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Will 5G mean airplanes falling from the sky?

When digital mobile phone technology was first introduced in the US, electric wheelchairs began behaving erratically. The pulsing signal interfered with their controls. The solution: simple shielding to stop the interference.

When phones using the international GSM digital standard were first introduced in the US, hearing aids would buzz. The hearing aids, which had been designed for the analog world, were suddenly confronted by a new digital reality. The solution was once again updating the old way of doing things to recognize the new environment.

And if you want to talk life-and-death, how about pacemakers? Again, early in the digital phone era these life-savers could malfunction when hit by a cell phone signal. The short-term solution was for doctors to tell pacemaker patients not to carry their phone in the shirt pocket. Long term, shielding solved the problem.

These stories all come to mind as the Federal Aviation Administration (FAA) has objected to the Federal Communications Commission’s (FCC) authorization to use newly opened airwaves for 5G networks. Their concern is that the 5G signals could possibly interfere with the radio altimeters used in automated aircraft landings.

The 5G-aviation safety issue combines the two most important components of public policy decision-making: public safety and national security. No one can question the importance of the safety of passengers on commercial and private aircraft. Similarly, everyone recognizes that the United States is in a technological horse race with China, which has been able to reap the rewards of its embrace of 5G networks.

The Shared Spectrum Resource

The forward march of technology has once again tripped over the old way of doing things.

The airwaves (often referred to as “spectrum”) are a shared national resource that is subject to the pulls and tugs of changing technologies.

As these technologies change, the assumptions that previously governed the spectrum-based environment also change. What was an adequate product design in the earlier era—like the wheelchairs, pacemakers, and hearing aids—may require a redesign. Neither the device manufacturer nor the spectrum users were at fault. The device manufacturers built to the realities that existed when the product was designed. The new spectrum users were building into a new world without any intention of causing harm.

I was president of the wireless industry trade association CTIA during each of the earlier interference issues. I remember the surprise when the issues first developed. I recall the headlines and the emotion. I remember how some companies tried to profit from the problem.

Years later, I was Chairman of the FCC, and know the agency’s responsibility to protect consumers while keeping the United States at the forefront in wireless applications and services. I also recall how the FCC was constantly being called upon to play referee between various users of spectrum, and how easy it was to allege “interference” as a competitive strategy or a financial tactic.

From both those experiences, I learned that the challenges created by technological change can be solved if people of good will leave their respective corners and PR campaigns, and instead come together in a shared commitment to a solution. Beyond the issue of goodwill, however, is the need for federal leadership. Such leadership in the form of a national spectrum policy was notably absent during the Trump administration.

A Lack of Leadership

The airwaves are a shared national resource and exist in an environment of continual technological change and marketplace development. As a result, the federal government must have a set of underlying policies to guide the difficult and highly technical decisions about spectrum allocation and its ultimate effects on incumbent as well as new users. Unfortunately, the Trump administration had no such unified spectrum policy; as a result, policy ended up being made by individual agencies.

Less than 14 months after President Obama took office, his administration produced an integrated spectrum plan and broadband plan. It was not until 20 months into the Trump administration that there was even an attempt to create a national plan for spectrum usage. In October 2018, President Trump ordered the plan to be available in six months. But it never happened.

The Department of Commerce’s National Telecommunications and Information Administration (NTIA) is supposed to be the telecommunications advisor to the president. It was NTIA that was tasked with developing the national spectrum plan that never was. Unfortunately, and reportedly as a consequence of a spectrum dispute, the NTIA head was axed and the agency remained without a permanent leader for the last 20 months of the Trump administration.

The consequence of this absence in both framework and leadership meant there was no underlying rationale nor consistent team to adjudicate among the various spectrum claimants. This left government agencies free to advocate their own spectrum policies. In such a situation, it is only natural that the individual agencies would retreat into their comfort zones and view spectrum only within their parochial interests. No one ever wants to change the way things have always been done by revisiting the best use of spectrum. In the absence of White House leadership on a national policy, agencies such as the FAA, Department of Defense, and FCC quite naturally prioritized the interests of their own constituencies.

Avionics and 5G

The spectrum used by aeronautical navigation systems as well as so-called C-band wireless are internationally allocated. On the spectrum allocation chart, the aeronautical frequency allocation runs between 4.2 and 4.4 gigahertz (GHz). One of the key uses of the aeronautical allocation is the transmission of information to and from aircraft altimeters, especially when they operate below 2500 feet, to facilitate computer-assisted landings. Next to that allocation is the C-band spectrum used for 5G. In the U.S., C-Band use is authorized for between 3.7 and 3.98 GHz.

The airlines and associated industries are warning that 5G networks operating in the C-band “have the potential to cause harmful interference to radio altimeters.” Their concern is that the radios being used with the altimeter may not appropriately filter out signals lapping over from another part of the spectrum (called spurious emissions). In response, the FAA issued a Special Airworthiness Bulletin (SAIB) to airlines and pilots to “be prepared for the possibility that interference from 5G transmitters and other technology could cause certain safety equipment to malfunction.” The Canadian government responded by restricting C-band usage around airports.

Two words are central to the statements of the airlines and FAA. The airlines talk about the “potential” of interference. The FAA talks about the “possibility” of interference. Clearly, the safety of air traffic requires mitigating even the “potential” or “possibility” of problems. Yet clear heads are needed to separate what is only hypothetical possibility based on worst-case assumptions from what is highly probable based on real-world use.

This is where the spectrum management expertise of the FCC is essential. The FCC is the nation’s spectrum referee on commercial spectrum interference matters. As such, the agency’s engineers are used to constantly dealing with the evolution from one generation of spectrum-related technology to another. It is a challenge made all the more difficult by the need to balance the national interest in technological advancement with the private interest of manufacturers and users of equipment designed for another spectrum environment.

What Happened with 5G and Altimeters?

The 5G technology is built to exacting standards. There are no official altimeter standards. As the FCC was working on reallocating portions of the C-band to delivering 5G signals, the issue of potential interference to radio altimeters became a matter of great discussion. But there were no common altimeter standards to measure against.

The aviation industry submitted a study by the Aerospace Vehicle Systems Institute (AVSI) that simulated worst-case 5G signal emission and its impact on avionics. The FCC’s analysis of the AVSI study found, “there may be a large variation in radio altimeter receiver performance between different manufacturers.” In other words, some altimeters were equipped with radio receivers with good filters to protect against spurious emissions, while others allowed signals from outside the 4.2 to 4.4 GHz allocation to intrude.

A 5G proponent, T-Mobile, submitted a study by Alion, an engineering firm critiquing the AVSI study. This analysis found the assumptions used in the study to be extreme, thus leading to extreme conclusions. In addition, the Alion analysis concluded, two of the test altimeters had failed “due to interference from other altimeters,” not 5G interference. After reviewing this study, AVSI told the FCC “further analysis is required to consider more sophisticated propagation models.”

The FCC’s Report and Order making the C-band available for 5G directly addressed this issue. The FCC engineers concluded the “AVSI study does not demonstrate that harmful interference would likely result under reasonable scenarios” or even “reasonably ‘foreseeable’ scenarios.”  The FCC encouraged the aviation industry “to take account of the RF [radio frequency] environment that is evolving.” In other words—like wheelchairs, pacemakers, and hearing aids— to recognize that what was “good enough” design in a previous spectrum environment could be affected by the new environment.

Nevertheless, the FCC created a guard band between the 5G spectrum and the avionics spectrum in which 5G was forbidden. Boeing, in a filing with the FCC, had proposed just such a solution. The Boeing proposal was to prohibit 5G “within the 4.1-4.2 GHz portion of the band.” The FCC agreed and then doubled the size of Boeing’s proposed guard band to a 220 MHz interference buffer between the upper 5G usage at 3.98 GHz, and avionics usage at 4.2 GHz.

When the FAA issued its bulletin, the 5G industry pulled back the C-band launch. Originally planned for December 5, the launch of service in the new spectrum was postponed by 30 days.

The aviation industry, in a letter to the White House National Economic Council (NEC), has pledged to work diligently “to develop new standards, equipment, and aircraft/helicopter integration solutions.” Interestingly, according to a Reuters report, the White House “reviewed the FAA safety bulletin before it was cleared for release.”

Next Steps

The resolution of this issue should not be a drawn-out process. The Biden White House is now involved and should be the driving force. Acting quickly to convene the parties is an important step to keep them from retreating into their own corners. The White House should take the aviation industry up on its pledge to “develop new standards.”

The working group should have a tight deadline to report its conclusions and be true to its name: a working group, not a study group, nor a debating society. The physics involved in this situation are well known. The mitigation techniques are well known. The standard-setting process is well known. The importance of getting 5G up and running while protecting flyers is well known.

Related Books

The Biden administration has prided itself on being science-based. The science here is pretty clear—it is hard to repeal the laws of physics. The real politick of this comes down to the costs of fixing the altimeters, just like the wheelchairs, hearing aids, and pacemakers were fixed. As the FCC engineers concluded, “well-designed equipment should not ordinarily receive any significant interference (let alone harmful interference).”

Let’s hope this is more than a gambit to hold 5G hostage to get someone to pay to fix the problem altimeters. There are only three sources of such funds for the aviation industry. The government could pay out of the almost $82 billion generated by the sale of licenses to use the C-band; that would probably require an act of Congress. The wireless industry could pay an additional tariff on top of the billions already spent for spectrum the government said would be ready for use on December 5. The aviation industry, having known for some time of the new 5G allocation, could pay to fix the offending altimeters.

More generally, this brouhaha also highlights one more area where the Biden administration needs to repair what was left behind by the Trump administration: the lack of a spectrum plan for the nation. The 21st century will be the wireless century. Already work is underway on 6G. The use of the spectrum necessary for the connecting pathway of the new era requires a going in strategy rather than a policy that distributes policymaking on an ad hoc basis.

T-Mobile is a general, unrestricted donor to the Brookings Institution. The findings, interpretations, and conclusions posted in this piece are solely those of the author and not influenced by any donation.

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