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Network World - Identifying and using vacant "white space" spectrum for Wi-Fi may get simpler, more efficient, and cheaper thanks to a new project by Microsoft and a team of Chinese researchers.
The project focused specifically on analyzing indoor white spaces, a name for vacant VHF and UHF TV channels. Then the researchers created algorithms and software, used with RF sensors, to create a system to identify and track this indoor spectrum. The system, called White-space Indoor Spectrum EnhanceR or WISER, is able to identify 30% to 50% more white space spectrum than alternative methods, most of which have been designed for outdoors.
A paper outlining the project and the prototype system is available in on online PDF file. The authors are Ranveer Chandra, with Microsoft Research, and five colleagues with the Chinese University of Hong Kong: Xuhang Ying, Jincheng Zhang, Lichao Yan, Guanglin Zhang, and Minghau Chen.
A cluster of RF sensors in a building sample the airwaves to identify and assess indoor white spaces. That data, along with the locations of wireless access points and of self-reporting clients, is stored in geo-location database. Some of the WISER algorithms deal with profiling the building, others with where to place the sensors, according to Chandra.
[FROM THE ARCHIVES: White spaces: Technology overview]
For the prototype sensors, the researchers used Universal Software Radio Peripheral (USRP) devices, which are computer-hosted software radios, but they could have been “any spectrum analyzer with a low noise floor -- there are a few available in the market,” Chandra says. In this case, the sensors ran simple software to talk via HTTP with the geo-location database.
One key advance with WISER is that a wireless client device doesn’t have to do the white space spectrum sensing itself. It simply determines its location using any indoor location technique, via Wi-Fi or Bluetooth for example, and then reports its position to the geo-location database. In response, the database returns the set of white space channels available at that location, and the client uses one of them to connect to the Internet, Chandra says.
WISER itself can be embedded in future Wi-Fi access points, “which would make it very simple to deploy,” Chandra says. Alternatively, a building owner could deploy small WISER sensors that could be plugged into wall outlets, scan the white space spectrum, and report their findings to the database over the interior electrical wiring by Powerline or via Wi-Fi.
Interest in white spaces has exploded since the 2008 FCC ruling that allowed unlicensed devices to use locally vacant TV channels. Regulators in other countries have followed suit. These devices, like Wi-Fi ones today in some 5-GHz channels, have to detect that the channel is vacant before taking it over. [See also “White spaces: Technology overview” from 2010.]
These unused channels, if they can be efficiently and accurately identified, promise a big boost in spectrum for Wi-Fi use. The biggest demand for that spectrum is indoors, according to Chandra. A six-month analysis of white space spectrum in Hong Kong locations found that there is about 40% more white space spectrum available indoors than outdoors.