http://www.tvtechnology.com/dailynews/one.php?id=4296
Date posted: 2006-09-29
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.
