08.27.2009 03:00 PM
TVB Tech Alert: Microsoft Bows WhiteFi
REDMOND, WASH.: Microsoft is testing a white-space system
similar in nature to WiFi. The company unveiled its plan recently at a trade
conference in Barcelona, Spain, in a white paper entitled, “White Space
Networking with WiFi-like Connectivity.” It won the best paper award at the
even, SIGCOMM 2009, according to the Harvard Sensor Networks Lab.
The “WhiteFi” concept resembles WiFi, but the application will be far more
complicated. Unlike a continuous WiFi network, white spaces are individual
bands of spectrum scattered throughout TV channels 21 (512 MHz) to 36, and 38
through 51 (698 MHz). White spaces, also referred to in broadcasting as “taboo
channels,” were established in analog broadcasting to prevent adjacent-channel
The buffer zone is considered unnecessary in digital broadcasting, so the
Federal Communications Commission handed white spaces over to Microsoft and a
group of other computer giants to populate with unlicensed devices. The term
refers to the fact that all other radio frequency use must be licensed by the
FCC. The white space ruling is the first time the commission has granted the
free use of spectrum.
Microsoft researchers describe the fundamental differences between WiFi and how a WhiteFi network would have to function.
“Networking over UHF white spaces is fundamentally different from conventional Wi-Fi along three axes: spatial variation, temporal variation, and fragmentation of the UHF spectrum,” the paper states. “Each of these
differences gives rise to new challenges for implementing a wireless network in
this band. We present the design and implementation of WhiteFi, the ﬁrst Wi-Fi
like system constructed on top of UHF white spaces.
“WhiteFi incorporates a new adaptive spectrum assignment algorithm to handle
spectrum variation and fragmentation, and proposes a low-overhead protocol to
handle temporal variation. WhiteFi builds on a simple technique, called SIFT,
that reduces the time to detect transmissions in variable channel width systems
by analyzing raw signals in the time domain. We provide an extensive system
evaluation in terms of a prototype implementation and detailed experimental and
“White Space Networking with WiFi-like Connectivity” is available on Microsoft’s