Wireless Interference and Wireless Traffic

Cognitive coexistence radio and other technologies will help alleviate spectrum congestion for wireless devices writes Eric Bender of the MIT Industrial Liaison Program. Eric states that smartphone’s communications reduces when the device competes with other mobile traffic to send and receive data, and that competition will only intensify in the near future. It is estimated that more than a billion smartphones are expected to be shipped this year. Plus additional wireless traffic will come in from tablets, and more will come from “Internet of Things” devices, car-to-car communications, and other sources.

“Everything in high-speed networks is about how you deal with interference,” notes Dina Katabi, professor of electrical engineering and computer science and head of the MIT Center for Wireless Networks and Mobile Computing.

wireless-interference_0However, Wireless spectrum is scarce and expensive. In dealing with this scarcity, wireless providers have extended the reach of their networks within existing frequencies by various means. For instance, the U.S. Federal Communications Commission has raised $60 billion since 1994 by auctioning off cellular spectrum.

“As you put more small cells out there, you are also putting out a lot of little interfering signals, and today’s devices can’t handle all that noise adding up and getting in the way of the signals they want to hear,” says Rachel Learned, a researcher at MIT’s Lincoln Laboratory. “We want to get past that.”

According to Eric “One strategy that has gained popularity in the last decade is to add small cell base stations, also known as femtocells or picocells, in places with high traffic density such as inside buildings or in densely populated urban neighborhoods. These lower-powered versions of wireless macro cell towers can fill gaps in coverage in these high-density locations, using the same frequency bands and hooked to the cellular network via landline. Business customers now are also installing small cell base stations at a rapidly accelerating pace, and this arrangement is backed by operators ranging from AT&T to Korea’s SK Telecom. Informa Telecoms and Media estimates that the market for small cell base systems will reach $22 billion by 2016.”

This blizzard of base stations, however, can interfere with operation of towers and with each other, boosting the numbers of degraded connections and calls that are dropped or never connected.
In solving base station spectrum scarcity, a Cognitive coexisting radio (CCR) technology developed by Learned and her colleagues helps to overcome interference problems by intelligently exploiting the spectrum already in use for other transmissions, dramatically boosting connections while living comfortably side by side with those existing transmissions. Moreover, the CCR approach can be added to existing off-the-shelf wireless components, and it doesn’t require changes to existing wireless infrastructure, active management by the small base station operator, or collaboration with other users of the spectrum.

“The CCR system monitors the power and the rates of the other transmitters to understand their use of the spectrum,” she explains. “It predicts when its presence is likely to cause little harm, then makes use of the channels occupied by likely oblivious links, all while watching to see if the existing link adapts too much. If the other users react too much, it can play nice, by going away or reducing its power. If they react just a little, the system will conclude that it’s okay to coexist with these links.”

“The system also has a learning capability that can improve the prediction over time and reducing the chance of causing problems,” Learned says. “So it has a pretty good chance of not hurting any of the existing macro or small cells, all the while providing additional high-throughput small cell links without needing more spectrum.”

“Basically it’s like when you walk down a sidewalk and someone’s in front of you,” she adds. “You do that little dance for a second and then you figure it out and pass each other. You don’t have to talk to each other but you do have a little impact on each other. After a few encounters, you even learn the customary side to favor, and may have to do the dance less often as you travel the sidewalk. So that’s what your phone does with CCR — it does the sidewalk dance with other phones.”

Other MIT efforts to optimize the use of wireless spectrum include a cognitive radio technology that weaves together available frequencies and technologies that aim to improve network performance via smart antennas.

Katabi’s group developed SWIFT (Split Wideband Interferer Friendly Technology), a “cognitive aggregation” radio technology designed to let high-throughput network nodes efficiently coexist with unknown low-throughput devices. “SWIFT can detect the bandwidth of use by others in the spectrum, and it can weave the bandwidth available together so that it can get a very wide spectrum,” she says. “If there are holes in the spectrum that are used by other people, it doesn’t interfere with them and it still gets very high data rates.”

Other MIT programs look at methods to achieve five to 10 times higher data rates under certain conditions using smart antenna technology, in ways that could aid small cell base stations as well as other wireless systems, Katabi says.

“Everyone wants to use the cellular network,” says Afarin Bellisario, MIT technology licensing officer. “People are mobile and increasingly urban, the Internet of Things is arriving to create smart cities and smart highways, and it all consumes bandwidth. With people increasingly living, working, or taking trains in very close proximity, we need an enabling and robust wireless infrastructure.”


MIT News