Running Interference

Is Ligado Networks’ proposed terrestrial nationwide network a threat to GPS or a boon to 5G?

The Global Positioning System has always faced challenges inherent in its design (weak signal, orbital and clock errors, receiver noise, dilution of precision), as well as from natural phenomena (ionospheric and tropospheric delays, solar flares), local topography and the built environment (signal attenuation and occultation, multipath), and human activities (unintentional RF interference, spoofing, and jamming).

A decade ago, the GPS vendor and user community faced a new threat: the prospect of interference from LightSquared, which sought to develop a 4G LTE wireless broadband network using spectrum in the L-Band. After a battle that lasted more than a year, in 2011 the Federal Communications Commission (FCC) denied LightSquared’s proposal until it could remove the risk of harmful interference to GPS. The company went bankrupt in 2012.

However, this threat to GPS resurfaced in February 2016, when LightSquared was reborn as Ligado Networks. On April 20, 2020, the company secured a victory when the FCC, reversing its 2011 decision, voted unanimously to approve its plan to “deploy a low-power [9.8 dBW] terrestrial nationwide network in the 1526-1536 MHz, 1627.5-1637.5 MHz, and 1646.5-1656.5 MHz bands [of the electromagnetic spectrum] that will primarily support Internet of Things (IoT) services.” These frequencies, traditionally used for satellite operations, are adjacent to the most widely used GPS band.

The reaction from the GPS community was swift, forceful, and widespread. The FCC has already received eight petitions for reconsideration and a petition for stay totaling a couple of hundred pages of detailed critiques of its decision. These petitions have broad support from the aviation, satellite communications, and GPS industries, as well as the U.S. departments of Defense (DOD), Transportation (DOT), Homeland Security, Interior, and Justice, the Federal Aviation Administration (FAA), and other federal agencies. Congress is also likely to weigh in soon.

The FCC’s Decision

The FCC’s 2011 decision came after a thorough series of tests, overseen jointly by GPS manufacturers and LightSquared. It proved extensive interference with GNSS devices operating in the L1 band, which is centered at 1575.42MHz, from transmissions in the upper and lower bands of the 1526MHz to 1559MHz section of the spectrum, in which Ligado wants to operate. The National Telecommunications and Information Administration (NTIA), which advises the president on telecommunications policy issues, concluded that there was no practical way to mitigate potential GPS interference.

LightSquared was rescued from bankruptcy by private investment groups that bought its assets and relaunched it as Ligado. In 2015, it began to promote a variation on its predecessor’s plan to convert frequencies previously allocated for satellite communications to a new ground-based network in support of the emerging 5G technology for mobile devices and applications.

The company proposed the creation of a buffer zone, 23MHz wide, between its frequencies and those used by GPS and cutting the transmission power of its base stations by an order of magnitude, to 9.8dBW. Yet, despite these adjustments, tests conducted in 2016 by DOT revealed that Ligado’s new plan continued to endanger the accuracy and reliability of GPS receivers.

In deciding to nevertheless accept Ligado’s plan, the FCC accepted the standard of “harmful interference” that the company advocates, replacing the long-established international standard of 1dB degradation of the power density ratio in GNSS receivers. By defining interference in terms of receiver malfunction, the FCC shifted to GPS users the burden of detecting and reporting interference. It failed, however, to formulate a plan to inform public, commercial, and individual users of this threat — nor could the latter begin to mount a defense because Ligado has not yet announced the number and location of its proposed transmitters. Moreover, the FCC’s order delegates to Ligado responsibility for verifying whether its own network is the source of interference.

The FCC did impose on Ligado several conditions:

  • increasethe distance on the spectrum between its planned terrestrial network and the GPS band 
  • increasethe width of the guard band between its terrestrial service and the GPS band 
  • createguard bands between its terrestrial service and other users 
  • reducepower levels at its base stations to 99.3 percent less than those it had proposed in 2015 
  • reportthe locations of its proposed base stations 
  • setup a system to receive and address reports of interference.

The late Javad Ashjaee, founder of JAVAD, used to argue that receivers could and should filter out interference such as that potentially caused by Ligado’s proposed network. However, while that may be a solution for new, high-end receivers, it does not apply to consumer receivers nor to the roughly one billion receivers already deployed (mostly in cell phones).

According to the FCC’s order, Ligado would have to pay to replace impacted receivers only if they are owned by the U.S. federal government. Additionally, filtering reduces a receiver’s ability to collect the energy of the GPS signals, which is already extremely low.

Regarding the standard that the FCC applied in its Ligado decision, a letter by electronics manufacturer CalAmp stated: “Each different IoT application is potentially subject to distinct metrics for successful operation, such as the accuracy of position, velocity, acceleration, and timing. Because considering each different metric for every type of IoT application is not practical, and because the state of the art in cutting edge technologies is always advancing […], the best metric for protecting GPS is to use a 1-dB degradation in carrier to noise ratio (C/N0) […]. Indeed, as Trimble Inc. has stated, the FCC’s record ‘conclusively demonstrated that a 1dB adverse change was correlated with degradation of GPS receiver performance.’ Further, NTIA expressed that ‘testing based on the use and application of a 1dB [C/N0] degradation metric is valid and should not be disregarded.’”

The Reaction

The overwhelming majority of the GPS community found these conditions to be wholly insufficient to address their concerns about Ligado’s plan. Some GPS receiver manufacturers, while not too bothered by Ligado’s uplink or handset operations, which would roam and operate at low power, are very worried about its plan to build a nationwide wireless network, which would require a consistent level of energy throughout a service area, affecting every GPS receiver.

Dr. Brad Parkinson, one of the principal creators of GPS, in his capacity as first vice-chair of the National Space-Based Positioning, Navigation, and Timing Advisory Board, a federal interagency group, declared that the FCC had “made a grave error in authorizing a high-power, terrestrial communication-network in the mobile satellite service (MSS) radio spectrum adjacent to GPS” and called for the FCC to immediately rescind its order. The full board endorsed Parkinson’s statement.

DOD told Congress that it had been “completely caught off guard” by the FCC’s decision, which the agency had circulated in draft form only four days before announcing it. Dr. Michael Griffin, Under Secretary of Defense for Research and Engineering, asserted that any ground transmissions, regardless of power level, “would drown out the very weak signals that come from [GPS] satellites,” likening the effect of the proposed Ligado network on GPS to attempting to listen to the rustling of leaves while 100 jet aircraft took off simultaneously.

In the spring, a large bipartisan group of members of the U.S. House Armed Services Committee also wrote to the FCC to express concern, followed by an even larger bipartisan group of U.S. Senators, who urged the FCC to reconsider its decision. Both the House and the Senate have proposed Ligado– or GPS interference-related legislation in their respective versions of the FY2021 National Defense Authorization Act.

The forces opposing the FCC’s Ligado decision also include the Keep GPS Working Coalition, formed in June by the Association of Equipment Manufacturers, the American Farm Bureau Federation, the American Road & Transportation Builders Association, the Aircraft Owners & Pilots Association, and the Boat Owners Association of The United States (BoatU.S.), jointly representing thousands of companies and millions of GPS users. On September 29, the Agricultural Retailers Association, the American Soybean Association, the Equipment Dealers Association, the Iowa-Nebraska Equipment Dealers Association, the National Corn Growers Association, the National Cotton Council of America, and the USA Rice Federation joined the coalition.

As its first act, the Keep GPS Working Coalition endorsed the Recognizing and Ensuring Taxpayer Access to Infrastructure Necessary for GPS and Satellite Communications (RETAIN) Act, introduced by Sens. Jim Inhofe (R-Okla.) and Jack Reed (D-R.I.). Among other things, the act mandates Ligado to “upgrade, repair, or replace” impacted GPS receivers owned by federal agencies — but not state and local governments and private users — and to reimburse them for costs they incurred due to interference from its network. In June, the Senate Armed Services Committee approved nearly unanimously the 2021 defense budget, which contained language criticizing the FCC’s “misguided decision,” prohibiting the use of DOD funds to comply with it until the secretary of defense provides an estimate of the costs of remedying any interference from Ligado, and directing the secretary to commission an independent study from the National Academies of Science and Engineering on the company’s and the department’s testing methodologies.

In an opinion piece on October 20, J. David Grossman, executive director of the GPS Innovation Alliance, questioned Ligado’s claim that its proposed system would be essential to the development of 5G. He pointed out that Ligado’s spectrum blocks of 10 noncontiguous megahertz represent less than one percent of the spectrum the FCC has auctioned or proposed be made available for 5G services.

Furthermore, he wrote, Ligado’s use of the L-band for a high-power terrestrial service threatens to undermine the foundation for existing 3G and 4G networks, as well as mainstream 5G networks, because the advanced radio features associated with 5G have made even more critical the extremely accurate timing alignment that is enabled by GPS.

The latter point is supported by a new GNSS User Technology Report published by the European Global Navigation Satellite Systems Agency, which states that “the timing synchronization accuracy requirement is expected to ramp-up from 1.5 microseconds for 4G, to 130 nanoseconds for 5G” and “could even go up to 65 nanoseconds at the next phase of the 5G development.”

In an October 27 letter to the chairman and ranking member of the U.S. Senate’s Committee on Commerce, Science, and Transportation, 79 companies and trade associations representing mostly the aerospace, agricultural, airline, transportation, and weather sectors, expressed their “profound concern” over the FCC’s “flawed” Ligado order.

The letter stated that, if left in place, the order “would upend decades of sound spectrum policy, negatively impact a significant cross-section of commercial, federal, and academic users who rely on the many different L-band satellite services, and threaten the safety of most Americans.”

It argued that “the Ligado Order failed to take full account of the diverse services in the L-band, including those relied on by military, federal, and public safety users, that would be stranded or significantly impaired […] by the harmful interference caused by Ligado’s proposed terrestrial network.”

The signers urged the Committee to “work with the [FCC] to set aside the flawed Ligado Order in favor of a process that is responsive to the concerns of the incredibly broad cross-section of L-band operators and users representing the aviation, aerospace, agriculture, GPS, ground transportation, mapping, marine, metrological, public safety, satellite communications, and surveying industries and professions.”

Secretary of State Mike Pompeo, Attorney General William Barr, and other Trump administration officials, however, continue to support Ligado’s plan, which Pompeo and Barr have advocated as essential to maintain U.S. economic and technological superiority to China. FCC chairman Ajit Pai has rejected the concerns of the House Armed Services Committee, arguing that his agency’s decision did not “authorize any spectrum sharing between Ligado and GPS,” underlining the conditions it had imposed on the company, and declaring “false” the accusation that DOD had not been afforded an opportunity to present its side of the story.


Why did the FCC vote 5-0 in Ligado’s favor? Industry insiders have many theories. For starters, they note, Ligado, which, according to one source, has contracts with 20 lobbying firms, has visited the FCC’s offices every few months for years, pushing its narrative that it has dramatically reduced its proposed transmission power and that it has reached agreements with several of the major GPS receiver manufacturers.

However, after it went bankrupt, the company filed lawsuits against Deere, Garmin, and Trimble, claiming billions of dollars in damages. Deere, which had already spent a lot of money on litigation years earlier in the first round of the fight, settled. While Trimble and Garmin also settled, the former retained the right to advocate for a package of proposals, including further studies by DOT of the downlink in the 1526MHz to 1536MHz band, and the latter retained the right to advocate for the 1dB standard as the correct one to evaluate interference and to speak to the impact on certified aviation receivers, which it has done. In all three settlements, Ligado agreed to give up forever any claims to use the spectrum directly adjacent to that used by GPS base stations, which is 1545MHz to 1555MHz.

Hexagon, Topcon, and a few other manufacturers who also entered into agreements with Ligado, were certainly aware of Ligado’s lawsuits. Others may have also settled in return for payments from Ligado. Some, like uBlox, which recently sold it 500 millionth GPS receiver, declined to settle. On September 21, electronics manufacturer CalAmp, which has sold 20 million GPS receivers, filed a letter with the FCC to “express its concerns” about the agency’s Ligado order.

Ligado’s terrestrial operations,” it stated, “will cause significant harmful interference to [GPS] receivers, including those used in [IoT] devices and services manufactured, marketed, and sold by CalAmp. To prevent such harmful interference, the Commission should stay the Ligado Order and reconsider the conditions under which it will allow Ligado to operate.”

It also pointed out that CalAmp products, like many IoT devices in service today, were recent innovations not included in the testing programs that the FCC considered and “were simply not designed to tolerate interference from dense terrestrial broadcast communications in the L-Band adjacent to our highly sensitive GNSS receivers.”

Pai was in Verizon’s Government Affairs group when Ivan Seidenberg was the company’s CEO and Bill Barr its general counsel; he is also from Kansas, like Pompeo. This suggests, at a minimum, that Pai could count on powerful support in the administration for his agency’s stance.

According to one industry insider, Ligado does not have any support except from Nokia and Ericsson, which are both vendors to it. 


With opposition to its plan from powerful federal departments, members of Congress, and a broad spectrum of industry and user groups, Ligado is facing hard times. According to a September 15 article in the Wall Street Journal, it was “in talks with key creditors and shareholders to restructure about $8 billion in debt and other obligations while buying time to monetize its 5G-network assets.”

The most likely outcome of this dispute is action by Congress. Alternatively, a court could reverse the FCC’s decision on appeal, if it concluded that it was badly written and there were obvious gaps in the record. Finally, the FCC could void its prior decision and deny Ligado’s request or order Ligado to pay all the expenses or replace all affected receivers.

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