Rethinking the 5G and Radar Altimeter Problem

Public concern about interferance from new C-band 5G network deployments to aviation radar altimeters is just the latest example of differing economic interests competing for limited natural resources. In this case, the limited natural resource is the radio spectrum—the portion uniquely suited for wireless mobile communication services. For now, federal and industry stakeholders are looking to testing, operational restrictions, upgrades, and new standards to fix the problem. A broader question for policymakers is whether operating radar altimeters in this spectrum band is in the best interest of the national and global economy. 

There are precedents for changing spectrum allocations for various services based on emerging technological changes and economics needs. The best long-term solution in this case may well be to relocate the operation of radar altimeters to a higher band. Such a multiyear effort would require significant effort and resources, but it could free up hundreds of megahertz of valuable mid-band spectrum for mobile networks while also advancing aviation safety.

Altimeters and 5G compete for spectrum

Because of physical limits of technology and radiowave propagation in the environment, the useful spectrum for mobile services is roughly limited to .03–5 GHz. Radar altimeters have operated in the 4.2–4.4 GHz band since their introduction after World War II. Because of outdated designs, some of these radar altimeters require substantial guard bands on either side of this range to protect them from interference. 

The aviation industry recently sought to restrict commercial 5G operations on the lower end to as low as 3.7 GHz. This implies that radar altimeters, including both the 4.2 GHz radar altimeter band plus the aviation industry’s desired limits on 5G operation within .500 GHz on each side, need to have 1.2 GHz of total spectrum to operate. This represents nearly a quarter of the total suitable mobile spectrum. Recent industry testing and FAA actions have relaxed this demand somewhat, but there remains a fundamental question about radar altimeter and C-band 5G coexistence.