US engineers test wireless data delivery over active TV channels

Engineers have devised a system that allows wireless data transmissions over ultra-high frequency channels while the TV is on.

Rice University researchers said the technology could be incorporated into next-generation TVs or smart remotes, expanding so-called super Wi-Fi networks in urban areas.

Lead researcher Edward Knightly said: “Due to the popularity of cable, satellite and Internet TV, the UHF spectrum is one of the most underutilised portions of the wireless spectrum in the US. That's a bitter irony because the demand for mobile data services is expected to grow tenfold in the next five years, and the UHF band is perfectly suited for wireless data.”

The UHF spectrum, which ranges from 400 to 700MHHz, is often called the ‘beachfront property’ of the wireless spectrum. Unlike the higher frequency signals used for existing Wi-Fi hotspots, UHF signals carry for miles and are not blocked by walls or trees. Because of these advantages, wireless data hotspots that use UHF are often referred to as super Wi-Fi.

In the US, TV broadcasters have been given preferential access to the UHF spectrum for more than 50 years. If no TV broadcaster has laid claim to a UHF channel, the Federal Communications Commission allows secondary users to transmit wireless data on that channel, provided that the transmissions do not interfere with TV broadcasts in any part of the UHF spectrum. The rules governing this secondary access are known as 'TV white space' rules.

“Unfortunately, in the most densely populated areas of the country, where the need for additional wireless data services is the greatest, the amount of available white space is extremely limited,” Knightly said. “In our most recent tests in Houston, one channel is open in parts of the city and none are available in others. This is fairly typical of a large US urban area.”

The researchers said that athough most of the UHF band is already taken in US cities, it is largely underutilised, with fewer than 10 per cent of households relying on over-the-air broadcasts for TV programming. To demonstrate that, wireless service providers could make use of the UHF spectrum without interfering with TV broadcasters. Knightly and Rice graduate student Xu Zhang developed a technology called Wi-Fi in Active TV Channels, or WATCH, and received FCC approval to test it.

This way TV signals were broadcast as normal and the WATCH system actively monitored whenever a nearby TV was tuned to a channel to avoid interfering with reception. One aspect of WATCH monitors TV broadcasts on a channel and uses sophisticated signal-cancelling techniques to insert wireless data transmissions into the same channel, “that eliminates TV broadcasts from interfering with the super Wi-Fi data signals being sent to computer users,” Knightly said.

The other aspect of WATCH ensures that certain data transmissions do not interfere with TV reception. “This part of the technology would require TVs to report when they are being tuned to a UHF channel,” Knightly said.

It could be accomplished with either smart TV remotes or next-generation TV sets, but in the tests Zhang designed a smart-remote app that reported whenever a test television in the lab was tuned to a UHF channel. When that happened, the WATCH system automatically shifted its data transmissions to another part of the UHF spectrum that wasn't being used.

“Our tests showed that WATCH could provide at least six times more wireless data compared with situations where we were limited only to the traditionally available white-space spectrum,” Knightly said.

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