This week, as I'm sure most
broadcasters know by now, the FCC approved rules allowing unlicensed devices to
use “vacant” TV channels.
As of 1 a.m. Friday morning (EST) the
FCC had not released the text of the Second Report and Order establishing the
rules, but commissioner comments suggest they have endorsed power levels that
are well above those shown to cause interference in FCC testing.
Listening to the commissioners'
statements during the long delayed open Commission meeting, I heard them state
they were concerned about interference to broadcast and over-the-air TV
reception but that they had been assured by the scientists and engineers at the
FCC's Office of Engineering and Technology and the FCC Laboratory that it would
not be a problem.
“I have placed much faith in the Chief
of OET, Julie Knapp, and his entire staff of engineers,” said Deborah Taylor
Tate. “Their recommendations, while always useful in any rulemaking, played an
especially persuasive role in my final decision to support this item. I have
been assured by Chief Knapp and our top engineers that the risks of
interference have been appropriately considered.”
Tate expressed doubts, however, about
the lack of specific details on how the FCC will deal with interference
Commission, through our Enforcement Bureau and in consultation with the Office
of Engineering and Technology, will investigate complaints of interference and
take appropriate action, as we do with all cases of interference. I regret that
my colleagues were unwilling to set forth in this item a more specific and
swift process to deal with complaints of interference. I remain concerned that
the item is too vague and does not provide necessary protections after the
interference has occurred. I also would
like to acknowledge the legitimate concerns of the many industries that already
provide valuable services using the core TV bands. Regarding the concerns of my
friends in the broadcasting industry, I want to recognize the important service
they provide, especially all they currently are doing to make the DTV
transition as smooth as possible. ... In addition, broadcasters play a key role
in providing emergency alerts to the public. It is, therefore, imperative that
TV broadcasting continue to be protected from interference.
After expressing these concerns, she
said, “The power limits and other technical rules, proposed by OET and adopted
here are designed to do just that.”
I'm concerned by her solution to WSD
interference to cable TV reception, an issue I raised in last week's RF Report. Tate said:
regard to cable systems in the home, OET has attempted to establish power
limits that will lower the risk of interference between devices in the home,
though this risk is not, in my mind, fully mitigated. However, the Commission
does not generally focus on interference that users cause to themselves. Just
as we have all learned to move devices away from each other in the office and
we no longer place our cell phones next to the computer, so might consumers
need to reduce interference inside their home by moving devices, at least until
the next generation of cable equipment becomes more widely disseminated.
As with the potential for interference
to broadcast reception and wireless microphones, Commissioner Tate doesn't seem
to be completely comfortable with the rules.
Unfortunately, the solution she
mentions about moving the device away from the cable box or TV set won't work
in a condominium or apartment house, where the device may be located in a home
office far away from the user's TV set but only one wall away from the living
room or bedroom cable box of their neighbor! What will that neighbor do when
his or her favorite channel disappears from the cable box? How will they know
it's the person in the next unit using a white space device that's wiping out
their reception? It is unlikely “the next generation of cable equipment” will
solve the problem, since digital cable channels were affected as much as analog
channels in the FCC testing. Replacing the wiring in the condo or apartment
with laboratory quality cable, as was done in the FCC testing, might solve the
problem but that's unlikely to happen in older apartment buildings.
I'm not picking on Commissioner Tate.
Of all the Commissioners, she had the best appreciation of the impact white
space devices have on over-the-air and cable TV reception. I quote her because
listening to her presentation and reading her comments,
it's clear she isn't happy with the protections offered TV viewers in the
Second Report and Order.
In the headline I note, “It could have
been worse.” The good news is that at this time only devices with geolocation
capability are allowed. They will have to access a database of available
channels before transmitting and while I feel the allowed power levels are too
high, the requirement for adaptive power control should reduce the actual power
of devices communicating with other devices inside a dwelling. However, it may
not help much if the devices are communicating with distant fixed transmitters.
Devices will require an ID, which will
probably be something similar to the MAC address on all Wi-Fi and Ethernet
devices. Through the geolocation database, it may be possible to shut off
devices that are identified as causing interference. If transmitter power can
be controlled through the geolocation database, it may even be possible to
force units causing interference to cable reception to reduce power below the
maximum the rules allow. Conceivably, if this turns out to be as big a fiasco
as some fear, it may even be possible to turn off all the devices or limit them
to a smaller number of channels that cable operators could avoid using for
The rules will allow for sensing only
devices to be sold once they pass a rigorous series of tests. There may be a
lot of pressure to lower the threshold to get sensing-only devices on the
market. Broadcasters and wireless microphone operators will need to carefully
watch the testing to make sure devices are sensitive enough to detect a DTV or
wireless microphone signal.
Sensing must work even in situations
where the sensing receiver is blocked from the DTV transmitter or microphone if
it could cause interference to receivers at locations where the channel is
receivable. I'm not sure that's physically possible, but detecting weak DTV
signals from a “hidden” location is the only way sensing can be used without
wrecking havoc on the reception of DTV signals over a wide area.
I discuss the MSTV and NAB comments in
another article in this week's RF Report.
Meanwhile, take some time to review the comments of Commissioner Deborah Taylor
Tate and the other commissioners at the FCC Web
site. I'll cover the technical details after the text of the Report and
Order is released.