Over 70% of TV spectrum left unused indoors

Researchers at The Chinese University of Hong Kong (CUHK) and Microsoft have successfully developed a new system, WISER (White-space Indoor Spectrum EnhanceR), that improves indoor access to radio frequency spectrum which can enhance the performance of wireless technologies.

In most places, radio spectrum is allocated by strict licensing to different wireless applications in a way that is highly inefficient. Some spectrum frequencies are highly congested while some are idle. A growing number of countries have thus begun to allow users to get access to certain spectrum frequencies on a licence-exempt basis, which is similar to Wi-Fi. Given the rapid growth of worldwide demand for radio spectrum in wireless communication, TV white spaces, the unused portions of TV spectrum, offer the first and promising opportunity to provide additional spectrum for users.

“TV white spaces have the potential to provide a significant amount of additional spectrum that is needed for wireless applications,” said Ranveer Chandra, senior researcher at Microsoft. “Although 70 per cent of the demand for spectrum comes from 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.”

“We identified and formulated the problem with Microsoft in 2010, and have been collaborating on solving the problem in urban locations since then,” said Professor Minghua Chen, Department of Information Engineering, CUHK. “On average we found 40 per cent 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.”

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 which can be expensive and difficult to implement. Most regulations allowing DSA requires devices to query a geo-location database to determine available frequencies, but the results are very conservative. There is often more spectrum available for use than indicated by the geo-location database, especially in metropolitan cities such as Hong Kong where the wireless environment is complex.

“The geo-location approach has been studied extensively. While it does work, it has severe limitations,” said Professor Minghua 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.”

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