Verizon’s director of network planning, Sanyogita Shamsunder, talks with Scientific American's Larry Greenemeier about the coming 5G and EM-spectrum-based communications in general.
Steve Mirsky: Welcome to Scientific American "Science Talk" posted on May 30, 2017. I'm Steve Mirsky. Larry Greenemeier is our technology editor. Larry was recently at the Mobile World Congress 2017 conference in Barcelona, where he spoke with Verizon's director of network planning, Sanyogita Shamsunder. You had 3G, you have 4G. Well, get ready for 5G, and, along the way, get a primer on how electromagnetic, spectrum-based communications happen, starting with good old AM and FM.
Larry Greenemeier: This may sound like a cliché, but what does 5G mean to you, because it doesn't really exist, so when you think about 5G, what are you thinking?
Sanyogita Shamsunder: Our definition of 5G is 5G in what we call millimeter wavebands, which are very high-frequency bands, and there are many opportunities. I mean there are challenges with that band because physics says that if I go high in frequency, my energy dissipates faster, it can't go too far, so that's the challenge. But, then, there are new technologies that help you overcome some of those challenges. You can't, I guess, overcome physics, but there are things you could do better that form the energy in such a way that you can go further. What we are doing ‒
Greenemeier: Wasn't the understanding that millimeter waves were not going to be good for communications, or was it the spectrum?
Shamsunder: Well, for very long-distance communications, no, because, again, energy dissipates at the square root _____ _____ proportional to the frequency. The higher the frequency, the faster the energy dissipation, so that is there. That rule doesn't change, but what you can do is you can have a better concentration of energy. If you radiate it everywhere, then that's a problem. But, if you have a better concentration focused towards where the target is, where the communication is, then you can go further than that. That's essentially the physics behind it. What we are testing for is basically we have deployed several base stations in these 11 markets, and we have clusters, which means we have not just one base station but a cluster of three or four fuel-based stations, a total of a couple of hundred in all these markets.
We are going to be testing how the performance is at various points in that big cluster. We will test fixed, we will drive around and test what is the expedience around in that area. Why are we doing that? Well, first of all, to understand how millimeter wave behaves in different geographies, different environments, different topographies because the signals bounce differently with different building material types, and different leaves, different trees. There is only so much you can test in the lab, and there is only so much you can simulate on a computer, so we felt it was important to understand what the expedience to the end customer is.
Greenemeier: Trees and other things interfering with signals. Is that more of a problem with millimeter wave technology than with the current ‒
Shamsunder: Yeah. Yeah, so if you look at, again, the physics, there is more dispersion with leaves, the more leaves there are, it doesn't, so you need to find the nooks and crannies between the leaves to propagate. There are new technologies, like beam forming and beam tracking that help you do that, because if it finds that a particular part is not good, then it might choose a different beam that can traverse with fewer blockages. That technology is relatively new for this millimeter wave. Yeah, so leaves are more of a problem for millimeter wave than for low frequencies.
Greenemeier: So you'll be happy when it's winter as opposed to summer.
Shamsunder: Yeah. Well, in general, for _____, I mean summer is more challenging because the leaves do come out, and you can see some difference in performance.
Greenemeier: Just basically, what kind of infrastructure are we talking about? I mean someone yesterday had mentioned new satellites. I think he was saying lower-orbit satellites, and more of them. I mean is it that much infrastructure, where we're talking from the satellites down to the handsets, or is it not quite ‒
Shamsunder: No, satellites have come and gone many years. I mean at one point in my life, I was working on a satellite, mobile satellite broadband system. At that time, Microsoft had announced a series, a constellation of satellites, lower-orbit satellites. I don't remember what it was called, but there would be, I don't know, 600-something satellites orbiting in the near-Earth obit and that would be connecting essentially for providing broadband. That never materialized, and then there was ‒
Greenemeier: Well, it's expensive. I mean ‒
Shamsunder: It's very expensive. It's very expensive, and of course the satellite industry has evolved, too. We have space _____ trying to get things done in a different way, but still there are challenges. When you put something up in the air, in the atmosphere, it has several years of life and upgrading is a problem. You may overbuild it for the future, and all those challenges. No, we are looking still at Earth-based systems. We have a lot of experience building networks. We have a coast-to-coast network today on 4G, and we are _____, which means we are adding more nodes, as we call it, more base stations to help with the capacity. I mean the usage, as you know, people love to use their smart phones all the time, so wherever there is a need for capacity for a wireless network, we are adding capacity, so that means we need to add more and more nodes. We'll continue to build that out and add millimeter wave as required on those nodes.
Greenemeier: Does that mean more fiber in the wireless part of the network or ‒
Shamsunder: Yeah, probably. Probably, yeah. Yeah, because all our cell sites now are connected through some type of fiber, because whatever the customer is using, those bits need to travel back to the Internet, so that kind of _____ connectivity is needed from the cell site to the Internet, so we have fiber, we have gigabit Ethernet, we have 10 gig and 100 gig Ethernet on the cell side. Further densification, obviously, requires more. There is an opportunity to do wireless _____, as well, so there are different ‒
Greenemeier: What would that be, wireless _____?
Shamsunder: Actually using a concentrated wireless link to connect _____. People use that today, and there are opportunities to use ‒ in 5G, they are talking about using the same spectrum for the customer as well as for _____, so you share that time, and then you use it to connect to the user and then connect to the _____, so there are those opportunities, as well. But, yeah, more fiber is definitely, in general, needed for wireless network densification.
Greenemeier: Okay, so what is the role that spectrum plays in 5G?
Shamsunder: Absolutely, I mean spectrum is the bread and butter of the wireless industry, right? I mean we absolutely need spectrum. We say it's never enough, spectrum is never enough, because people just consume, and, without spectrum, you can't do wireless without spectrum, so it's an important part of the industry.
Greenemeier: I'm going to ask you a very basic question that I need to know because I've tried to understand the concept of spectrum. When you talk about spectrum, you're talking about wavelength or ‒
Shamsunder: Yeah. It's electromagnetic spectrum.
Greenemeier: Right, but what I'm trying to figure out is when you talk about ‒ it doesn't necessarily go from 1 to 100, where you've got zones and you can send signals through specific zones. Is that ‒
Shamsunder: That's what it is. We have from zero to, I don't know, 100,000 gigahertz, or whatever, lots. I mean you can go beyond, but at some point it has no value because you can't do much with it. You have the radio waves, so you have the AM/FM, right? That's at very low frequencies. You see on your radio dial, FM 97 something megahertz ‒
Greenemeier: In order to broadcast at that frequency, whatever the content is, it's got to go at that speed? Is that ‒
Shamsunder: No. What happens is it's something called modulation, basic. FM modulation ‒ or actually, AM is easier to understand. Let me explain AM to you. AM modulation is nothing but you take a wave, a sine wave. A sine wave is oscillating, which means it has a frequency of, whatever, 880 something, some unit. It's electromagnetic. You don't see it, right? There are waves all around us.
Shamsunder: So, 880 megahertz, 800 kilohertz is the frequency, so when you do AM, which is amplitude modulation, you vary the amplitude of the wave according to the message that you're sending.
Greenemeier: Could you send that same message over a higher frequency?
Shamsunder: Yes, absolutely, you can.
Greenemeier: Okay. What do you need to do to the signal to be able to do that?
Shamsunder: You take the same message and modulate it ‒ the different types of modulations, amplitude modulation was one of the first ones, very old. I mean that's where the radio came from, and then there is FM, frequency modulation. In frequency modulation, what they actually do is they change the frequency of the signal according to the message. If you look at the amplitude, it is constant, but the frequency of the signal varies as you change the message. That's called frequency modulation, and now there are more and more sophisticated modulation schemes. You must have heard CDMA, OFDM, all that, so there are different ways of changing the characteristics of that signal to convey the message.
Greenemeier: Regardless of what the content is, if you're talking about 24 gigahertz or 28 gigahertz, the same message, but you're sending it at a different speed or sending it in a different ‒
Shamsunder: Right, so now there is a slight _____ nuance. I told you AM/FM, that that's basic modulation mechanisms. When we went to the digital age, we started changing our message and representing them by bits with a computer, right? The letter A, let's say, is five bits long, 0101 something, so you encode every message into a binary number with zeros and ones, and now you take those zeros and ones and then use that to modulate the signal, so that's your message now. You take packets of information, packets of bits. If you take eight bits together, it's a byte, right? So, take a byte and encode, what we call encode the frequency. The higher the frequency, the more the bandwidth you have to encode, so you can send more bits over. That's why it's important to get higher frequencies, because at 880 hertz, I can only do so much with frequency. I can transmit effectively speech, I can transmit effectively music, but I can't do several megabits per second, several gigabits per second. That requires more bandwidth.
Greenemeier: Is there a particular bandwidth that 5G, or something at the level of 5G will function best at, if you're communicating with a connected car or if it's a medical device?
Shamsunder: Yes, so it depends on the application, again, right? For a smart phone or for a camera, a remote camera, you would need a lot of bandwidth because images and video take up a lot of bandwidth. They generate a lot of bits, because imagine a 2-D picture, I have colors and it's changing fast, I need a lot of bits to represent that image, and that means it requires more bandwidth. I generate more bits per second. But, on the other side, if you look at an IoT application, a meter buried under a parking spot, all it needs to do is tell me if the spot is occupied or not, yes or no, zero or one. That's it. I really don't need a whole lot of bandwidth for that. I just need to send a message, "Hey, by the way, every five minutes," or something like that, I don't know, whatever you decide the frequency you want to know whether the parking spot is occupied or not, I send one bit saying, "This spot is free," or available. It really depends on the application that you're looking at, and they have different requirements.
Greenemeier: Something that takes a lot of bandwidth would want a higher frequency?
Shamsunder: It is not easy to build systems that have very wide bandwidths at low frequencies, okay? Let's say I am operating at 1 gigahertz frequency. At 1 gigahertz, to get a 1 gigahertz worth of bandwidth is impossible because I'm at 1 gigahertz already. I don't know where I connect. But, at 1 gigahertz, I can get maybe 100 megahertz, 200 megahertz perhaps, and so that's why you need to go to higher frequency. You look at the percentage of the bandwidth, percentage of the _____ frequency, so typically it's 10 percent, so 10 percent of 1 gigahertz is what I can get bandwidth-wise at 1 gigahertz. If I go to 28, 10 percent of 28 is 2.8 gigahertz, so I've got two times the bandwidth, so that's why I need to go to higher frequencies. It's not because higher bandwidths require higher frequencies. It's because higher bandwidths, for me to effectively communicate, requires more spectrum, and that spectrum is only available at higher frequencies.
Greenemeier: The next question would be in terms of spectrum freeing up, it's not just that more spectrum is freeing up, it would be where on the spectrum you get it?
Shamsunder: Yeah, right. That, too. That, too, right? Of course, more spectrum wherever is good, but there are some frequencies, I mean, again, there is physics involved. For example, if you look at the electromagnetic spectrum, if you look at Professor Rappaport's website at NYU, he talks about difference frequency bands, where some of them are better suited for propagation than the others. Some, there's more absorption due to moisture, so there are some other effects in the electromagnetic frequency spectrum that don't make it easy to use, plus there are also different users, and there is the defense industry that uses spectrum. It's not like everything is available for you to use. It's being used by other applications or it is not the right spectrum, and so on, so there are some constraints that make it a challenge.
Greenemeier: Tell me what you're working on now related to 5G that's exciting that you want people to know more about. You said you've got these tests, was it nine cities, did you say, or ‒
Greenemeier: Eleven cities.
Shamsunder: Eleven cities, yeah. Yeah, so we are excited about that. I mean we have done initial testing and it's been fantastic. We are seeing good results. Now the question is how well we can ‒ we are an operator, so this needs to be real, right? I mean we can't be hand-tuning everything, so we need to understand the rules of how this works in a larger environment like ours, with different parts of geography, different deployment scenarios, and so on. I'm excited to gather data, understand it, analyze it, and operationalize it, more importantly.
Greenemeier: Do you feel a lot of pressure with people putting this number of five years or so on 5G?
Shamsunder: Five years is too far away. I wouldn't _____ pressured in five years.
Greenemeier: Okay. That's good.
Mirsky: That's it for this episode. Get your science news at our website, www.scientificamerican.com. We're also now bundling our daily 60-second science podcasts into weekly editions posted on YouTube, where you can enjoy them by subscribing to the Scientific American channel. Follow us on Twitter, where you'll get a tweet whenever a new item hits the website. Our Twitter name is @sciam. For Scientific American "Science Talk", I'm Steve Mirsky. Thanks for clicking on us.
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