AVSI Project AFE 76s2 measured the response of commercial radar altimeters to out-of-band interference representative of new 5G cell phone signals.
AVSI is supporting efforts to preserve the safe operation of radio altimeters through research conducted under AFE 76s2 – Out-of-band Interference with Radio Altimeters. Radio altimeters are safety-critical equipment that have been used for decades in all types of aircraft, providing accurate indication of height above ground level for applications such as cockpit display, terrain avoidance warning systems, and auto-landing systems. Most altimeters used in commercial transport aircraft are frequency-modulated continuous wave (FMCW) with a typical chirp bandwidth of ~100-180 MHz centered at 4300 MHz.
The FCC issued a Report and Order (R&O) in March 2020 that authorized the sale of spectrum for flexible use in the 3700 – 3980 MHz frequency band. AVSI AFE 76s2 had provided information  to the Commission informing them of potential interference issues prior to the release of the R&O, but the Commission chose not to address those issues at that time. AVSI then supported a more comprehensive analysis performed by a multi-stakeholder group under RTCA SC-239  by providing empirical measurements (in the form of Interference Tolerance Masks or “ITMs”) of the effects of out-of-band interference on a set of commercial radar altimeters. The RTCA MSG Report established the credible risk for harmful interference to radar altimeters from new 5G emissions under the rules established in the R&O.
The FCC proceeded with the auction of spectrum in the C-band between 3700 MHz – 3980 MHz in December 2020 and initial operations in the 3700 – 3800 MHz portion are scheduled to begin in January 2022. There has been significant concern in the aviation community, based on the findings of the RTCA MSG Report, that the rules governing these C-band operations will lead to harmful levels of interference to existing radar altimeters. The FAA issued a Special Airworthiness Information Bulletin (SAIB) requesting information from radar altimeter equipment manufacturers, aircraft OEMs, and aircraft operators to help them determine what, if any, operational mitigations will be necessary to avoid interference incidents.
The AFE 76s2 Project Participants agreed that it was in the best interest of aviation safety to work with the wireless industry and regulators to resolve these outstanding concerns in order to minimize impact to aviation operations while supporting the least restrictive rollout of 5G. To this end, AFE 76s2 has published a comprehensive report that provides all the data that was used to generate the ITMs in the RTCA MSG Report. The report provides experimental details and anonymized raw data suitable for third party analysis and corroboration of the findings.
This report is structured in three volumes:
- Volume I contains the introduction, test procedures, and test results from out-of-band interference representative of 5G fundamental signals. Volume I can be downloaded here: AVSI AFE 76s2 Project Report – Volume I
- Volume II contains the test results from in-band interference representative of 5G spurious signals and identifies changes to the test conditions and analysis for spurious tests. Volume II can be downloaded here: AVSI AFE 76s2 Project Report – Volume II
- Volume III contains additional manufacturer-provided test results.
These will be released sequentially, upon completion and release approval of each individual volume.
Based at Texas A&M University, AVSI is an aerospace industry research cooperative that facilitates collaborative research and technology projects for its members. This project (AFE 76s2) included representatives from Airbus, Aviation Spectrum Resources Inc. (ASRI), Collins Aerospace, Embraer, Federal Aviation Administration (FAA), Garmin, Honeywell, the International Air Transport Association (IATA), Lufthansa Technik, National Aeronautics and Space Administration (NASA), Texas A&M University, Safran, and Thales. Project Participants contributed the subject matter expertise necessary to complete this project, including radar altimeter design engineers, aircraft systems integration experts, and aviation spectrum regulators.
1. An AFE 76s2 project member has produced a detailed overview of radar altimeter operating principles and parameters that can be downloaded here: Radar Altimeter Overview
2. See AVSI “Preliminary Report: Behavior of Radio Altimeters Subject to Out-Of-Band Interference” (Oct. 22, 2019), appended to Letter of Dr. David Redman, AVSI, to Marlene H. Dortch, Secretary, Federal Communications Commission, filed in GN Docket No. 18-122 (Oct. 22, 2019). See also AVSI “Supplemental Report: Effect of Out-of-Band Interference Signals on Radio Altimeters” (Feb. 4, 2020), appended to Letter of Dr. David Redman, AVSI, to Marlene H. Dortch, Secretary, Federal Communications Commission, filed in GN Docket No. 18-122 (Feb 4, 2020).
3. See “Assessment of C-Band Mobile Telecommunications Interference on Low Range Radar Altimeter Operations,” RTCA Paper No. 274-20/PMC-2073 (rel. Oct. 7, 2020), attachment to Letter of Terry McVenes, President & CEO, RTCA, Inc. (“RTCA”), to Marlene H. Dortch, Secretary, FCC, GN Docket No. 18-122 (filed Oct. 8, 2020). The report is available from RTCA at https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-Interference-Assessment-Report_274-20-PMC-2073_accepted_changes.pdf.