Motorola touts geolocation for TV ‘white spaces’
Use of geolocation technology could help ensure that devices operating in TV “white spaces” spectrum do not interfere with broadcast signals, thereby potentially unlocking significant swaths of spectrum for wireless communications, according to Motorola.
TV “white spaces” is spectrum between the 6 MHz-wide channels used for by active TV broadcaster. The FCC has been testing devices that use sensing to determine whether spectrum is clear before transmitting a signal—a technology similar to one used for cognitive radio communications. While the first set of devices provided by Microsoft and Philips failed in lab tests, a second set of devices have done well enough in the laboratory that the FCC is beginning outdoor field testing of the devices.
While the FCC tests have focused only on sensing technology, many in the industry believe sensing is not enough to prevent interference, noting that there may be locations where the TV signal is so weak—for example, next to a building—that it cannot be detected, so the device might inadvertently send a signal that disrupts the TV broadcasts.
Motorola equipment is among the second group of devices being tested, said Stu Overby, Motorola’s senior director of global spectrum strategy. Although these devices have been tested for their sensing capability, Motorola also has demonstrated geolocation technology to the FCC that maps the location of the device and compares it to the location of TV stations in area. The device is instructed not to transmit signals on frequencies where TV broadcasters operate, addressing the problem sensing-only devices could have.
“For example, if there’s a TV station on Channel 46 and a low-power TV station on Channel 31, it won’t transmit on those channels,” Overby said. “Sensing can be good, but if you want full confidence in it, we think you need to use geolocation primarily and supplement it with the sensing.”
Geolocation should work well in the TV white spaces, because TV stations rarely change, Overby said. Likewise, geolocation can be used to protect LMR systems operating in the Channel 14-20 spectrum, because those systems must be licensed with the FCC, he said.
Exactly how much “white spaces” spectrum would be available depends on the location—densely populated areas typically have more TV stations operating than rural areas—and the rules the FCC establishes to ensure that wireless devices do not create adjacent-channel interference. Overby said Motorola believes at least 20-40 MHz of spectrum could be available in even the largest TV markets, but the commission must determine the proper balance in its rules governing the airwaves.
“If you have more protection than you need, you would be eliminating TV white space that could be used,” he said. “If you have less than you need, you’re going to run a higher risk of interference.”
Not surprisingly, TV broadcasters have expressed concern that wireless devices operating in the white-spaces could disrupt their signals, but Overby said he believes technology exists that would allow both uses to co-exist in the spectrum.
“The broadcasters obviously have expressed concern. What we’re saying is, ‘Hey, there’s a way to ensure there’s no interference,’” Overby said. “The technical approaches we’re talking about provide greater integrity and protection.
“Our goal here is to protect TV and to make TV white space useful. I think we can do both.”