The fight is on over 5G. Telecommunication companies and the US government promote the latest mobile broadband because it will provide faster data-transfer rates than the current broadband communication standard. Faster, more reliable digital communication is needed for the newest technologies—autonomous vehicles, internet-of-things devices, and smart energy grids, among others. But meteorologists, US science agencies, and other countries worry that strong 5G signals, if not properly regulated, may interfere with satellites that are crucial to weather forecasting.
Today’s 4G network, nearly a decade old, moves data by bouncing radio waves between cell towers and devices such as smartphones. A 5G network would operate similarly but use a wider frequency range and more bandwidth, which would increase data-transfer rates by an order of magnitude. The higher-frequency signals proposed for 5G can’t travel through buildings like their lower-frequency 4G counterparts, but specialized antenna arrays would transmit the 5G signal across long distances. Earlier this year, two telecom companies in South Korea launched small 5G networks using busy lower-frequency bands, and Verizon deployed a 5G test in Chicago at the higher-frequency 28 GHz band.
Widespread 5G deployment will depend on building a new infrastructure of antennas that operate in high-frequency radio bands. Telecom companies and US regulators support 24 GHz for 5G networks because of its greater bandwidth and because the 1–6 GHz radio spectrum is already crowded with 4G, digital TV, radar, and other applications. (The 24 GHz band spans 24.25–24.45 GHz and 24.75–25.25 GHz.)
Spectrum is a finite resource, and the Federal Communications Commission (FCC), which coordinates the commercial use of spectrum in the US, is racing to allocate as much higher-frequency spectrum as possible for 5G technology. The FCC “5G FAST” plan, unveiled in September 2018, is bringing more spectrum to market, updating infrastructure policy, and modernizing regulations. Other bands are being considered, including 28, 37, 39, and 47 GHz.
In October at the United Nations International Telecommunication Union Radiocommunication Sector (ITU-R) conference, member countries will discuss and vote on how to regulate the 5G signal in the 24 GHz band. The US is poised to push for a higher maximum 5G signal power than what European countries favor. Lower signal power would decrease the range of the 5G signal.
“The precipitating issue here is the potential for what’s called out-of-band interference,” says Jordan Gerth of the University of Wisconsin–Madison. Water-vapor molecules emit electromagnetic radiation at 23.8 GHz, and instruments such as the Advanced Technology Microwave Sounder aboard NOAA’s Joint Polar Satellite System infer atmospheric air-temperature and moisture data from the 23.6–24.0 GHz emission band. The measurements are used to calibrate numerical weather-prediction models, such as NOAA’s Global Forecast System (see Physics Today, May 2019, page 32).
Radio signals transmit at their highest power at a central frequency, and the signal progressively loses power at more distant frequencies. A 5G signal, therefore, could leak across the 250 MHz gap between the water-vapor emission band and the 24 GHz 5G band, which could make it nearly impossible for microwave instruments to differentiate between water vapor and emissions from multitudes of 5G smartphones. Microwave instruments have no other frequencies they can use to sense water vapor. Filtering for noise from a 5G network would be difficult, especially for broadband transmitters, says Joel Johnson of the Ohio State University. “If there’s thousands of these little transmitters all over the place, then it’s very hard to correct for them.” Documents provided by two other passive microwave experts—who, like many sources for this story, spoke on condition of anonymity—indicate that 16 operational weather satellites worldwide use passive microwave sounders or imagers to gather water-vapor data. Another 18 future satellites worldwide scheduled for deployment from 2021 through 2036 could be affected by 24 GHz 5G interference.
The FCC, NASA, the US Navy, and NOAA have been analyzing the potential for 5G interference since 2017. During a hearing of the House Science, Space and Technology Subcommittee on Environment on 16 May 2019, Neil Jacobs, a NOAA assistant secretary of commerce, explained that using the 24 GHz band for 5G with the signal strength proposed by the FCC, −20 decibel watts per 200 MHz, would decrease the data collected from microwave instruments by 77%.
Jacobs said that such data loss “would degrade the forecast skill by up to 30%” and return the US weather prediction capability to “somewhere around 1980.” Citing an unpublished NOAA study, he further testified that a lower signal strength of −40 or −50 dBW per 200 MHz “would result in roughly zero data loss.” That range, one-hundredth to one-thousandth of the FCC’s proposed limit, was determined with guidance from the ITU-R and industry.
However, on 12 June, FCC chairman Ajit Pai told the Senate Commerce, Science, and Transportation Committee, “We [at the FCC] believe that our protection limits are appropriate…. In our view, the assumptions that undergird that [NOAA] study are fundamentally flawed.” Pai noted that the NOAA study did not consider beamforming technology, which employs adaptive antenna arrays to focus radio waves to specific receivers and is already used in 4G networks and other applications.
Beamforming, though, would not solve the interference problem, according to two experts in passive microwave sensors and the regulatory process. The technology wouldn’t mitigate out-of-band interference. Furthermore, beamforming wouldn’t protect satellite instruments against interference from upward-scattered signals in urban environments, according to the experts.
Despite concerns from NASA, NOAA, and several countries, the FCC auctioned 24 GHz spectrum this past spring. The two highest bidders, T-Mobile and AT&T, respectively paid about $1 billion and $800 million for licenses. T-Mobile didn’t return a request for comment, and an AT&T spokesperson said the details were still under a company “quiet period.” An FCC source confirmed that the license contracts do not specify signal strength. In a different auction earlier this year, the FCC sold 28 GHz spectrum for 5G: Verizon paid $500 million for licenses, and T-Mobile spent $40 million.
The FCC has a pre-auction commenting period to help determine how to regulate the use of spectrum. “As a matter of practice, the FCC does not conduct its own studies,” says a source at the FCC. But according to a lobbyist for the meteorological community, the commenting process is so convoluted that “it’s become the realm of regulatory attorneys” rather than concerned citizens and scientists. “You really need to have a full-time law firm to be able to track this stuff,” the lobbyist said, and added that the FCC has “experts in wireless technology, but it does not mean that they have any expertise in meteorology or meteorological technologies.”
The 5G conflict escalated when Commerce secretary Wilbur Ross and NASA administrator Jim Bridenstine sent Pai a cease-and-desist letter a week before the 24 GHz auction. Pai refused to delay the process. In the immediate aftermath, David Redl resigned from his post as assistant secretary of the National Telecommunications and Information Administration, which manages federal spectrum use and identifies other spectrum bands for commercial use. Several sources say that Redl’s resignation is a direct result of the interagency dispute.
The meteorology lobbyist and a telecom lobbyist both said that the White House has pressured the FCC to quickly bring spectrum to market. They said President Trump hopes that touting auction revenue and bringing broadband to rural voters will help his 2020 campaign. The FCC source denied any pressure, saying that “spectrum policy is driven by the FCC.”
According to a May 2019 report by the White House Office of Science and Technology Policy (OSTP), the Trump administration believes that 5G is “one of four industries of the future that will ensure American prosperity and national security.” In a separate interview, the OSTP director, atmospheric scientist Kelvin Droegemeier, said he is “absolutely convinced we’ll address [5G] in a way that will bring maximum benefit to taxpayers and minimum disruption to the services we need to provide.” (See “Q&A: Kelvin Droegemeier, President Trump’s science adviser,” Physics Today online, 30 May 2019.)
A trade association of telecommunication companies, CTIA, supports the White House in wanting 5G implemented quickly across many currently unused bands. In a May 2019 blog post, CTIA executive vice president Brad Gillen argued that the Commerce Department’s caution regarding interference from 5G is “undermining our global leadership efforts.” Establishing a national position on 24 GHz for 5G, Gillen claimed, is critical before October, when the monthlong ITU-R World Radiocommunication Conference (WRC-19) takes place in Egypt.
At WRC-19, expert study groups organized by the ITU-R will discuss the results of their 24 GHz interference analyses before UN member countries vote on 5G signal strength. Paolo de Matthaeis, a remote-sensing researcher at NASA’s Goddard Space Flight Center and technical chair of the IEEE Geoscience and Remote Sensing Society’s committee on frequency allocations in remote sensing, says a majority of member nations must agree in order to issue a new regulation or alter an existing one. By arguing that the FCC has already set a 5G signal level through various auctions, he says, the US could negotiate for a looser regulation of the 24 GHz band.
Member countries are not obligated to follow an ITU-R regulation if their activities don’t affect others. But if the US adopts a stronger signal for the 24 GHz band, global weather models may suffer. Other member countries could argue for the US to adhere to the proposed ITU-R regulation, says de Matthaeis.
ITU-R member countries at WRC-19 will consider about a dozen other bands above 24 GHz for 5G use. A report by the UK-based trade group GSMA recommends using the 26, 28, 40, and 66 to 71 GHz bands. The report says that the 26 and 28 GHz bands have the most international support because they are adjacent and easily harmonized, so they can be allocated for use across country borders.
The US ITU-R delegation is finalizing its official position on allowable signal levels for 5G networks. The Inter-American Telecommunication Commission (CITEL), a coalition of North, Central, and South American countries, will discuss the limits for the 24 GHz band this month in Ottawa, Canada. “The US will try to convince the other CITEL countries to adopt its position,” says de Matthaeis. “If that happens, it will carry considerable weight into WRC-19.”