Wireless tech means safer drones, smarter homes and password-free WiFi

We’ve all been there, impatiently twiddling our thumbs while trying to locate a WiFi signal. But what if, instead, the WiFi could locate us?

According to researchers at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL), it could mean safer drones, smarter homes, and password-free WiFi.

In a new paper, a research team led by Professor Dina Katabi present a system called Chronos that enables a single WiFi access point to locate users to within tens of centimeters, without any external sensors.

A new wireless technology developed by MIT researchers could mean safer drones, smarter homes, and password-free WiFi. The team developed a system that enables a single WiFi access point to locate users to within tens of centimeters, without any external sensors. They demonstrated the system in an apartment and a cafe, while also showing off a drone that maintains a safe distance from its user with a margin of error of about 4 centimeters.

Video: MIT Computer Science and Artificial Intelligence Laboratory

The group demonstrated Chronos in an apartment and a cafe, while also showing off a drone that maintains a safe distance from its user with a margin of error of about four centimeters.

“From developing drones that are safer for people to be around, to tracking where family members are in your house, Chronos could open up new avenues for using WiFi in robotics, home automation and more,” says PhD student Deepak Vasisht, who is first author on the paper alongside Katabi and former PhD student Swarun Kumar, who is now an assistant professor at Carnegie Mellon University. “Designing a system that enables one WiFi node to locate another is an important step for wireless technology.”

Experiments conducted in a two-bedroom apartment with four occupants show that Chronos can correctly identify which room a resident is in 94 percent of the time. For the cafe demo, the system was 97 percent accurate in distinguishing in-store customers from out-of-store intruders - meaning it could be used by small businesses to prevent non-customers from stealing their WiFi. (32 percent of Americans have copped to this cyber-crime.)

Chronos locates users by calculating the “time-of-flight” that it takes for data to travel from the user to an access point. The system is 20 times more accurate than existing systems, computing time-of-flight with an average error of 0.47 nanoseconds, or half than one-billionth of a second.

Vasisht presented the paper at this month’s USENIX Symposium on Networked Systems Design and Implementation (NSDI '16).

How it works
Existing localization methods have required four or five WiFi access points. This is because today’s WiFi devices don’t have wide enough bandwidth to measure time-of-flight, and so researchers have only been able to determine someone’s position by triangulating multiple angles relative to the person.

What Chronos adds is the ability to calculate not just the angle, but the actual distance from a user to an access point, as determined by multiplying the time-of-flight by the speed of light.

“Knowing both the distance and the angle allows you to compute the user’s position using just one access point,” says Vasisht. “This is encouraging news for the many small businesses and consumers that don’t have the luxury of owning several access points.”

Exploiting the fact that WiFi lets you hop on different frequency channels, the team programmed the system to jump from channel to channel, gathering many different measurements of the distance between access points and the user. Chronos then automatically “stitches” together these measurements to determine the distance.

“By devising a method to rapidly hop across these channels that span almost one gigahertz of bandwidth, Chronos can measure time-of-flight with sub-nanosecond accuracy, emulating with commercial WiFi what has previously needed an expensive ultra-wideband radio,” says Venkat Padmanabhan. a principal researcher at Microsoft Research India. “This is an impressive breakthrough and promises to be a key enabler for applications such as high-accuracy indoor localization.”

That said, getting an accurate time-of-flight with this method still isn’t easy, due to three sets of delays that happen during the transfer.

First, when you wirelessly send a piece of web data, there is a delay in detecting the presence of the “packet” that is hard to distinguish from the actual time-of-flight. To account for it, the team exploits the fact that WiFi uses an encoding method that transmits bits of packets on several even smaller frequencies.

Secondly, if you’re indoors the WiFi signals can bounce off walls and furniture, meaning that the receiver gets several copies of the signal that each experience different times-of-flight. To identify the actual direct path, researchers developed a mechanism to algorithmically determine the delays experienced by all of these copies. From there, they can identify the path with the smallest time-of-flight as the direct path.

Lastly, the team’s channel-hopping approach leads to one other complication: every time Chronos hops to a new band, the hardware resets, adding a delay known as a “phase offset.” To address this the team used the fact that in WiFi, you get an acknowledgement back for each data packet that your phone sends. The team uses these acknowledgements to intelligently cancel out the phase offsets.

The success of Chronos suggests that WiFi-based positioning could help for other situations where there are limited or inaccessible sensors, like finding lost devices or controlling large fleets of drones.

“Imagine having a system like this at home that can continuously adapt the heating and cooling depending on number of people in the home and where they are” says Katabi. “Eliminating the need for cooperation between WiFi routers opens up many exciting new applications for localization.”

Can technology help teach literacy in poor communities?

For the past four years, researchers at MIT, Tufts University, and Georgia State University have been conducting a study to determine whether tablet computers loaded with literacy applications could improve the reading preparedness of young children living in economically disadvantaged communities.

At the Association for Computing Machinery’s Learning at Scale conference this week, they presented the results of the first three deployments of their system. In all three cases, study participants’ performance on standardized tests of reading preparedness indicated that the tablet use was effective.

The trials examined a range of educational environments. One was set in a pair of rural Ethiopian villages with no schools and no written culture; one was set in a suburban South African school with a student-to-teacher ratio of 60 to 1; and one was set in a rural U.S. school with predominantly low-income students.

In the African deployments, students who used the tablets fared much better on the tests than those who didn’t, and in the U.S. deployment, the students’ scores improved dramatically after four months of using the tablets. "The whole premise of our project is to harness the best science and innovation to bring education to the world’s most underresourced children," says Cynthia Breazeal, an associate professor of media arts and sciences at MIT and first author on the new paper. "There’s a lot of innovation happening if you happen to be reasonably affluent — meaning you have regular access to an Internet-connected computer or mobile device, so you can get online and access Khan Academy. There’s a lot of innovation happening if you’re around eight years old and can type and move a mouse around. But there’s relatively little innovation happening with the early-childhood-learning age group, and there’s a ton of science saying that that’s where you get tremendous bang for your buck. You’ve got to intervene as early as possible."

Breazeal is joined on the paper by Maryanne Wolf and Stephanie Gottwald, who are, respectively, the director and assistant director of the Center for Reading and Language Research at Tufts; Tinsley Galyean, a research affiliate at the MIT Media Lab and executive director of Curious Learning, a nonprofit organization the researchers created to develop and deploy their system; and Robin Morris, a professor of psychology at Georgia State University.

Self-starting

The concentration on early literacy reflects Wolf’s theory, popularized in her book "Proust and the Squid," that the capacity to read, unlike the capacity to process spoken language, is not hard-coded into our genes. Consequently, early training is essential to establishing the neurological machinery on which the very capacity for literacy depends.

The researchers’ system consists of an inexpensive tablet computer using Google’s Android operating system. Wolf and Gottwald combed through the literacy and early-childhood apps available for Android devices to identify several hundred that met their quality criteria and addressed a broad enough range of skills to lay a foundation for early reading education. The researchers also developed their own interface for the tablets, which grants users access only to approved educational apps. Across the three deployments, the tablets were issued to children ranging in age from 4 to 11.

"When we do these deployments, we purposely don’t tell the kids how to use the tablets or instruct them about any of the content,dz Breazeal says. DzOur argument is, if you’re going to be able to scale this to reach 100 million kids, you can’t bring people in to coach kids what to do. You just make the tablets available, and they need to figure everything out from then on out. And what we find is, the kids do it. When we first did Ethiopia, we had all these protocols and subprotocols. What if it’s a week and they haven’t turned them on? What if it’s three weeks and they haven’t turned them on? Within minutes, the kids turn them on. By the end of the day, they’ve literally explored every app on the tablet."

Results

The Ethiopian trial, which the researchers conducted in collaboration with the One Laptop per Child program, involved children aged 4 to 11 who had no prior exposure to spoken English or any written language. After a year using the tablets, children were tested on their understanding of roughly 20 spoken English words, taken at random from apps loaded on the tablets. More than half of the students knew at least half the words, and all the students knew at least four.

When presented with strings of Roman letters in a random order, 90 percent could identify at least 10 of them, and all the children could supply the sounds corresponding to at least two of them. Perhaps most important, 35 percent of the children could recognize at least one English word by sight. These figures roughly accord with those of children entering kindergarten in the U.S.

In the South African trial, rising second graders who had been issued tablets the year before were able to sound out four times as many words as those who hadn’t, and in the U.S. trial, which involved only 4-year-olds and lasted only four months, half-day preschool students were able to supply the sounds corresponding to nearly six times as many letters as they had been before the trial.

Since the trials reported in the new paper, Curious Learning has launched new trials in Uganda, Bangladesh, India, and the U.S. In all, 2,000 children have had the opportunity to use the tablets.

Currently, the team is concentrating on analyzing data collected from the trials. Which apps do the children spend most time with? Which apps’ use correlates best with literacy outcomes? Curious Learning is also looking for partners to help launch larger pilot programs, with 5,000 to 10,000 children.

"There’s a core scientific question, which is understanding what the nature of this child-driven, curiosity-driven learning looks like," Breazeal says. "We need to understand how they learn, which is a fundamentally social process, where they explore the tablet together, they discover things through that exploration, and then they talk-talk-talk-talk, and they share those ideas. So it’s a profoundly social, peer-to-peer-based learning process. We have to have create a technology and an experience that supports that process."

Higher coal use in Asia could increase water stres

Coal burning, despite recent signs of having peaked in China and pledges made at the Paris Climate talks in December, remains the primary source of electric power in Asia. In both China and India, it’s responsible for the lion’s share of human-made sulfur dioxide (SO2) emissions, which drive up concentrations of sulfate aerosols in the atmosphere. These aerosols not only endanger public health in the region but also contribute to local and global climate change. 

Just how much climate change will depend on Asia’s energy choices in the years and decades to come. At one extreme, economic growth and energy demand in China, India, and other fast-growing Asian nations would lead to rapid increases in coal use, resulting in more significant climate impacts; at the other, Asia would gradually lessen these impacts by shifting from coal to cleaner burning fuels such as natural gas, and low-carbon energy technologies such as wind turbines and photovoltaics. Now a new study in the Journal of Climate assesses the climate’s likely response to aerosol emissions at both extremes, resulting in likely lower and upper bounds for the impact of Asian aerosols on regional surface temperature and rainfall.

According to the study, a high coal-use future — in which today’s emissions of sulfur dioxide and black carbon aerosols from Asia’s industry, energy, and domestic sectors are set to twice their year-2000 values from 2030 to 2100 — would entail significant local and global climate impacts.

The increased aerosol levels would have a large cooling effect throughout the Northern Hemisphere, partially offsetting warming from greenhouse gas emissions (including increased carbon dioxide emissions associated with coal burning, which the study did not model). Significant cooling would also be felt especially in South and East Asia.

“Much of these results are related to the impact of sulfates on clouds, which lowers surface temperatures indirectly by increasing the clouds’ reflectivity,” explains study co-author Chien Wang, a senior research scientist in the MIT Joint Program on the Science and Policy of Global Change and the MIT Department of Earth, Atmospheric and Planetary Sciences. These aerosols may also lower surface temperatures by reflecting sunlight skyward.

But as they help offset warming, the aerosols would also weaken several major monsoon systems, suppressing precipitation over vast land masses.

“For the high-emissions scenario, we found reductions in rainfall across much of Asia, especially East Asia (including China) and South Asia (including India), and a remote effect leading to a possible increase in rainfall in Australia as well as a suppression of rainfall in the Sahel region of Africa,” says Benjamin Grandey, a research scientist in Wang’s research group at the Singapore-MIT Alliance for Research and Technology. “We see more reductions in rainfall than increases, especially in regions already struggling with water resources.”

To assess climate impacts of the two scenarios, the researchers used a coupled atmosphere-ocean configuration of the Community Earth System Model (CESM) that uses the fifth version of the Community Atmosphere Model (CAM5). Unlike many previous studies, their modeling framework included a three-dimensional, dynamic representation of the oceans that enables more accurate projections of climate responses to aerosols.

The study was funded primarily by the National Research Foundation of Singapore through the Singapore–MIT Alliance for Research and Technology, with additional support from the U.S. National Science Foundation, Department of Energy, Environmental Protection Agency, and A*STAR Computational Resource Centre of Singapore.