文档介绍：White working with Wi-Fi like Connectivity Paramvir Bahl*, Ranveer Chandra*, Thomas Moscibroda*, Rohan Murty**, Matt Welsh** *Microsoft Research, Redmond, WA **Harvard University, Cambridge, MA In proceedings of M 2009
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TV Transition from Analog to Digital
TV transition from analog to digital
The switch to all-digital broadcasting freed up parts of the broadcast spectrum for public munications
city council workers, utility workers, fire department, police, etc.
Digital TV allows transmitting a High-Definition (HD) program, or multiple Standard Definition (SD) programs simultaneously; multicasting
Some of the spectrum can be leased panies to provide wireless broadband
More can be found on:
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White working
The unused portions of the UHF spectrum are called “White Spaces”
Earlier research focused on detecting the presence of RF signals
More recently, the focus is on establishing a wireless link between white space devices
This paper researches how to build Wi-Fi-work (multiple links) in white spaces
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Wi-Fi (ISM)
Broadcast TV
3 kHz
300 kHz
3 MHz
30 MHz
300 MHz
3 GHz
30 GHz
300 kHz
3 MHz
30 MHz
300 MHz
3 GHz
30 GHz
300 GHz
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Measurements
dbm
Frequency
-60
-100
“White spaces”
470 MHz
700 MHz
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The Challenges
FCC ruling on Nov 4, 2008 allowed using unlicensed devices in white spaces
Condition: non-interference with primary users
The aim is to set up one wi-fi like AP with multiple connected stations
Spatial variation
Primary users change from a location to another
Spectrum fragmentation
Primary users can operate on parts of the white space
Temporal variation
A microphone of primary users has on/off traffic
The research in this paper shows that one packet transmitted has an audible effect!
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Spatial Variation
The usage of white spaces changes with the location
In large-scale
TV broadcasting
In small-scale
Wireless mircophone (used in classrooms, sporting events, concerts)
TV Stations in America
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Spectrum Fragmen