Even the recent uncertainty about a shifting date for the DTV cutover (and all of the complications that would entail) hasn’t completely extinguished the spotlight on white space device (WSD) concerns.
That was in evidence at the Thursday evening (Jan. 22) meeting of the Washington, D.C., SMPTE section. Officially the meeting topic was “DTV Transition: White Spaces and Other Issues,” but very little was said about the transition itself. The focus was on WSDs, and four invited speakers played to a packed house at NAB headquarters here.
James Snyder, who handles broadcaster frequency coordination in the D.C. area, led off with some stats from the just completed presidential inaugural event, a major spectrum-user event that had kept him and many others very busy.
“Almost every spare television channel was used for mics and radios, including all the 700 MHz channels,” Snyder said. “From my perspective as a freq coordinator in a major metropolitan area with large scale news operations, the concept of white space is pretty much a fallacy. There’s always somebody operating there. There’s no such thing as empty spectrum in any of the top 100 markets because of protected contours of the television stations.”
Snyder stated that even the personal electronic devices in use today can cause interference to legitimate spectrum users, stating that he commonly sees cases of interference to wireless mics from cell phones.
“The proliferation of low-cost digital devices has increased the potential for IF and baseband interference,” he said, noting that he observed a large number of “pings” along the inaugural parade route.
“These were not all from the DOD or other groups we can’t mention,” he said.
With the anticipated proliferation of WSDs, Snyder envisioned an environment in which not only off-air television reception would be affected, but also newsgathering and other television broadcast functions.
“What will happen when we have millions of these devices operating in confined metropolitan areas?”
He admitted that he couldn’t say the devices wouldn’t work without generating interference, but he remained skeptical.
“At this point I haven’t seen anything that gives me a great deal of comfort that they will work without affecting, very negatively, the services that are already there, services that allow many of us in this room to bring news to the general public.”
“Given my perspective—having just gone through a major inaugural—I believe that the potential for major interference is high, and interference in general is pretty much guaranteed,” Snyder said. “My experience in the last several years as a frequency coordinator is that if something can interfere it will interfere. No operator that uses broadcast TV spectrum will be unaffected.”
Snyder said that he was not convinced that the full scale deployment of WSDs was carefully thought out by those involved in policy making.
“Real world decisions are being made by folks who haven’t worked in this environment and that concerns me,” he said. “We need to make sure that the decisions are realistic.”
Alan Stillwell, deputy chief of the FCC’s Office of Engineering and Technology, said that some of the white space device concerns may be overblown.
“The picture isn’t quite as pessimistic as James is painting,” Stillwell said. “I think he’s correct in that the amount of white space spectrum in major markets in particular is going to be pretty limited. You have TV there, you have wireless microphones, you have public safety [radios]. On the other hand, there is white space out there and we already have white space devices. These are called wireless microphones. ...I think that everybody in this room knows that people are using these microphones illegally, and that is a practice that has developed over many years.”
Stillwell addressed several of the fears and misconceptions associated with the use of WSDs and enumerated the protective measures that would be built into the system governing WSD operation.
“What we saw was not a sufficient level of performance that we felt could be relied upon to protect licensed services,” Stillwell said. “So we did not allow sensing-only devices.”
He said that WSDs could be identified by the fact that they do not operate continuously, and if a particular situation was problematic, an enforcement action could be initiated to resolve the interference. He also said that WSD allowable power levels would have to comply with existing rules governing RF exposure to persons within their field of operation.
Bruce Franca, vice president of policy and technology for the Association for Maximum Service Television (MSTV), examined the FCC’s testing program leading to the adoption of the current policy on the implementation of white space devices, addressing what the commission got right and what it got wrong.
On the positive side, Franca acknowledged that the FCC was correct in requiring geo-location and not basing WSD operation on sensing. Other pluses were acknowledged for providing some “set-aside” for operation of wireless mics, and in recognizing the need to protect cable headends, low power television and translator operations.
One area of the white space plan that he criticized was the decision to allow personal portable WSDs to operate at a 40 mW level on an adjacent channel within a television station’s service contour. Another was in adopting a sensing level of -114 dBm and not defining how sensing levels were to be measured.
Franca said that experience with digital television reception showed that it took far less to knock out reception.
“There really is a big difference in analog and digital television interference,” he said. “In the analog world we’ve lived in, interference can increase by about 8 dB before a viewer sees a change in their picture. Actually interference can increase by 20 to 30 dB before the picture becomes unusable. That’s not the case with digital.
“Most digital sets go from a perfect picture and sound to no picture and sound with one dB [of interference]. In fact [in testing] some of the sets went from perfect pictures and sound to no picture and sound with a tenth of a dB,” he said. “We don’t have the margin anymore.”
Franca said that another area where the FCC had failed was in assuming that consumer television antennas would provide sufficient rejection of interfering signals to protect DTV reception. In some cases commonly used antennas missed the mark by 16 to 26 dB.
Franca added that the decision to allow white space device operation was based on policy and not science.
“Bill Gates called the shots,” he said. “It’s all about new technology getting access to broadcast spectrum. And it’s not just a U.S. issue; it’s a global threat.”
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James E. O’Neal has more than 50 years of experience in the broadcast arena, serving for nearly 37 years as a television broadcast engineer and, following his retirement from that field in 2005, moving into journalism as technology editor for TV Technology for almost the next decade. He continues to provide content for this publication, as well as sister publication Radio World, and others. He authored the chapter on HF shortwave radio for the 11th Edition of the NAB Engineering Handbook, and serves as editor-in-chief of the IEEE’s Broadcast Technology publication, and as associate editor of the SMPTE Motion Imaging Journal. He is a SMPTE Life Fellow, and a Life Member of the IEEE and the SBE.