Drones relay RFID signals for inventory control

Radio frequency ID tags were supposed to revolutionize supply chain management. The dirt-cheap, battery-free tags, which receive power wirelessly from scanners and then broadcast identifying numbers, enable warehouse managers to log inventory much more efficiently than they could by reading box numbers and recording them manually.

But the scale of modern retail operations makes even radio frequency ID (RFID) scanning inefficient. Walmart, for instance, reported that in 2013 it lost $3 billion in revenue because of mismatches between its inventory records and its stock. Even with RFID technology, it can take a single large retail store three months to perform a complete inventory review, which means that mismatches often go undiscovered until exposed by a customer request.

MIT researchers have now developed a system that enables small, safe, aerial drones to read RFID tags from tens of meters away while identifying the tags’ locations with an average error of about 19 centimeters. The researchers envision that the system could be used in large warehouses for both continuous monitoring, to prevent inventory mismatches, and location of individual items, so that employees can rapidly and reliably meet customer requests.

The central challenge in designing the system was that, with the current state of autonomous navigation, the only drones safe enough to fly within close range of humans are small, lightweight drones with plastic rotors, which wouldn’t cause injuries in the event of a collision. But those drones are too small to carry RFID readers with a range of more than a few centimeters.

The researchers met this challenge by using the drones to relay signals emitted by a standard RFID reader. This not only solves the safety problem but also means that drones could be deployed in conjunction with existing RFID inventory systems, without the need for new tags, readers, or reader software.

“Between 2003 and 2011, the U.S. Army lost track of $5.8 billion of supplies among its warehouses,” says Fadel Adib, the Sony Corporation Career Development Assistant Professor of Media Arts and Sciences, whose group at the MIT Media Lab developed the new system. “In 2016, the U.S. National Retail Federation reported that shrinkage — loss of items in retail stores — averaged around $45.2 billion annually. By enabling drones to find and localize items and equipment, this research will provide a fundamental technological advancement for solving these problems.”

The MIT researchers describe their system, dubbed RFly, in a paper they presented this week at the annual conference of the Association for Computing Machinery's Special Interest Group on Data Communications. Adib is the senior author on the paper, and he’s joined by Yunfei Ma, a postdoc in the Media Lab, and Nicholas Selby, an MIT graduate student in mechanical engineering.

Phase shift

Relaying RFID signals and using them to determine tags’ locations poses some thorny signal-processing problems. One is that, because the RFID tag is powered wirelessly by the reader, the reader and the tag transmit simultaneously at the same frequency. A relay system adds another pair of simultaneous transmissions: two between the relay and the tag and two between the relay and the reader. That’s four simultaneous transmissions at the same frequency, all interfering with each other.

This problem is compounded by the requirement that the system determine the location of the RFID tag. The location-detection — or “localization” — system uses a variation on a device called an antenna array. If several antennas are clustered together, a signal broadcast toward them at an angle will reach each antenna at a slightly different time. That means that the signals detected by the antennas will be slightly out of phase: The troughs and crests of their electromagnetic waves won’t coincide perfectly. From those phase differences, software can deduce the angle of transmission and thus the location of the transmitter.

The drone is too small to carry an array of antennas, but it is continuously moving, so readings it takes at different times are also taken at different locations, simulating the multiple antenna elements of an array.

Ordinarily, to combat interference, the drone would digitally decode the transmission it receives from the tag and re-encode it for transmission to the reader. But in this case, the delays imposed by the decoding-encoding process would change the signals’ relative phases, making it impossible to accurately gauge location.

All radio systems encode information by modulating a base transmission frequency, usually by shifting it slightly up and down. But because an RFID tag has no independent power source, its modulations are detectably smaller than those of the reader. So the MIT researchers devised an analog filter that would subtract the base transmission frequency from the signals that reach the reader and then separate the low-frequency and high-frequency components. The low-frequency component — the signal from the tag — is then added back onto the base frequency.

Frame of reference

At this point, however, another problem still remains. Because the drone is moving, the phase shift of the signals that reach the reader result from not only the drone’s position relative to the RFID tag but also its position relative to the reader. On the basis of the received signal alone, the reader has no way to tell how much each of those two factors contributed to the total phase shift.

So the MIT researchers also equip each of their drones with its own RFID tag. A drone alternates between relaying the reader’s signal to a tagged item and simply letting its own tag reflect the signal back, so that the reader can estimate the drone’s contribution to the total phase shift and remove it.

In experiments in the Media Lab that involved tagged objects, many of which were intentionally hidden to approximate the condition of merchandise heaped in piles on warehouse shelves, the system was able to localize the tags with 19-centimeter accuracy while extending the range of the reader tenfold in all directions, or one hundredfold cumulatively. The researchers are currently conducting a second set of experiments in the warehouse of a major Massachusetts retailer.

“Relays have been used in communications for a long time, even to bring networks to rural areas,” says Swarun Kumar, an assistant professor of electrical and computer engineering at Carnegie Mellon University. “What changes here is that one of the ends is battery-free, and they want to location-track the battery-free device, which requires need phase-consistent measurements. These together make the problem quite challenging. That’s what I think is the conceptual novelty in this work. I anticipate that there might be a lot more applications than the inventory tracking problem — which in and of itself is quite important.”

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How Much Do Software Engineers Really Earn?

If you’re a software engineer, chances are that at some point you considered Silicon Valley for your career. Even if you aren’t considering moving there, it’s a good bet that the Valley is still the first place that comes to mind when you wonder where the best software engineering jobs are. While it’s true that Silicon Valley and the Bay Area in general offer enticing salaries—an average of $110,554 USD per year, according to Glassdoor—many engineers may not ...

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Water war: East campus versus west

The idiom “wet behind the ears” may be a good way to describe new MIT students because, thanks to several MIT traditions, students spend their first few days on campus getting soaked.

Many people know about the swim test that first-year students take during orientation, but soon after students dry out, it’s time for another wet MIT tradition — the water war. The annual water war is an official part of Residential Exploration (REX) that began at MIT in the early 2000s. The war pits east campus against west in a battle on Killian Court that combines water balloons with student ingenuity.

The war is a carefully orchestrated event. With the help of the Dormitory Council, REX chairs help to coordinate the event each year. Henry Shackleton and Yanisa Techagumthorn, REX chairs from East Campus, explain that scheduling can actually the most challenging part of the war. “Finding a time for the water war can be hard; there’s a lot of events during REX. But once it’s on the schedule people start to prep,” says Techagumthorn. This prep includes filling balloons, designing catapults, building duck chariots, and creating a contraption known as Hurricane Fred — a long plastic dumpster turned water hose built by East Campus students.

While almost every dorm participates in the war, Shackleton and Techagumthorn say the biggest showing each year comes from East Campus, Next House, and Simmons. “But East Campus always wins,” Shackleton laughs. With serious equipment like water hoses, it’s no surprise that the war usually doesn’t last more than 10 minutes before being called — but it does include some great pageantry. “We usually give a dramatic speech to assemble to troops at the dorm,” Shackleton says. Once all dorms arrive at Killian Court, REX chairs from east and west campus meet in the middle of the court, shake hands, and announce a start to the war. Despite the intensity, the water war comes with some battlefield reunions. “You might see people you haven’t seen all summer. You say, ‘Hi,’ and throw a water balloon at them,” Techagumthorn says.

While the war is for current students, a small audience forms around it each year. David Bragdon ’62 caught the East Campus crew preparing for the war and was intrigued. “He saw what we were doing and followed us down to the war,” explains Techagumthorn. “I was embedded with the troops,” Bragdon says. This embed gave a him a front row seat at how the war ended earlier this year. “At the end, peace broke out with all of us chanting ‘MIT, MIT, MIT!’ It was very moving,” he says

While the water war is friendly combat, Techagumthorn says there are a few casualties each year — in the form of brass rats. “We get a ton of emails about people losing theirs,” she says. Despite the potential ring loss, the war has a big appeal to students new and returning. “I love the water war. It was the first time in my freshman year that I got a sense of some sort of community. It’s a great tradition that I’ve enjoyed,” Shackleton says.

This article first appeared on the Slice of MIT blog.

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Experiments confirm theory of “superballistic” electron flow

When many people try to squeeze through a passageway at the same time, it creates a bottleneck that slows everyone down. It turns out the reverse is true for electrons, which can move through small openings more quickly when travelling in large groups than when flying solo.

The theory of so-called superballistic flow predicts that electrons can pass more easily through constrictions by interacting with one another, and thereby “cooperating,” than they can individually. The theory was proposed in a paper earlier this year by a team led by MIT professor of physics Leonid Levitov.

Now, in a paper published this week in the journal Nature Physics, a team at the University of Manchester in the U.K., working alongside Levitov and MIT undergraduate Haoyu Guo, have confirmed the theory in an experiment employing devices built from an atomically thin layer of graphene.

The idea behind superballistic flow is that interactions among electrons make them move in a highly coordinated manner, mimicking the behavior of particles in highly viscous fluids.

When electrons traveling individually pass through a constricted opening, they will bounce off the walls at either side, losing their momentum as well as some of their energy.

But when the electrons travel in dense groups, they are much more likely to bounce off each other than the walls. Such electron-electron collisions are known as “lossless,” since the total energy and the net momentum of the two particles are conserved. The momentum of individual electrons can change rapidly in the process, however the overall momentum conservation ensures that the losses are very low. 

As a result, together the electrons are able to travel more quickly, and pass through the constriction more easily, than they would alone.

“Viscous flows of electrons have been anticipated in theory but never observed, partly because the materials were not good enough at the time, and partly because there were no good proposals of what to look for,” Levitov says.

To make viscous flow easier to identify, Levitov’s theoretical paper suggested forcing electrons to travel through a constriction, generating an electric current. This is a similar idea to the way in which 19th century researchers studied viscosity by passing fluids through a narrow channel.

“If you run current through a constriction, and the conditions are right and the flow is viscous … the resistance of that flow will be anomalously low, namely lower than that expected for free particle flow,” Levitov says.

This drop in resistance can be measured, revealing the presence of viscous flow.

Using the experimental set-up described theoretically in Levitov’s previous paper, the Manchester researchers, led by professor of physics and Nobel laureate Andre Geim, carefully etched a series of constrictions, or pinch points, within pieces of graphene encapsulated between boron-nitride crystals.

“The team etched the graphene sheets into a shape where they formed several constrictions, arranged in sequence, and they then applied a current such that it flowed through all of these constrictions one by one,” Levitov says.

The researchers then measured the drop in electric potential over each constriction independently, allowing them to detect the flow rate through each pinch point in the device.

They found that the conductance of the electrons exceeded the maximum conductance possible for free electrons, known as Landauer’s ballistic limit.

They also found that the conductance of the electrons increased with a rise in temperature.

In this way the researchers were able to verify Levitov and Guo’s original predictions within just a few days. Levitov says this is probably the fastest experimental confirmation of one of his predictions in his entire career, with the longest taking around 20 years to prove.

To confirm their findings, the researchers then repeated the experiment with a range of different graphene devices, and obtained the same results.

The work points toward the possibility of using interactions among electrons to design low-power electronics, Levitov says.

But more fundamentally, he says, it opens up new territory in our understanding of charge flow physics, in which electrons behave in a collective manner.

Electron-electron interactions have been responsible for a huge variety of novel and exciting physics, but the effects of these interactions typically become stronger as the temperature is reduced, says Amir Yacoby, a professor of physics at Harvard University, who was not involved in the research.

“The hydrodynamic electron flow regime is yet another incredibly rich manifestation of electron-electron interactions, and this time it grows with increasing temperature,” Yacoby says.

This suggests that some of these effects might become more accessible to observation than ever before.

“The particular phenomena described in the theory and experiment are a beautiful example of a new regime of conductance that has not been explored before,” he says.

Levitov and his team are now investigating the implications of these findings. In particular they plan to study heat transport within the new fluid mechanics regime.

“It looks like heat transport in this new regime is also very surprising, and more interesting than we initially thought,” he says. “This fluid mechanics regime could possibly be used to control heat flow in electronic systems in new ways.”

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For the love of ice: Journeys to the remote and inhospitable

Ice has always been fascinating to Alison Criscitiello PhD '14.

“I had a science teacher who did a short unit on glaciers … I couldn’t believe they were real,” she says. That classroom encounter when she was in eight grade in Winchester, Massachusetts, had a lasting impact.

Criscitiello went on to earn MIT’s first PhD in glaciology, and now she is an adjunct assistant professor of glaciology at the University of Calgary in Canada. She studies the history of sea ice and polar marine environments, primarily by drilling ice cores on land-based ice sheets and ice caps in both the Arctic and Antarctic. In March, Criscitiello became the technical director of the newly-created Canadian Ice Core Archive at the University of Alberta, where scientists will have access to 1.7 kilometers of core samples.

“The very northernmost reaches of the Canadian High Arctic are incredibly understudied and under­sampled,” says Criscitiello. To reach remote sites, she often must take several small prop plane flights and then ski in to the destination. On trips to such places as West Antarctica and Greenland, she has had to camp on ice sheets; in Greenland, she’s even slept with a shotgun in case of polar bear attacks.

In a 2014 Lady Paragons Women in STEM podcast, Criscitiello said she does not mind the hardships: “For me, there is really nothing else in the world that compares to that feeling of being somewhere incredibly remote and frozen, even if it’s inhospitable.”

Her 40-day winter ski traverse with Rebecca ­Haspel and Kate Harris SM ’10 through the Pamir Mountains of Central Asia in 2015 is the subject of the new documentary "Borderski." In it, the women travel along Tajikistan’s border with Kyrgyzstan, China, and Afghanistan to bring attention to conservation of the area’s migratory wildlife. The three reunited this winter to bike a 1,450-kilometer ice road that connects remote communities in northern Canada.

Criscitiello has also led the first all-women’s summit of Pinnacle Peak in the Indian Himalayas. Recent expeditions have included summiting Mount Logan, Canada’s highest peak, and the first all-female ascents of mixed routes off Alaska’s Pika Glacier.

In 2016, Criscitiello cofounded Girls on Ice Canada, a nonprofit wilderness and science education program that gives First Nations girls free opportunities to experience scientific mountain expeditions. In her free time, she blows glass and plays the mandolin.

Why the mandolin? “It’s very portable,” she says, “and I can take it on trips.”

This article originally appeared in the July/August 2017 issue of MIT Technology Review magazine.

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Monitoring network traffic more efficiently

In today’s data networks, traffic analysis — determining which links are getting congested and why — is usually done by computers at the network’s edge, which try to infer the state of the network from the times at which different data packets reach their destinations.

If the routers inside the network could instead report on their own circumstances, network analysis would be much more precise and efficient, enabling network operators to more rapidly address problems. To that end, router manufacturers have begun equipping their routers with counters that can report on the number of data packets a router has processed in a given time interval.

But raw number counts are only so useful, and giving routers a special-purpose monitoring circuit for every new measurement an operator might want to make isn’t practical. The alternative is for routers to ship data packets to outside servers for more complex analysis, but that technique doesn’t scale well. A data center with 100,000 servers, for instance, might need another 40,000 to 50,000 servers just to keep up with the flood of router data.

Researchers at MIT, Cisco Systems, and Barefoot Networks have come up with a new approach to network monitoring that provides great flexibility in data collection while keeping both the circuit complexity of the router and the number of external analytic servers low. They describe the work in a paper they’re presenting this week at the annual conference of the Association for Computing Machinery’s Special Interest Group on Data Communication.

Dubbed Marple, the system consists of a programming language that enables network operators to specify a wide range of network-monitoring tasks and a small set of simple circuit elements that can execute any task specified in the language. Simulations using actual data center traffic statistics suggest that, in the data center setting, Marple should require only one traffic analysis server for every 40 or 50 application servers.

Future-proofing

“There’s this big movement toward making routers programmable and making the hardware itself programmable,” says Mohammad Alizadeh, the TIBCO Career Development Assistant Professor of Electrical Engineering and Computer Science at MIT and a senior author on the paper. “So we were really motivated to think about what this would mean for network-performance monitoring and measurement. What would I want to be able to program into the router to make the task of the network operator easier?

“We realized that it’s going to be very difficult to try to figure this out by picking out some measurement primitives or algorithms that we know of and saying, here’s a module that will allow you to do this, here’s a module that will allow you to do that. It would be difficult to get something that’s future-proof and general using that approach.”

Instead, Alizadeh and his collaborators co-designed the Marple language and the circuitry required to implement Marple queries, with one eye on the expressive flexibility of the language and another on the complexity of the circuits required to realize that flexibility. The team included first author Srinivas Narayana, a postdoc at MIT’s Computer Science and Artificial Intelligence Laboratory; Anirudh Sivaraman, Vikram Nathan, and Prateesh Goyal, all MIT graduate students in electrical engineering and computer science; Venkat Arun, an undergraduate at the Indian Institute of Technology Guwahati who visited MIT for a summer; Vimalkumar Jeyakumar of Cisco Tetration Analytics; and Changhoon Kim of Barefoot Networks.

The idea behind Marple is to do as much analysis on the router itself as possible without causing network delays, and then to send the external server summary statistics rather than raw packet data, incurring huge savings in both bandwidth and processing time.

Marple is designed to individually monitor the transmissions of every computer sending data through a router, a number that can easily top 1 million. The problem is that a typical router has enough memory to store statistics on only 64,000 connections or so.

One-way cache

Marple solves this problem through a variation on the common computer science technique of caching, in which frequently used data is stored close to a processing unit for efficient access. Each router has a cache in which it maintains statistics on the data packets it’s seen from some fixed number of senders — say, 64,000. If its cache is full, and it receives a packet from yet another sender — the 64,001st — it simply kicks out the data associated with one of the previous 64,000 senders, shipping it off to a support server for storage. If it later receives another packet from the sender it booted, it starts a new cache entry for that sender.

This approach works only if newly booted data can be merged with the data already stored on the server. In the case of packet counting, this is simple enough. If the server records that a given router saw 1,000 packets from sender A, and if the router has seen another 100 packets from sender A since it last emptied A’s cache, then at the next update the server simply adds the new 100 packets to the 1,000 it’s already recorded.

But the merge process is not so straightforward if the statistic of interest is a weighted average of the number of packets processed per minute or the rate at which packets have been dropped by the network. The researchers’ paper, however, includes a theoretical analysis showing that merging is always possible for statistics that are “linear in state.”

“Linear” means that any update to the statistic involves multiplying its current value by one number and then adding another number to that product. The “in state” part means that the multiplier and the addend can be the results of mathematical operations performed on some number of previous packet measurements.

“We found that for operations where it wasn’t immediately clear how they’d be written in this form, there was always a way to rewrite them into this form,” Narayana says. “So it turns out to be a fairly useful class of operations, practically.”

"While much work has been done on low-level programmable primitives for measuring performance, these features are impotent without an easier network programming environment so that operators can ask network-level queries without writing low-level queries on multiple routers,” says George Varghese, Chancellor's Professor of Computer Science at the University of California at Los Angeles. “This paper represents an important step toward a programming-language approach to networks, starting with a network programming abstraction. This is in stark contrast to the state of the art today, which is individual router programming, which is fault prone and gives little visibility into the network as a whole. Further, the network programming language is intuitive, using familiar functional-language primitives, reducing the learning curve for operators."

The new work was supported by the National Science Foundation, the U.S. Defense Advanced Projects Agency, and Cisco Systems.

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Saving Venice, MIT-style

This summer, MIT professors Paola Malanotte Rizzoli of the Department of Earth, Atmospheric and Planetary Sciences (EAPS) and Andrew Whittle of the Department of Civil and Environmental Engineering (CEE) led an intensive workshop with several Italian faculty exploring key challenges facing Venice. Ten MIT students and seven students from the University of Venice (IUAV) joined their engineering and urban planning expertise during the first two weeks at a research camp in Pellestrina, a small island in the Venetian Lagoon. Donning fluorescent orange vests and hard hats, the bilingual group worked in a pop-up classroom on a live construction site for the massive flood gates built to protect Venice from high waters.

Through a combination of lectures, interviews with local residents, and on-site visits to observe the city's Experimental Electromechanical Module (MOSE) floodgates in action, MIT and IUAV students set to work developing solutions to pressing engineering and climate change challenges.

Rizzoli explained the dynamics of rising sea levels, storm surges, and wind waves in the Venetian Lagoon under various climate change circumstances. IUAV Professor Laura Fregolent discussed depopulation, another major threat to Venice. Looking at solutions, Whittle compared the novel technology of the MOSE gates with about 15 major storm surge barriers worldwide. MIT students speculated about the risk of flooding back home, and what could be learned from the MOSE project as Boston considers building a four-mile barrier restricting the flow of water into the city.

Outside of the classroom, camp participants were treated to what Whittle describes as “an engineer’s delight” — the opportunity to observe the precise positioning of a 95-foot-long steel gate through four underwater cameras. Rising MIT junior Malik Coville enthusiastically concurred. “As a mechanical engineer, typically we tend to mess with smaller technologies in class,” he explains. “This is the first time I was introduced to something much larger.”

After the first week, MIT and IUAV students bridged divides across cultures and disciplines through field work, data collection, and big-picture ideas. One group performed statistical and spatial analysis of flood risk in the Venetian Lagoon and analyzed historical data to create projections for the years 2050 and 2100. Another group formed a think-tank to develop repopulation strategies, formulating plans to refurbish urban workspaces with 21st century technology and self-sustaining energy systems. They also created strategies to involve local students in community development by collaborating with Italian universities. A third group conducted extensive mapping and interviews to explore the impact and the perception of the MOSE project among Pellestrina’s inhabitants.

Paige Midstokke, MIT grad student in civil engineering and technology and policy, worked on mapping and data analysis, and appreciated her group’s multicultural, multidisciplinary composition. “It’s a really interesting group, a mix of Italian and U.S. university students with different styles of working and different perspectives on this place,” Midstokke said.

Of the 10 MIT students who participated in the research camp, eight stayed for an additional two-month period to continue their research. Hosted by IUAV and Consorzio Venezia Nuova, they continued to work on meteorological statistical models, urban issues, and prototyping an electrical system to control the MOSE floodgates. Thanks to their extensive contacts with Italian experts and locals, the MIT students came to view Venice not only as a unique research lab, but also as a deeply-rooted way of life. They embraced the urgency of the problems and the applied character of their research. “For one, it’s the most hands-on thing that we’ve ever dealt with,” Coville said. “We’re applying what we’re learning to actually save a city.”

Rizzoli, in agreement with Whittle, the Italian partners, and MIT-Italy Program Co-Director Serenella Sferza, praises the initiative as “successful beyond expectations.” She is working with EAPS, CEE, and all others involved to replicate the workshop next summer. “This is an exemplary prototype of how a global classroom should work,” Rizzoli says.

The students who participated in this year’s pilot experience will present their research, made possible by support from IROP, other academic grants, and MIT International Science and Technology Initiatives (MISTI), on Sept. 8 from 11 a.m. to 12:30 p.m. in Room 54-915 within the Department of Earth, Atmospheric and Planetary Sciences.

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