Cognitive radios hold great promise for solving the bandwidth scarcity problem in wireless networks by opportunistically accessing unused portions of the TV spectrum. Although the policy makers are taking quick strides to legalize the use of these frequencies, there is limited technology to fully utilize the available spectrum. To bridge this gap, we have initiated a cross-group research project called KNOWS. The initial goal of our project is to enhance the state of the art by demonstrating a working cognitive radio prototype that looks for "white spaces" by sensing the TV spectrum; dynamically switches to an available white space, and operates in it without hurting incumbent TV receivers. In addition, we are also designing a new spectrum-aware access protocol that maximizes the total throughput of our system.

The KNOWS prototype consists of a scanner and a reconfigurable radio. The scanner periodically searches for open frequency bands (white spaces) in the TV spectrum. Neighboring KNOWS systems collaborate by exchanging local scanning results for detecting white spaces. When a open frequency band is located, the parameters of the reconfigurable radio (such as frequency, bandwidth, and power) are tuned in less than 50 microseconds and the system begins operating in that band. Access to the white space is controlled by bSMART, a distributed, spectrum-aware medium access control protocol. Each node running bSMART maintains a dynamic table to track the overall spectrum usage. It uses this table to decide the portion of spectrum it should operate in. Through theretical analysis and simulations we have shown that bSMART achieves near-optimal throughput.

The figure above illustrates our KNOWS architecture. In addition to the hardware, we are actively working on other layers of the networking stack to help them better utilize widely varying radio characteristics.

• A Hardware Platform for Utilizing the TV Bands with a Wi-Fi Radio
  Srihari Narlanka, Ranveer Chandra, Paramvir Bahl, John Ian Ferrell.
  To appear in Proceedings of IEEE LANMAN, Princeton, NJ (June 10-13, 2007)



• Allocating Dynamic Time-Spectrum Blocks in Cognitive Radio Networks
  Yuan Yuan, Paramvir Bahl, Ranveer Chandra, Thomas Moscibroda, Srihari Narlanka, Yunnan Wu.
  To appear in Proceedings of ACM MobiHoc, Montreal, Canada (September 9-14, 2007)



• KNOWS: Kognitiv Networking Over White Spaces
  Yuan Yuan, Paramvir Bahl, Ranveer Chandra, Philip A. Chou, John Ian Ferrell, Thomas Moscibroda, Srihari Narlanka, Yunnan Wu.
  Proceedings of IEEE DySPAN, Dublin, Ireland (April 17-20, 2007)



• Towards an Architecture for Efficient Spectrum Slicing
  Vladimir Brik, A. Mishra, Suman Banerjee, Paramvir Bahl
  HotMobile 2007, Tucson, Arizona, (February 2007) (pdf, 644 Kbytes)



• DSAP: A Protocol for Coordinated Spectrum Access
  Vladimir Brik, Eric Rozner, Suman Banerjee, Paramvir Bahl
  Proceedings of IEEE DySPAN 2005, Baltimore, MD (November 2005) (pdf, 146 Kbytes)



• On the Efficacy of Separating Control and Data into Different Frequency Bands
  Pradeep Kyasanur, Jitendra Padhye, Paramvir Bahl
  IEEE BroadNets 2005, Boston, MA (October 2005) (pdf)



• Wi-Fi Alliance White Paper On Spectrum Sharing and Co-existence - First Phase
  Paramvir Bahl, Pierre DeVries, Amer Hassan, J. Kruys (Cisco), and S. Mangold (Philips)
  Internal Wi-Fi Alliance Paper (will be available shortly)



• Microsoft's Proposal for Initiating Discussions on Spectrum Etiquette in the 5 Ghz Band
  Pierre DeVries and Paramvir Bahl
  (Real Time Video from Stanford Law School, 3/2/03, 42 mins. 58 secs)



• Draft Proposal for Comment: Etiquette Rules and Procedures for Unlicensed Bands"
  Paramvir Bahl, Amar Hassan, and Pierre DeVries
  Proposal to the Industry and the FCC to generate discussions and interest, Version 1.1, (January 27, 2003)

• Technology Review, Microsoft said prototype Internet device was broken when FCC tested and failed it, Associated Press, August 13, 2007
• Yahoo News, Microsoft to dispute FCC on vacant TV airwaves, Reuters, August 13, 2007
• Information Week, FCC And Vendors Are Developing Wireless 'White Space' Devices, by W. David Gardner, August 10, 2007
• Information Week, Microsoft Preps Cognitive Radio Prototype For Use With TV Spectrum by Thomas Clayburn, February 12, 2007
• Bloomberg News, Microsoft, Google want FCC to test wireless device by Molly Peterson, February 10, 2007
• Seattle PI, Microsoft: FCC filing doesn't signal a Zune phone, February 8, 2007
• MarketWatch, Microsoft to submit wireless device for FCC testing by John Letzing, February 8, 2007

• FCC Filing, August 13, 2007
• FCC Filing and Q/A, February 5, 2007

• The KNOWS project is a joint collaboration between the Networking Research Group, the Communications and Collaboration Systems Group, the Wireless Incubation Group, and Windows PC Ecosystem Technologies Group.