Meteorologists and other experts are urging the Federal Communications Commission to drop a spectrum-sharing plan that they say could interfere with transmissions of weather-satellite imagery.

The dispute is over the 1675-1680MHz frequencies and is separate from the other FCC/weather controversy we've been covering, which involves the 24GHz band and has pitted the FCC against NASA, the National Oceanic and Atmospheric Administration (NOAA), and the US Navy.

The American Geophysical Union (AGU), American Meteorological Society (AMS), and National Weather Association (NWA) told the FCC in a filing last week that its plan for 1675-1680MHz should be scrapped because of the "likelihood of interference with the reception of weather satellite imagery and relayed environmental data to receive-only antennas that members of America's weather, water, and climate enterprise use."

The 1675-1680MHz band is used today by NOAA for government-owned satellites that transmit data to antennas on the ground, but the Ajit Pai-led FCC has proposed rules that would force federal government users to share the spectrum with wireless broadband services. The FCC is targeting the 1675-1680MHz band in part because it is adjacent to 1670-1675MHz, which is already allocated for wireless services.

Reallocation of the spectrum is needed for "the nation's wireless networks [to] keep pace with ever-increasing demand for wireless broadband," the FCC plan said. The FCC is taking public comments on the Notice of Proposed Rulemaking until July 22 before making a final decision. If the FCC gives final approval to the plan, the commission would use an auction to sell licenses in the 1675-1680MHz band to wireless-network operators.

LightSquared successor wants spectrum

The main industry proponent of the FCC's 1675-1680MHz plan is Ligado—formerly known as LightSquared, which failed to win government clearance to build a 4G-LTE network on different spectrum in 2012 because testing showed the network would interfere with GPS devices. Now Ligado is trying to build a 5G network.

Ligado petitioned the FCC to open the 1675-1680MHz spectrum for sharing in 2012 and has made 10 filings since April in support of the FCC's current plan. Ligado already leases access to the adjacent 1670-1675MHz, which it could pair with 1675-1680MHz to get 10MHz of contiguous spectrum. Ligado claims there's no reason to be concerned about interference with weather-satellite data transmissions.

The FCC spectrum plan is also supported by CTIA, the wireless lobby group that represents AT&T, Verizon, T-Mobile, and Sprint.

Separately, Ligado this week also asked the FCC to rule on its December 2015 application for a license modification that would allow it to use the 1526-1536MHz band with limits on power levels to protect GPS devices. Including other bands, Ligado is seeking to build a 5G network on a total of 40MHz.

Boeing and AccuWeather raise concerns

Boeing, a frequent government contractor, explained in a filing that the 1675-1680MHz spectrum is "used by the FAA, NASA, NOAA, the National Weather Service, the Department of Defense, the Department of Interior and the Department of Agriculture to receive real-time data downlinks from NOAA's Geostationary Operational Environmental Satellites ('GOES') that include weather and hydrological (i.e., flooding) information."

There are also many non-federal users who "operate unregistered receive-only earth stations for the reception of GOES weather and flooding data, including users in the aviation industry, state and local governments, and in shipping for environmental monitoring, operational planning, and disaster preparedness," Boeing said. Boeing itself said it uses the spectrum "for communications involving in-flight tests of aircraft manufactured for the US government, and for the development of wireless communications equipment for both commercial and governmental use."

Boeing didn't outright oppose the FCC plan, but it urged the commission to require systems that protect both federal and non-federal GOES receivers and ensure "that their reception of weather and other critical data is not impaired as a result of harmful interference."

Internet-based system could be less reliable

The FCC's call for public input asked whether "an Internet-based or private network content delivery system" could be used instead of the current system to make the GOES data available without the need for earth stations.

Boeing objected "that the Internet does not ensure real-time reception of GOES data" and that its speed and reliability can be inconsistent during disasters.

AccuWeather also said in an FCC filing that an Internet-based system would not be appropriate. The current, satellite-based system "was designed to an uptime specification of 99.988% over a 30-day time period, leaving room for only 5 minutes of downtime per month," AccuWeather said. Internet services won't necessarily provide that same level of uptime, "especially in times of natural disasters," the company said.

"After Hurricane Michael struck the Gulf Coast in 2018, numerous fiber lines were cut and major carriers had to deploy mobile towers to support Internet functionality during this 'unprecedented' outage," AccuWeather told the FCC. "It is exactly at these times where satellite data is needed most and GRB [GOES Rebroadcast] requires little infrastructure, only relying on the cable connecting the satellite dish to the data center. Even if there was a private Internet network or direct fiber used by the CDN, it could be rendered unusable in the event of a natural disaster such as Michael." The GRB system also has lower latency, AccuWeather said.

AccuWeather is skeptical that the FCC can prevent interference by imposing power limits on broadband networks in the 1675-1680MHz band. With the satellite data transmissions, "the downlink power is far weaker than what would be utilized by a wireless network and could be completely overwhelmed," AccuWeather said.

The American Weather and Climate Industry Association (AWCIA), a trade group for weather professionals, argued that "radio frequency interference that can be generated from strong terrestrial downlinks, which share the same spectrum as the relatively weak signals from GOES in space, would have a devastating impact on our members."

During severe storms and natural disasters, cellular and other broadband networks "are often taxed to their maximum," AWCIA said. By contrast, the current systems for receiving GOES satellite data "are always there and have very little infrastructure that is subject to failure during stressing conditions," the group said.

Spectrum is “under threat”

NOAA hadn't filed comments with the FCC as of today. But a Florida Department of Transportation (FDOT) document from February 2018 describes a joint study conducted by FDOT and NOAA and said weather-related uses of 1675-1680MHz spectrum are "under threat" from signals in adjacent bands.

The spectrum used for GOES has already "been reduced by more than half compared to 20 years ago," and "[t]he spectrum on both sides of the GOES down link are now used for cellular communications," the FDOT document said.

Ligado's plan for the spectrum would "only protect a limited number of Federal earth stations," and "no non-federal earth stations will be protected," the document also said.

"If Ligado (or another carrier) is allowed to share the spectrum at 1675-1680MHz there is [a] good chance the earth station performance WILL be impacted," it said.

NOAA is now conducting a study on how spectrum sharing could impact weather services, the American Geophysical Union, American Meteorological Society, and National Weather Association said in their filing. The groups urged the FCC to wait until the study is completed before taking any action.

Ligado: No need to worry

A Ligado filing on Friday pointed out that NOAA's weather-balloon operations in the 1675-1680MHz are already being moved to different spectrum in order to accommodate the results of a previous FCC auction. That's supposed to be done by 2021, reducing NOAA's need to use the spectrum at issue, Ligado argued.

But Boeing urged the FCC to ignore any argument "premised on the possibility that these critical weather services will be retired." One GOES satellite is "scheduled to operate until at least 2025," and another is scheduled to operate until at least 2036, Boeing said.

"The technical capabilities of these satellites (and their resulting spectrum needs for data downlinks) continue to increase commensurate with the critical need for this data to forecast and monitor increasingly variable weather and flooding conditions," Boeing said.

Ligado also argued that interference can be prevented by the use of protection zones that would limit data transmissions near government-operated earth stations that need to receive signals from satellites.

But not all earth stations would be protected under Ligado's proposal. Ligado urged the FCC to make it clear that "non-federal users have no legal claim to continue to listen in on this spectrum."

"They are, quite simply, eavesdroppers—and are therefore not entitled to any protections licensees or even registrants might receive," Ligado said.

Ligado also argues that an Internet-based system could provide data to weather researchers "in a faster and more reliable way than they currently receive it."

"Obtaining this data via a satellite dish costs over $125,000 and takes months to install and obtain the necessary permissions," the company said. "With a CDS [content delivery system], obtaining the same data with comparable reliability and latency is fast, easy, and cheap." (However, this tutorial shows how to set up a system for receiving the satellite data for about $185, including the cost of a Raspberry Pi computer and cheap antenna.)

Ligado may get what it wants from the FCC by the end of this year. Pai already finished the 24GHz auction while saying that NASA and NOAA haven't provided convincing evidence that using that spectrum for 5G will harm weather forecasts.

When the FCC voted on its 1675-1680MHz Notice of Proposed Rulemaking, Pai said, "I look forward to working with [FCC staff] and our federal counterparts in the months to come so that we can bring this rulemaking to a prompt resolution."