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As the preceding section explained, while the FCC can satisfy intermediate scrutiny with spectrum access restrictions or regulations designed to avoid or mitigate harmful interference, it becomes crucial to address what constitutes harmful interference and what does it mean to narrowly tailor a restriction for that purpose. This requires keeping in mind that to pass intermediate scrutiny, a content-neutral regulation of speech must (1) address a substantial or important government interest; (2) be demonstrably effective in addressing that interest; and (3) do so in a narrowly tailored manner that does not unduly burden First Amendment interests in comparison to available alternatives.¹

The FCC’s rules define harmful interference as: “Interference which endangers the functioning of a radionavigation service or of other safety services or seriously degrades, obstructs, or repeatedly interrupts a radiocommunication service operating in accordance with [the ITU] Radio Regulations.”² The commission has consistently stated “that ‘harmful interference’ is different and distinct from ‘interference.’”³

Clearly the FCC has never sought to manage use of the airwaves to avoid any degree of interference. Microwave ovens, electric drills, computer monitors, and a multitude of other consumer goods all emit electromagnetic radiation that at times interrupt or degrade other transmissions, however slightly or fleetingly. While FCC device certification rules seek to minimize the risk of harmful interference, these unlicensed devices are allowed. With intermediate scrutiny in mind, it is even more clear that non-disruptive or very fleeting interference is not sufficient for the government to prohibit spectrum access for the purpose of communicating (e.g., broadcast or wireless broadband services). As the FCC pointed out in its April 2020 Report and Order authorizing unlicensed sharing of the 6 GHz band, “such a prohibition would rule out virtually all services and unlicensed operations, given that there is virtually no type of RF-emitting device that does not have the potential for causing such interference if used incorrectly.”⁴

Defining harmful interference is made more difficult by the fact that the FCC reviews requests to use spectrum on a prospective basis, which necessitates making a judgment call about how likely, how frequent, and how severe that interference will be. Incumbent users typically present engineering evidence to persuade the commission that even a relatively small probability of fleeting interference should be considered harmful enough to block a new entrant (and possible competitor) from using the spectrum.

Accordingly, the FCC has very explicitly authorized new users in occupied bands where, despite acknowledging some additional interference, the agency found that with appropriate technical restrictions (e.g., low power, indoor-only use), or with minor accommodations by incumbent users (e.g., notifying a database), the degree of harmful interference that would justify excluding the new use could be avoided. ⁵ Professor Benjamin provides the example of handheld radios that picked up static from new FM stations, interference that would disappear if the device was moved a few feet.⁶ There are two ways to prevent this static: Either the government can prevent the new user from accessing the airwaves, or the radio user (who is, after all, making use of the public airwaves at no cost) can take self-help to move their device a minimal amount.

This balancing approach has played out in practical terms recently. The FCC’s unanimous April 2020 decision allowing unlicensed devices to share the 6 GHz band (described earlier) is an example of the public interest balancing analysis that has properly become the norm. The FCC authorized unlicensed use at low-power across the entire 1,200 megahertz (5925 to 7125 MHz) despite vehement opposition from incumbents concerned about interference.⁷ After considering multiple technical studies from both proponents and opponents, the FCC decided that the degree of risk of sustained harmful interference to incumbent services are so low that opening the band to facilitate the next generation of high-capacity Wi-Fi and other innovation should not be denied.⁸ The commission even sought to optimize unlicensed access by creating two separate authorizations. The FCC authorized indoor-only use at a greatly reduced power level across all 1,200 megahertz and standard unlicensed (Part 15) power levels for both indoor and outdoor use subject to control by an Automated Frequency Coordination system.

The FCC explicitly rejected AT&T’s claim that the Communications Act “generally prohibits the Commission from authorizing a service or type of unlicensed operation that can cause harmful interference, regardless of whether the probability of such interference is low.”⁹ The Report and Order explained that the FCC is authorized to strike a balance that best serves the general public interest: “In rulemakings, the Commission may authorize operations in a manner that reduces the possibility of harmful interference to the minimum that the public interest requires, and it will then authorize the service or unlicensed use to the extent that such authorization is otherwise in the public interest.”¹⁰

Another example, also adopted unanimously in April 2020, involved the FCC rejecting objections from the Defense Department (DoD) and the Federal Aviation Administration (FAA) that new and more intensive terrestrial use of licensed spectrum for low-power 5G and industrial IoT services would cause interference to certain high-resolution GPS uses. After many years of protracted rulemaking and contested technical studies, the FCC granted final authorization to Ligado to use its mobile satellite spectrum (MSS) near the band designated for GPS spectrum to launch a new terrestrial 5G service of far greater value than its MSS-only operations.¹¹ The FCC mandated that Ligado set aside a portion of its own spectrum to create a 23 MHz guard band to protect GPS users. Technical reports indicated with high confidence that any remaining risk of interference could be ameliorated if the DoD upgraded their outdated receivers to better distinguish the signals in the two distinct frequency bands. Ligado even offered to pay for the upgrades, a tiny cost relative to the additional billions of dollars in commercial value created by Ligado’s new services. It does not take a devotee of the law and economics school of policymaking to recognize it is far more sensible to allow the new market entrant, in this case Ligado, to pay to upgrade outdated receivers used by incumbents rather than to indefinitely prohibit more intensive and valuable use of the spectrum.

In addition, the FAA and DoD insisted that the commission adopt a new type of threshold for harmful interference at a uniform level (1 dB) that is unrelated to actual device performance, virtually indistinguishable from the natural noise floor in the band, and far lower than any level the FCC has previously found to be harmful.¹² Despite the national security implications, the FCC rejected the argument and “concluded that a performance-based metric—which more closely aligns with the Commission’s ‘harmful interference’ definition—is more reliable and should be used when evaluating the harmful interference concerns pertaining to GPS receivers.”¹³ The FCC authorized Ligado to deploy, subject to a variety of conditions.¹⁴

These decisions mesh well with the FCC’s acknowledgement elsewhere that the optimal spectrum policy is one that results in a non-zero amount of interference.¹⁵ Designing a spectrum allocation with zero risk of interference would be like creating a traffic management system with zero risk of car accidents. One could set speed limits to five miles an hour and triple the size of lanes. However, as Ronald Coase recognized, this approach to regulation would both fail to guarantee safety and would artificially limit the utility of the road.¹⁶ Moreover, unlike traffic management, the First Amendment claims of parties seeking access to unused spectrum for the purpose of communications requires a strong preference by the FCC for more diverse and intensive spectrum use.

The burden is on the government—and not just on band incumbents—to articulate and substantiate a persuasive reason to deny a request to make use of unused spectrum on a non-interfering basis that also satisfies intermediate scrutiny. It is unacceptable for the FCC to reject proposals without explanation, or on purely economic grounds, if a new shared use of a band can be accommodated, even if only on an opportunistic or contingent basis. To that end, the FCC should find an opportunity to further clarify the operational definition of harmful interference to make clear that the intention is to enable the greatest possible productive use of spectrum bands.