Most Commercial GPS Safe From Ligado 5G, Military Faces Problems


A study by the National Academies of Sciences has determined that most civilian GPS services won’t suffer significant interference from Ligado’s new 5G cellular and data service but the military might be in some trouble. The study, which was ordered by Congress and funded by the Pentagon, determined that the Ligado network, which will carry 5G signals in frequency bands close to those used by GPS, “will not cause most commercially produced general navigation, timing, cellular or certified aviation GPS receivers to experience harmful interference.”

The study did say that some high-precision commercial GPS receivers used in agriculture, surveying and geodesy (the science of accurately measuring and understanding Earth’s geometric shape and size and orientation in space, and gravity) sold before 2012 “can be vulnerable to significant harmful interference.” But it appears the main effect will be on Iridium satellites, which are under contract to the Defense Department. It says Iridium terminals “will experience harmful interference” within 2,401 feet of Ligado terminals. The study says that interference could affect critical national security operations. It also noted that satellite services provided to the military by Iridium’s competitor Globalstar are unlikely to be affected.

Iridium spokesman Jordan Hassin told Defense News the study confirms what Ligado opponents have said all along. “The findings from the [National Academies of Sciences] are consistent with the opposition from 14 federal agencies, more than 80 stakeholders and Iridium’s concerns that Ligado’s proposed operations will cause harmful interference,” he said. 

Ligado spokeswoman Ashley Durmer said the study also confirms what her company and its supporters have argued. “A small percentage of very old and poorly designed GPS devices may require upgrading,” Durmer said. “Ligado, in tandem with the FCC [Federal Communications Commission], established a program two years ago to upgrade or replace federal equipment, and we remain ready to help any agency that comes forward with outdated devices. So far, none have.”

Ligado will soon begin operational testing of its 5G system. It was given a license to use a portion of the L-Band radio spectrum by the FCC two years ago. That prompted the formation of the Keep GPS Working Coalition that has been lobbying Congress and organizing opposition to force the FCC to overturn its spectrum award to Ligado.

Russ Niles
Russ Niles is Editor-in-Chief of AVweb. He has been a pilot for 30 years and joined AVweb 22 years ago. He and his wife Marni live in southern British Columbia where they also operate a small winery.

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  1. “It says Iridium terminals “will experience harmful interference” within 2,401 feet of Ligado terminals.”

    Not half a mile. Not twenty-four hundred feet. No, the problem is within 2,401 feet precisely. Watch your step.

  2. Russ:

    Did you notice the part that said:

     DoD and interagency partners conducted testing to determine the impacts to GPS
    (captures FCC Order 20-48’s authorized deployment). The tests demonstrated that
    the proposed signal introduces harmful interference to critical national security
    mission capabilities.
     The terrestrial network authorized by FCC Order 20-48 will create unacceptable
    harmful interference for DoD missions. The mitigation techniques and other
    regulatory provisions in FCC Order 20-48 are insufficient to protect national security

    Yeah, you were only reporting on the civil part, but it looks like some more work to do that is germane.



  3. Somehow, I’m not reassured that “critical national security mission capabilities” depend on systems that can so easily be trashed by incidental out of band transmissions. What will we do when the enemy infantryman fires up his $13.95 battery powered on-frequency pocket jammer?

  4. Dear Russ: What did they say about high precision GPS systems used in farming? The problem with using RF guardbands is signal lobes harmonics will be present upband and down band and that is the reason these guardbands were established in the first place. Legado and its defunct predecessor, LightSquared demonstrated that same approach. Nothing has changed. Terrestrial Demonstration Testing done at 1/10th power in Las Vegas disrupted GPS air navigation for nearly 1000 miles at altitude then. What has Legado done differently from Lightsquared and how has it been tested? It is my understanding that the same issues remain, and it is unlikely that the physics of RF generation and propagation have markedly changed since Phil Harbin first gave big bucks to Obama to get the original and since rejected FCC waivers necessary to use the very cheap spectrum he bought which is now Legado networks after he was shut down. Perhaps a more in depth survey would be useful: Like perhaps calling Garmin, King and others for their data and comments?

  5. Oh, joy. Just when technology is developed to precisely and accurately spry, map, and evaluate my crops, along comes corporate greed to mess it up! No transmitter issues just one signal frequency. There are harmonics above and below the actual target frequency. A good design has these harmonics at a much lower power than the main, but they exist nonetheless. Transmitters then utilize filters to attenuate those unwanted signals. But, again, nothing is perfect. Signal strength decreases with the square of the distance increase, so obviously towers at a significant distance are no issue. But they are growing out of the earth like weeds – a VZW tower (type yet unknown) just appeared about 1,000 yds from my home – direct line of view. I have had paging services of years gone by “tramp” on my commercial two-way system. Took over three months and several calls ( and a threat to involve the FCC) to rectify the issue. Let’s hope for the best, in a guarded way!