Communications of the ACM

they are moving? Can you tell how many people there are? It turns out you can, because they are breathing… So what other physiological signals can you extract?

And these questions are extremely intellectually interesting, but it’s not just that; they have very practical and useful applications to people’s lives!

You’re now working, through a start-up called Emerald, to commercialize the technology and develop some of those applications—for instance, remotely monitoring people’s health.

We talk a lot about the smart home, but really the smartest thing a home can do is to take care of us and our health. Our vision is to have a technology that disappears into the environment; I don’t have to enter information about my heartrate, or put some device on myself and remember to charge it. I don’t need to change my behavior in any way, but still there is a home that’s watching over my health and keeping track of problems early on—or even before they occur—and alerting doctors or the hospital or a caregiver.

That sounds promising. Where are you
in your efforts?

At this early stage, our focus is to work with healthcare providers, on the one hand, and with the biotech and pharma industry, on the other. It turns out there are many deep physiological signals we can extract, so we need to connect with people who understand what those signals mean in the context of diseases. I can tell you that my mom is walking well or that she fell—that’s the extent of it. I couldn’t tell you if the patterns of information indicate we should change the dose on her Parkinson’s medication.

One of the most consistently cited fea-
tures of your work is creativity.

In general, in almost all the stuff I do, I’m driven by curiosity. I’m always interested in trying something where I don’t know the answer, or where I’m not sure whether the answer is “yes” or “no.”

Leah Hoffmann is a technology writer based in Piermont, NY, USA.

coding was defined in the context of something called multicast.

Multicast is a communications protocol in which you deliver the same information to a group of destinations simultaneously.

But in networking, typically, that’s not how it works. In networking, you typically have unicast, where one sender transmits to a single destination. Even when you are sending something like broadcast television over the Internet, your broadcast is actually using unicast. You have your server turning that traffic to all the individuals who are interested in it.

What Muriel and I did was try to take that really beautiful, elegant theory, and think about it in the context of real networks. I felt wireless networks, in particular, might be the right environment for this technology. Wireless is way more limited in terms of data rate and bandwidth than wired networks, and it’s also less reliable. So network coding is an ideal solution when you make an error in your transmission.

In your recent work, you’ve used wire-
less signals to track people’s mo-
tions—even through walls. How did
you get that idea?

When we began, it was really curiosity. Let’s say there is a room and you don’t have access to it. Can you tell if there are people in the room? If you can tell there are people, can you tell how many people? When we tried that, we didn’t really know whether or not it was possible, and we certainly didn’t know what kind of application you’d use it for. All we knew is that we have been able to track people using their cellphones—so, using a wireless signal, but a wireless signal that is emitted from a device. And we have some understanding of how wireless works in an indoor environment and propagates through walls and materials.

After your initial demonstrations were
successful, the questions got more
complex, and practical applications
began to present themselves.

Once we started working with it, we began to have all these ideas— why stop at just being able to see if people are moving? Can you tell how

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