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National Academies issues report on Ligado interference

The National Academies of Sciences, Engineering and Medicine (NASEM) has issued a report discussing whether a terrestrial wireless network proposed by Ligado Networks — and approved by the Federal Communications Commission (FCC) in April 2020 —will cause widespread interference to millions of GPS receivers.

The 77-page report reviews order FCC 20-48, which authorized Ligado Networks LLC to operate a low-power terrestrial radio network adjacent to the GPS frequency band. It considers how best to evaluate harmful interference to civilian and defense users of GPS, the potential for harmful interference to GPS users and DOD activities, and the effectiveness and feasibility of the mitigation measures proposed in the FCC order.

Section 1663 of the Fiscal Year 2021 National Defense Authorization Act called on the Department of Defense (DOD) to enter into an agreement with the NASEM to carry out “an independent technical review of the order and authorization [of  FCC 20-48] to the extent that such Order and Authorization affects the devices, operations or activities of the Department of Defense.”

The committee formed in response met weekly from September 2021 to April 2022 to plan the study; receive briefings from experts and stakeholders; and review relevant reports, technical literature, and written submissions to the committee. In addition, a cleared subset of the committee received a set of classified briefings.

Most receivers in the clear,
high-precision and Iridium vulnerable

The committee found that most commercial and certified aviation GPS receivers will not experience significant harmful interference from Ligado emissions as authorized by the FCC.

However, high-precision receivers are vulnerable. That said, the committee claims current technology enables building a receiver robust to Ligado signals for any GPS applications.

“All GPS receiver manufacturers could field new designs that could coexist with the authorized Ligado signals and achieve good performance even if their existing designs cannot,” the report states.

For Iridium, the report states, “Iridium terminals will experience harmful interference on their downlink caused by Ligado user terminals operating in the UL1 band while those Iridium terminals are within a significant range of a Ligado emitter — up to 732 meters.”

For defense devices, operations and activities, the committee acknowledged that proposed mitigation procedures may be effective, but “may be impractical without the extensive dialog among the affected parties,” and mitigation “may not be practical at operationally relevant time scales or at reasonable cost. ”

This report concludes, “Spectrum real estate is a living asset and approaches must allow not only for a degree of confidence that a deployed system will not be compromised by future, unforeseen entrants, for a period of time, but also must recognize that capabilities will evolve.

“Some form of more definitive receiver standards and establishment of set time periods where adherence to those receiver standards will ensure successful operation for a frequency band’s incumbents and new entrants seem to be important tools in this regard.”

Responses to the Report

Ligado Networks

“Ligado’s licensed and authorized operations can co-exist with GPS. As the report concludes, the technology to enable compatibility has been in use for over a decade, and most consumer equipment, commercial general navigation, timing, cellular and aviation receivers will not experience harmful interference from Ligado’s operations.

“The NAS found what the nation’s experts at the FCC already determined: A small percentage of very old and poorly designed GPS devices may require upgrading. Ligado, in tandem with the FCC, 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.

“Now that the review is completed, it is our sincere hope the DOD and the NTIA will stop blocking Ligado’s license authority and focus instead on working with Ligado to resolve potential impacts relating to all DOD systems, including but not limited to GPS. We will continue working with all involved stakeholders to determine a mutually beneficial way forward.”

U.S. Department of Defense

“National security missions that our service men and women execute every day are of the utmost importance and require a solution that ensures continued operations of critical systems.

“The NASEM study confirms that Ligado’s system will interfere with DOD GPS receivers, which include high-precision GPS receivers. The study also confirms that Iridium satellite communications will experience harmful interference caused by Ligado user terminals. Further, the study notes that when DoD’s testing approach, which is based on signal-to-noise ratio, is correctly applied, it is the more comprehensive and informative approach to assessing interference. The study also concludes that the Federal Communication Commission’s (FCC) proposed mitigation and replacement measures are impractical, cost prohibitive, and possibly ineffective.

“These conclusions are consistent with DoD’s longstanding view that Ligado’s system will interfere with critical GPS receivers and that it is impractical to mitigate the impact of that interference.

“DoD looks forward to continuing to work with the National Telecommunications and Information Administration, FCC and Ligado on this complex and important issue.”

GPS Innovation Alliance

Acting Executive Director of the GPS Innovation Alliance (GPSIA), Alex Damato, issued the following statement on the release of the National Academies of Sciences, Engineering, and Medicine study on reviewing the FCC’s Ligado Order:

“GPSIA and the GPS industry applaud the National Academies of Sciences, Engineering, and Medicine’s reaffirmation that Ligado’s terrestrial operations would have a harmful, real-world impact on the millions of federal and commercial users that rely on GPS, satellite communications, and weather forecasting services every single day. The report’s evaluation of the materials, developed over years of extensive and technically rigorous testing, demonstrates that Ligado would pose an unacceptable risk to services critical to safety-of-life operations, our national security, and our economy. It also builds on the broad consensus, including within fourteen federal agencies and departments, that Ligado’s proposed deployment would result in widespread interference to a substantial number of GPS receivers.

“Following the release of this study, GPSIA urges government action to address the imminent, but preventable, harm that would result from Ligado’s deployment.”

**Consistent with the terms of their litigation settlements with Ligado, GPSIA members Deere & Company and Garmin International, Inc. do not affirmatively endorse or oppose the deployment of Ligado’s proposed communications network.**

Keep GPS Working Coalition

The Keep GPS Working Coalition was formed in response to the FCC order. Spokesperson Dale Leibach issued the following statement.

“The NAS report, which follows the analysis of an immense amount of technical information and review by experts from a broad range of disciplines, highlights the fundamental flaws in the FCC’s Ligado decision. The order must therefore be vacated in its entirety, so that millions of GPS devices are protected from harmful interference caused by Ligado’s planned network.

“It is important to note that the potential for interference arises because Ligado proposed, and the FCC approved, a fundamental change in the use of the spectrum adjacent to the band used by GPS. With this approval, the FCC essentially authorized terrestrial operations in a satellite band without adequately considering the impact Ligado’s proposed operations would have on countless consumers, farmers, ranchers, pilots, boat owners, surveyors, construction companies and others.

“Furthermore, the FCC’s decision failed to take into account that there are more than a billion GPS receivers in use in the United States. The NAS report notes, and the Keep GPS Working Coalition acknowledges, that the majority of GPS receivers will not be harmed by Ligado’s operations. However, the massive GPS user base means that tens of millions of devices will suffer harmful interference if Ligado deploys its network. And, as stated in the report, the risk of interference is greatest for high precision receivers used in some of the most significant sectors of the U.S. economy.

“Lastly, the NAS report describes in detail the fundamental flaws in the safeguards the FCC adopted to address harmful interference where it occurs. It is simply not feasible, nor reasonable, to force first responders, farmers, boat owners, and the many other owners of equipment and machines that rely on GPS to police interference and bear the costs of addressing it. The best approach is to avoid interference altogether by rescinding Ligado’s authorization to conduct terrestrial operations under its satellite license.

“While Ligado may seek to cherry pick details to fit its misleading narrative, the truth is that this report validates the concerns raised by virtually everyone who has taken a position on this matter other than the FCC and Ligado itself. In particular, the report highlights significant national security concerns raised by the U.S. Department of Defense, which has said the FCC Ligado order will put missions and troops at risk. Likewise, the National Telecommunications and Information Administration, the Departments of Homeland Security, Transportation, Interior and Justice, the Federal Aviation Administration and other expert agencies all opposed the FCC order because of the substantial harm it would cause to critical civilian industries and users.”


“The findings from NAS 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. The NAS study clearly demonstrates what the rest of the industry has known for years: the prior FCC order failed to fully consider the risk of harmful interference posed to mission-critical satellite systems. Iridium urges the FCC to take swift action to reverse the order before Ligado starts its technical demonstrations this fall.”

Satellite Safety Alliance

“The Satellite Safety Alliance applauds NAS for its comprehensive review of the record and findings that Ligado’s plan threatens vital GPS and satellite communications services. These findings align with the concerns across the vast federal and commercial user base of GPS, satellite communications, and weather forecasting services.

“This study is a reminder to our nation’s leaders and the Federal Communications Commission that Ligado’s harmful interference will disrupt day-to-day operations and cost billions of dollars to the consumers of these mission-critical services. The FCC must stay or reverse the Ligado order to address the imminent — but preventable — harm from the company’s proposed terrestrial network that it intends to deploy a test network this fall.”

National Telecommunications and Information Administration, U.S. Department of Commerce

“The Report from the National Academies indicates that Ligado’s terrestrial operations would cause harmful interference to GPS devices and that a number of the FCC’s mitigations would be practically unworkable. NTIA will review this detailed report more carefully, but we believe this offers the commission an important opportunity to reconsider Ligado’s authorization.”

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