A story that made the rounds last weekend claimed 5G will kill weather forecasting. The story is terrifying – imagine being struck by a hurricane on a sunny day – but it has little to no factual foundation.

The story emanates from the Commerce Department, the  organization that produced a proposal to nationalize 5G networks in the name of security. That didn’t work, so some suspect Commerce’s new tactic is to raise fears about weather forecasting. Whatever the agency’s motive may be, there do appear to be significant problems with its analysis of 5G propagation.

Normally, the analysis of and coordination with government radio systems is the job of NTIA, but with that agency rudderless following the unexpected resignation of Administrator David Redl, NASA and NOAA are asserting their own institutional interests without technical  supervision.

Career Implications

NOAA understands how its sensing systems work, but it’s not well versed in 5G; hence it struggles to characterize interference. Nobody wants to be the guy who said the weather systems will be fine only to discover that they’re not, but there’s no career damage in shrieking that the sky is falling when you can’t be proved wrong for a decade or so.

At issue is the interaction of active 5G data systems with a passive satellite-based system that measures water vapor from space. While this is a very roundabout way to measure evaporation, it’s useful because it doesn’t require any ground-based sensors.

The major downside of NOAA’s approach is that it has to capture very faint analog microwave signals (caused by evaporation) from a great distance, after they’ve left the atmosphere. Vapor sensors can only operate at one frequency – from 23.6 to 24.0 GHz – so it’s incumbent on regulators to protect them.

Good Neighbors

The FCC has auctioned off spectrum in the 24 GHz and 28 Ghz bands, with AT&T, T-Mobile, and Verizon the high bidders. The nearest allocation to the vapor sensors starts at 24.25 GHz, 250 MHz away from NOAA’s assignment.

The huge guard band would normally be more than enough to protect neighboring bands – after all, we separate most allocations by 2.5 – 10 MHz. And there are already  thousands of microwave allocations immediately below the NOAA band, with no separation at all.

This is doable because earth-based systems transmit narrow beams of energy horizontally, while NOAA is looking for signals going straight up to the heavens. 5G will work in much the same way as today’s microwave data systems, so there’s no obvious reasons why it would interfere when incumbent systems don’t.

Measurement vs. Simulation

While it’s possible to measure interference between existing systems, we can only use simulation to predict interference between systems that are not yet deployed. So a person could measure interference between existing microwave-based data systems and the NOAA sensors provided they have a testable interference model.

I don’t know whether such testing has been done in a formal way, but NOAA reports that its sensors operate reliably today. We can take that report as the equivalent of testing as the vapor sensors have been operating in various forms since the Nimbus-3 satellite launched in 1969.

The JPSS-1/NOAA-20 satellite launched by NOAA in 2017 features an Advanced Technology Microwave Sounder (ATMS) vapor sensor as well as four other sensors. The combination of five sensors allows NOAA to map short and long term changes in temperature, water vapor, precipitation, snow and ice cover each day, as well as the state of the ozone layer.

The current suite of sensors, collectively known as the Microwave Integrated Retrieval System (MiRS), map atmospheric changes accurately despite their adjacency to the microwave data systems.

Simulation Inputs are Dubious

NOAA has developed simulations of radiation produced by 5G at frequencies separated from ATMS by 250 MHz, as they should. But their simulation is problematic because it ignores many salient facts about 5G:

• 5G is a low power system designed to propagate over short distances, typically a few hundred feet. Hence, we can’t expect a single 5G signal to travel very far through a vapor-rich atmosphere. Water, bodies, and trees absorb most 5G signals and it propagates best with direct line-of-sight and reflection off hard surfaces such as pavement and buildings.
• 5G base stations propagate downward, reaching the ground in the area where receivers are expected to be. 5G also uses beam-forming, which ensure that signals don’t propagate in all directions. No well-aimed 5G transmitter points upward.
• 5G stations – both fixed base stations and mobile devices – reduce (modulate) their power according to their distance from the device at the other end of their transmissions. Battery powered devices don’t waste battery life by shouting when they can whisper.
• 5G handsets and base stations take turns transmitting; they don’t talk over each other. 5G signals concentrate >95% of their power in their assigned frequencies; only Out of Band (OOB) energy could possibly reach ATMS.
• Across a broad sample period and area, there will be little variation in total energy emitted by collections of 5G systems. We know that there are almost no variations in data volume across aggregated data links (Internet backbones) that aren’t predictable by time of day and day of week.
• 5G will not be the most significant source of energy radiation over land in frequency bands it doesn’t use directly.

Hence, the NOAA simulation model needs to be validated against measured behavior. If we can’t wait for 5G deployment to do this, it should be done against the existing microwave services operating adjacent to ATMS on the lower edge of its reserved band.

NOAA’s Rhetoric is Inconsistent

In the CBS story from last weekend, a weather scientist stresses the importance of hurricane prediction. Surely this problem requires accurate wind, vapor, and temperature data from the breeding ground of hurricanes, the ocean.

5G devices make no sense on the ocean and other large bodies of water. Their only conceivable use in the Atlantic would be aboard ships that generate several times more radio noise from the engines, navigation systems, and electric systems.

5G energy is going to be very constant, perhaps adding an infinitesimal factor to the background noise that NOAA already has to filter out; in most scenarios there wouldn’t be more than fractions of milliwatts OOB.

NOAA’s systems depend on patterns of variation from sources of vapor that change in regular and predictable ways over large sample periods and areas. Surely the agency already has the ability to distinguish weather events from man-made ones.

NOAA is Under Stress

There’s no question that NOAA workers are suffering under the present climate change skeptic regime in Washington. Many politicians would be happy for NOAA to just shut up and go away because its measurements prove that climate change is really, truly, certainly happening.

Many career government workers chafe under the not-entirely-rational leadership of the current appointees. In such a setting, it’s very hard for the professionals to do their jobs exceptionally well; it’s likely that they don’t have adequate resources either internally or externally.

The wireless industry will need to devote some personnel to work with NOAA on developing meaningful interference models. This begins with understanding exactly how and when data signals can confuse ATMS. It then extends to understanding the propagation patterns of 5G data signals.

All in all, NOAA’s simulations are far too rough for the upcoming World Radio Conference (WRC-19) in October and November without a lot of work. The slow progress NOAA has made on this problem puts the whole process in doubt.