POLICY
FAA forced delay in 5G rollout despite having no proof of harm to aviation
US delays even as 40 countries use C-band with no reports of harm to altimeters.
Two weeks ago, AT&T and Verizon reluctantly agreed to delay the launch of 5G on newly acquired C-band spectrum licenses for one month, until January 5, in response to the Federal Aviation Administration's claim that the new service could interfere with radio altimeters used in airplanes.
Mobile carriers aren't alone in being frustrated by the delay. Telecom-industry observers point out that the Federal Communications Commission approved use of the C-Band spectrum from 3.7 to 3.98 GHz only after analyzing the aviation industry's interference claims and finding no evidence to support the claims. The FCC also required a 220 MHz guard band that will remain unused to protect altimeters from interference. That guard band is more than twice as big as the 100 MHz buffer initially suggested by Boeing, the FCC has said.
Moreover, this spectrum is reportedly already being used for 5G in nearly 40 countries without evidence of the problems that US aviation officials are warning of. "Tick, tick, tick... US wireless leadership and national security await 'resolution' of unfounded concerns by FAA," former FCC Commissioner Mike O'Rielly tweeted yesterday.
Verizon and AT&T dominated auction
Verizon and AT&T dominated the C-band auction when the results were announced in February 2021, with Verizon's winning bids totaling $45.45 billion and AT&T's adding up to $23.41 billion. T-Mobile spent $9.34 billion on C-band spectrum, but is primarily using 2.5 GHz frequencies for its midband 5G deployment. The FCC issued the C-band licenses in July 2021. Verizon and AT&T have big plans for the C-band. They expect the 3.7-3.98 GHz spectrum to boost 5G networks with faster speeds than are provided on sub-1 GHz spectrum and larger coverage areas than are possible with millimeter-wave spectrum, which doesn't perform well with obstacles or long distances. The radio altimeters used to determine airplane altitudes rely on spectrum from 4.2 GHz to 4.4 GHz. The adjacent C-band was previously allocated to satellite service before the FCC repurposed it for cellular use. The band technically extends from 3.7 to 4.2 GHz, but the FCC limited cellular use to 3.98 GHz and below to create the 220 MHz guard band.FAA slammed for “new heights of irresponsibility”
The FCC is the expert agency on spectrum interference, and some industry observers say that other US agencies have a history of claiming interference problems without good evidence. The "federal government's processes for addressing spectrum policy [are] severely broken," Harold Feld, a long-time telecom attorney and senior VP of consumer-advocacy group Public Knowledge, wrote in a lengthy blog post on the dispute last week. "Unhappy federal agencies that don't like the outcome of an FCC proceeding respond by undermining the FCC in the press and trying to wage proxy wars through allies in Congress. But the FAA's actions here take this behavior to new heights of irresponsibility and danger." Feld—a frequent critic of how telecom companies treat users—wrote that he sides with the wireless industry on this issue in part because the "FAA had a year to collect information on what altimeters were out there and start collecting data on whether 5G would cause harmful interference to any models, and what interference mitigation might be necessary to avoid any potential for harmful interference... Instead, the aviation industry (with the silent support of FAA) basically went for all or nothing. Every correspondence in the FCC record requests that the FCC prevent activation of 5G networks on any part of the C-Band until the aviation industry was satisfied that there was no potential risk of harmful interference." In some of the countries already using the C-band, "5G signals operate in spectrum adjacent to aviation equipment. US airlines fly in and out of these countries every day," the wireless industry group CTIA's president and CEO, Meredith Attwell Baker, wrote today. "If interference were possible, we would have seen it long before now. Nevertheless we've added a layer of protection in the United States, called a guard band, that is hundreds of times greater than the separation that exists between wireless and other critical spectrum users."FAA acknowledged no “proven” interference
The FAA issued a November 2 bulletin that warned of "potential adverse effects on radio altimeters," but that bulletin acknowledged there have been no "proven reports of harmful interference," even in countries that allow 5G transmissions above the 3.98 GHz limit set by the FCC. "Many countries around the world are already deploying wireless networks in the bands from 3300-4200 MHz; some countries have implemented temporary technical, regulatory and operational mitigations, including temporary proximity and power restrictions, on wireless broadband networks operating in bands ranging from 3700-4200 MHz," the FAA wrote. "There have not yet been proven reports of harmful interference due to wireless broadband operations internationally, although this issue is continuing to be studied." The US has deployed wireless broadband in 3.65-3.7 GHz since 2007, the FAA noted. In its February 2020 decision to reallocate C-band spectrum, the FCC said the aviation industry's research was unrealistic and urged the industry to conduct more testing, saying that "further analysis is warranted on why there may even be a potential for some interference given that well-designed equipment should not ordinarily receive any significant interference (let alone harmful interference) given these circumstances." About 20 months later, in the bulletin issued this month, the FAA recommended that "radio altimeter manufacturers, aircraft manufacturers, and operators voluntarily provide to federal authorities specific information related to altimeter design and functionality, specifics on deployment and usage of radio altimeters in aircraft, and that they test and assess their equipment in conjunction with federal authorities." The FAA's new warning to the aviation industry also noted that the FCC first sought comment on using the C-band for mobile broadband in 2017. "The 5G C-band issue has been pending for YEARS... why are they only now looking at better standards for altimeters?" spectrum technology and policy consultant Michael Marcus, an engineer who spent over two decades working for the FCC, wrote on Twitter yesterday. Marcus also pointed to a July 2012 report by a White House advisory council that recommended "methodologies for spectrum management that consider both transmitter and receiver characteristics to enable flexible sharing of spectrum" because "receiver characteristics increasingly constrain effective and flexible spectrum usage." In other words: receivers should be designed well enough to protect themselves from interference from transmissions in other spectrum bands. The FAA told the FCC in December 2020 that it "expect[s] that the cost of replacement or retrofit of radar altimeters will be substantial."200,000 base stations operating without problems
CTIA told the FCC this month that the nearly 40 countries using this spectrum "have already adopted rules and deployed hundreds of thousands of 5G base stations in the C-Band at similar frequencies and similar power levels—and in some instances, at closer proximity to aviation operations—than 5G will be in the US. None of these countries has reported any harmful interference with aviation equipment from these commercial deployments." In Japan, "tens of thousands of 5G base stations have been deployed up to 4100 MHz—meaning there is just a 100-megahertz guard band between 5G operations and where radio altimeters operate," and there have been no claims of interference, CTIA wrote. "The US will have four times the guard band with this year's Phase 1 deployments (3700-3800 MHz), and two times the guard band following the full C-Band transition in 2023 (3700-3980 MHz)." In Europe, where 3.4-3.8 GHz is used, 5G has been deployed on "more than ten thousand base stations in more than 20 countries for up to three years at power levels substantially similar to US C-Band 5G levels, without harmful interference claims—including in the band segment where Phase 1 5G operations will launch in the U.S. this year (3700-3800 MHz)," CTIA wrote. CTIA criticized an October 2020 report by RTCA (formerly the the Radio Technical Commission for Aeronautics), writing that "at least two hundred thousand 5G base stations are already operating today in at least a dozen countries with technical rules and proximity to radio altimeter operations that the RTCA Report would suggest should be seeing harmful interference, yet no known reports of interference exist."Well-designed altimeters shouldn’t be affected
Peter Rysavy, a wireless technology analyst with about three decades of experience, wrote that aviation-industry test results are apparently driven by altimeters that are "built to decades-old specifications" and lack adequate filtering. He continued:Well-designed equipment with reasonable filtering should not be adversely affected by other equipment operating in adjacent bands—or hundreds of MHz away. Based on the modeling assumptions RTCA and AVSI [Aerospace Vehicle Systems Institute] are using, other systems, even in the absence of 5G, would be interfering with altimeters today. For example, Navy radar, such as the AN/SPN-43 radar, operates in mid-band frequencies at extremely high power with ground transmitters pointing at aircraft in geographical areas where US planes operate. Such potential interference, however, has not been a problem in the real world.Rysavy also wrote that "France and Norway conducted specific flight tests of 5G coexistence with altimeters to determine if harmful effects might exist and found none." While Japan "imposed some mitigation measures" in the upper part of the C-band to protect altimeters, those limits apply "only in 4.0-4.1 GHz, with no restrictions below 4 GHz," the part of the spectrum allocated in the US, Rysavy wrote. Despite the seemingly large amount of evidence that C-band transmissions can safely coexist with altimeters, the aviation industry told the FCC this month that there is a "lack of necessary data in the FCC public record for the Aviation Community to make data-driven decisions on air safety." That letter was signed by Airbus, Boeing, Garmin, Honeywell, and over a dozen aviation industry trade groups. They said it will take them "many years to design and deploy the next generation of RAs [radio altimeters]" that can handle transmissions from 5G despite the 220 MHz guard band.
220 MHz is “double the minimum” suggested by Boeing
Boeing told the FCC in 2018 that "band pass filters that are incorporated into radio altimeters... have limited ability to reject transmissions close to the edges of the 4.2-4.4 GHz band. As a result, relatively powerful mobile communications in the adjacent band could overload the radio altimeter receivers on aircraft, inhibiting their accurate operation." Boeing said that interference could come from transmissions in the upper part of the C-band. "In summary, it would not be possible to permit P2MP [fixed point-to-multipoint] transmitters or mobile base stations to operate in the 4.1-4.2 GHz band because of the interference that would result to radio altimeter receivers on aircraft," Boeing wrote. Boeing's reference to 4.1-4.2 GHz transmissions seemed to indicate that a 100 MHz guard band would be sufficient. The FCC said that the 220 MHz guard band it adopted "is double the minimum guard band requirement discussed in initial comments by Boeing and ASRC [Aviation Spectrum Resources]."FCC poked holes in aviation industry study
Aviation industry concerns were detailed by AVSI in an October 2019 study. Garmin cited AVSI's research in an FCC filing this week, saying it showed altimeters "subjected to simulated 5G interference sources" output misleading data on a plane's height above the ground, and this incorrect data "would not be able to be detected by downstream safety-critical systems that enable safe operation of aircraft in all weather conditions." The FCC found that AVSI's report "does not demonstrate that harmful interference would likely result under reasonable scenarios (or even reasonably 'foreseeable' scenarios to use the parlance of AVSI)." The FCC summarized the AVSI study as follows:AVSI's study simulated an aggregate 5G emission for various amounts of allocated spectrum and measured the received power level at which the accuracy of height measurements exceeds certain criteria. In one scenario, AVSI modeled a worst-case scenario with an aircraft altimeter operating at 200 feet AGL [Above Ground Level], with numerous other altimeters nearby creating in-band interference and aggregate base station emissions across the 3.7 to 4.0 GHz band. The preliminary results show that there may be a large variation in radio altimeter receiver performance between different manufacturers.T-Mobile hired consultancy firm Alion to conduct an analysis of the AVSI study. The FCC generally agreed with T-Mobile and Alion's conclusions, pointing to Alion's finding that "AVSI's analysis identified levels of interference where performance degradation occurred, but did not investigate whether these levels would occur in any reasonable scenario." Moreover, "two of the initial altimeter types failed due to interference from other altimeters and the scenario had to be adjusted," and the simulated emissions in the AVSI study "would not comply with the emission limits for virtually any services associated with a base station or fixed station governed by FCC rules." The 220 MHz guard band and "technical rules on power and emission limits we set for the 3.7 GHz Service" are enough to prevent problems, the FCC found. The FCC's two Democrats voted against the February 2020 C-band order—but not because of interference concerns. "We force C-band auction winners to pay nearly $10 billion to incumbent satellite operators over and above their relocation costs" without citing "any legal authority or precedent that allows us to do so," Commissioner Jessica Rosenworcel said at the time. Rosenworcel is now FCC chairwoman, and she oversaw completion of the auction and the FCC process for distributing the spectrum licenses.
Does physics work differently in the US?
Feld wrote that "the technical evidence on which the FAA bases its interference concerns have a lot of problems—not least of which [is] that about 40 other countries operate similar 5G deployments in the same C-Band without any interference showing up. Either physics works differently in the US, or the report at the center of this controversy needs to explain why this hasn't shown up in any other country where deployments are either authorized or have already taken place. What is worse, the FAA has basically been playing 'chicken' with the FCC by failing to turn over needed information to verify the report or replicate the results until literally the day before FAA staff leaked the 'planes are gonna fall out of the sky' story to the Wall Street Journal," Feld continued. Feld was referring to this WSJ article that previewed the FAA's warning to pilots and airlines. The October 29 article was published one day after "AVSI finally provided to the FCC documents to back up its now 1-year old study on potential interference," Feld wrote. "Unfortunately, because AVSI used the procedure for filing proprietary documents, there is no way to evaluate [this] filing." The aviation industry last week asked for a longer delay to the carriers' deployment, calling on the National Economic Council "to work with the FCC and FAA to convene a joint industry working group and continue to delay the deployment of 5G technologies in this band until the safety and efficiency of the NAS [National Airspace System] is ensured."FAA says altimeters will be updated (eventually)
One of the latest developments came Tuesday when FAA Administrator Steve Dickson talked to reporters. Bloomberg paraphrased Dickson as saying that "flight restrictions may be needed as air carriers adjust to 5G signals that could interfere with navigation electronics." But Dickson also said the FAA was having "very productive discussions" with the FCC "and we will figure this out... It remains to be seen what mitigations—whether it's adjustments to [5G] deployment or actions that we need to take in the aviation sector—what those will look like." Dickson said the FAA is considering changes to radio-altimeter standards. Bloomberg wrote:Dickson said for the first time that the FAA is looking at updating the standards for the devices known as radio altimeters, which use signals to determine a plane's altitude above the ground. "There's going to be new standards developed for radio altimeters," Dickson said. "What that looks like in terms of retrofits remains to be seen." One issue is that older radio altimeters may be more vulnerable to interference, so improving them might prevent the interference.
