During last months, we have seen some news regarding the problems issued by aeronautical industry because of the interference caused by 5G systems in the C band (3400-4200 MHz) in the United States. Just last week, on February 23, 2022, the FAA issued an Airworthiness Directive for airports and airplanes that can suffer from interference by 5G systems. Although the allocation of this band to IMT systems was extensively discussed in different regulatory forums (ITU, CITEL, CEPT, APT, etc) and the band was initially allocated for IMT during the WRC-07 by some countries (ITU Region 2 and Region 3) and discussed again during WRC-19 and allocated as primary basis finally, with differences in the frequency range, most of the discussions were focused on possible interference to the satellite service. Only the ICAO and some regulators raises a concern about possible interference with radio altimeters, which is paradoxical because it was a security issue. In 3GPP, these bands appear as 3GPP band n77 (3300–4200 MHz) and 3GPP band n78 (3300–3800 MHz). Currently many countries are deploying networks in these bands, therefore is possible that similar concerns raise again in the near future when more countries start to deploy 5G networks using this band around the world. In the EU, this issue is under study by the ECC PT1.

Then, the question is why, after more that 10 years of technical discussions and coexistence analysis, we have complains from airlines? Some discussions regarding this issue can be found in the Comsoc techblog (https://techblog.comsoc.org/2021/12/07/faa-order-to-avoid-interfering-with-5g-c-band-services-rootmetrics-touts-coverage-vs-performance-advantages-for-5g/ ) and references cited in this blog, as well as in https://www.aviationtoday.com/2022/02/04/podcast-ieees-david-witkowski-talks-5g-c-band-aircraft-radio-altimeter-interference. Additionally, after a search in different academic tools like IEEEXplore and Google Scholar, using search terms like “interference studies 5G networks in 3500MHz band” and “C band coexistence studies radio altimeter”, most of the results were oriented to issues related with satellite systems. Using the search term “radio altimeter interference C band” better results were obtained, but most of them refer to the Wireless Avionics Intra Communications Networks (WAIC). Just some papers in IEEEXplore refer to this specific problem, and others refers to radio altimeters but in other scenario (WAIC). Other coexistence studies refer to general issues and mainly to the Fixed Satellite Service (FSS). Even a recent report from APT refers basically to possible interference with FSS, but a document from IATA, issued in 2020 refers to this interference issue as a safety risk and mention an example case in Israel.

In Latin America, countries like Chile and Uruguay already have 5G networks operating in 3500 MHz band. Mexico and Brazil recently auctioned the band. Colombia and other countries are in the process to auction the band and start the deployment, after some pilots to check coverage and capacity. Therefore, we expect to have 5G networks in 3500MHz band operating alongside Latin America during 2022, and we need to be aware of possible interference issues.

The motivation for this message in GCN is to raise the importance of our role as communications engineers and Comsoc members to support national regulators in these technical aspects. Some of us probably are working in regulatory issues or in interference analysis, or just have an informed opinion about this. Also, it is a good opportunity to organize seminars or forums with student chapters to raise the issue and disseminate information about some of the roles of our technical society and communications engineers in such important matter like the aviation safety.

I want to invite our global Comsoc members to check the situation in their countries (3500 MHz band allocation and auction process) and foresee possible interference problems in the near future and report to us using the communication channels we have in the different regions. Our communications team will be glad to include these discussions and news from different countries in our communications channels.