Radio navigation

Radio navigation is poised to make a global comeback as a GPS backup, as cyber

Enlarge / This is how we used to identify ourselves.

In the 1980s, when I was a young naval officer, the global positioning system was still in the experimental stage. If you were in the middle of the ocean on a cloudy night, there was practically only one reliable way to know where you were: Loran-C, the low-frequency hyperbolic radio navigation system. Using a global network of ground-based radio beacons, Loran-C gave navigators aboard ships and aircraft the ability to get a fix on their location within a few hundred feet using the timing difference of two or more beacon signals.

An evolution of WWII technology (LORAN was an acronym for long-range navigation), Loran-C was considered obsolete by many once GPS became widely available. In 2010, after the US Coast Guard said it was no longer needed, the US and Canada shut down their Loran-C beacons. Between 2010 and 2015, almost everyone also shut down their radio beacons. Trial of an improved Loran service called eLoran that was accurate to less than 20 meters (65 ft) also ended during this time.

But now there are growing concerns about the navigation field’s overreliance on GPS. Since GPS signals from satellites are relatively weak, they are subject to interference, accidental or deliberate. And GPS can be jammed or tampered with – handheld devices can easily drown out GPS or broadcast false signals that can cause GPS receivers to give incorrect position data. The same goes for the Russian-made GLONASS system.

In recent years, the US Coast Guard has reported several episodes of GPS jamming in non-US ports, including an incident reported to the Coast Guard Navigation Center in June that occurred on the Black Sea. South Korea has repeatedly claimed that North Korea blocked GPS near the border, interfering with the navigation of aircraft and the fishing fleet. And in the event of a war, it is possible that an adversary could destroy GPS satellites with anti-satellite weapons or some kind of cyber attack on a satellite network.

As Director of National Intelligence Dan Coates told the Senate Intelligence Committee in May:

The global threat of electronic warfare (EW) attacks against space systems will increase in the coming years, both in number and types of weapons. Development will most likely focus on jamming capabilities against dedicated military satellite communications (SATCOM), Synthetic Aperture Radar (SAR) imaging satellites and enhanced capabilities against Global Navigation Satellite Systems (GNSS). ), such as the US Global Positioning System (GPS).

The risk to GPS has prompted a number of countries to review terrestrial radio navigation. Today there is widespread support worldwide for a new radio navigation network based on more modern technology – and the system that has taken the lead in this role is eLoran. As Reuters reports, South Korea is preparing to bring back radio navigation with eLoran as a backup system for GPS, and the United States is considering doing the same.

Diff-eq

The eLoran system obtains its improved accuracy the same way enhanced GPS equipment extracts greater accuracy from the civilian GPS signal for tasks such as surveying and mapping, using differential correction. A fixed receiver at a known fixed location checks the signal from the beacon and measures the difference between its actual distance from the beacon and the distance calculated from the signal (based on the difference between the timestamp of the signal and the time at which it was actually received).

In differential GPS, differential information is broadcast by a base station at the known differential point; in eLoran, the data is sent back to the eLoran transmitter, and the transmitter applies the differential correction to its own signal. eLoran being regional, the differential calculus remains relatively accurate over its entire coverage area.

Because it uses low frequency radio waves (in the 90-110 kHz range), you are unlikely to see eLoran embedded in your smartphone. While the antenna required to receive eLoran signals is relatively small (about two square inches), that’s a pretty significant amount of real estate for a smartphone to devote to a backup navigation system. But this size could be reduced with an investment in antenna miniaturization. And although eLoran only works in two dimensions (it doesn’t provide elevation data) and only works regionally (with a range of 800 miles), it has one major advantage over GPS: its powerful low-frequency signals are much less likely to jam. or identity theft. The signal from eLoran beacons is 1.3 million times stronger than GPS signals. A 2006 MITER study found that attempts to jam or spoof eLoran would be very unlikely to work.

“[eLoran] is a deterrent to deliberate jamming or impersonation because such hostile activity can be rendered ineffective,” said Brad Parkinson, the retired U.S. Air Force colonel who managed the program. original GPS development, according to Reuters A report Parkinson contributed to for an Institute for Defense Analytics Independent Assessment Team in 2014 found that “eLoran is the only cost-effective backup for national needs.”

The administrations of George W. Bush and Barack Obama pushed for a national eLoran system, but their efforts were never funded by Congress. However, the version of the Department of Homeland Security funding bill for 2018 that just passed the House of Representatives in July includes language calling on DHS to fund the construction and maintenance of a new eLoran system. “in addition to and in support of” the GPS system. And the South Korean government has already put forward plans to have three active eLoran beacons by 2019 – that’s enough to provide accurate fixes for all shipments in the region if North Korea (or someone other) tries to block the GPS again.