Future of Radio Altimeters Emerges as Major Issue in Upper C-Band Comments
CTIA and the wireless industry emphasized the importance of the upper C-band auction to the future of wireless communications in comments on an NPRM that commissioners approved in November (see 2511200046). Aviation safety and protection for radio altimeters were among major themes in the filings, most of which were posted Wednesday in docket 25-59. The upper C-band auction is expected to be the biggest spectrum auction under FCC Chairman Brendan Carr (see 2512260002).
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Major aviation associations stressed that radio altimeters “are vital to aviation safety, providing accurate height above terrain measurements that support critical flight operations, particularly in adverse weather or challenging environments.” The devices operate in the adjacent 4.2-4.4 GHz band.
Rules approved by the FCC should align with timelines for radio altimeter “redesign and retrofit/replacement with a ‘one-and-done’ approach, ensuring that radio altimeter equipment and affected aircraft undergo a single, coordinated change process,” the aviation groups said. Financial incentives or compensation mechanisms should "adequately reflect the costs and operational impacts borne by the aviation sector to implement these equipment changes." The filing was endorsed by a broad group of entities representing aeronautics companies, pilots and others.
Airlines for America (A4A), which signed the joint industry filing, said separately that negotiations between airlines and wireless carriers can build on the “lessons learned” when the lower C band was deployed. The proposed next-generation upgrade of radio altimeters “represents a critical step for coexistence between 5G services in the Upper C-Band and aviation safety services in the 4.2-4.4 GHz band.” The group suggested that the FCC use its emerging technologies framework “to facilitate and accelerate the next-generation upgrade of radio altimeters.”
Boeing said coexistence and expansion of licensed wireless service in the upper C band “will require close coordination between the Commission and the FAA, as well as the [DOD], and among the wireless and aviation industries.”
CTIA argued that the FCC should make as much upper C-band spectrum available for full-power licensed use as it can “as quickly as possible, while providing certainty regarding when wireless providers will gain access to the band.” Data shows that fixed satellite service use of the band is “diminishing, and a variety of alternatives can accommodate incumbent operations.”
CTIA also recognized the importance of concerns about radio altimeters. Since 2019, the aviation industry has been working to revise its international minimum operational performance standards for the devices, and the “timely resolution” of the standard has been acknowledged by international aviation regulators as “long overdue,” the group said.
Verizon endorsed most of the positions taken by CTIA. Rules for the spectrum should “mirror those” for the lower C band, and the FCC should “reallocate the maximum amount of spectrum” possible for mobile broadband, the carrier said. New radio altimeter standards “have been under development for the past several years,” and “aviation interests and the wireless industry are collaborating on how to promote coexistence.”
AT&T said the upper C band “will play a key role in 5G and beyond.” The band is “internationally harmonized and adjacent to an existing mobile broadband allocation,” providing “a critical opportunity to expand terrestrial 5G operations.” The upper C band is also “unpaired and available in the wide, contiguous swaths that are critical for the highest performance 5G functionality,” AT&T added.
Verizon and AT&T were the dominant bidders in the initial C-band auction (see 2107260052), but T-Mobile also filed comments urging FCC action on the spectrum. T-Mobile “fully endorses the Commission’s efforts to repurpose the maximum amount of Upper C-band spectrum for terrestrial use, while adopting a consistent regulatory framework for terrestrial mobile use.”
Roberson and Associates, meanwhile, filed a technical paper on the coexistence of 5G and radio altimeters. “The general specifications for the successful implementation and deployment of new or updated [altimeters] are well defined,” the CTIA-funded paper said. “There are no technological, regulatory, or deployment issues preventing the commercial cellular industry from using spectrum from 3.98 to 4.16 GHz as described in the NPRM for 5G (and 6G).”