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10.07.2013
Originally featured on BroadcastEngineering.com
New technology makes identifying 'white space' spectrum easier
Researchers found that on average, 40 percent more TV spectrum is available indoors than outdoors. They've now figured out a way to efficiently use it.

WISER (White Space Indoor Spectrum Enhancer) is a new technology that improves indoor access to radio frequency spectrum that can improve reception performance of wireless technologies. WISER was developed by researchers at the Chinese University of Hong Kong (CUHK) and Microsoft Corp.

The researchers claim WISER can identify 30 percent to 50 percent more white space spectrum than alternative methods, most of which have been designed for outdoor use. The project focused on analyzing indoor white spaces, a phrase for vacant VHF and UHF TV channels. They used algorithms and software, coupled with RF sensors, to create a system to identify and track this indoor spectrum. Some of that spectrum is congested, while some frequencies are idle.

In most places, radio spectrum is allocated by strict licensing to different wireless applications in a way that is highly inefficient. However, a growing number of countries have begun to allow users to get access to certain spectrum frequencies on a license-exempt basis, which is similar to Wi-Fi.

“TV white spaces have the potential to provide a significant amount of additional spectrum that is needed for wireless applications,” Ranveer Chandra, senior researcher at Microsoft, told Advanced Television. “Although 70 percent of the demand for spectrum comes from the indoor environment and significantly more TV band spectrum is left unused indoors than outdoors, most trials and studies of white spaces done before have focused on outdoor scenarios.”

Minghua Chen, professor in the Department of Information Engineering at CUHK, told Advanced Television, “We identified and formulated the problem with Microsoft in 2010, and have been collaborating on solving the problem in urban locations since then. On average, we found 40 percent more TV spectrum to be available indoors, but there was no prior study showing how to use this additional spectrum. Our study addresses that gap.”

Currently, devices that use white space spectrum for wireless communications must first detect what frequencies are available for use in their current location by dynamic spectrum access (DSA) technologies. This method can be expensive and difficult to implement. It requires devices to address a geo-location database to determine available frequencies, but the results are very conservative.

Often, there is more spectrum available for actual use than indicated by the geo-location database, especially in metropolitan cities where the wireless environment is complex.

“The geo-location approach has been studied extensively. While it does work, it has severe limitations,” said Chen. “As an alternative, we have developed a new system, WISER, that uses sensing technology in a more efficient and cost-effective way than ever before.”

One key advance with WISER, reported Network World, is that a wireless client device doesn’t have to do the white space spectrum sensing itself. Chandra said it simply determines its location using any indoor location technique — via Wi-Fi or Bluetooth — 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.

WISER itself could be embedded in future Wi-Fi access points, “which would make it very simple to deploy,” Chandra added. 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.



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