The UK Royal Institute of Navigation has released a special report on GNSS-interference and its impact on the maritime sector.
Impacts of GNSS Interference on Maritime Safety is a special report by the RIN Maritime GNSS Interference Working Group on the impacts of GNSS Interference. Survey data was compiled from more than 100 sector experts and 300 vessel captains, supported by interviews with dozens of people involved in the operations and supply chain of vessels that regularly encounter GNSS interference.
GNSS interference refers to anything that disrupts a ship’s satellite-based positioning signals, usually caused by jamming and spoofing.
In 2025, at least two collisions and groundings were reported in mainstream media linked to GNSS interference in regions such as the Baltics, Straits of Hormuz and the Red Sea. With hundreds of vessels being affected daily, the RIN report details for the first time the scale of the problem on modern digital vessels, where GNSS jamming and spoofing present a significant cybersecurity vulnerability and urgent risks to maritime safety.
Survey data exposes the vulnerability of critically important systems such as Global Maritime Distress and Safety Systems (GMDSS) and other SOLAS-mandated equipment that rely on satellite positioning and timing.
“The report has highlighted serious safety concerns and has underlined the fact that these issues are rooted in significant cybersecurity vulnerabilities, and are not just disruptions to navigation,” said Ramsey Faragher, director of the RIN.
Operating within regions of known GNSS interference carries serious safety-of-life and liability implications, as key systems are expected to fail or malfunction with high probability in these conditions. The report also highlights unnecessary dependencies between GNSS receivers and a range of onboard electronics — including radar, radios (VHF/MF/HF), Navtex, speed logs, ship clocks and satellite communications — many of which do not require GNSS data for their primary function, creating avoidable points of failure and compounding operational risk.
“The issue of GNSS interference must be taken seriously. It cannot be overcome by traditional navigation techniques when GNSS receivers are ‘baked in’ to modern ships’ critical systems, including safety systems,” said Ivana-Maria Carrioni-Burnett, maritime captain and chair of the RIN Maritime Navigation Group. “These are no longer isolated incidents and pose a real risk to life: people, property and the environment. We must do more to safeguard our seas today and the shipping of tomorrow.”
“Despite measures to improve resistance to jamming, spoofing and other harassment measures, the threat is real and growing,” said Retired Commodore James Taylor OBE and fellow of the RIN advises. “And this threat is not only to positioning and navigation; it is to every part of every transport and navigation means and to every part of national infrastructure where timing is derived from space-based timing signals.”
The Royal Institute of Navigation will continue to work with report partners (GLA, IALA, Nautical Institute and others) and regulatory bodies to provide expert guidance to mitigate these issues, and to establish industry-wide adoption of solutions to this problem. RIN thanks National PNT Office for its support.
The culmination of several years of test and analysis conducted by the U.S. Department of Transportation, the assessment will play a key role in the Federal Communications Commission’s upcoming decision on a proposal from Ligado Networks.
The long-awaited Final Report for the U.S. Department of Transportation’s Adjacent Band Compatibility (ABC) Assessment was released on April 26.
The report is the culmination of several years of test and analysis conducted by the DOT, with input and assistance from the public and federal agency stakeholders. Though not explicitly motivated by it, the assessment appears to be responsive to the Positioning, Navigation, and Timing (PNT) Executive Committee’s (EXCOM’s) Jan. 13, 2012, memorandum to the National Telecommunications and Information Administration (NTIA) that sought to develop metrics to inform commercial non-space proposals for use of frequency bands adjacent to those used by GPS, so that existing and evolving space-based PNT services “vital to economic, public safety, scientific and national security needs” were not affected by implementing such proposals.
The assessment will likely play a key role in the Federal Communications Commission’s upcoming decision on a proposal from Ligado Networks to add an extensive complex of powerful ground transmitters to its system, broadcasting on frequencies allocated for satellites.
Open and Transparent. Two key attributes of the ABC assessment were that it was conducted openly and transparently, with numerous public workshops announced via the Federal Register, and it was agnostic to any particular proposal for use of bands adjacent to GPS/GNSS services. The approach chosen by DOT in performing its assessment was to develop maximum tolerable effective isotropic radiated power (EIRP) levels that could be transmitted at differing frequency offsets from the GPS L1 center frequency.
The term “adjacent” in this regard is a bit of a misnomer in that the assessment range extended to 100 MHz on either side of the GPS L1 center frequency of 1575.42 MHz. This approach was recently validated by the National PNT Systems Engineering Forum (NPEF), which found the ABC assessment was the only one of five test and analysis efforts conducted since 2011 on adjacent-band terrestrial operations that met all six of the test criteria recommended by the experts serving on the National PNT Advisory Board. The NPEF analysis is available here.
Measurements on 80 civil GNSS and GPS receivers were performed at White Sands Missile Range (WSMR) in New Mexico. The Air Force conducted a prior week of testing on military GPS receivers at WSMR, and while the results of that testing are classified, an Air Force briefing at the November 2017 PNT Advisory Board meeting indicated the military receiver test results supported the conclusions drawn by the DOT ABC assessment. Certified aviation GPS/GNSS receivers were analyzed by RTCA Inc. and are being analyzed by the FAA in terms of determining power levels in adjacent bands that don’t exceed FAA Technical Standard Orders. However, the overall ABC assessment indicates that certified aviation receivers are not the limiting case for tolerable interference from adjacent-band services to GPS and GNSS receivers.
Test Procedures
Compatibility assessment for the civil receivers consisted of conducting the initial measurements at WSMR for six categories of receivers: aviation (non-certified), cellular, general location/navigation, high-precision, timing, and space-based receivers. These were evaluated to determine what DOT called Interference Tolerance Masks (ITMs) for each category of receiver and each receiver tested. The ITMs define the maximum aggregate interfering power that can be tolerated by a given GPS or GNSS receiver. The ITMs are based on the internationally accepted Interference Protection Criterion (IPC) of a 1-dB drop-in carrier-to-noise density ratio (C/NO) for the receiver, or, equivalently, an interference density-to-noise ratio (IO/NO) of –6 dB. This 1 dB IPC standard, which NTIA directed to be used in the NPEF evaluation of the original LightSquared (now Ligado) adjacent-band proposal in late 2011, is explained in great detail in a white paper the Air Force made publicly available in 2017.
The assessment then developed, with input from the public at several workshops convened by the DOT, use cases to determine how close a receiver for a particular GPS or GNSS application might be to a base station or handset of a commercial terrestrial service in an adjacent band. Proximity distances of 10 and 100 meters were selected from these use cases, and maximum tolerable transmit EIRP levels for a given frequency offset were determined; see Figure 1. The high-precision receivers (HPRs) were the most susceptible to interference from terrestrial operations in the adjacent bands.
Figure 1. Maximum tolerable power level for GPS/GNSS receivers at 1530 MHz. (Table: DOT)
One thing that seems clear is that, with tolerable transmit power levels in the milliwatt and microwatt range, the potential to use the bands near GPS frequencies for commercial terrestrial wireless services may be limited. Illustrating that point further, the assessment shows that, based on the assumptions in the study, HPRs can be affected at distances beyond 14 kilometers (see Figure 2), and that loss of lock for low-elevation satellites can occur at distances of up to 3 kilometers from a base station providing terrestrial services using characteristics adopted internationally in the International Telecommunication Union (ITU) study groups.
Figure 2. Impact of a 29-dBW cellular base station transmitting at 1530 MHz on a high-precision GPS/GNSS receiver. (Chart: DOT)
Moreover, the assessment determined that the potential interference to other GNSS systems may be more problematic, noting that “the levels that protect all GNSS signals can be as much as 15 dB lower than those needed to protect L1 C/A signals from base station emissions with an average difference of 3.5 dB across all frequencies and five categories considered.”
Galileo’s Role. Since 2013, according to a Public Notice from the FCC, the European Commission has sought a waiver of FCC rules that require licensing of receivers operating with foreign satellites so that Galileo service can be provided in the United States. The FCC has yet to act on this waiver request, which was issued in a January 2017 Public Notice, despite overwhelming public support and a positive recommendation from the Executive Branch in 2015.
Figure 3. Bounding masks for each category corresponding to the 10 MHz LTE interference signal and L1 C/A GPS signal: general aviation, general location and navigation, high precision, timing, space-based, cellular. (Graph: DOT)
Conclusions
It is well known that all receivers take in some power from signals transmitted in nearby frequency bands. Considering this fact, the ABC assessment is relatively unique in that it examines the overall spectral environment in which GPS/GNSS operations can be affected rather than just the band allocated to the Radionavigation-Satellite Service (RNSS, the broad radiocommunication service defined in the ITU and in domestic rules under which GPS and other GNSS systems operate) between 1559–1610 MHz. That the overall environment should be considered is an important aspect of any discussion of protecting GPS and other GNSS services given the U.S. National Space Policy that was signed into effect June 28, 2010, that directs the U.S. government to “take necessary measures to sustain the radiofrequency environment in which critical U.S. space systems operate.” This policy is still in effect, and it would be difficult to argue that GPS is not a critical U.S. space system.
Recently, the reconstituted National Space Council adopted four recommendations, one of which related to spectrum used for satellite services and said that NTIA should coordinate with the FCC to ensure “the protection and stewardship of radio frequency spectrum necessary for commercial space activities.” Stewardship that is consistent with National Space Policy would include sustaining the RF environment for GPS.
As the PNT EXCOM has made clear, GPS is “vital to economic, public safety, scientific, and national security needs” of the U.S. Moreover, economic analysis presented to the PNT Advisory Board in 2015 estimated the economic benefit to the nation of GPS services at over 68 billion dollars annually. With the release of the ABC assessment, definitive information is now available to inform decisions on use of frequencies near those used to provide space-based PNT services so these critical services are not disrupted or degraded.
An independent technical review published earlier this month found sufficient data in three government-conducted tests to assess the risk of using frequencies near the GPS band for a ground-based communications network — specifically, the one proposed by Ligado Networks. The panel rejected two tests sponsored by Ligado Networks, saying they did not meet minimum criteria for inclusion or use.
The testing and various hearings before the Federal Communications Commission (FCC) come in response to increasing demand for commercial spectrum to support broadband wireless communications. The FCC and other branches of U.S. government are giving serious consideration to repurposing various radio frequencies, including the satellite communications bands next to GPS, to accommodate this.
Ligado Networks has petitioned the FCC to repurpose satellite frequencies near GPS to also support terrestrial telecom services, effectively transferring its license for space-based broadcasting to powerful terrestrially-based broadcast towers. Ligado’s custom networks would provide services for industrial operations such as power grids and connectivity for drones and driverless cars, in addition to consumer broadband services.
The National Executive Committee of the government’s National Coordination Office for Space-Based Positioning, Navigation, and Timing released the assessment by its National Space-Based PNT Systems Engineering Forum (NPEF) of testing methodologies used to analyze the impacts of adjacent band interference on GPS receivers. The assessment is also known as the “gap analysis.”
The NPEF evaluated five tests performed by the following organizations, the first three of them government organizations and the last two private tests sponsored by Ligado with little or no public or government input:
Federal Communication Commission (FCC)-mandated Technical Working Group (TWG) — done in 2011.
National Space-Based PNT Systems Engineering Forum (NPEF) — done in 2011.
Department of Transportation (DOT) Adjacent Band Compatibility (ABC) — done in 2017 but not previously released.
Roberson and Associates (RAA)
National Advanced Spectrum and Communications Test Network (NASCTN).
The gap analysis concluded that the results from the first three tests are sufficient and appropriate to inform spectrum policy makers on the major impacts of a proposed LTE network on GPS receivers. The DOT test results revealed the power levels that GPS and GNSS receivers can tolerate from interference sources in the adjacent band in an effort to inform the enforcement of a GPS interference protection criterion.
PNT Advisory Board’s set of minimum criteria. The two Ligado-sponsored tests are the RAA and the NASCTN. (Image: PNTAB)
The NPEF team found the scope and framework of the last two tests, sponsored by Ligado, to be insufficient when evaluated against the PNT Advisory Board’s set of minimum criteria. Key among these criteria is one that specifies use of the internationally accepted 1 dB degradation Interference Protection Criterion (IPC): a one-decibel (1 dB) degradation in C/N0, the carrier-to-noise power density ratio. Ligado has tried to redefine the standard measurement of interference to one more in its favor: a change in positioning and timing accuracy.
For further background on this and other aspects of the gap analysis, see the January 2018 GPS World article by Brad Parkinson, “A Grave Threat to GPS and GNSS.”
The NPEF strongly recommended that decisions impacting the GPS radio frequency environment be informed by data from tests that align with the PNTAB’s set of minimum criteria and with full consideration of the potential operational, scientific, and economic impacts.
The full gap analysis study can be downloaded here.
The NPEF is co-chaired by the Departments of Defense and Transportation and consists of representatives from at least 14 federal agencies.
