All the wireless services we now enjoy require careful licensing and regulation to prevent interference. That’s why the US Federal Communications Commission (FCC) and similar agencies in other countries carve up the electromagnetic spectrum into blocks and auction them to companies. The FCC began a new round of auctions earlier this year focusing on the upper microwave band, which could be valuable for delivering 5G mobile service. However, two US Senators are asking the FCC to delay issuing the licenses until it can verify 5G networks won’t scramble weather forecasting services.
At issue here is the auction for 24.25 – 24.45 GHz and 24.75 – 25.25 GHz bands. These frequencies are perilously close to the 23.6 – 24 GHz bands both NASA and NOAA use to monitor the weather. The navy wrote an internal memo in late March asking that the FCC take a second look at mitigating problems with interference from the eventual 5G signals.
The memo was made public along with a request by Senators Ron Wyden (D-Ore.) and Maria Cantwell (D-Wash.). According to the Navy memo, the ability of NASA and NOAA to detect water vapor via adjacent frequencies could be partially or completely blocked in some cases. The report says that measurements in urban areas will be most seriously impacted as that’s where carriers are expected to deploy those high-frequency 5G bands first. This could have impacts on military and space launch operations where weather prediction is essential, as well as severe weather forecasting.
The Navy memo asked the FCC to tighten the out-of-band interference from 5G bands by reducing the “bleed-over” limits to -57dB, much lower than the current standard. It also suggested the FCC continue to monitor the actual impacts of 5G deployment in the 24GHz range.
In spite of the Navy memo, the FCC has gone forward with the auction. Wyden and Cantwell have sent a series of questions to FCC chair Ajit Pai, demanding answers by June 11. They want proof that 5G in the 24GHz band won’t affect weather forecasting at 23.8GHz, as well as analysis of the risk to expensive weather forecasting infrastructure. The pair also wants information on how the FCC decided to move forward with the auction after objections from NASA and NOAA.
US carriers are currently rolling out so-called millimeter wave networks in the same general frequency range. These signals support very high bandwidth, but propagation is poor. That means a lot of high-power cell towers that could interfere with weather forecasting. It will be a few years before any carrier can roll out 24GHz support, so hopefully, there’s time to get all the issues worked out.