Unlicensed white space devices will cause broadcast ‘nightmare’
As the FCC moves forward on the question of allowing unlicensed devices into TV spectrum, “HD Technology Update” spoke with David Johnson, director of technology for broadcast media at WFAA-TV in Dallas-Fort Worth, to get a broadcaster’s view of the issue.
WFAA, a top 25 market station, seemed like a good choice because the area’s flat terrain makes over-the-air TV reception ideal. As a result, the market has one of the lowest cable TV penetration rates among the top markets, with less than 50 percent of the area’s households relying on cable service for television.
Johnson shed some light on what WFAA and other broadcasters would face in dealing with white space device interference.
HD Technology Update: What will be the impact of allowing unlicensed devices to operate in the TV band on your station and your viewers in the Dallas area?
David Johnson: As a broadcaster in the VHF band, WFAA’s signal is on VHF Channel 9, so it’s down in a frequency band that is already prone to interference from other devices like paging towers and other communications devices. So we take a lot of calls from viewers who are trying to make the digital transition and trying to get their set-top box set up, and we’ve already had a lot of calls about interference-related issues.
We’ve had several neighborhoods in Plano that were knocked out of our Channel 9 reception because a paging tower went off frequency, and we were able to track down and locate that paging tower and work with the owners to correct the problem.
That’s one situation that made it fairly easy to locate. You can imagine if consumers all over Dallas-Fort Worth have these transmitting devices, and they start causing interference for whatever reason to my digital signal. You can imagine what kind of nightmare it is going to be for me to try to work with our viewers to resolve interference issues.
What we have also discovered is that DTV converter boxes are highly prone to impulse noise from electrical devices in the house. What happens is when you get one of these pulses that just blips for a second, in the VHF band, then it causes the receiver to unlock, you lose audio and your picture goes away for a second. Then it recovers.
So, they are very susceptible to interference. It’s not like the old analog where you might see the picture fuzz up for just a second, but you don’t ever truly lose anything.
In a digital situation, any interference at all will result in a complete interruption of audio and video.
HD Technology Update: You discussed the paging tower interference that you corrected. If you look forward and these consumer white space devices are allowed to roam freely in your service area, is WFAA specifically, and are TV stations in general, equipped to identify these sources of interference and take steps to correct the situation?
David Johnson: No, we are not. That would be a nightmare. We got lucky in the paging tower situation, because we know where communications towers are located in our area. There are quite a few of them, but if we have an interference issue, we can fairly easily look to see what towers are near to the interference, and usually that is where it is coming from. Then we can triangulate in and we can pinpoint that.
With consumer devices spread out all over the DFW area, that would be a nightmare to the broadcaster. We don’t have the staffing. We may deal with one or two interference issues a year. We are in no way staffed to run down on a daily or weekly basis interference from consumer devices.
HD Technology Update: Local news is an important aspect of what WFAA does, and what many broadcasters do. How do you see this issue playing out for news crews in the field when it comes to wireless mic use and other wireless devices?
David Johnson: Wireless mic interference is going to be a big issue. If they allow consumers in, that will definitely be an interference issue. Take an NFL football game on a Sunday afternoon; there is coordination that goes on to make sure that the hundreds of media representatives that are there to cover the game all coordinate their wireless frequencies, so nobody steps on anyone and you can here the referee call the penalty out in the middle of the field.
You start introducing unlicensed devices into the mix, and you can see that without proper coordination, people are going to get stepped on. Our news crews could be out informing the public of some emergency situation, and they’re going to be subject to this interference.
HD Technology Update: How about the impact on the effort to introduce mobile TV devices that rely on off-air reception of ATSC transmission?
David Johnson: We just did some testing in Dallas a couple of weeks ago of the prototype on the VHF band, so we configured our encoders and exciters to carry WFAA’s regular programming, but at the same time we were transmitting the MPH signal out. Then there was a test truck driving around to take measurements.
The mobile receivers, although they are supposed to be more robust, could definitely be affected by white space interference from an unlicensed device. Admittedly, I don’t have as much experience with mobile TV, but I got to participate in a demonstration at NAB in Las Vegas last year, in which we drove around and had our little mobile MPH receivers and it was very robust. Also, there were no consumer devices out there transmitting.
These mobile TV receivers are probably going to be little devices out there closer to these unlicensed white space transmitting devices.
HD Technology Update: Is there anything else you would like to add about what broadcasters will have to deal with if the commission authorizes the use of these devices in the TV band?
David Johnson: The commission has already put a lot on broadcasters. We are dealing with this Feb. 17, 2009, DTV deadline and many unknowns about the preparedness of people out there to receive our signal. We are going to be overwhelmed just trying to deal with people who are trying to pick up our signal over the air without interference.
I don’t know when they were planning on allowing this, but if it is anywhere near Feb. 17, it would really be a nightmare. But that’s going to linger on, because after Feb. 17, we’re going to have a pretty long period of time in which people still haven’t made the switch. They are going to be going out buying converter boxes, and they’ll have no analog to reference to. In digital, it’s either there or it isn’t. So, if interference from white space devices is present and you have somebody who is trying to pick up our digital signal for the first time, you can imagine how much confusion there is going to be around that.
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