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Week of April 15, 2013

Research


New software reduces interference of Wi-Fi, Bluetooth, ZigBee

The explosive popularity of wireless devices — from Wi-Fi laptops to Bluetooth headsets to ZigBee sensor nodes — is increasingly clogging the airwaves, resulting in dropped calls, wasted bandwidth and botched connections. New software being developed at U-M works like a stoplight to control the traffic and dramatically reduce interference.

The software, GapSense, lets these devices that can’t normally talk to one another exchange simple stop and warning messages so their communications collide less often.

GapSense creates a common language of energy pulses and gaps. The length of the gaps conveys the stop or warning message. Devices could send them at the start of a communication, or in between information packets to let other gadgets in the vicinity know about their plans.

“All these devices are supposed to perform their designated functions but they’re using the same highway and fighting for space,” said Kang Shin, the Kevin and Nancy O’Connor Professor of Computer Science.

“Since they don’t have a direct means of communicating with each other because they use different protocols, we thought, ‘How can we coordinate them so that each can perform their functions while minimizing interference with the others?’”

The researchers tested GapSense and found that it could reduce interference by more than 88 percent on some networks with diverse devices. Shin and Xinyu Zhang, a former doctoral student in electrical engineering and computer science, will present the work Thursday at the IEEE International Conference on Computer Communications in Turin, Italy.

To get a sense of how many wireless devices exist today, CTIA, the Wireless Association in 2013 counted more than 321 million Wi-Fi-enabled cell phones, laptops and tablets in the United States. That’s more than one device per person, and it’s just the items that use Wi-Fi, the protocol that transmits big chunks of data over relatively long distances.

Bluetooth and ZigBee use the same wireless spectrum as Wi-Fi, but they all speak different languages. Bluetooth, shorter range and less powerful, can connect headsets and keyboards to phones and computers, for example. ZigBee, the lowest powered of the group, links networks of small radios to automate home and building systems such as lighting, security alarms and thermostats. It’s also found in hospitals, where it gathers medical data from patients.

All these devices are already equipped with the standard “carrier sense multiple access,” or CSMA, protocol that programs them to listen for radio silence before they send their own transmissions. But often it doesn’t work.

ZigBee takes 16 times longer than Wi-Fi to gear up from its idle state to transmit information, so sometimes it might sound to Wi-Fi that the coast is clear when a ZigBee packet is on its way out.

“The little guy might be talking, but big guy cannot hear it,” Shin said. “So the little guy’s communication will be destroyed.”

That’s just one of several potential problems GapSense can help remedy. The researchers tested the software in a simulated office environment. With moderate Wi-Fi traffic, they detected a 45 percent collision rate between ZigBee and Wi-Fi, and GapSense reduced that to 8 percent.

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STAFF SPOTLIGHT

Karen Simpson, student financial assistant, Student Financial Services, on the increase in technology in her 35 years at U-M: “When I first came here we were typing student checks on typewriters. Now, everything is very modernized, very streamlined.”

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“Crazy for You,” 7:30 p.m. April 18, 8 p.m. April 19-20 and 2 p.m. April 21, Power Center for the Performing Arts.

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