,

Wireless Communication and Applications Above 100 GHz: Opportunities and Challenges for 6G and Beyond

Marconi Society 6G

Testimony before the Federal Communications Commission, March, 2019

By Ted Rappaport

We have never, in the history of the US, opened up spectrum above 95 gigahertz (GHz).

Now the FCC is opening up new spectrum, which allows us to move all the way up to the terahertz (THz) range. In this range, there are things we can do that we never thought our smart phones would do.

For the past ninety years, everything has been below 6 GHz – from FM radio to cellular to wifi. Opening the mmWave spectrum has given the US a great ability to compete on the world stage as we move above 6 GHz with bandwidths that we never thought would be possible.

Some people believe that you cannot do much with these frequencies above 95 GHz, but that’s what they thought about mmWave frequencies above 6 GHz. At NYU we showed that applications could work even better at these higher frequencies with more bandwidth than before.

When you get up to 100 GHz, you still have amazing amounts of spectrum – far more than we’ve ever had historically. This is because the air attenuation, or how much the oxygen and water vapor attenuate signals, is not bad up to 500 GHz. You can still have mobile communications, wifi, rural backhaul and so many other key capabilities at these frequencies. Because rain attenuation flattens out at 100 GHz, going above that frequency means that more rain will not impact the signal. Because of this, we will be able to design links well into the future.

Other parts of the world are already looking at the spectrum above 95 GHz. In Japan, there is an unlicensed band available up around the 120 GHz band and the FCC’s proposal provides some harmonization there.

The applications that become possible at frequencies over 95 GHz are amazing. When you have such great bandwidth, and as we move to higher bandwidth channels in the future (20 GHz or more), you can start having data rates that approach the bandwidth needed to provide cognition. I call this wireless cognition, where the computations of the human brain at those data rates could actually be sent on the fly over wireless. In this scenario, you could have low power, low cost computing devices like drones or robotics, actually receive in real time, over wireless, the kind of perception and cognition that the human brain could provide. That’s unheard of, but it will allow amazing applications in robotics and machine communications.

At these frequencies, you will be able to sense your personal health. There will be applications for air quality and detecting explosives. There will be gesturing applications, where you move and the wireless wavelength is so small that you can pick up very tiny movements and actually never have to touch your smart phone. We’ll be talking and moving our fingers without touching an appliance at these frequencies.

The wireless communications bandwidths will be so wide and so fast that we can imagine wireless replacing a lot of entrenched aging cable and providing new bandwidths that we have never seen.

There could be applications in imaging, where you can detect things in a chocolate bar or see around corners to know that you’re not going to collide with anything as we are able to sense within centimeter accuracy.

Wireless communications, not just backhaul and mobile, certainly will be possible. Along these lines, though, we’ll enable chip-to-chip and data center communications where the computational speeds can be carried at close range or over distances of several hundreds of meters for cellular.

At NYU WIRELESS, were doing some of the first measurements at 140 GHz. We’re studying the outdoor and indoor propagation characteristics so that the wireless industry can learn to build systems and wifi networks, just like we did in 5G.

We have learned something remarkable that most of the industry does not understand.

Most engineers think that, as you go higher in frequency and you go out to distance in wireless networks, that you get more loss. That’s the conventional wisdom. That’s only true, though, if you use an omni-directional antenna – the old way of doing cellular 10 and 20 years ago. When you start using directional antennas, you actually do better as you go higher in frequency for a given power level and a given antenna physical size. We have simulations and measurements that totally debunk the myth that most of the industry believes, which is that higher frequencies are more lossy.

It’s true that weather and rain can create problems. But in clear weather, you actually get more power received for a given physical size of the antenna and as you go up higher in frequency, you get better signal to noise ratio. You basically get more bandwidth for free for the same battery power.

It’s a remarkable result.

We’ve measured penetration loss through typical materials – glass, drywall – and we can now predict the scattering, or what happens when you bounce a radio wave off a drywall or a building. We have papers coming out that will help the industry design future mobile, fixed and unlicensed systems.

Some of our early results look at what happens when you go from 28 to 73 to 140 GHz. Indeed you get a bit more loss trying to go through drywall or glass, but the loss is not that substantial – a few dB. You can make up a few dB by an antenna at the same physical size.

Research papers showing these early results on work above 100 GHz are here:

https://arxiv.org/pdf/1808.07594.pdf

https://arxiv.org/pdf/1903.02657.pdf

We’re going to get much more focused energy going up to higher frequencies in the same physical area, so we can combat all of these things that we’re seeing. This means that the frequencies above 95 GHz are the future bastion for mobile, fixed and wireless.

See Ted’s testimony before the FCC here, starting at 2:57: https://www.youtube.com/watch?v=em12zw1RiMw&t=22s

Slides can be found here: https://www.fcc.gov/document/rappaport-presentation-wireless-applications-above-100-ghz