THREAD) Last week, the International Telecommunication Union (ITU) issued their regulations for the use of the 26 GHz radio band for 5G cell service.
Some have decried the result as a threat to weather forecasting.
So, what is this all about?
nature.com/articles/d4158…
Some have decried the result as a threat to weather forecasting.
So, what is this all about?
nature.com/articles/d4158…
Firstly, the ITU is a specialized body organized by the UN to coordinate the fair use of radio waves (itu.int/en/about/Pages…).
By international treaty, their decisions are binding on most countries. 2/
By international treaty, their decisions are binding on most countries. 2/
Why do we need the ITU? Because radio waves are a limited resource.
If you have cell phone signals, TV broadcasts, and GPS signals all trying to broadcast on the same frequencies, you get interference, and nothing works. 3/
If you have cell phone signals, TV broadcasts, and GPS signals all trying to broadcast on the same frequencies, you get interference, and nothing works. 3/
So ITU, with input from countries and companies, decides what kinds of signals can be sent on each part of the radio spectrum.
Called spectrum management, this gets complicated quickly, as this US spectrum allocation indicates. 4/
Source: en.wikipedia.org/wiki/Spectrum_…
Called spectrum management, this gets complicated quickly, as this US spectrum allocation indicates. 4/
Source: en.wikipedia.org/wiki/Spectrum_…
But the recent dispute isn't about the whole spectrum, but rather a very specific piece, the 23.6 - 24.0 GHz band.
Shown here as reserved for Earth Exploration and Space Research. 5/
Shown here as reserved for Earth Exploration and Space Research. 5/
Why is it reserved? Because that is one of the natural emissions frequencies of water vapor.
Many Earth observing satellite measure the 23.8 GHz frequency to determine how much water vapor is in the air.
As shown here, this can be is very useful for weather forecasting. 6/
Many Earth observing satellite measure the 23.8 GHz frequency to determine how much water vapor is in the air.
As shown here, this can be is very useful for weather forecasting. 6/
The 23.8 GHz frequency is protected, but ITU has been deciding on rules for its new neighbor, 5G cell phones, at the 24.25 - 27.5 GHz frequency (sometimes called the 26 GHz band). 7/
Cell phone providers want to be able to deliver more data, and the easiest way to do that is to move into higher frequencies.
A 26 GHz cell phone signal can easily carry more than 10 times the data as the ~2 GHz signals used today. 8/
A 26 GHz cell phone signal can easily carry more than 10 times the data as the ~2 GHz signals used today. 8/
The problem is that radio transmissions tend to bleed across frequencies. So a 26 GHz cell phone signal might be mistaken as water vapor by satellites that observe at 23.8 GHz.
To prevent that, the world must set limits on how much crossover each device is allowed to have. 9/
To prevent that, the world must set limits on how much crossover each device is allowed to have. 9/
The satellites are VERY sensitive. The sensors can register the faint water vapor signals down to -166 dBW (~25 attowatts = 2.5 × 10⁻¹⁷ W).
However, the satellites are also very far away, 500-800 km above the Earth, so all signals are weak up there. 10/
However, the satellites are also very far away, 500-800 km above the Earth, so all signals are weak up there. 10/
Each transmitter on a 5G cell tower might emit a few Watts in the 26 GHz band, while each handset can emit ~15 mW.
For safety, the World Meteorological Organization proposed that 5G devices should each allow no more than ~3.2 μW to cross into in the critical 23.8 GHz band. 11/
For safety, the World Meteorological Organization proposed that 5G devices should each allow no more than ~3.2 μW to cross into in the critical 23.8 GHz band. 11/
In the estimation of the WMO, this ~3.2 μW limit (-55 dBW) would allow 5G to be densely deployed in a major city without being spuriously detectable by satellites designed to measure water vapor. 12/
So what was the actual limit adopted by the ITU?
They said 5G devices can allow up to 500 μW to pass into the 23.8 GHz band through 2027 and 125 μW after that.
Dare I say, there is a big difference between the 3 μW the WMO wanted and 500 μW that the ITU adopted. 13/
They said 5G devices can allow up to 500 μW to pass into the 23.8 GHz band through 2027 and 125 μW after that.
Dare I say, there is a big difference between the 3 μW the WMO wanted and 500 μW that the ITU adopted. 13/
Still, it could have been far worse. The Trump Administration proposed allowing up to 10,000 μW per transmitter to crossover into the 23.8 GHz band. 14/
What happens next will depend on how widely and quickly 5G devices are deployed.
Ericsson expects that there will be ~2.5 billion 5G devices by 2025. That is potentially a huge number of transmitters bleeding power into the water vapor bands. 14/
zdnet.com/article/global…
Ericsson expects that there will be ~2.5 billion 5G devices by 2025. That is potentially a huge number of transmitters bleeding power into the water vapor bands. 14/
zdnet.com/article/global…
If WMO is right about the magnitude of the risk, and most devices are allowed to bump up against the ITU limits, then weather forecasters may have to deal with spurious 5G-related "water vapor" signals from every population center bigger than ~50,000 people. 15/
That's quite unfortunate, but probably not insurmountable. Satellite operators can learn to mask out or correct for spurious signals from urban areas, and they will probably still have clean data from oceans and rural areas. 16/
Learning to make corrections for 5G-related "water vapor" signals is probably possible, but it will eat up resources that could have been devoted to other things.
And while weather forecasters learn to adjust, accuracy may take a small hit. 17/17
And while weather forecasters learn to adjust, accuracy may take a small hit. 17/17
