Spectrum Showdown: Why RF Coexistence Testing Is Now a National Security Priority

With over 30 billion connected devices jostling for space on a finite RF spectrum, and more than 4,000 allocation changes globally, the risk of catastrophic interference has never been higher. A new wave of coexistence testing is emerging as the only bulwark against failures in safety-critical systems, from aircraft radar to GPS navigation.

"We are seeing a perfect storm of spectrum congestion," said Dr. Alex Tan, senior RF engineer at the National Spectrum Consortium. "Without rigorous coexistence testing, we risk compromising both military readiness and commercial reliability."

The expansion from 11 to over 80 cellular bands has intensified contention, creating interference risks between 5G C-band transmitters and aircraft radar altimeters, and between terrestrial L-band networks and GPS receivers not designed for adjacent high-power signals. These are not theoretical risks—real-world failures have already been documented.

"These aren’t hypothetical scenarios," warned Emily Carter, a former FCC engineer now with the Institute for Spectrum Policy. "We’ve already documented real-world failures that could have been prevented with proper coexistence testing."

Background

Shared spectrum frameworks like CBRS (Citizens Broadband Radio Service) aim to dynamically allocate spectrum among incumbents and new users. CBRS uses a cloud-based Spectrum Access System (SAS) and environmental sensing to protect incumbent Navy radar while enabling commercial cellular services across three priority tiers.

This tiered approach—incumbent access, priority access, and general authorized access—allows for efficient spectrum use but introduces complex interference dynamics. Without rigorous testing, even well-designed systems can fail when multiple transmitters share the same band.

Coexistence test architectures now rely on controlled environments: anechoic chambers, over-the-air signal generation, and standards like ANSI C63.27. These setups simulate real-world interference conditions to evaluate device performance before deployment.

What This Means

The implications are profound. Safety-critical systems—including aviation radar altimeters, GPS receivers, and military communications—face increasing interference threats as spectrum becomes more crowded. A failure in one system can cascade, jeopardizing lives and national security.

"The stakes are life-and-death," said Dr. Tan. "We need industry-wide adoption of coexistence testing protocols, not just for new devices but for legacy systems that must operate in today’s crowded environment."

Regulators and standards bodies are pushing for mandatory coexistence testing, especially for devices that operate in shared bands. The FCC has already referenced ANSI C63.27 in its rules, and similar moves are expected globally.

For military applications, coexistence testing is critical to ensure that advanced communications and radar systems can operate without interference from commercial networks. The Department of Defense is investing in test facilities and working with industry to refine testing methodologies.

In the coming year, more than 20 billion new IoT devices are expected to come online, further straining the spectrum. The time to act is now. Industry experts urge immediate adoption of coexistence testing to prevent future failures.