09.29.2006 12:00 AM
White Space Debate Heats Up IEEE Event
Things got lively at the 56th Annual IEEE Broadcast Symposium in Washington, D.C. this week when the talk turned to white spaces.
On the second day of the annual three-day event, presentations dealt with operation of unlicensed devices in the television broadcast bands, with representation from both advocates and foes of the plan.
"Repeat after me, 'he is not the enemy,'" said Carl Stevenson from WK3C Wireless LLC, as he launched into his report on the progress of the IEEE 802.22 standards group. The goal of the group is to establish operating standards for proposed wireless regional area networks--WRANs--aimed at delivering broadband communications to rural and remote urban areas of the country.
Stevenson told the audience of mostly broadcast engineers that his group is "picking on your bands" because the FCC has suggested that a lot of space for WRAN communications exists there, and because the propagation characteristics in the white spaces there are ideal for such networks.
"Using higher frequencies would require six to eight times as many base stations for equivalent coverage," Stevenson said. "Nominal base station coverage radius would be 30 to 40 kilometers."
"It's pretty clear from both the FCC and Capitol Hill that some other use of these channels will be permitted," he said, adding that broadcasters and broadcaster groups including MSTV, NAB, Fox and CBS have been actively participating in the work of 802.22, "making sure that we get it right."
Countering remarks by Stevenson that cognitive radio device technology would enable television signals and unlicensed devices to coexist, Dr. Oded Bendov, a consulting engineer, presented information indicating that harm could result from unlicensed devices.
"Interference to DTV by unlicensed devices will be insidious because consumers will need a spectrum analyzer to identify it," Bendov said. "At least two unused TV channels must separate unlicensed devices from licensed TV services. Even a single device, fixed or portable, in compliance with FCC rules, will cause unacceptable interference." Bendov recommended packing all DTV channels into a contiguous spectrum after the 2009 digital broadcasting transition.
Khalil Salehian, representing the Communications Research Centre in Ontario, Canada, said that two basic problems exist with allowing unlicensed devices to operate in TV channel spectrum--desensitization of DTV receivers and adjacent channel interference due to in-band emissions.
Another proponent of allowing consumer devices to operate in white spaces was Alan Waltho, from the Intel Corp. He said that cognitive radio technology would allow low-power devices to operate in white spaces, provided that rules are followed.
Waltho said that with proper technologies in place, white space for the operation of unlicensed devices exists even today.
"Even in areas like New York, Los Angeles and Chicago, there are some channels that are available today with potentially more [spectrum] after the transition," Waltho said. "There are some five channels available today in New York."
Waltho did express concern that the operation of wireless microphones could result in interference as they operate with a power level of a few milliwatts and bandwidths of 200 KHz. He said that "they might be difficult to detect," but felt that there was a solution.
Victor Tawil, representing the MSTV, reminded the audience that the proposal to use television white space was the first attempt to allow Part 15 devices in that region of the spectrum, and said that limits in Part 15.209 of the commission's rules are not sufficient to protect TV operations. Tawil said that he thinks the FCC numbers for out-of-band emissions are incorrect.
"Tests show that 100 milliwatt unlicensed devices can cause interference to adjacent channel DTVs up to 780 meters away," Tawil said.
The subsequent question-and-answer session elicited a number of remarks from the floor.
"This is a disaster. You guys are out of your minds," said Mark Fehlig, director of engineering for Georgia Public Television. Fehlig said that he advocated repacking the television broadcast channels, and doing it like the BAS transition--"have someone who will benefit come in and pay the freight."
Bill Hayes, director of engineering at Iowa Public Television, also questioned the white space proposal, asking if someone couldn't hack unlicensed devices to defeat any sort of cognitive power limit control. Bill Meintel, with Meintel, Sgrignoli & Wallace, asked about how much spectrum would be needed to support the unlicensed communication devices.
Intel's Waltho responded that if HD transmissions were contemplated, then probably six to eight MHz would be required to accommodate such a data rate.
The three-day event drew 167 people from 11 countries.