5G vs Aircraft
Radio Altimeters, SATCOM, and GPS, and all that jazz...
Many people ask me whether flying in an airplane is safe these days considering all the news about 5G cell phones and towers (and satellites) reportedly interfering with so much of the equipment on aircraft, whether it's radio altimeters (radalts), GPS receivers, or SATCOM equipment.
Bottom line: Flying remains the second safest form of transportation, after trains, and that's not likely to change anytime soon. So hop onto your flight with your mind at ease...
My recommendation: Out of an abundance of caution, you can always do you part and just turn off that 5G cellphone during Taxi, Takeoff, and Landing.
However, here's my attempt to demystify some of the issues for that lay-person...
WhAt do I know about The 5G Issues?
I have personal and professional experience dealing with some of the issues 5G has created with Large Transport category civil aircraft. I won't share specifics about the impact to certain aircraft models, for the sake of ethics and professionalism... But I will quote some public sources which summarize the dilemma pretty well.
I also have a Certificate of Proficiency in Amateur Radio issued by Industry Canada, so I know a thing or two about radio frequency (RF) interference...
What is 5G?
In telecommunications, 5G is the 5th-generation technology standard for broadband cellular networks.
The industry consortium setting standards for 5G, the 3rd Generation Partnership Project (3GPP), defines "5G" as any system using 5G NR (5G New Radio) software - a definition that came into general use by late 2018.
Like its predecessors (4G/LTE, 3G/Edge, 2G, etc...), 5G networks are broadband cellular networks in which the service area is divided into small geographical areas called cells. All 5G wireless devices in a cell communicate by radio waves with a cellular base station via fixed antennas, over frequency channels assigned by the base station. The base stations, termed nodes, are connected to switching centers in the telephone network and routers for Internet access by high-bandwidth optical fiber or wireless backhaul connections.
As in other cellular networks, a mobile device moving from one cell to another is automatically handed off seamlessly. All 5G wireless devices in a cell are connected to the Internet and telephone network by radio waves through a local antenna in the cell.
The new networks will support higher download and upload speeds, eventually reaching up to 10 gigabits per second (Gbit/s). In addition to 5G being faster than existing networks, 5G has higher bandwidth and can therefore connect more devices and even improve the quality of Internet in crowded areas like stadiums and arenas.
5G is the planned successor to the 4G networks which provide connectivity to most current cellphones and smartphones. Most cellphones or smartphones with 4G capability alone are not able to use the 5G networks; you need a 5G-capable cellphone or smartphone (and these usually also support 4G, for backward compatibility).
Cellular phone companies began deploying 5G worldwide in 2019. 5G is expected to support up to a million devices per square kilometer, and 5G networks are predicted to have more than 1.7 billion subscribers and account for 25% of the worldwide mobile technology market by 2025, according to the GSM Association and Statista.
Due to the increased bandwidth, it is expected the networks will increasingly be used as general internet service providers (ISPs) for laptops and desktop computers, competing with existing ISPs such as cable internet, and also will make possible new applications in internet-of-things (IoT) and machine-to-machine areas.
But with high bandwidth comes a greater risk of harmful interference in adjacent bands... So that's where the 5G spectrum comes into play...
5G spectrum compared to other wavelengths and uses
Cellphone companies are vying to license spectrum to accelerate the implementation of 5G worldwide
Before a cellphone company can deploy 5G, it needs to purchase a license for the right to use a specific 5G spectrum, otherwise knowns as a radio frequency (RF) ranges or bands. It must purchase these licenses from the radio-telecommunications regulators in each country, such as the Federal Communications Commission (FCC) in the U.S.A., or ISED in Canada. Since many cellphone companies are competing for the bands, the regulators are usually using highest-bidder auctions to sell off these bans.
The currently-accepted standard air interface defined by 3GPP for 5G is known as New Radio (5G NR), and the specification is subdivided into two frequency bands:
FR1 (below 6 GHz), further subdivided between the low band (below 1 GHz) and mid band (1-6 GHz)
FR2 (24–54 GHz), also known as the high band or mmWave.
Many specific frequency ranges or bands within FR1 and FR2 are already licensed by the regulators for other uses (satellite communications, astronomical and weather observation, etc...) so cellphone companies must choose smaller ranges of frequencies within FR1 and FR2 and work with the regulators to designate those smaller ranges, or bands, for 5G use (or flexible use, or even shared use). The 3GPP 5G NR standard does specify a few such bands (such as n77 and n78), but it doesn't limit the ability to use other smaller ranges or bands within FR1 and FR2. So a cellphone company can choose to purchase (or license) any smaller frequency range or band within FR1 or FR2 to offer its 5G cellular services. These can range from bands in the existing conventional radio spectrum, cellphone spectrum, and even microwave frequencies (see adjacent Figure).
As of today, large quantities of new radio spectrum (5G NR frequency bands) have been allocated to 5G.
For example, in July 2016, the U.S. FCC freed up vast amounts of bandwidth in underused high-band spectrum for 5G. The Spectrum Frontiers Proposal (SFP) doubled the amount of millimeter-wave unlicensed spectrum to 14 GHz and created four times the amount of flexible, mobile-use spectrum the FCC had licensed to date. In 2020, the FCC also agreed to free up some of the C-band and L-Band for 5G.
In March 2018, European Union lawmakers agreed to open up the 3.6 (C-Band) and 26 GHz bands by 2020.
As of today, there are reportedly 89 countries, territories, special administrative regions, disputed territories and dependencies that are formally considering introducing certain spectrum bands for terrestrial 5G services, are holding consultations regarding suitable spectrum allocations for 5G, have reserved spectrum for 5G, have announced plans to auction frequencies or have already allocated spectrum for 5G use. This includes countries like Tanzania.
However, the allocation of 5G spectrum is creating the risk of hamrful RF interference to other users of adjacent or shared spectrum, especially Aviation and scientific users. And some regulators, like the U.S. FCC, are plowing ahead despite fierce opposition.
So let's dive deeper into the 5G spectrum harmful interference issues.
Pros and Cons of various 5G Spectrums
Each frequency range or band offers its advantages and inconveniences, mainly in terms of:
Coverage (also sometimes a factor of Penetration Distance)
Lower frequencies offer more Coverage and better Penetration Distance. This can be important when deploying in cities where the cost of leasing real estate to install cellphone towers is a factor, and where good building penetration distance is required.
Higher frequencies offer better Data Throughput and lower latencies. This can be important when cellphone companies want to offer new high bandwidth low-latency services, especially in metropolitan areas, such as multiple simultaneous video streams (imagine assistant a sports event in a stadium and the cellphone company offers you the ability to get multiple video angles of the actions that you're witnessing live)
So cellphone companies often bid high prices for the more sought-after bands, especially those in the mid-band (FR1) range. Let me give you an overview of most of the more popular radio frequency (RF) ranges or bands used for 5G.
Mid band (FR1) - 1 GHz - 6 GHz range
Spectrum in the 1 GHz - 6 GHz range is mid-band (FR1) spectrum and it is considered ideal for 5G because it can carry plenty of data while also travelling significant distances. The GSMA describes spectrum in the 3.3-3.8 GHz range (also known as C-band in the USA) as particularly appealing. The organization explained in a recent white paper that this spectrum is ideal because many countries around the world have already designated it for 5G. However, this is also the band where there's the biggest clash with Aviation users. More on that below.
However, other mid-band spectrum is also being used for 5G. For example, operators in China and Japan are planning to use 4.5 GHz -5 GHz spectrum for 5G. And some operators in U.S. and Canada are planning to use (or are already using) the 1700 MHz, 1800 MHz, 2.3 GHz and the 2.5 GHz-2.6 GHz spectrum for 5G.
Sprint is currently operating a live 5G network in nine cities including Phoenix; New York City; Washington, D.C., Los Angeles; Atlanta; Houston, Dallas-Fort Worth; Chicago; and Kansas City using its 2.5 GHz spectrum. Sprint has said that its 5G network covers approximately 16 million people in those cities.
Besides Sprint, some U.S. operators are also planning to refarm (or re-use) some mid-band spectrum (such as the 1800 MHz) that is currently being used for 3G services and use it for 5G. Verizon said in a December 2018 SEC filing that it is “aggressively” refarming 3G bands for LTE.
Mid band spectrum vs. RadAlt spectrum, and overview of spectrum allocations around the world
The C-band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 4.0 to 8.0 GHz. However, the U.S. FCC designated 3.7–4.2 GHz as C-band, differing from the IEEE's designation. In the rest of this article, I will refer to the U.S. C-band since that's the band where most of the contentious issues arise and it's the commonly used designation for the spectrum causing some of the issues.
The US C-band is used for many satellite communications transmissions, some Wi-Fi devices, some cordless telephones, as well as some Radar and weather radar systems. The communications C-band was actually the first frequency band that was allocated for commercial telecommunications via satellites. The same frequencies were already in use for terrestrial microwave radio relay chains.
Nearly all C-band communication satellites use the band of frequencies from 3.7 to 4.2 GHz for their downlinks, and the band of frequencies from 5.925 to 6.425 GHz for their uplinks.
Note that by using the band from 3.7 to 4.0 GHz, this C-band overlaps somewhat with the IEEE S band for radars.
The C-band communication satellites typically have 24 radio transponders spaced 20 MHz apart, but with the adjacent transponders on opposite polarizations such that transponders on the same polarization are always 40 MHz apart. Of this 40 MHz, each transponder utilizes about 36 MHz. (The unused 4.0 MHz between the pairs of transponders acts as "guard bands" for the likely case of imperfections in the microwave electronics.)
One use of the C-band is for satellite communication, whether for full-time satellite television networks or raw satellite feeds, although subscription programming also exists. This use contrasts with direct-broadcast satellite, which is a completely closed system used to deliver subscription programming to small satellite dishes that are connected with proprietary receiving equipment.
The satellite communications portion of the C-band is highly associated with television receive-only satellite reception systems, commonly called "big dish" systems, since small receiving antennas are not optimal for C band. Typical antenna sizes on C-band-capable systems range from 6 to 12 feet (1.8 to 3.5 meters) on consumer satellite dishes, although larger ones also can be used. For satellite communications, the microwave frequencies of the C band perform better under adverse weather conditions in comparison with the Ku band (11.2–14.5 GHz), microwave frequencies used by other communication satellites. Rain fade – the collective name for the negative effects of adverse weather conditions on transmission – is mostly a consequence of precipitation and moisture in the air.
The US C-band also includes the 5.8 GHz ISM band between 5.725 and 5.875 GHz, which is used for medical and industrial heating applications and many unlicensed short-range microwave communication systems, such as cordless phones, baby monitors, and keyless entry systems for vehicles. The C-band frequencies of 5.4 GHz band [5.15 to 5.35 GHz, 5.47 to 5.725 GHz, or 5.725 to 5.875 GHz, depending on the region of the world] are used for IEEE 802.11a Wi-Fi wireless computer networks.
As part of the Trump administration’s 5G FAST Plan, in March 2018, the MOBILE NOW Act directed the U.S. FCC to evaluate the feasibility of commercial wireless deployments in the C-Band which was until then was used by satellite operations. By repacking existing satellite operations into the upper 200 megahertz of the band (and reserving the 20 MHz between 3980–4000 MHz as a guard band and not available for auction), the Commission makes 280 MHz of spectrum available for flexible use throughout the contiguous United States, and does so in a manner that ensures the continuous and uninterrupted delivery of services currently offered in the band.
The FCC started a proceeding in May 2018 and adopted the C-band Report and Order authorizing flexible use of the 3.7-3.98 GHz band in March 2020 to reform the use of the 3.7-4.2 GHz band (FCC adopted rules).
Satellite companies agreed to vacate their holdings in exchange for accelerated payments from an FCC Auction, a relocation process to be finalized by December 2023. The prospective bidders will pay holders for their spectrum rights so they can deploy next generation wireless services like 5G, a more valuable use. The FCC was hoping to sell more than 5,000 new flexible-use overlay licenses for C-band spectrum in the 3.7–3.98 GHz frequency.
This graphic shows how C-band 5G spectrum is "close" to the RadAlt spectrum, separated by only ~0.2GHz, showing how OOBE might create harmful interference
This graphic shows how an aircraft's attitude, altitude, and position can have an effect on the level of harmful 5G intereference to its radalts
Typical RadAlt receiver filtering of OOBE
Automated safety systems in aircraft that could potentially be affected by harmful 5G interference to aircraft radalts. Image used courtesy of the FAA. I would also add Head-Up Displays (HUDs) to this list.
This is excerpt from a Transport Canada presentation on 5G and RadAlts given during the CARAC Plenary Day 1 on November 23rd, 2021, explaining how RadAlt measurements feed into a number of Safety Critical Aircraft Systems. This is serious stuff...
C-Band vs. Aircraft Radio Altimeters (RadAlts)
The U.S. Federal Aviation Administration (FAA), which is under the U.S. Department Of Transportation (DOT), has warned that radio (radar) altimeters (shortened as "RadAlts") which are installed on practically every kind of medium or large aircraft (civilian and military airplanes and helicopters), and which operate in an internationally reserved band between 4.2 and 4.4 GHz, might be affected by 5G operations between 3.7 and 3.98 GHz. This is particularly an issue with older altimeters using older RF filters which lack protection from neighbouring bands.
RadAlts are used by aircraft to get an independent and accurate measurement of their height Above Ground Level (AGL) when they're operating close to terrain, such as when taking off or landing. On more modern aircraft, the integrity and accuracy of the RadAlt height measurement is vital for ensure the aircraft and its systems operate safely. For example, when performing approaches and landings in fogged out airports, the pilots and aircraft rely on the RadAlt height measurement to accurately gauge how close they are to the runway and the preceding terrain. If the accuracy of the RadAlt height is affected due to harmful 5G interference, you can imagine what could happen...
Most aircraft and radalt manufacturers have radalts designed to meet the currently published standards:
RTCA DO-155, “Minimum Performance Standards Airborne Low-Range Radar Altimeters”, published November 1, 1974
EUROCAE ED-30, “Minimum Performance Specification for Airborne Low Range Radio (Radar) Altimeter Equipment”, published March 1980
These existing radalt standards DO NOT address 5G/C-Band RF Interference.
This is not as much of an issue in Canada, Europe, and Japan, where mitigation measures were put in place to lessen the impact of 56 C-band to Aviation users:
use lower frequencies between 3.4 and 3.8 GHz (lower C-band, or n78 band) (sometimes with dedicated guard bands between the Radalt bands and the 5G C-bands). The 5G out-of-band emissions in the n78 band are less likely to interfere with aircraft radalts than say the out-of-band emissions in the n77 band.
implement base station power limits
implement base station antenna tilt-down requirements (to avoid sending maximum power directly overhead towards aircraft)
Nonetheless, the DGAC in France, after performing dedicated tests using military helicopters, has also expressed similar worries and recommended 5G phones be turned off or be put in airplane mode during flights. More on that below.
In fact, the claims of harmful 5G interference to aircraft RadAlts was carefully studied by the Radio Technical Commission for Aeronautics (RTCA)'s Special Committee 239 (SC-239) on Low Range Radio Altimeters. Full disclosure: I've participated in some of the SC-239's activities, so I'm a bit biased.
In October 2020, the RTCA issued it's now infamous RTCA Paper No. 274-20-PMC-2073, titled “Assessment of C-Band Mobile Telecommunications Interference Impact on Low Range Radar Altimeter Operations”, dated 2020-10-07.
The report characterizes the potential interference based on fundamental emissions in the U.S. for various category of aircraft, and various scenarios (like worse case landing scenarios).
The report concludes unacceptable level of risk on certain category of aircraft and helicopters, including business aircraft.
In general, most aircraft and radalt manufacturers supported the conclusions of the RTCA SC-239 special paper paper., notably the following conclusion:
For Usage Category 2, which covers commercial airplanes used for regional air transport as well as business and general aviation airplanes, the impact of 5G interference from base stations is inescapable. Every base station configuration produces harmful interference both from fundamental emissions in the 3.7–3.98 GHz band and spurious emissions in the 4.2–4.4 GHz band, across virtually all operational scenarios and relative geometries between the aircraft and base station. In the worst case, the safe interference limit for the fundamental emissions is exceeded by over 47 dB, and the safe interference limit for the spurious emissions is exceeded by over 27 dB.
It was widely reported that Alan Burke, the Pentagon’s chair for the interagency Aviation Cyber Initiative Task Force, said that "Rather than push back at the FCC, Pentagon (US DOD) officials believe their energies are best spent focused on studying how the deployment of 5G networks throughout U.S. metropolitan areas will impact military aircraft and putting in place a strategy to mitigate any safety concerns."
Notwithstanding the RTCA special paper, or the petitions by the FAA & the aviation industry to pause the auction, or even the White House getting involved, the FCC auction 107 (aka C-band auction) for flexible‐use overlay licenses in 3.7GHz to 3.98GHz spectrum began on December 8th, 2020. On February 24th 2021, the FCC announced Winning Bidders in Phase 1 of the FCC auction 107 (aka C-band auction) of 3.7 GHz Service. This was the highest-grossing spectrum auction ever in the USA for the private-sector purchase of spectrum licenses in the C-band. Gross proceeds for the auction were above USD$80.9 billion. Winners: mostly AT&T, Cellco Partnership (dba Verizon Wireless), and T-Mobile.
AT&T & Verizon collectively spent nearly USD$70 billion to gain access to a bunch of C-band spectrum that was up for auction.
What was the most surprising in all of this was that the FCC failed to retain any of the aviation industry's comments, and unlike other countries in the world that used precautionary principles to put in place mitigation measures, the FCC totally failed to retain any of the proposed mitigation measures. In fact, the FCC authorized the highest power outputs in all of the world for 5G in C-band, exceeding by more than 2.5× the power output of other deployments throughout the world. This created even bigger concerns of harmful interference in U.S. airspace compared to other areas in the world.
Considering the RTCA paper, the International Civil Aviation Organisation (ICAO), a branch of the United Nations (UN) that governs international aviation, issued a Letter on March 25th 2021, stated “Potential Safety Concerns Regarding Interference to Radio Altimeters” and requested ICAO member States to “Consider as a priority, public and aviation safety when deciding how to enable cellular broadband/5G services in radio frequency bands near the bands used by radio altimeters” •
On November 5th, 2021, an aviation industry coalition spearheaded by AIA sent a letter to the US National Economic Council (NEC) [White House] urging additional delays in C-band 5G rollouts and the formation of joint FAA/FCC industry working group. Letter was co-signed by a bunch of signatories including Airbus, Boeing, GAMA (BA participating through GAMA), ALPA, Honeywell, Collins, Garmin etc:
The FAA issued a Special Airworthiness Information Bulleting (SAIB) AIR-21-18 on November 2nd, 2021, to sensitize aircraft operators of the impending activation of C-band 5G in the U.S. and the potential effects from harmful 5G interference to aircraft radalts.
Most aircraft manufacturers issued similar advisories to their aircraft operators worldwide.
The FAA then issued an Airworthiness Directive (AD) 2021-23-12 (for airplanes) and AD 2021-23-13 (for helicopters), both issued and effective on 2021-12-09, with appreciable Aircraft Flight Manual (AFM) operational restrictions for ALL aircraft operating in U.S. airspace as of January 5th 2022 for certain airports and airspace which would issue NOtices To Air Missions (NOTAMs) where certain operations requiring a high integrity radalt height measurement are prohibited where 5G C-Band interference is likely. An AD is like a car recall but intended for aircraft, however unlike car recalls, it's mandatory (law) for aircraft operators to adhere to an AD within the published compliance time.
The ADs required inserting the following into AFMs, effectively prohibitting the following types of aircraft operations within NOTAM'd U.S. airports and airspace:
It's interesting to note that Canada and many other countries that have bilateral aviation safety agreements with the U.S.A. adopted the FAA ADs, but the European Aviation Safety Agency (EASA) did not adopt the FAA AD, citing a lack of similar risk in European airspace, despite many european-registered aircraft operating transatlantic flights to the U.S.A. where they could still be at-risk.
A letter dated December 20th 2021 obtained by Reuters featured comments by Boeing Chief Executive Dave Calhoun and Airbus Americas CEO Jeffrey Knittel citing Airlines for America (A4A) analysis that if the latest 5G directive from the FAA had been active in 2019, about "345,000 passenger flights and 5,400 cargo flights would have faced delays, diversions or cancellations." Boeing, Airbus executives urged delay in U.S. 5G wireless deployment.
The FAA also issued a Safety Alert For Operators (SAFO) 21007 on December 23rd, 2021, to provide further guidance on how the new NOTAMs will identify the geographic areas and airports where certain operations requiring a radalt are prohibited where 5G C-Band interference is likely:
The FAA issued a revised SAIB AIR-21-18R1 on the same day with updated info on delayed implementation, and updated warnings to operators.
On December 31st, 2021, U.S. Transportation Secretary Pete Buttigieg and Steve Dickinson, administrator of the FAA, asked the chief executives of AT&T and Verizon to delay 5G implementation in the lower C-band (3.7 and 3.98 GHz) over aviation concerns. The government officials asked for a two-week delay starting on January 5, 2022, while investigations are conducted on the effects on radalts. The government transportation officials also asked the cellular providers to hold off their new 5G service near 50 priority airports, to minimize disruption to air traffic that would be caused by some planes being disallowed from landing in poor visibility.
As a solution, AT&T CEO John Stankey and Verizon CEO Hans Vestberg suggested that instead of delaying the 5G deployment, the telecommunication companies would adopt the same C-band radio exclusion zones already in place in France near runways at certain airports.
"France provides a real-world example of an operating environment where 5G and aviation safety already co-exist," the companies' CEOs wrote in its response letter to the FAA.
After coming to an agreement with government officials the day before, Verizon and AT&T activated their 5G networks in the C-band, but limited to 3.6 to 3.8 GHz (a.k.a. the lower C-band), on January 19th, 2022, except for certain towers near approx ~90 airports where they agreed to limit base stations to reduced power (62 dBm/MHz) for six months until July 5th, 2022 (65 dBm/MHz thereafter). AT&T scaled back its deployment even further than its agreement with the FAA required.
The FAA rushed to test and certify radalts for interference so that planes could be allowed to perform instrument landings (e.g. at night and in low visibility) at affected airports. By January 16th, 2022, it had certified equipment on 45% of the U.S. fleet, and 78% by January 20th, 2022. Airlines complained about the avoidable impact on their operations, and commentators said the affair called into question the competence of the FCC and FAA. Several international airlines substituted different planes so they could avoid problems landing at scheduled airports, and about 2% of flights (320) were cancelled by the evening of January 19th, 2022.
By January 26th, 2022, the FAA:
put in place buffer areas around 87 airports where Verizon/AT&T are deploying nearby 5G C-band base stations at reduced power (62 dBm/MHz) for six months (65 dBm/MHz thereafter), though the list will be updated on a monthly basis as AT&T/Verizon communicate their deployment plans to the FAA, and the FAA refines their interference analysis.
published almost all NOTAMS covering all the 46 FCC 5G C-band market areas. Cautionary note by the FAA: new NOTAMS may be added and some NOTAMS might be refined as Verizon/AT&T provide more data on their planned deployment of antennas and the FAA refines its existing analysis, and FAA performs further analysis covering custom instrument approach procedures at smaller airports.
created a tool with proprietary precise 5G C-band antenna locations that AT&T/Verizon will deploy, updated on a monthly basis as AT&T/Verizon communicate their deployment plans to the FAA. Only the FAA can evaluate which airports/rwys are safe to operate at depending on aircraft/radalt combo.
granted Alternative Means of Compliance (AMOCs) to AD 2021-23-12 clearing 90% of US commercial fleet (incl. Boeing, Airbus, MD, Embraer (E170/190), DHC-8, MHIRJ, ATR) to perform low-visibility landings at airports with nearby 5G deployments. Since then, the AMOCs were updated on a monthly basis as AT&T/Verizon communicate their deployment plans to the FAA, and the FAA refines their interference analysis methods from protection surfaces around runways using 2D only circles (AMOC V1 around end of January 2022), to protection surfaces using 14CFR Part 77 runway surface areas combined with a 3D fixed radius method using 62 dBm/MHz power + 6dB margin (AMOC V2 around February 2022), and finally a more realistic parametric model of base stations combined with a 3D Variable Radius Method using 62 dBm/MHz power + 6dB margin (AMOC V3 around end March 2022). For most aircraft with modern radalts, the computed interference radius was less than 400ft, so those aircraft were cleared to operate on any runways and approach paths where 5G C-band base stations were farther away than their specific computed interference radius. But many older aircraft using older radalts with old RF filters remained highly susceptible to harmful interference at much greater distances, so no AMOC relief was granted for those aircraft, which remained restricted per AD 2021-23-12.
ICAO NAM/CAR/SAM also issued a Letter on January 25 2022 citing “Potential Safety Concerns Regarding Interference to Radio Altimeters" – States were “urged to carry out evaluations of their operations, especially at international airports, to assess the impact that the implementation of 5G technology may have on operational safety."
ICAO HLCC 2021 also made Recommendation 5/5:
Since then, the FAA also issued aircraft-model-specific Airworthiness Notifications and ADs to reduce the risk to other critical aircraft systems that was not previously covered by the generic AD 2021-23-12 or 2021-23-13.
On 2022-01-14, FAA required operators of Boeing 787s to take additional precautions when landing on wet or snowy runways at airports where 5G C-band service is deployed. During the two-week delay in deploying new 5G service, safety experts determined that 5G interference with the aircraft’s radio altimeter could prevent engine and braking systems from transitioning to landing mode, which could prevent an aircraft from stopping on the runway. The Airworthiness Notification requires crews to be aware of this risk and to adopt specific safety procedures when landing on these runways. The directive affects 137 aircraft in the United States and 1,010 worldwide.
On 2022-01-25, FAA issued an AD prohibiting Boeing B747-8, 747-8F and 777 airplanes from landing at airports where 5G interference could occur. Link to Airworthiness Directive (AD). The AD does not apply to landings at airports where the FAA determined the aircraft altimeters are safe and reliable in the 5G C-band environment. It also does not apply to airports where 5G isn’t deployed. The FAA issued the AD because many systems on Boeing 747-8, 747-8F and 777 aircraft rely on the altimeter, including autothrottle, ground proximity warning, thrust reversers and Traffic Collision Avoidance System. The AD affects approximately 336 airplanes in the United States and 1,714 worldwide. Compliance time is within two days of the effective date of the AD.
RTCA Special Committee SC-239 and EUROCAE Working Group WG-119 started working jointly to address minimum performance requirements for radio altimeters when subjected to RF interferences, considering the ongoing deployments of 5G and other broadband technologies. The original work plan was to completely re-write the MOPS document (including the addition of new RF interference requirements and test procedures) and to release the entire DO-155A/ED-30A MOPS update by December 2022. Since the immediate need by industry and regulators are the RF interference requirements & associated tests, the work plan has been revised to first release a new DO-XXX/ED-XXX document “Technical Standard on RF Interference Environment for Radar Altimeters” in December 2022, followed by the DO-155A/ED-30A MOPS revision in December 2023.
In addition, a new joint RTCA Special Committee SC-242 and EUROCAE Working Group WG-124 has been initiated. The WG is intended to provide guidance to ensure that the radio frequency characteristics of aeronautical Communications, Navigation and Surveillance (CNS) systems use the spectrum efficiently while respecting the necessary safety margins. The guidance is intended to facilitate any future evaluation of compatibility with other systems and ensure that the usage of the allocated spectrum is as efficient as possible, fully taking into account the specificities of aeronautical CNS systems. The deliverables are envisaged to be referenced by EASA, FAA, other CAAs, ICAO, and national/international spectrum regulators, as appropriate, in guidance material for aviation systems.
On June 17th 2022, the FAA issued a statement with a major update:
"Key stakeholders in the aviation and wireless industries have identified a series of steps that will continue to protect commercial air travel from disruption by 5G C-band interference while also enabling Verizon and AT&T to enhance service around certain airports.
“We believe we have identified a path that will continue to enable aviation and G C-band wireless to safely co-exist,” said Acting FAA Administrator Billy Nolen. “We appreciate the willingness of Verizon and AT&T to continue this important and productive collaboration with the aviation industry.”
The phased approach requires operators of regional aircraft with radio altimeters most susceptible to interference to retrofit them with radio frequency filters by the end of 2022. This work has already begun and will continue on an expedited basis.
At the same time, the FAA worked with the wireless companies to identify airports around which their service can be enhanced with the least risk of disrupting flight schedules.
During initial negotiations in January, the wireless companies offered to keep mitigations in place until July 5, 2022, while they worked with the FAA to better understand the effects of 5G C-band signals on sensitive aviation instruments.
Based on progress achieved during a series of stakeholder roundtable meetings, the wireless companies offered Friday to continue with some level of voluntary mitigations for another year.
“We all agreed when we began these meetings that our goal was to make July 5, 2022, just another date on the calendar, and this plan makes that possible,” Nolen said.
Airlines and other operators of aircraft equipped with the affected radio altimeters must install filters or other enhancements as soon as possible.
Filters and replacement units for the mainline commercial fleet should be available on a schedule that would permit the work to be largely completed by July 2023. After that time, the wireless companies expect to operate their networks in urban areas with minimal restrictions.
The radio-altimeter manufacturers have worked at an unprecedented pace with Embraer, Boeing, Airbus and Mitsubishi Heavy Industries to develop and test filters and installation kits for these aircraft. Customers are receiving the first kits now. In most cases, the kits can be installed in a few hours at airline maintenance facilities.
Throughout this process, the FAA will work with both industries to track the pace of the radio altimeter retrofits while also working with the wireless companies to relax mitigations around key airports in carefully considered phases.
The agency also will continue to engage with the National Telecommunications and Information Administration and the Federal Communications Commission on technical issues associated with these efforts."
Just prior to the 2022-2023 holidays, a similar debacle unfolded, where the FAA was notified by telecommunications providers that 5G C-band deployments in the 3.8-3.98 GHz frequency band are expected to begin deploying at selected locations beginning January 1, 2023, earlier than the planned earliest dates of July 2023. Considering the closer proximity of this frequency range to the protected radalt band, the FAA advised aircraft manufacturers right away and asked that they use the same Variable Radius Method (AMOC V3) Spreadsheet used for the previous data submittals to support the AMOCs, but reflecting the new frequency range and incresed power levels, to determine the computed interference radius for the radalt models installed on their aircraft. For most aircraft with modern radalts, the computed interference radius jumped from less than 400ft to around 1,000ft (sometimes up to 1,2000ft)! In fact, when looking at the FAA ASIAS data (notably the publically available NASA ASRS data), you can find many incidents where pilots reported aircraft systems failing at around 1,200ft!
In June 2018, Canada's Innovation, Science and Economic Development Canada (ISED) released Spectrum Outlook 2018 to 2022, which included plans to release spectrum that would support 5G services. The Outlook indicated that releasing the 3450–3650 MHz band (referred to as the 3500 MHz band), a key band for 5G, was a high priority.
In Canada, contrary to the U.S.A., the Aviation industry was mostly successful in lobbying the regulators, ISED, to put in place mandatory nationwide mitigation measures to reduce the impact of 5G C-band to Aviation users.
In June 2019, ISED published the Decision on Revisions to the 3500 MHz Band to Accommodate Flexible Use and Preliminary Decisions on Changes to the 3800 MHz Band as the first step toward making this band available.
Through the release of the Policy and Licensing Framework for Spectrum in the 3500 MHz Band, ISED is setting the rules for the upcoming spectrum auction, the next step toward making this band available for 5G services.
ISED is making 200 MHz of spectrum available in the 3500 MHz band for “flexible use” licensing that allows licensees to choose the type of services they will deploy, such as mobile (5G) or fixed wireless services (e.g. Internet-to-the-home).
ISED planned to auction 3450–3650 MHz band (referred to as the 3500 MHz band) spectrum with bidding to start on 2021-06-15. See https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/h_sf11519.html
On October 13th, 2020, Transport Canada Civil Aviation (TCCA)'s Standards branch sent a public letter (reference SLPB-002-20) to ISED, titled “Consultation on the Technical and Policy Framework for the 3650-4200 MHz Band and Changes to the Frequency Allocation of the 3500-3650 MHz Band”, dated 2020-10-13, RDIMS #16921882, and which stated:
"There are liability concerns with 5G implementation and ISED needs to consider the seriousness of harmful interference to aircraft onboard radar altimeter equipment that may be caused by 5G telecommunications systems in the 3.7–3.98 GHz band implementation in Canada with the potential loss of lives if an Aviation accident would occur due to 5G interference with Radar Altimeter or WAIC. ISED needs to establish appropriate safety 4 measures to respect the ICAO 6 dB safety margin, by implementing specific technical requirements and mitigation measures. Frequency band selection should not be swayed by economic reasons or harmonization with the USA, rather human safety should be the priority. ISED should also consider reducing the 5G operational bandwidth in some geographical areas near airports to increase the frequency guard band with the aviation frequency band in order to ensure aviation safety.
TCCA also released CASA 2021-08 Issue 01 on June 15th, 2021, titled "Potential Risk of Interference of 5G Signals on Radio Altimeter".
ISED published the Consultation on Amendments to SRSP-520, Technical Requirements for Fixed and/or Mobile Systems, on 2021-08-06. The Canadian aviation industry applauded ISED‘s recently proposed changes in the technical consultation which would:
Modify outdoor antenna tilt requirements in all areas, and,
Limit outdoor operations in areas immediately surrounding specific airports in order to help ensure radio altimeters are not affected by 3500 MHz operations.
An October 9th 2021 Ottawa Sun article explained that ISED has responded to Transport Canada’s recommendations curtailing deployment of 5G base stations around airports because of this concern. Canadian telecoms like Bell, Rogers, and Telus, were not very happy with the restrictions, but they took the hit like champs and amended their deployment strategy and proceeded to finalize their bids on the ISED planned to auction 3450–3650 MHz band (referred to as the 3500 MHz band) spectrum.
On November 18th, 2021, ISED issued restrictions on antenna location close to airports with CAT I/II/III approaches (they called these exclusion zones and protection zones), antenna tilt restrictions, and other operational limitations.
Consultation on Amendments to SRSP-520, Technical Requirements for Fixed and/or Mobile Systems, Including Flexible Use Broadband Systems, in the Band 3450-3650 MHz
TCCA also issued an Airworthiness Directive (AD) CF-2021-52 in December 2021, adopting the FAA AD 2021-12-23. Generic AMOC issued to allow automatic TCCA acceptance of FAA Global AMOCs. TCCA AD CF-2021-52 was superseded by TCCA AD CF-2023-46 which was issued and became effective in June 2023, and adopting the latest FAA AD 2023-10-02. Similar ADs were issued for helicopters in Canada.
In July 2023, ISED issued its Decision on SRSP-520, issue 3 and RSS-192, issue 5 which summarizes the medium-term plan to allow a safe rollout of 5G in Canada. To summarize the aircraft-related provisions:
Decision 1: ISED will impose exclusion and protection zones for both 3500 MHz and 3800 MHz bands that take into account OCS and adopt Transport Canada’s proposed e.i.r.p. spectral density curves around 35 airports identified in the Map of Exclusion Zones and Protection Zones (SRSP-520). In simple terms, Canadian telecom companies won't be allowed to blast high-powered high bandwidth 5G signals around airports like allowed in the US. Makes sense, right? Typical Canadian approach: let's not do something that creates useless risk. This mitigation measure will apply until January 1, 2026 (see Decision 6 on sunset date below).
Decision 2: ISED will impose a national e.i.r.p. mask. In simple terms, Canadian telecom companies won't be allowed to blast high-powered high bandwidth 5G signals everywhere else in Canada. This mitigation measure will apply until January 1, 2026 (see Decision 6 on sunset date below).
Decision 3: ISED will impose an airport e.i.r.p. mask around the 35 protected airports for both 3500 MHz and 3800 MHz bands in SRSP-520, issue 3, until January 1, 2026. From January 2, 2026 to December 31, 2027, this airport e.i.r.p. mask will only apply to the 3800 MHz band in former exclusion zones and in protection zones (see Decision 6 on sunset date below).
Decision 4: ISED will not impose exclusion and protection zones around H1 classified heliports across Canada.
With regards to advanced notice from the telecommunication industry, ISED requires 3500 MHz and 3800 MHz licensees to provide pre-operation reports 15 days prior to the operation of base stations in protection zones around protected airports. ISED will extend that requirement to include the submission of these reports directly to TC to facilitate their planning process.
If Transport canada requires additional notifications and data beyond what is described above, they are encouraged to discuss directly with 3500 MHz and 3800 MHz licensees to obtain the information, similar to the voluntary arrangements made between the FAA and mobile operators in the US. ISED encourages licensees to collaborate with Transport canada in providing the necessary information to facilitate TC’s planning of aviation restrictions and alleviations accordingly.
In order to strike the right balance between providing sufficient time for aircraft operators to retrofit and minimizing impact on 5G deployments in Canada, ISED will extend the sunset date by 9 months, to January 1, 2026. On this date, the national e.i.r.p. mask, exclusion zones and the height and power restrictions within the protection zones for 3500 MHz and 3800 MHz bands will be removed.
Further, elevated MDUs are typically not authorized along airport runway paths to provide proper clearance for landing and take-off of aircraft. As such, an antenna uptilt would be even less expected in areas around airports. Nevertheless, ISED will maintain an airport e.i.r.p. mask in the area covered by the former 3800 MHz exclusion zones and in the 3800 MHz protection zones. This mask will only apply to base stations operating in the 3800 MHz band around the 35 protected airports until December 31, 2027 to provide a predicable radio frequency environment around these airports. Based on expected 5G deployment scenarios, retaining an airport e.i.r.p. power mask within the exclusion and protection zones until December 31, 2027, around these 35 protected airports, will have negligeable impact on 5G deployments in Canada.
ISED will continue to monitor domestic and international developments on coexistence between 5G operations and radio altimeters.
Decision 6: ISED will impose the following sunset dates:
As of January 1, 2026, the national e.i.r.p. mask, the exclusion zones and the height and power restrictions within the protection zones around the 35 airports in the 3500 MHz and 3800 MHz bands will be removed.
From January 2, 2026 to December 31, 2027, the airport e.i.r.p. mask will only apply to the 3800 MHz band base stations within the former exclusion zones and within the protection zones around the 35 airports.
As of January 1, 2028, all mitigation measures specified above will be removed.
Decision 7: Due to the minimal impact of extending the majority of the mitigation measures by 9 months (January 1, 2026), and the negligeable impact of the airport e.i.r.p. mask on 5G deployments in Canada, ISED will not extend the 3500 MHz and 3800 MHz licence terms.
In the proposed changes to the RSS, ISED included a spurious (unwanted) emission limit of -33 dBm/MHz in the 4200-4400 MHz band, the operating band of radio altimeters, in order to minimize the potential of harmful interference to radio altimeters.
In addition, ISED proposed to increase the limit for indoor base stations from 33 dBm to 39 dBm TRP and proposed to revise the limit for subscriber equipment other than fixed subscriber equipment from 23 dBm/10 MHz to 30 dBm e.i.r.p. per channel bandwidth. Comments were provided on these amendments, including out-of-band emission limits of equipment and the transition period between issue 4 and issue 5 of the RSS.
Stakeholders from the telecommunications industry which included Bell, MIG, RABC, Rogers, Sasktel and TELUS, suggested ISED should adopt a spurious emission limit of -30 dBm/MHz instead of -33 dBm/MHz. In their comments, these stakeholders highlighted that 5G base stations transmit using two polarizations while radio altimeter antennas detect only one polarization, which means that a signal received by a radio altimeter antenna from a 5G base station would be 3 dB lower in power. Therefore, they suggested that a spurious emission limit of -30 dBm/MHz for a base station, which would translate to -33 dBm/MHz for the radio altimeter, would be a more suitable limit.
ISED recognizes that 5G equipment is designed to meet international regulatory requirements, including specifications set forth in industry standards. For instance, the 3rd Generation Partnership Project (3GPP) standard body specifies two categories of equipment that meet either a -13 dBm/MHz or -30 dBm/MHz spurious emissions limit in frequency bands above 1 GHz (as specified in TS 38.104). Equipment meeting a -30 dBm/MHz limit is typically adopted in equipment deployed in European markets to meet European regulatory requirements, while a -13 dBm/MHz limit is for North American markets to meet Canadian and US regulatory requirements.
In the US, the FAA secured a voluntary agreement with the four largest mobile operators to deploy base stations with spurious emission levels of -48 dBm/MHz or less in the 4200-4400 MHz band. This -48 dBm/MHz spurious emission level includes a 6 dB aviation safety margin and an additional 6 dB margin to account for aggregate emissions from multiple base stations (see FAA NPRM, Airworthiness Directives; Various Helicopters).
ISED notes that the agreement between the FAA and the four US mobile operators is a voluntary operational specification rather than a regulatory certification requirement mandated by the US spectrum regulator, the FCC. ISED also notes that the FCC has not adopted a more stringent spurious emission limit, as -13 dBm/MHz remains the current regulatory limit. If ISED were to adopt a limit of -48 dBm/MHz as part of the certification process for 5G base stations, it could result in a Canadian-only ecosystem, leading to higher cost of 5G services for Canadians.
ISED reviewed its own laboratory results and radio altimeter manufacturer data, and compared it with new data shared by TC. TC’s data included margins for unit-to-unit and temperature variance. ISED found that its original ITM, described in annex A of the Consultation, sufficiently captured the performance of all radio altimeters for which ISED had data.
ISED is of the view that an additional safety margin of 6 dB was not required in its computational analysis. The ICAO Handbook notes that a minimum 6 dB safety margin is generally required to account for risk that some factors cannot be foreseen or quantified (e.g. aggregate emissions). In its computational model, ISED made multiple additive worst-case assumptions to minimize the risk of harmful interference between 5G operations and radio altimeters. ISED did not include factors that would have improved coexistence between 5G systems and radio altimeters, such as typical digital tilt of base station which limits skyward antenna lobes (up to 3 dB), base station Time Division Duplex (TDD) duty cycle (up to 3 dB) and typical traffic load (up to 3 dB), and polarization losses (up to 3 dB). Moreover, ISED’s computational analysis model assumed that the following events would all occur at the same time: worst-case antenna coupling, spurious emissions magnitude, base station antenna pointing angle and radio altimeter loop loss factor. The omission of factors that would improve coexistence and the assumption of worst-case events occurring simultaneously provided a safety margin significantly higher than the ICAO 6 dB safety margin.
Decision 14: ISED will adopt a spurious emission limit of -30 dBm/MHz in the 4200-4400 MHz band in RSS-192, issue 5.
Decision 15: ISED will increase the maximum power limit for indoor base stations to 39 dBm TRP and the limit for subscriber equipment, other than fixed subscriber equipment, to 30 dBm/channel bandwidth e.i.r.p in RSS-192, issue 5.
These values could be revisited in future revisions of the technical standard based on the evolution of the technology.
Decision 16: ISED will adopt a -13 dBm/MHz unwanted emission limit above 3900 MHz for outdoor equipment in RSS-192, issue 5.
The MIG, RABC, Rogers, Sasktel and TELUS recommended that the -30 dBm/MHz limit for unwanted emissions for indoor base stations apply above 3980 MHz rather than 3910 MHz. They highlighted that the proposed recommendation would make a broad indoor base station ecosystem available to the Canadian service providers, including those designed for the US market.
ISED agreed with the Canadian telecom providers.
Decision 17: ISED will adopt a -30 dBm/MHz out-of-band unwanted emission limit above 3980 MHz for indoor base stations in RSS-192, issue 5.
In France, Japan, and other places around the world
Most other regulators in other countries who authorized the deployment of 5G in C-band capped the power output at 100 watts.
Eurocontrol published on June 30th, 2022, the latest edition of its "Think Paper" series, which concludes that the risk of 5G C-band wireless network deployment in Europe having an impact on aircraft radio altimeter (RADALT) performance in European airspace is relatively low, due to a number of key differences between how radio spectrum is managed in the band closest to where radio altimeters operate in Europe.
Specifically, internationally, radio altimeters operate within the 4.2-4.4 GHz frequency range. However, in the U.S., AT&T and Verizon are deploying wireless network services in a band closer to that range than has been permitted in Europe. In the U.S., the services have been allocated in the 3.7-3.98 GHz range, while in Europe it is 3.4-3.8 GHz.
In the paper, Eurocontrol notes, the European Commission has dedicated the band closest to radio altimeters to "so-called 'verticals' (company and factory-internal networks operating at lower power levels)."
"Furthermore, the US permits higher maximum power compared to what is generally implemented in Europe," Eurocontrol notes in the Think Paper. "Taken together, this has created a real risk of interference in the US that, for now, is not considered to be a problem requiring immediate safety mitigations in Europe."
The agency does acknowledge the possibility of future risk though, based on demand for the coveted C-band spectrum range from wireless networks in Europe. This is especially a possibility because of the larger scale at which telecommunications services providers operate, with Eurocontrol noting in the Think Paper that the global mobile phone market is "160 times larger than the CNS avionics market in total sales volume."
It was also reported that India just started rolling out 5G networks after much anticipation and years-long delay, by as early as the end of 2023. Service operators expect to bring next-generation cellular connectivity to every town in the world’s second-largest wireless market.But while the rollout is currently at its initial phase, New Delhi last week directed telecom operators to not set up 5G infrastructure around areas close to airports to avoid interference with flight operations.
In response to concerns raised by the Indian Directorate General of Civil Aviation (DGCA), the Department of Telecommunications (DoT), the government body that handles telecom operations in India, in its recent order to telecom operators Reliance Jio, Bharti Airtel and Vodafone Idea, directed them to restrict their infrastructure enabling C-Band 5G networks (between 3.3-3.67GHz) from over 1.3 miles (2.1 kilometers) away from runway endpoints at all airports in the country. It also ordered all three operators to limit the power emission of their equipment installed after the given range.
US C-band spectrum bandplan, with 3GPP 5G standard bands.
C-Band vs. satellite Stations
Also, a number of 5G networks deployed on the radio frequency band of 3.3–3.6 GHz is expected to cause interference with C-Band satellite stations, which operate by receiving satellite signals at 3.4–4.2 GHz frequency. This interference can be mitigated with low-noise block downconverters and waveguide filters.
Ligado 5G vs GPS
Demand for commercial spectrum to support broadband wireless communications has led the government to consider repurposing various radio frequencies, including the satellite communications bands next to GPS. However, the GPS industry has raised concerns of harmful interference with GPS receivers in the L1 band ranging from 1565 to 1586 MHz (centred at 1575.74 MHz). Nearly every civilian (consumer and enterprise) GPS receiver supports GPS’s L1 signal.
Back in 2003, the U.S. FCC established rules to permit mobile satellite services (MSS) licensees to seek authority to operate Ancillary Terrestrial Component (ATC) stations. An ATC system consists of terrestrial base stations and mobile terminals licensed to the operator of an MSS system, which allow an MSS licensee to integrate ATC in their MSS networks for the purpose of filling-in gaps in the MSS coverage area, particularly in urban areas or inside buildings.
Ligado Networks LLC, was authorized to provide MSS in the 1525-1559 MHz and 1626.5-1660.5 MHz bands, with the lower band allocated for downlink transmissions (from MSS satellites to mobile earth stations) and the upper band for uplink transmissions (from mobile earth stations to MSS satellites).
In 2004, Ligado, formerly known as LightSquared, applied for and was granted authorization for ATC operations, which allowed it to deploy ATC, provided that it met the conditions required by the FCC’s rules. In March 2010, Ligado applied for and was granted a waiver of certain of the ATC operating terms and conditions. In November 2010, Ligado requested a modification of its ATC authorization to accommodate its plans to deploy a nationwide 4G satellite/terrestrial network under its ATC authority. In January 2011, the International Bureau granted Ligado a waiver of the FCC’s integrated service rule, modifying its ATC operations authorization conditioned on it addressing the GPS industry’s interference concerns. The 2011 Order and Authorization established a working group (Technical Working Group) process wherein Ligado would work with the GPS industry, the National Telecommunications and Information Administration (NTIA), and other appropriate federal agencies to study the potential for overload interference to GPS devices and to identify any measures necessary to prevent “harmful interference” to GPS. With a focus on Ligado’s proposed terrestrial network, the Technical Working Group was specifically tasked with issuing a report to “provid[e] recommendations on steps that can be taken going forward to permit broadband wireless services to be provided in the L-Band MSS frequencies and co-exist with GPS devices” and “identify[ ] near-term technical and operational measures that can be implemented to reduce the risk of overload interference to GPS devices.” The International Bureau stated that it expected the GPS industry to work in good faith with Ligado to ameliorate the interference concerns. The 2011 FCC Order and Authorization provided that “once the Commission, after consultation with NTIA, concludes that the harmful interference concerns have been resolved,” Ligado could commence terrestrial operations. The Technical Working Group filed its technical report on June 30, 2011. That report, which identified different categories of GPS receivers— cellular, general location/navigation, high-precision, timing, networks, space-based, and aviation receivers—failed to reach consensus on whether concerns about harmful interference to GPS had been resolved.
Global Naviagation Satellite System (GNSS) Frequence Bands. The Ligado application has a risk of interefering with the GPS L1 frequency band.
Ligado's requested ATC spectrum vs. other adjacent spectrum.
Notes: Numbers show frequency ranges of each segment in MHz.
Source: Adapted by US Congressional Research Service from Richard N. Clarke, "Are Popular Wireless Services Like Wi-Fi and GPS Becoming the Pirate Radio of the 21st Century?", June 28, 2016.
The extent of GPS dependencies. It's vital for the USA to keep GPS running without interference.
Source: "PNT Homeland Security Official Links GPS Interference to Wider Cybersecurity Concerns", dated June 18, 2012. Inside GNSS
In 2012, the U.S. National Executive Committee for Space-Based Positioning, Navigation, and Timing (a.k.a. PNT EXCOM) proposed to draft new GPS spectrum interference standards to inform future proposals for non-space, commercial use of the bands adjacent to the GPS signals. The Department of Transport (DOT) was involved as a major stakeholder in crafting a safe future proposal.
The 2012 GPS Adjacent-Band Compatibility Assessment Plan provided the framework for DOT's development of power limit criteria for transmitters in the bands near GPS. The plan identified the processes to:
(a) derive power limit criteria to ensure new adjacent-band applications do not disrupt current GPS services and
(b) determine similar levels needed for future GPS equipment using modernized and interoperable GNSS signals.
These processes were used to develop and specify adjacent-band transmitter power limits needed to protect GPS/GNSS signals for civil applications.
In 2015, Ligado filed an initial application for ATC authority, and during subsequent modifications to its proposed ATC networks, Ligado has faced opposition from the GPS industry and others who express concern that Ligado’s proposed terrestrial operations will interfere with existing GPS systems. The relevant stakeholders have periodically reached consensus on certain discrete issues, however, such as in 2004 with respect to out-of-band emissions (OOBE) limits that would protect GPS inside the RNSS allocation.
DOT began testing GPS/GNSS receivers in April 2016 pursuant to the final test plan published in March 2016. Device testing took place at the U.S. Army Research Laboratory at the White Sands Missile Range (WSMR) facility in New Mexico. All GPS device manufacturers had an opportunity to participate in the testing.
Note: the National Advanced Spectrum and Communications Test Network (NASCTN) tested LTE impacts to GPS devices, which was independent of the DOT testing.
A second round of DOT testing occurred in July 2016 at Zeta Associates in Fairfax, Virginia, and MITRE Corporation in Bedford, Massachusetts. The goals of the additional lab testing were:
Receiver characterization for comparison with results obtained in April at the anechoic chamber at the U.S. Army Research Laboratory;
Evaluation of Out Of Band Emission (OOBE) interference at prescribed and proposed levels with Long Term Evolution (LTE) uplink and downlink signals;
GPS/GNSS signal acquisition characterization; and
The DOT's approach to this task was to develop power limit criteria for transmitters in the bands near GPS. In April 2018, DOT released the final report of its GPS Adjacent Band Compatibility Assessment.
In March 2018, the PNT EXCOM released an 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 NPEF evaluated five tests performed by the following organizations:
Federal Communication Commission (FCC)-mandated Technical Working Group (TWG)
National Space-Based PNT Systems Engineering Forum (NPEF)
Department of Transportation (DOT)
Roberson and Associates (RAA) - which is a pro-Ligado report claiming no harmful interference to most GPS receivers.
National Advanced Spectrum and Communications Test Network (NASCTN)
The gap analysis concluded that the results from three of the five 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.
In 2018, Ligado made another amendment to its ATC license modification applications, and as a condition for operating in the 1526-1536 MHz band, to gain the FCC’s approval considering the growing concern with GPS interference, Ligado made significant modifications to its original proposal, including greatly reduced power levels, the addition of new guard bands to protect and provide even more spectrum separation to adjacent services, and reaching co-existence agreements with manufacturers of high-precision GPS receivers.
The U.S. Air Force (USAF) also provided a background paper regarding the use of the 1 dB decrease in the carrier-to-noise density ratio (C/N0) as the appropriate interference protection criterion (IPC) for GPS and other Radionavigation Satellite Service (RNSS) receivers. They stated that the use of the 1 dB IPC has significant domestic and international precedence, is consistent with the protection afforded other radiocommunication services, and is the only reliable mechanism to ensure adequate protection for civilian and military GPS receivers.
The GPS/SATCOM Coalition, which also opposed Ligado’s proposal, pointed to the March 2018 NPEF Gap Analysis, which supports DOT and other testing that relied on the 1 dB metric and concluded that Ligado’s transmissions would result in unacceptable interference to GPS receiver operations.
Initially, major GPS manufacturers like Garmin, Trimble, and Deere had been a participant in this proceeding, and their devices have been tested in the different studies and reports submitted in this proceeding since 2011 including in the RAA and NASCTN Reports. They all had, at some time prior to entering into coexistence agreements with Ligado, expressed significant concerns about Ligado’s ATC network and had completely opposed authorizing Ligado’s ATC operations. They each have abandoned their earlier oppositions and have reached agreement with respect to Ligado’s 2015 license modification applications. However, although Garmin, Trimble, and Deere have reached their own co-existence agreements with Ligado, they continue to support the use of the 1 dB metric to assess harmful interference, and they objected to Ligado’s proposal to use an alternative metric to assess potential harmful interference. Trimble stated that the GNSS industry, the FCC, and NTIA have used the 1 dB metric in various contexts for many years. Garmin contended that the 1 dB metric should be applied to protect GPS devices not only from OOBE that emanate from services in adjacent bands (here, Ligado’s transmissions in the MSS band) and fall within the RNSS band where GPS operates, but also to overload interference that emanates from services in adjacent bands (here Ligado) and falls outside the RNSS band.
Ligado responded that the USAF memorandum relies on “irrelevant and misleading data.” Ligado asserted that the Air Force memorandum ignores “what is perhaps the most critical and basic fact” that the proposal before the Commission is Ligado’s 2018 amended applications in which its operations would be limited to 9.8 dBW, not the earlier proposed operating level of 32 dBW. Ligado stated that under a maximum power level of 9.8 dBW, almost all of the high-precision devices tested in the 2016 RAA Reports that were affected at 32 dBW are not affected, and that the affected devices were manufactured by GPS device manufacturers who have co-existence agreements with Ligado and do not object to Ligado’s proposed operations. Ligado further asserted that extensive testing and the co-existence agreements with major GPS device manufacturers, as set forth in the record, establish that the operations of GPS devices “will not be compromised,” and that the USAF memorandum does not provide any new technical evidence in the record regarding potential harmful interference to GPS devices. Ligado also rejected the USAF’s contention that many high-value uses of civil GPS devices not owned by the government would be vulnerable to interference, pointing to its co-existence agreements with GPS manufacturers. In addition, Ligado contended that claims of threats to military use are unsupported insofar as they inappropriately rely on a 1 dB metric.
In December 2018, the PNT EXCOM wrote to the National Telecommunications and Information Administration (NTIA) and suggested that tests indicate that proposals to operate services in bands adjacent to GPS should not be approved unless, at a minimum, they do not exceed the tolerable power transmission limits described in the U.S. DoT's GPS Adjacent Band Compatibility Assessment Final Report (from April 2018). With regard to the license modification application of Ligado Networks to the FCC, it was clear that the proposed service would exceed the tolerable power limits necessary to prevent disruption of GPS receivers. Based on the results of the extensive studies the PNT EXCOM suggested that the NTIA should recommend to the FCC against approval of the license modification. The NTIA sent a similar letter to the FCC in December 2019 and on April 10th, 2020, recommending against approval of the Ligado license modification unless these concerns were addressed.
The DND and DoT and other U.S. government departments and agencies also sent similar opposition letters to both the NTIA and FCC.
Despite all the fierce opposition, on April 20th, 2020, the FCC announced that, "it has approved with conditions Ligado's application to deploy a low-power terrestrial nationwide network in the L-Band that will primarily support 5G and Internet of Things services." In its decision, the FCC was overtly critical of the DoT's ABC Final Report. In addition to agreeing to Ligado's 2018 amendments, the FCC decision also includes extensive additional protections to adjacent band operations, including requirements for Ligado to perform drive tests and 24/7 monitoring of transmit power levels, among other detailed protection mechanisms. The decision effectively authorizes Ligado to deploy a low-power terrestrial U.S.-wide network in the 1526-1536 MHz, 1627.5- 1637.5 MHz, and 1646.5-1656.5 MHz bands that will primarily support Internet of Things (IoT) services.
The U.S. Executive Branch (which is separate from FCC) remains concerned because Ligado's proposed transmission power exceeds the thresholds established by the GPS Adjacent Band Compatibility study to protect GPS users from harmful interference. However, not much can be done at this point, apart from reporting known cases of harmful GPS interference to the FCC and hoping they intervene. But don't hold your breathe.
High Band (FR2) or mmWave- 24–54 GHz
The third bucket of spectrum where wireless operators are deploying 5G is in the millimeter wave spectrum. This is very high on the spectrum chart in the 24 GHz band and higher. The GSMA recommends that operators support millimeter wave spectrum in the 26 GHz, 40 GHz, 50 GHz and 66 GHz bands for mobile services. However, the association also notes that spectrum in the 26 GHz and 28 GHz already have strong momentum from operators and added that these bands are adjacent and therefore make it easier for handsets to support.
Millimeter wave spectrum is limited because signals can’t travel very far — in some cases the signal will travel less than a mile — and they are also susceptible to interference from things like trees and buildings and even glass.
But the benefit of millimeter wave spectrum is that if the signal is unencumbered users can get connection speeds between 1 Gbps to 3 Gbps or even higher.
Besides its low-band 5G offering, AT&T also has a high-band 5G, which it’s calling 5G+. This is deployed in the company’s 36 GHz band millimeter wave spectrum and it offers extra speed and capacity and is intended for high-traffic areas like campuses and arenas. AT&T’s 5G+ is available in parts of 23 cities and the company is making it available to only enterprises.
Likewise, T-Mobile also has deployed 5G in six markets using millimeter wave that supplements its 600 MHz 5G network. The company has said it is using 39 GHz spectrum in its Las Vegas market and 28 GHz spectrum in the other five markets.
Meanwhile Verizon is currently only offering 5G using millimeter wave spectrum. The company deployed its 5G service in 31 cities so far and is also using spectrum in the 28 GHz and 39 GHz bands. In earnings calls with investors, Verizon executives have said that millimeter wave spectrum works better than many experts thought and the company is using beam-forming technology coupled with 5G small cells to get more coverage.
Interference with Weather and Earth Observation Satellites
The spectrum used by various 5G proposals, especially the n258 band centered at 26 GHz, will be near that of passive remote sensing such as by weather and Earth observation satellites, particularly for water vapor monitoring at 23.8 GHz.
Interference is expected to occur due to such proximity and its effect could be significant without effective controls. An increase in interference already occurred with some other prior proximate band usages. Interference to satellite operations impairs numerical weather prediction performance with substantially deleterious economic and public safety impacts in areas such as commercial aviation.
The concerns prompted U.S. Secretary of Commerce Wilbur Ross and NASA Administrator Jim Bridenstine in February 2019 to urge the FCC to delay some spectrum auction proposals, which was rejected. The chairs of the House Appropriations Committee and House Science Committee wrote separate letters to FCC chairman Ajit Pai asking for further review and consultation with NOAA, NASA, and DoD, and warning of harmful impacts to national security. Acting NOAA director Neil Jacobs testified before the House Committee in May 2019 that 5G out-of-band emissions could produce a 30% reduction in weather forecast accuracy and that the resulting degradation in European Centre for Medium-Range Weather Forecasts (ECMWF) model performance would have resulted in failure to predict the track and thus the impact of Superstorm Sandy in 2012. The United States Navy in March 2019 wrote a memorandum warning of deterioration and made technical suggestions to control band bleed-over limits, for testing and fielding, and for coordination of the wireless industry and regulators with weather forecasting organizations.
At the 2019 quadrennial World Radiocommunication Conference (WRC), atmospheric scientists advocated for a strong buffer of −55 dBW, European regulators agreed on a recommendation of −42 dBW, and US regulators (the FCC) recommended a restriction of −20 dBW, which would permit signals 150 times stronger than the European proposal. The ITU decided on an intermediate −33 dBW until September 1, 2027, and after that a standard of −39 dBW. This is closer to the European recommendation but even the delayed higher standard is much weaker than that requested by atmospheric scientists, triggering warnings from the World Meteorological Organization (WMO) that the ITU standard, at 10 times less stringent than its recommendation, brings the "potential to significantly degrade the accuracy of data collected". A representative of the American Meteorological Society (AMS) also warned of interference, and the ECMWF, sternly warned, saying that society risks "history repeat[ing] itself" by ignoring atmospheric scientists' warnings (referencing the monitoring of global warming, which could be in peril). In December 2019, a bipartisan request was sent from the US House Science Committee to the Government Accountability Office (GAO) to investigate why there is such a discrepancy between recommendations of US civilian and military science agencies and the regulator, the FCC.
Footnotes and References
U.S. PNT EXCOM's NPEF Gap Analysis, dated March 2018
U.S. DOT's GPS Adjacent Band Compatibility Assessment Final Report, dated April 2018
FCC Unanimously Approves Ligado's Application to Facilitate 5G and Internet Of Things Services. DA/FCC #: FCC-20-48. Docket/RM: 11-109, 12-340. FCC Record Citation: 35 FCC Rcd 3772 (5)
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