nobody regulates the receiver

Problem statement

Radio spectrum is repurposed constantly — a band once used lightly by satellites is auctioned for 5G, a guard band shrinks — and each change succeeds or fails depending on whether the receivers already operating nearby can reject signals outside their own band. Yet U.S. spectrum governance regulates almost exclusively the transmitter side: the FCC "has not generally imposed performance requirements on nonfederal receivers, but rather relies on the marketplace to design appropriate equipment," while NTIA maintains mandatory receiver standards only for federal systems. Receiver owners have no incentive to build in tolerance for a future neighbor that does not yet exist ("unless there is a performance or safety issue, it is not feasible for incumbents to regularly update their receivers just in case"), receivers in aviation and space are built to last 30 years or more and often cannot be physically modified, and the party that benefits from a new allocation (the new licensee) is not the party that bears the retrofit cost (the incumbent). The result is a recurring governance failure — the 2020 Ligado L-band decision and the 2021–2023 5G C-band versus radar-altimeter dispute are the recent cases — in which newly licensed spectrum is delayed or constrained while agencies, industries, and courts fight over whose modeling assumptions are right and who should pay.

Why this matters

Spectrum auctions had raised over $230 billion by 2023, and the ability to place dissimilar services closer together is the main way more wireless capacity gets created without new physics. The altimeter case shows the stakes: FAA reported that approximately 5,300 aircraft and 11,500 radio altimeters needed retrofit, an airworthiness directive barred certain low-visibility landings after 30 June 2023 unless aircraft had 5G-tolerant altimeters or filters, and the applicable minimum performance standard for those altimeters dated from a 1980 EUROCAE document — meaning safety-of-life receivers certified against a spectrum environment four decades old were the binding constraint on a nationwide 5G rollout. FAA officials put the asymmetry plainly: "while a 1 percent chance of a short-term coverage outage may be acceptable to commercial wireless services, a 1 percent chance of a catastrophic accident in low visibility operations is exponentially more frequent and unacceptable." Because the environment is "more congested than 10 years ago" and repurposing decisions arrive faster than 30-year equipment cycles, the same fight will recur band by band unless the receiver side of the rules is designed.

What’s been tried and why it hasn’t worked

The FCC's Technological Advisory Council proposed in 2013 the "harm claim threshold" idea — publish, per band, the interference level above which an incumbent may claim protection, so receiver owners know what to design for — and the FCC has occasionally set minimum receiver performance as a condition of protection (e.g., in the 800 MHz band, systems below the minimum "are not entitled to full protection from interference"). GAO reported in 2013 that stakeholders cited a lack of cross-industry coordination on receiver standards, a lack of incentives, and difficulty accommodating a changing environment, and in 2024 found the environment "even more challenging and complex." The FCC opened a 2022 Notice of Inquiry on receiver interference immunity and in April 2023 adopted a policy statement with nine spectrum-management principles, including that users should design receivers expecting interference from nearby services — but GAO found the FCC had not defined measurable goals, strategies, or barriers for implementing them, and recommended it do so (plus that NTIA assess its information gaps on federal receiver performance). Underneath the policy churn, five obstacles persist per GAO's stakeholder interviews: the spectrum environment changes faster than equipment can be designed for; information does not flow — commercial parties treat device characteristics as proprietary, federal parties cite national security, and joint compatibility studies "are rarely conducted early in the rulemaking process"; genuine physical tradeoffs (a stronger filter adds latency an altimeter cannot afford); cost, including who pays and the absence of appropriations to retrofit federal hardware outside the Spectrum Relocation Fund; and disagreement about what interference is "harmful." No mechanism yet allocates the cost of adaptation between newcomer and incumbent or forces receiver robustness to be priced in at design time.

What would unlock progress

The reframing is to treat receiver tolerance as a governed quantity with a price: harm-claim thresholds or receiver-performance floors published per band well ahead of repurposing, a data-sharing regime (possibly with a trusted third party) that lets adjacent-band operators model each other without disclosing proprietary or classified parameters, and an explicit cost-allocation rule — perhaps funded from auction proceeds — for retrofitting legacy safety-of-life receivers. Adjacent precedents: building codes that set performance floors for structures against a specified environment rather than certifying only the hazard; and the Spectrum Relocation Fund itself, which already pays federal incumbents to move but not to harden. The engineering is largely known; the mechanism design and institutional plumbing are not.

Entry points for student teams

An RF/economics team could take one real repurposing case (C-band/altimeters is well documented) and simulate a harm-claim-threshold regime: what threshold, published when, would have made incumbents' design choices and the newcomer's deployment compatible, and what would the retrofit have cost under alternative cost-sharing rules — a design proposal grounded in public FCC/FAA/RTCA material. A policy team could draft the "receiver-side" companion to a hypothetical FCC allocation order: what receiver information must be disclosed, to whom, and how confidentiality is protected. A systems team could design a receiver-characteristics registry schema and governance model that NTIA and FCC could jointly maintain. Relevant skills: RF engineering, regulatory economics, mechanism design, telecommunications law.