White Spaces Remain Murky

Unlicensed-device tests yield conflicting interpretations from broadcasters, technology firms.
Author:
Publish date:

Recent tests by the Federal Communications Commission of prototype wireless radios that would use unoccupied parts of the broadcast spectrum -- the so-called white spaces -- and that wouldn’t require an FCC license to operate on broadcast channels seem to have meant very different things to those who are opposing their use and companies backing the new technology.

The idea of using unlicensed devices to transmit data in the white spaces is being backed by technology giants such as Microsoft, Google and Motorola. But broadcasters have been lobbying aggressively against the proposed devices on the grounds that they will cause unacceptable interference to existing operations -- both to the reception of digital-TV broadcasts by consumer receivers and to the operation of wireless microphones that are routinely used for sports and news coverage.

Sports leagues have weighed in on the issue, saying that interference from devices operating in the white spaces could knock out microphones used for live-event coverage and also disrupt headsets used by coaches and game officials. Broadway-theater owners have also expressed concern because of their heavy use of wireless mics in onstage productions.

To address those issues, the FCC’s Office of Engineering and Technology has been testing the devices in the laboratory and recently organized field tests including: a sports-production test during the Washington Redskins-Buffalo Bills preseason National Football League game outside of Washington, D.C., Aug.9, and a theater-production test during the Aug. 12 performance of musical Phantom of the Opera at the Majestic Theater in New York. The prototype devices tested were developed by Philips and Singapore’s Institute for Infocomm Research (I2R).

The tests were designed to gauge the performance of spectrum analyzers in the prototype devices, which are supposed to be sensitive enough to identify the operation of both existing UHF broadcast channels and wireless mics and, thus, not transmit in channels where they would cause interference to existing signals.

The tests had the device first do a sweep for UHF broadcast channels, then check for wireless mics with none turned on in the area, then repeat the sweep with multiple mics fired up.

The FCC has yet to formally disclose the results, which it is expected to analyze in order to determine the future viability of unlicensed devices. But both sides of the white-spaces issue were left claiming victory after the tests.

According to Mark Brunner, a spokesman for wireless microphone manufacturer Shure, who attended both events, the field tests didn’t show the prototype devices to be very accurate in sensing the operation of wireless mics in a live environment.

“They had problems in opposite directions,” Brunner said. “The Philips device indicated that the channels were already occupied prior to the mics being turned on. So there was not much new information -- turning on the mics essentially made no change in the display. On the other hand, the I2R device’s initial sweep indicated that the channels were open. Then when the mics were turned on, it would not detect them. In almost all test locations, both devices showed no change between the mics being on or off.”

Broadcast-spectrum watchdog group the Association for Maximum Service Television (MSTV) sent engineers to observe the field tests, and president David Donovan said they only confirmed MSTV’s original contention: that the unlicensed devices can’t adequately sense interference and, thus, aren’t ready for commercial deployment.

“The devices failed to sense and detect the presence of wireless microphones, and that is what the test is about,” Donovan said. “If you take a step back and look at this, these devices have fairly poor batting averages.”

Tom Ferrugia, director of government relations for the Broadway League, was at the Majestic Theater for the test during Phantom and was also unimpressed with the prototypes' performance in sensing wireless mics.

“These devices are not anywhere close to where they need to be in order to work in our environment,” Ferrugia said, nonetheless adding that he was happy that the FCC responded to theaters’ concerns and made the trip to New York for the test.

But Ed Thomas, a former FCC chief engineer who is now a policy adviser to the White Spaces Coalition (which counts Google, Microsoft, Dell and others as members), said the tests were successful and the prototype unlicensed devices performed exactly as expected.

“I think they went very well,” Thomas said. “The bottom line on this thing is that there was nothing unexpected from our perspective. The Philips device reached a decision in every case that wouldn’t interfere with wireless mics, and in no case did it say a channel was vacant when a device was on it.”

Thomas also said the Philips device successful identified at least one vacant channel when the mics were turned off. He explained that the high sensitivity of the Philips unlicensed device, which the FCC confirmed in lab tests, means that it is overpowered by existing DTV and analog signals, adding that if the FCC were to come up with rules that required less sensitivity, then the Philips device would do a better job of sensing wireless mics and would be able to identify more vacant channels.

Putting out devices with less sensitive spectrum analyzers, either with or without the approval of the FCC, is precisely what Donovan and Brunner are worried about. They are afraid that the current tests will indicate that the Philips device doesn’t cause interference to incumbent broadcasters, and the FCC will allow such devices into the UHF band. Then, manufacturers will start turning out devices with less sensitive spectrum analyzers that might work for white-spaces users but will interfere with DTV reception and wireless mics.

“If that thing indicates that there is no available spectrum, that would certainly protect the incumbents,” Brunner said. “But how useful will that be as a commercial device? There’s only one direction it can move in that [area], and that is to alter it in a way that it senses spectrum is available. And that’s where we expect big problems.”

Motorola is a proponent of unlicensed devices, but it was not involved in the field tests last week. The company thinks it has a solution to the interference issue by transmitting a “beacon” that unlicensed devices would detect that could be referenced against a “geolocation database” of existing spectrum users.

Steve Sharkey, senior director of regulatory and spectrum policy for Motorola, said the company will demonstrate its beacon technology to the FCC this week and will leave the commission a beacon device for further testing.

“I think it’s a fairly straightforward technology to implement,” he added.

The FCC is under pressure from Congress to rule on the white-spaces issue soon. Last Tuesday, eight members of the House of Representatives, including Energy and Commerce Committee members Jay Inslee (D-Wash.) and Marsha Blackburn (R-Tenn.), sent a letter to FCC chairman Kevin Martin extolling the potential of the white spaces for broadband access and urging the FCC to speed up the process.

“We encourage the FCC to conduct thorough testing of TVWS [TV white spaces] prototypes on as expedited a schedule as possible,” the House members wrote in the letter. “We look forward to FCC decisions within the next 90 days to promulgate rules to open the white-space spectrum and provide adequate protection to existing users.”

Related

NRB Warns FCC on White Spaces

National Religious Broadcasters: Allowing unlicensed mobile devices to share spectrum band with TV stations, wireless microphones could be 'one of the greatest technical blunders in our nation's history.'