a fully independent PNT network — in other words, a true backup PNT capability for safety-of-life navigation, for dispatching first responders, and for supporting critical national infrastructures.
This is an extremely positive development, especially in light of the LightSquared debacle and the now better-understood vulnerabilities of the very low-power GPS signals.
I hoped I would never have to type that word again, as a noun or a verb, but LightSquared did serve to point out a dire need and shortcoming in the U.S. PNT infrastructure. Fortunately, the proposed eLoran system appears to be on track to fill that need perfectly.
For the first 32 years that GPS signals were broadcast, Loran-C served as a timing backup and a less accurate but viable navigation alternative. In 2010, the current U.S. administration unplugged Loran-C, against the recommendations of the Department of Transportation’s Positioning and Navigation (PosNav) Committee, the Department of Homeland Security Geospatial Committee, the DOT Undersecretary for Policy, and the DHS Deputy Undersecretary for Preparedness and National Protection.
Long story short: non-technical people forced ill-advised technical decisions.
At that time, Loran-C was 80 percent of the way through a critical metamorphosis into a new digital version known as enhanced Loran or eLoran, with better, more reliable transmitters, smaller receivers, and a virtually jam-proof signal structure. Many likened eLoran to a strong ground-based GPS with coded signals for security.
Since then, the government has spent more money dismantling the legacy Loran-C infrastructure than it would have taken to complete the remaining 20 percent upgrade to eLoran.
Let’s hope the eLoran demonstrations continue successfully, and that a contract is forthcoming quickly before anyone forgets the LightSquared lessons learned — like we would ever let that happen.
This is a win/win proposition.