Katabi team making good use of scarce wireless space

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September 23, 2009

In a wireless network, different transmission frequencies work better for different users. That's because the same transmission reaches each user along several different paths; at one frequency, the signals arriving over different paths might reinforce each other, while at another frequency, they might cancel each other out.  Christine Daniloff

EECS Associate Professor and principal investigator in the Computer Science and Artificial Intelligence Laboratory, CSAIL Dina Katabi has been tackling the problem of wireless transmission and reception in increasingly crowded air waves. As reported by the MIT News Office, Sept. 22, Katabi and her team of graduate students are "teaching wireless technologies how to share what spectrum is left."

With the explosion of wireless devices that can interfere with each other for air wave space, the former practice of assigning segments of the electromagnetic spectrum for each new technology is not practical. Katabi and her team have suggested taking advantage of sharing the spectrum space made available when television switched from analog to digital--the so-called white space--by addressing two problems posed by spectrum sharing.

The first issue is to figure out which transmission channels in a given area are unoccupied at any given time and place. Counter to standard methods of judging usage--based on power in a certain frequency band--and therefore what frequency bands to avoid, Katabi has designed a method for tracking power over time to determine whether a particular choice of frequency is forcing other devices to slow down.

Today at the Mobicom mobile-computing and -networking conference in Beijing, Hariharan Rahul, a graduate student in Katabi's lab, is presenting the solution to the second problem in spectrum sharing: how to use the available channels efficiently. By analyzing how channel noise affects the bit patterns (pilots) created by orthogonal frequency division multiplexing (OFDM), a technique now used for most emerging wireless technologies, the system devised by Katabi and her lab is able to determine how well a given frequency will work for a given user and calculate the optimal transmission rate for each frequency.

Read more:

Katabi website: http://nms.csail.mit.edu/~dina/

MIT News "Sharing the air" Sept. 22, 2009