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Remember the 5G-airport controversy? Here’s how such disputes play out
The airline and cellular-phone industries have been at loggerheads over the possibility that 5G transmissions from antennas such as this one, located at Los Angeles International Airport, could interfere with the radar altimeters used in aircraft.
You’ve no doubt seen the scary headlines: Will 5G Cause Planes to Crash? They appeared late last year, after the U.S. Federal Aviation Administration warned that new 5G services from AT&T and Verizon might interfere with the radar altimeters that airplane pilots rely on to land safely. Not true, said AT&T and Verizon, with the backing of the U.S. Federal Communications Commission, which had authorized 5G. The altimeters are safe, they maintained. Air travelers didn’t know what to believe.
Another recent FCC decision had also created a controversy about public safety: okaying Wi-Fi devices in a 6-gigahertz frequency band long used by point-to-point microwave systems to carry safety-critical data. The microwave operators predicted that the Wi-Fi devices would disrupt their systems; the Wi-Fi interests insisted they would not. (As an attorney, I represented a microwave-industry group in the ensuing legal dispute.)
Whether a new radio-based service will interfere with existing services in the same slice of the spectrum seems like a straightforward physics problem. Usually, though, opposing parties’ technical analyses give different results. Disagreement among the engineers then opens the way for public safety to become just one among several competing interests. I’ve been in the thick of such arguments, so I wanted to share how these issues arise and how they are settled.
Not all radio spectrum is created equal. Lower frequencies travel farther and propagate better through buildings and terrain. Higher frequencies offer the bandwidth to carry more data, and work well with smaller antennas. Every radio-based application has its own needs and its own spectral sweet spot.
Suitable spectrum for mobile data—4G, 5G, Wi-Fi, Bluetooth, many others—runs from a few hundred megahertz to a few gigahertz. Phones, tablets, laptops, smart speakers, Wi-Fi-enabled TVs and other appliances, Internet-of-things devices, lots of commercial and industrial gear—they all need these same frequencies.
The problem is that this region of spectrum has been fully occupied for decades. So when a new service like 5G appears, or an older one like Wi-Fi needs room to expand, the FCC has two options. For a licensed service like 5G, the FCC generally clears incumbent users from a range of frequencies—either repacking them into other frequencies nearby or relocating them to a different part of the spectrum—and then auctions the freed-up spectrum to providers of the new service. To accommodate an unlicensed service like Wi-Fi, the FCC overlays the new users onto the same frequencies as the incumbents, usually at lower power.
The FCC tries to write technical rules for the new or expanded service that will leave the incumbents mostly unaffected. It is commonplace for newcomers to complain that any interference they cause is not their fault, attributing it to inferior incumbent receivers that fail to screen out unwanted signals. This argument usually fails. The newcomer must deal with the spectrum and its occupants as it finds them. Strategies for accomplishing that task vary.
This radio tower, located near downtown Los Angeles, is bedecked with 6-GHz fixed-microwave antennas that serve area police and fire departments.George Rose/Getty Images
Congress prohibits the FCC (and other federal agencies) from changing the regulatory ground rules without first soliciting and considering public input. On technical issues, that input comes mostly from the affected industries after the FCC outlines its tentative plans in a Notice of Proposed Rulemaking. There follows a back-and-forth exchange of written submissions posted to the FCC’s website, typically lasting a year or more.
Ordinarily, parties can also make in-person presentations to the FCC staff and the five commissioners, if they post summaries of what they say. Sometimes the staff uses these meetings to test possible compromises among the parties.
All this openness and transparency has a big exception: Other federal agencies, like the FAA, can and sometimes do submit comments to the FCC’s website, but they also have a back channel to deliver private communications.
The submissions in a spectrum proceeding generally make two kinds of points. First, the newcomers and the incumbents both present data to impress the FCC with their respective services’ widespread demand, importance to the economy, and utility in promoting education, safety, and other public benefits. Second, both the proponents and opponents of a new frequency usage submit engineering studies and simulations, sometimes running to hundreds of pages.
Predictably, the two parties’ studies come to opposite conclusions. The proponents show the new operations will have no harmful effect on incumbents, while the incumbents demonstrate that they will suffer devastating interference. Each party responds with point-by-point critiques of the other side’s studies and may carry out counter-studies for further proof the other side is wrong.
How do such alternative realities arise? It’s not because they are based on different versions of Maxwell’s equations. The two sides’ studies usually disagree because they start with differing assumptions about the newcomer's transmitter characteristics, the incumbent's receiver characteristics, and the geometries and propagation that govern interaction between the two. Small changes to some of these factors can produce large changes in the results.
Rather than settle anything, experiments just add fuel to the controversy.
Sometimes the parties, the FCC, or another government agency may conduct hardware tests in the lab or in the field to assess the degree of interference and its effects. Rather than settle anything, though, these experiments just add fuel to the controversy. Parties disagree on whether the test set-up was realistic, whether the data were analyzed correctly, and what the results imply for real-world operations.
When, for example, aviation interests ran tests that found 5G transmissions caused interference to radio altimeters, wireless carriers vigorously challenged their results. In contrast, there was no testing in the 6-GHz Wi-Fi proceeding, where the disagreements turned on theoretical analyses and simulations.
Further complicating matters, the disputed studies and tests do not predict interference as a binary yes/no but as differing probabilities for various degrees of interference. And the parties involved often disagree on whether a given level of interference is harmless or will cause the victim receiver to malfunction. Reaching a decision on interference issues requires the FCC to make its way through a multi-dimensional maze of conflicting uncertainties. Here are some concrete issues that illuminate this all-too-common dynamic.
Those ubiquitous sideways-facing dishes on towers and buildings are fixed‑microwave antennas. Equipment of this kind has operated reliably since the 1950s. The 6-GHz band, the lowest-frequency microwave band available today, is the only one capable of 100-kilometer hops, making it indispensable. Along with more pedestrian uses, the band carries safety-critical information: to coordinate trains, control pressure in oil and gas pipelines, balance the electric grid, manage water utilities, and route emergency telephone calls.
The red lines on this map of the 48 contiguous U.S. states show the location of existing 6-gigahertz fixed-microwave links, as recorded by Comsearch, which helps companies to avoid issues with radio interference. These links connect people in almost all areas, including far offshore in the Gulf of Mexico, where drilling platforms are common.Comsearch
Four years ago, when the FCC proposed adding Wi-Fi to the 6-GHz band, all sides agreed that the vast majority of Wi-Fi devices would cause no trouble. Statistically, most would be outside the microwave antennas’ highly directional main beams, or on the wrong frequency, or shielded by buildings, terrain, and ground clutter.
The dispute centered on the small proportion of devices that might transmit on a frequency in use while being in the line-of-sight of a microwave antenna. The Wi-Fi proponents projected just under a billion devices, operating among 100,000 microwave receivers. The opponents pointed out that even a very small fraction of the many new transmitters could cause troubling numbers of interference events.
To mitigate the problem, the FCC adopted rules for an Automatic Frequency Control (AFC) system. A Wi-Fi device must either report its location to a central AFC database, which assigns it non-interfering frequencies for that location, or operate close to and under the control of an AFC-guided device. The AFC system will not be fully operational for another year or two, and disagreements persist about the details of its eventual operation.
More controversially, the FCC also authorized Wi-Fi devices without AFC, transmitting at will on any 6-GHz frequency from any geographic location—but only indoors and at no more than one-quarter of the maximum AFC-controlled power. The Wi-Fi proponents’ technical studies showed that attenuation from building walls would prevent interference. The microwave operators’ studies showed the opposite: that interference from uncontrolled indoor devices was virtually certain.
How could engineers, using the same equations, come to such different conclusions? These are a few of the ways in which their analyses differed:
Wi-Fi device power: A Wi-Fi device transmits in short bursts, active about 1/250th of the time, on average. The Wi-Fi proponents scaled down the power by a like amount, treating a device that transmits intermittently at, say, 250 milliwatts as though it transmitted continuously at 1 mW. The microwave operators argued that interference can occur only while the device is actually transmitting, so they calculated using the full power.
Building attenuation: A 6-GHz signal encounters substantial attenuation from concrete building walls and thermal windows, less from wood walls, and practically none from plain-glass windows. The Wi-Fi proponents took weighted averages over several building materials to calculate typical wall attenuations. The microwave operators reasoned that interference was most likely from an atypical Wi-Fi device behind plain glass, and they calculated accordingly, assuming a minimal amount of attenuation.
Path loss: In estimating the signal loss from a building that houses a Wi-Fi device to a microwave-receiving antenna, the Wi-Fi proponents used a standard propagation model that incorporates attenuation due to other buildings, ground clutter, and the like. The microwave operators were most concerned about a device located with open air between the building and the antenna, so they used free-space propagation in their calculations.
Using their preferred starting assumptions, the Wi-Fi proponents proved that Wi‑Fi devices over a wide range of typical situations present no risk of interference. Using a different set of assumptions, the microwave operators proved there is a large risk of interference from a small proportion of Wi-Fi devices in atypical locations, arguing that multiplying that small proportion by almost a billion Wi-Fi devices made interference virtually certain.
Americans want their smartphones and tablets to have fast Internet access everywhere. That takes a lot of spectrum. Congress passed a statute in 2018 that told the FCC to find more—and specifically to consider 3.7 to 4.2 GHz, part of the C-band, used since the 1960s to receive satellite signals. The FCC partitioned the band in 2020, allocating 3.7 to 3.98 GHz for 5G mobile data. In early 2021, it auctioned the new 5G frequencies for US $81 billion, mostly to Verizon and AT&T. The auction winners were also expected to pay the satellite providers around $13 billion to compensate them for the costs of moving to other frequencies.
A nearby band at 4.2 to 4.4 GHz serves radar altimeters (also called radio altimeters), instruments that tell a pilot or an automatic landing system how high the aircraft is above the ground. The altimeter works by emitting downward radio waves that reflect off the ground and back up to a receiver in the device. The time for the round trip gives the altitude. Large planes operate two or three altimeters simultaneously, for redundancy.
Even though the altimeters use frequencies separated from the 5G band, they can still receive interference from 5G. That’s because every transmitter, including ones used for 5G, emits unwanted signals outside its assigned frequencies. Every receiver is likewise sensitive to signals outside its intended range, some more than others. Interference can occur if energy from a 5G transmitter falls within the sensitivity range of the receiver in an altimeter.
To make way for new 5G cellular services, the Federal Communications Commission reallocated part of the radio spectrum. That reallocation resulted in 5G transmissions that are close in frequency to a band used by aircraft radar altimeters.
The FCC regulates transmitter out-of-band emissions. In contrast, it has few rules on receiver out-of-band reception (although it recently opened a discussion on whether to expand them). Manufacturers generally design receivers to function reliably in their expected environments, which can leave them vulnerable if a new service appears in formerly quiet spectrum near the frequencies they receive on.
Aviation interests feared this outcome with the launch of C-band 5G, one citing the possibility of “ catastrophic impact with the ground, leading to multiple fatalities.” The FCC’s 5G order tersely dismissed concerns about altimeter interference, although it invited the aviation industry to study the matter further. The industry did so, renewing its concerns and requesting that the wireless carriers refrain from using 5G near airports. But this came after the wireless carriers had committed almost $100 billion and begun building out facilities.
Much as in the case of 6-GHz Wi-Fi, the 5G providers and aviation interests reached different predictions about interference by starting with different assumptions. Some key areas of disagreement were:
5G out-of-band emissions: The aviation interests assumed higher levels than the wireless carriers, which said the numbers in the aviation study levels exceeded FCC limits.
The FCC must regulate “in the public interest,” but the commissioners have to determine what that means in each case.
Off-channel sensitivity in altimeter receivers: There are several makes and models of altimeters in use, having varying receiver characteristics, leading to disagreements on which to include in the studies.
Altimeters in the same or other aircraft nearby. A busy airport has a lot of altimeters operating. Wireless carriers said these would overpower 5G interference. Aviation interests countered that multiple altimeters in the area would consume one another’s interference margin and leave them all more vulnerable to 5G.
Aircraft pitch and roll: Aviation interests argued that the changing angles of the aircraft as it approaches the runway can expose the altimeter receivers to more 5G signal.
Reflectivity of the ground: Aviation interests favored modeling with lower values of reflectivity, which reduce the received signal strength at the altimeter and hence increase its susceptibility to 5G interference.
The carriers temporarily paused 5G rollout near some airports, and the airlines canceled and rescheduled some flights. At this writing, the FAA is evaluating potentially affected aircraft, altimeters, and airport systems. Most likely, 5G will prevail. In the extremely improbable event that the FAA and the FCC were to agree that C-band 5G cannot operate safely near airports, the wireless carriers presumably would be entitled to a partial refund of their $81 billion auction payments.
These radio towers, which sit atop Black Mountain in Carmel Valley, Calif., include many drumlike antennas used for 6-gigahertz fixed-microwave links.Shutterstock
Making complicated trade-offs has long been the job of the five FCC commissioners. They are political appointees, nominated by the president and confirmed by the Senate. The four now in office (there is a vacancy) are all lawyers. It has been decades since a commissioner had a technical background. The FCC has highly capable engineers on staff, but only in advisory roles. The commissioners have no obligation to take their advice.
Congress requires the FCC to regulate “in the public interest,” but the commissioners must determine what that means in each case. Legally, they can reach any result that has at least some support in the submissions, even if other submissions more strongly support an opposite result. Submissions to the FCC in both the 6-GHz and 5G matters conveyed sharp disagreement as to how much safety protection the public interest requires.
To fully protect 6-GHz microwave operations against interference from the small fraction of Wi-Fi devices in the line-of-sight of the microwave receivers would require degrading Wi-Fi service for large numbers of people. Similarly, eliminating any chance whatsoever of a catastrophic altimeter malfunction due to 5G interference might require turning off C-band 5G in some heavily populated areas.
The orders that authorized 6-GHz Wi-Fi and C-band 5G did not go that far and did not claim they had achieved zero risk. The order on 5G stated that altimeters had “all due protection.” In the 6-GHz case, with a federal appeals court deferring to its technical expertise, the FCC said it had “reduce[d] the possibility of harmful interference to the minimum that the public interest requires.”
These formulations make clear that safety is just one of several elements in the mix of public interests considered. Commissioners have to balance the goals of minimizing the risk of plane crashes and pipeline explosions against the demand for ubiquitous Internet access and Congress’s mandate to repurpose more spectrum.
In the end, the commissioners agreed with proponents’ claims that the risk of harmful interference from 6-GHz Wi-Fi is “insignificant,” although not zero, and similarly from 5G, not “likely…under…reasonably foreseeable scenarios”—conclusions that made it possible to offer the new services.
People like to think that the government puts the absolute safety of its citizens above all else. Regulation, though, like engineering, is an ever-shifting sequence of trade-offs. The officials who set highway speed limits know that lower numbers will save lives, but they also take into account motorists’ wishes to get to their destinations in a timely way. So it shouldn’t come as a great surprise that the FCC performs a similar balancing act.
This article appears in the July 2022 print issue as “Radio-Spectrum Turf Wars.”
Mitchell Lazarus has earned his living as an electrical engineer, psychology professor, education reformer, educational TV developer, free-lance writer, and telecommunications attorney. Along with prior features in IEEE Spectrum, his many previous publications include the “Government Warning” on U.S. alcohol beverage labeling and a recent historical novel, The Implosion Method.
Discussions are underway about dividing and merging regions
Kathy Pretz is editor in chief for The Institute, which covers all aspects of IEEE, its members, and the technology they're involved in. She has a bachelor's degree in applied communication from Rider University, in Lawrenceville, N.J., and holds a master's degree in corporate and public communication from Monmouth University, in West Long Branch, N.J.
IEEE has been analyzing its region and geographic unit structure to ensure there is equitable representation across its global membership.
IEEE’s region structure organizes membership into 10 globe-spanning geographic organizational units. Each member is assigned to a local section within one of the 10 regions, and each region elects a representative to serve on the IEEE Member and Geographic Activities (MGA) Board and on the IEEE Board of Directors. The regional units work to fulfill IEEE’s mission and to meet the needs of IEEE members living within the region’s borders.
As of June, the distribution of the IEEE membership across the 10 regions is Region 1: 24,938 members; Region 2: 21,795 members; Region 3: 24,202 members; Region 4: 16,836 members; Region 5: 22,317 members; Region 6: 43,089 members; Region 7: 14,179 members; Region 8: 74,451 members; Region 9: 16,426 members; and Region 10: 151,421 members.
Last year, the MGA Board, which oversees IEEE membership and the activities of geographic units worldwide, formed a region realignment ad hoc committee to review the regional organization and propose recommendations for structural changes. The committee consists of current region directors among other MGA volunteers.
Based on the ad hoc committee’s recommendations, several actions have been taken to date. A formal plan will be presented to the MGA Board for approval at a meeting later this year.
A plan has been developed to divide Region 10, IEEE’s largest region, into two regions, to better meet the needs of its members in this region. Region 10 leadership and the MGA ad hoc committee have been working to develop the geographic boundaries of the two regions and have been creating implementation plans to execute this regional division following approval by the MGA Board and the IEEE Board of Directors.
To maintain a total of 10 regions across the world, IEEE Region 1 and Region 2 are proposing to merge formally into a single region with a single region director. The Region 1 and Region 2 Board of Governors and Executive Committees will work collaboratively to document and determine the best path forward in merging the two regions affairs, governance, and member activities.
While planning efforts for regional realignment are ongoing, another recent initiative has been the introduction of additional zone representatives at the MGA Board. A zone is a substructure within a region with a significant number of members. In these large regions, zone representatives can assist in the region and provide an additional voice for members within the zone.
To test the zone concept, in February the MGA Board approved the formation of four zones: two in Region 8 and two in Region 10. Representatives from the new zones participated in the MGA Board meeting held in June. The ad hoc committee is continuing to further develop specific responsibilities for the zone leaders.
The ad hoc committee is planning to bring motions forward to an upcoming MGA Board meeting to confirm the direction and next steps of the realignment, including next steps in the split of Region 10 into two regions, the consolidation of Regions 1 and 2 into a single region, and further definition of the zone concept.
If approved by the MGA Board, the vice president of MGA, David Koehler, will then present motions related to these matters for consideration by the IEEE Board of Directors at its November meeting.
The country gears up for lunar landings, in situ resources tests, and new huge rockets
Andrew Jones is a freelance journalist based near Helsinki. He writes about the space industry and technology with a particular focus on China's activities.
China’s Long March-5 Y5 rocket is pictured here at the Wenchang Spacecraft Launch Site in South China’s Hainan province.
This past weekend, NASA scrubbed the Artemis I uncrewed mission to the moon and back. Reportedly, the space agency will try again to launch the inaugural moon mission featuring the gargantuan Space Launch System (SLS) at the end of this month or sometime in October. Meanwhile, half a world away, China is progressing on its own step-by-step program to put both robotic and, eventually, crewed spacecraft on the lunar surface and keep pace with NASA-led achievements.
Asia’s rapidly growing space power has already made a number of impressive lunar leaps but will need to build on these in the coming years. Ambitious sample-return missions, landings at the lunar south pole, testing the ability to 3D print using materials from regolith, and finally sending astronauts on a short-term visit to our celestial neighbor are in the cards before the end of the decade.
The next step, expected around 2024, is Chang’e-6: an unprecedented attempt to collect rock samples from the far side of the moon.
The mission will build on two recent major space achievements. In 2019, China became the first country to safely land a spacecraft on the far side of the moon, a hemisphere which cannot be seen from Earth—as the moon is tidally locked. The mission was made possible by a relay satellite out beyond the moon at Earth-moon Lagrange point 2, where it can bounce signals between Chang’e-4 and ground stations in China.
Chang’e-5 in 2020 performed the first sampling of lunar material in over four decades. The complex, four-spacecraft mission used an orbiter, lander, ascent vehicle, and return capsule to successfully deliver 1.731 grams of lunar rocks to Earth. The automated rendezvous and docking in lunar orbit of the orbiter and ascent spacecraft was also seen as a test of the technology for getting astronauts off the moon and back to Earth.
Chang’e-6 will again attempt to collect new samples, this time from the South pole-Aitken basin, a massive and ancient impact crater on the far side of the moon. The science return of such a mission could likewise be huge as its rocks have the potential to answer some significant questions about the moon’s geological past, says planetary scientist Katherine Joy of the University of Manchester, in England.
“We think that the basin-formation event was so large that the moon’s mantle could have been excavated from tens of kilometers deep,” says Joy. Fragments of this mantle material originating from deep in the moon would help us to understand how the Moon differentiated early in its history, the nature of its interior, and how volcanism on the far side of the moon is different or similar to that on the nearside.
Chang’e-7, also scheduled for 2024, will look at a different set of questions geared toward lunar resources. It will target the lunar south pole, a region where NASA’s Artemis 3 crewed mission is also looking to land.
The mission will involve a flotilla of spacecraft, including a new relay satellite, an orbiter, lander, rover and a small “hopping” spacecraft designed to inspect permanently shadowed craters which are thought to contain water ice which could be used in the future to provide breathable oxygen, rocket fuel, or drinking water to lunar explorers.
Following this Chang’e-8 is expected to launch around 2027 to test in situ resource utilization and conduct other experiments and technology tests such as oxygen extraction and 3D printing related to building a permanent lunar base—for both robots and crew—in the 2030s, named the International Lunar Research Station (ILRS).
The upcoming Chang’e-6, 7 and 8 missions are expected to launch on China’s largest current rocket, the Long March 5. But, as with NASA and Artemis, China will need its own megarockets to make human lunar exploration and ultimately, perhaps, crewed lunar bases a reality.
In part in reaction to the achievements of SpaceX, the China Aerospace Science and Technology Corporation (CASC), the country’s main space contractor, is developing a new rocket specifically for launching astronauts beyond low Earth orbit.
The “new generation crew launch vehicle” will essentially bundle three Long March 5 core stages together (which will be no mean feat of engineering) while also improving the performance of its kerosene engines. The result will be a roughly 90-meter-tall rocket resembling a Long March version of SpaceX’s Falcon Heavy, capable of sending 27 tonnes of payload into translunar injection.
Two launches of the rocket will by 2030, according to leading Chinese space officials, be able to put a pair of astronauts on the moon for a 6-hour stay. Such a mission also requires developing a lunar lander and a new spacecraft capable of keeping astronauts safe in deep space.
For building infrastructure on the moon, China is looking to the future Long March 9, an SLS-class rocket capable of sending 50 tonnes into translunar injection. The project will require CASC to make breakthroughs in a number of areas, including manufacturing new, wider rocket bodies of up to 10 meters in diameter, mastering massive, higher-thrust rocket engines, and building a new launch complex at Wenchang, Hainan island, to handle the monster.
Once again NASA is leading humanity’s journey to the moon, but China’s steady accumulation of capabilities and long-term ambitions means it will likely not be far behind.
The webinar explores the use of artificial intelligence (AI) to solve wireless communications problems. After brief introductions of machine learning, deep leaning and reinforcement learning methodologies, we will cover typical applications, including how standards bodies are incorporating AI techniques in wireless standards. Learn the AI-driven system design workflow, and how to streamline data generation process, AI networks training, and design validation and testing. And, how to simplify deployment of your AI networks on embedded devices, enterprise systems and easily leverage existing deep learning networks outside MATLAB.
Houman Zarrinkoub, PhD., Principal Wireless Communications Product Manager, MathWorks