Conversations: Eisenstein on 5G

“Conversations” features faculty members addressing topical, occasionally polemical issues from an engineering perspective.

This month we focus on the rollout of 5G, the next generation of mobile phone connectivity that will drive a revolution in communications. Already underway in select cities across the nation (Philadelphia is not one of them), the 5G wireless network will use a higher frequency in the broadband spectrum for unprecedented speed, low latency, and access for the Internet of Things. But what does “5G” actually mean, and how is it going to impact our lives? Dr. Bruce Eisenstein, the Arthur J. Rowland Professor in the Department of Electrical and Computer Engineering, has a few answers.

What is 5G?

First of all, the “G” stands for generation. 5G is the fifth generation of mobile phones. I can give you the other generations and what they did. Zero generation was mobile radio, walkie-talkies, and versions of early mobile phones. Then first-generation cell phones came out and they were analog. The thing that makes a mobile phone a cell phone is that the subscription area is divided up into cells, and there has to be a way to hand off the customer when they go from one cell to another. So, the breakthrough came in the early 1980s when Bell Labs developed the cellular concept of handing off calls.

The 2nd generation was an evolution of that first generation, to digital. The 3rd generation was an evolution from the second. It was still digital and it was faster, but it was still somewhat limited. And by the way, 3G phones are still around today. As a matter of fact, the next evolution was 4G and when you don’t have 4G you’re automatically on 3G. So, there’s compatibility. The cell phones up to the point of 4G were evolutionary, going from one generation to the next. They were better, but they were still evolving fairly slowly from the previous generation.

What’s happened now is that 5G is no longer an evolution. It’s a fundamentally different system.

How is 5G different?

First of all, the speed. Speed is measured in bits per second. Right now with my 4G phone, if I am lucky, I can get 10 megabits per second. At Drexel we have a really good wireless connection, so here I can get up to 50 megabits—that’s 50 million bits per second; each bit of course is carrying one bit of information.

What they’re looking for with 5G is 20 gigabits per second—that’s 20 billion bits per second. And they’re talking even higher numbers than that eventually. It’s a vast change in speed.

The other part of it is, if you look at how the cellular system works when it handles data—meaning you make an inquiry on Google or you’re trying to get an Uber—there’s something called latency, which is the amount of time it takes for your command to be recognized by the system and to go back and forth. So, with the latency today here on the Drexel WiFi, I’m getting absolutely outstanding numbers: 298 megabits per second, with a latency of 4 milliseconds. This is absolutely incredible. But if I turn off that WiFi and am operating on cellular only, I get 2.4 megabits per second, with a latency of 20 milliseconds.

So now what we’re talking about with 5G is a wireless signal at 20 gigabits, or 20 billion bits per second. You can see how big that is. And the latency will be under 1 millisecond—it’s nearly instantaneous. In computer terminology a millisecond is forever. But for human beings a millisecond is, well, you could not discern it. As a matter of fact, even the 20 milliseconds I’m getting here you could not discern.

What enables this high-speed, low-latency technology?

The electromagnetic spectrum goes from very low frequencies like vibrations, and then up through things like radio, TV, through cellular phone systems, and all the way up into the millimeter waves and then into optical frequencies like infrared, visible light, and then up to X-rays and cosmic rays. That’s the spectrum. There’s a lot of spectrum.

The reason spectrum gets overcrowded is because as you get higher and higher in frequency, the amount of distance that you can get for signal propagation keeps going down. If I were to show you a flashlight, for instance, how far away would you be able to see with it in a useful way? Maybe 1,000 feet. That’s one way to think about propagation.

The way the cellular system works through 4G is, each one of the providers—Verizon, AT&T, Sprint, and T-Mobile—are given slices of bandwidth by the Federal Communications Commission (FCC). They pay for it; the FCC auctions off this bandwidth, and now each carrier has a slice of bandwidth. The slices are all over the place, and they try and package them together so they get contiguous spectrum. The bands that are available right now for the 4G system are 700 megahertz (MHz), 800 MHz, 1900 MHz, and 2100 MHz. The 1900 and 2100 could be written as 2.1 gigahertz. This is a fraction of the spectrum, a frequency portion of the spectrum.

So, here’s the problem. Where we are right now with the 4G system, it is a very crowded part of the spectrum. There are all sorts of things—GPS, your microwave oven, your cellular phone, your Department of Defense satellite communications—that are all in that same relative band of frequencies. To get additional bandwidth out of that is almost impossible. (NOTE: Here’s a story about some Drexel Dragons who are trying to do just that.) So what they’re doing with the 5G system is going way, way up in frequency. The initial rollouts will be at 6500 MHz, or 6.5 gigahertz. But we can’t get anywhere near that with the system we’re using now.

If I want to do 20 MHz per second down at the lower frequency, I need 50 bands like that in order to put together enough bandwidth to get this high-speed communication. Well, you can’t do it. There’s not enough space there. So we do it by going higher in frequency. If I’m up at 6500 MHz, I have a lot more bandwidth available to me. But that different frequency now has totally different characteristics. First of all, 6.5 GHz doesn’t propagate very far (think of the flashlight) and, secondly, antennas get to be very complicated at that frequency.

I have heard that the FCC has just released the 95,000 MHz frequency. So then you’re up at what’s called millimeter waves. Now, in order to get any range out of antennas at that frequency, you have to have a very complex antenna called a Phased Array Antenna, because that allows you to do what’s known as beam steering, where you can aim the antenna.

Is the 5G roll-out going to require all new infrastructure?

Yes, absolutely. What has to happen is they need antennas almost everywhere at several hundred feet apart, and we need them not very high off the ground. How do we do that? We have traffic lights all over our cities—we’ll put them on top of the traffic lights. And that’s what they’re doing. They’re rolling them out right now in the public right-of-way. Almost every traffic light or street light will have an antenna site on it for the 5G system. You’ll scarcely notice it unless you know what to look for. But they’re going to be all over the place.

Cell providers have access to public infrastructure; what do municipalities get in return?

I have had a private consulting practice for many years now in which I consult with municipalities on that exact question. The way it stands today is the FCC has put such a high priority on the 5G rollout that they’ve essentially removed any argument on this. For all practical purposes, municipalities have to allow it unless they can come up with some absolutely extreme reason why they shouldn’t have it. But the FCC has also put in a fee schedule. So municipalities can collect some money from that.

Is the FCC looking out for our interests as consumers?

There’s some concern that maybe they’re not. It’s very complicated. I understand the concerns. But I think the FCC feels this is so critical to the infrastructure of the United States that they can’t allow municipalities to stop it from happening. In order for the system to work, it has to be ubiquitous. That’s the way they see it.

How is 5G going to benefit consumers?

That’s a very interesting question. I’m asked that quite a bit. Let me tell you a story. Back in the early 1990s, some of my technicians here in the department came to me and said, you know Dr. Eisenstein, there’s this thing called the Internet and it’s going to be really important. And I said, what’s the use of it? I started reading about it and I did all the research and I thought, okay, it’s going to be really interesting. Here’s what I could not have foreseen: Amazon, Google, web browsers that we take for granted, the way in which we use it for Uber, emails, Facebook, plane reservations …. Just think about all these uses. Knowing the field as well as I did back then, I still could not imagine what was going to happen with the Internet.

The reason I tell that story is that, here we sit with the possibility that everywhere you’ll have a very, very high-speed wireless signal with low latency. So the question is, what can you do with that? That’s where the creativity of the engineers of the future is going to come in: what are the products and applications that we don’t have today and could not even perhaps envision today? How is everything going to change under this system?

One obvious example is self-driving cars.

Yes, let’s start with that. Right now, self-driving cars are very self-contained. They have all the sensors but also all the computers on board, and they’re figuring out for themselves where they have to go. But they don’t know what’s happening with the car next to them or the car behind them. If we had this ubiquitous wireless signal, the driverless car would not only have its on-board capability, but it would also know that the car in the right lane is going to make a left turn. And it would know that there’s a construction block ahead because it would get that wireless signal, and then it would tell all the cars around it that it’s going to re-route. In effect, the cars would run the way the air traffic control system works today, where you have someone in a control tower who’s controlling all the planes. So that’s something that you could do that would make self-driving cars safer. 

But it gets even better than that. Pedestrians walking along with their cell phones—the self-driving cars would know the pedestrian is about to step off the curb. And it would start to slow you down accordingly.

Will this impact the availability of spectrum the way 4G has?

Not immediately, no. There’s so much available at the millimeter bands that there will be no shortage of bandwidth.

How many years will rollout take?

I’d say less than three years. In the cities and suburbs. Internationally, too. For instance, Korea’s way ahead of us, and China.

How else will 5G benefit us?

The other thing you’ve probably heard about is the Internet of Things (IoT). So in IoT, you would have all the appliances in your house having their own connection—your toaster, your refrigerator, your microwave oven—all of these trivial and trite configurations. For example, your refrigerator might know when you’re getting low on milk and automatically put it on your shopping list.

So, the first two advantages of 5G are high speed and low latency. The third advantage is it can handle many, many more simultaneous users. Right now, if you tried to connect all the stuff in your house or in your office, it would overwhelm the system. But 5G can handle it.

What that means to the consumer is it would be possible for you to have computer controlled medical devices, for example, like an insulin pump or a heart monitor in case you have a heart condition. And from there, it’s a trivial extension for that device to do an EKG on you and automatically call the ambulance before you even fall over.

The third big use is what’s known as proxy computing. Let me explain what that is because it’s a very important concept. You know the cell phone is really a self-contained computer. But it’s limited. Your phone is basically acting like a sensor and a display terminal, and all the heavy lifting is done by this proxy computer. 5G enables your cell phone to do some very complicated things that could involve, for example, bio-measurements, or pollen sensing, or temperature and humidity—it could do these calculations and figure out from a big medical database whether you’re in danger of a major allergy attack. Your phone can’t do that because it can’t hold these big databases. So, you’ll have almost simultaneous access to massive databases, and apps could be made that would allow that to happen.

Would it enable machine learning on your cell phone at some point?

Exactly. Exactly right. There’s no limit to the measurements that could be made and the data you could analyze. The only limit right now is the connectivity, and that’s where the 5G comes in.

What are the routes of exploitation? What are your concerns about 5G?

Well, the obvious ones are privacy. If someone is walking around with a pacemaker that’s computer controlled and somebody hacks that computer, it could be considered murder. So those concerns about hacking and cybersecurity and data breaches and privacy, they’re legitimate.

All I can say is that those concerns are with us today, and they’re going to be with us in the future. We have a Cybersecurity Institute at Drexel and we’re looking into this to do everything we can to make them secure. And we’ll do the same thing with the 5G system. In spite of the fact that we hear about all the hacking, the systems today are much, much safer than the old cellular systems when someone could just pick up a radio and listen in to your cell phones.

I’m not saying that people should not be bothered or concerned. What I’m giving you is a personal view—it doesn’t bother me that they’re snooping on me, and that even more devices will be able to. It’s here already. It’s going to be here. It is a convenience for me.

What about issues of access for rural areas?

You get out to rural areas and you have houses that are 500 or 1000 feet from the road. I have a friend in New Hope who has a quarter-mile drive to his house, so there’s no way the signal can get there. He’s not going to have 5G; he’s going to have 4G until he drives into the city. But I’m thinking of really rural areas, like Wyoming. They’ll have 3G coverage. They’ll put up huge towers and they’ll get a lot of propagation through that, or they’ll have satellite coverage for TV.

But yes, there will definitely be a digital divide. The divide is a real one. The FCC’s aware of it. But you can put up a cellular system much easier than you can put up a wireless system, so rural areas will have wireless access. But they’re not going to have 5G.

What opportunities are open to CoE engineers under 5G?
That is exactly what I try and talk to my students about. I tell them that story about the Internet and how I couldn’t foresee all those things, and I say the same thing is going to happen again. You have to start thinking creatively about things that at present are unimaginable, things that you wouldn’t even think of doing that might be possible if you had that high speed and low latency.

So, I tell them to assume it’s going to be there: assume you’re going to have very high-speed wireless connectivity everywhere in the city. Now what do you do with that? What would you like to see happen? Think in terms of medical advances, automation and controlled machinery, self-driving cars, pedestrian control systems.

As for the concerns, this is what I think separates engineers from other people. Engineers will always look at these problems as opportunities. So yes, right now there’s unimaginable consequences that may be positive and that may be negative, and engineers will see all these as another way to try to make the system better. That’s what engineers do. We make the world better.