Massive MIMO Is Going to Revolutionize Cellular Connectivity - And It’s Also Really, Really Cool

“Daddy – how does the video get to my iPad, even when we’re driving in the car?”

Even as someone who works with mobile connectivity for a living, the question stopped me for a minute. I glanced at my 6 year old daughter in the rearview mirror, where she had paused from poking her tablet to ask a deceptively complex question.

And then I got to tell her, in simple terms, of the technological marvels that all have to work?together to keep her HBO Max streaming to keep her HBO Max streaming while we go 65 miles an hour down the highway.

It left me with a profound sense of how amazing our modern world is, and how we hardly think about it (unless something goes wrong. Or until our kids ask us how it works ??).

In my lifetime we’ve gone from landlines to car phones to cell phones to smartphones to connected devices. From black and white 12-inch TVs to ultra high-definition displays the size of a movie screen. And we’re just getting started with game-changing technology like 5G. We’re scaling new heights of human ingenuity every day.

But I want to focus on one example that I believe is exceptionally cool. Cell service is getting faster and smarter, with quicker response time, less buffering and more bandwidth. The key technology? Massive multiple-input/multiple-output (MIMO) cellular antennas – which are the latest generation of antennas that we deploy on those ‘towers’ you see when you are driving, to make sure your cellular service works no matter where you go.

And while antenna’s aren’t something most of us think about every day – they are an absolutely essential part of all of our lives. So here’s why I’m geeking out over MIMO.

What Is Massive MIMO and How Does It Work?

A massive MIMO transmitter has multiple cellular “radios” in one compact antenna. It may not be obvious from the ground, but traditional cell antennas are huge: those panels on top of cell towers are EIGHT FEET TALL. By contrast, massive MIMO radios can fit 64 transmitters in a single 2x2 foot square.

Here’s the difference in technology, explained in terms everyone can get behind: Ice cream.

Picture an outdoor ice cream stand on a hot day. People are lined up waiting. But no matter how fast the scooper is, they can only serve one customer at a time.

You get the same bottleneck with a radio using a single transmitter. Each customer has to queue up to get their data “scoops”. Even when it’s measured by microseconds, the delay is noticeable. And the longer the line gets, the worse the service is for everyone. With people increasingly relying on near-instant responses for their mobile workplaces, emergency services, and other critical applications, digital delays are even more frustrating than standing in the sun waiting for your mint chocolate chip.

By contrast, let’s think about a massive MIMO ice cream stand. Imagine four ice cream heroes serving up cones, but they’re not just handing them over the counter — they’re tossing treats directly to people on the sidewalk, before they even get in line. The service isn’t limited to one person at a time and it’s not bound to a queue.

That’s how massive MIMO works for cellular service. An array of antenna elements in the massive MIMO radio can be used to “beamform,” sending a narrow signal to specific devices. Each array can produce four of these targeted beams, serving four different devices simultaneously. That translates to handling four times the traffic without degrading service, or serving up four times the speed to the same traffic as towers with traditional antenna elements.

Beamforming - A Ripple Effect for Better Service

One of the coolest things about massive MIMO is its ability to create different shapes of signal beam. A massive MIMO array can target individual devices or focus its coverage on specific geographical areas – such as a trapezoid, square, or even diamond-shaped coverage zone. For example, here’s the coverage map of AT&T Stadium with and without customized beamforming:

Even cooler, there are no moving parts inside the massive MIMO radio’s array. It’s all done by resonating waves at different time delays. Think of dropping two pebbles into a pond - some ripples combine with each other, while others cancel out. That effect is what makes beamforming possible.

Ultimately that means massive MIMO is highly efficient at getting the signal where it’s needed.

Massive MIMO and 5G - A Perfect Match

Massive MIMO also helps us deploy 5G on towers originally configured for 4G.

4G towers were built to match the broadcast capabilities of the spectrum they were using. Certain types of spectrum that we are using to deploy 5G gives us increased speed and bandwidth, but the signal doesn’t travel as far as the spectrum we used for 4G. So we either have to build new towers that are closer together, or figure out how to use the 5G spectrum more efficiently.

Massive MIMO makes it possible to avoid coverage gaps when deploying 5G spectrum on existing tower locations designed for 4G. It’s exactly the type of smart infrastructure that is essential for our hyper-connected future (and present, for that matter).

What’s Next for Massive MIMO?

AT&T will continue expanding our network with massive MIMO radios. Even better, we’re still evolving the design. Right now, our massive MIMO radio can handle four simultaneous beams, either increasing traffic or average speed by four times over a single antennaBut we’re already looking at ways to work with our equipment partners to add more transmitters, shrink the size further, increase the signal strength, and more. The innovation never stops.

In the not-too-distant future, a dad like me could be headed down the highway and his daughter in the backseat might ask: “Hey Dad, how can the car drive itself while I play on my iPad and you make a video call?”

If that’s the future, I have no doubt massive MIMO is part of the infrastructure that will get us there.