Clarification: in principle, Ch 52-69 were taken away from TV, with the digital transition. However in fact, since new users of the 700 MHz band have found that adjacent channel interference with Ch 51 TV is or could be a problem, they have petitioned to have TV move off Ch 51 as well.
Search under "TV reverse auction," or pay attention to articles about this, to see what is being done to OTA TV these days.
White space devices are supposed to use two methods to determine if they can use a given frequency channel. One is a database, location-oriented. And the other is signal sensing. So if a licensed user comes on and takes one of the white space channels, the white space devices would have to vacate that channel.
Our household happens to use only OTA television for TV, so of course I'm all in favor of it surviving and thriving. And I have also witnessed plenty of new program channels on the air, since June 12, 2009. But the FCC, under the current leadership, thinks that wireless broadband is all there is for the future. And they're insisting on taking away another 1/3+ of the spectrum from OTA TV, after just having taken away Ch 51-69 with the digital transition, and Ch 70-83 previously. If they get their way, all channels above Ch 30 will be taken away from TV. So, not a good prospect for the future of OTA TV.
Furthermore, handset manufacturers and cell service providers do not see it in their financial interest to incorporate mobile TV receivers in their handsets, to receive OTA TV, if they can sell their own TV service like Vcast. So even that aspect makes OTA TV's survival somewhat iffy.
I'm curious as to what happens when a new station comes on air using the previously available "white space". Do the devices somehow sense that and change frequency or is there a receiver and controller in the device that enable it to be switched to another frequency? Also, I'm not sure that OTA television is undergoing a demise since I see more on air stations locally than I used to and with them now transmitting digital, we see excellent pictures over the air.
Oh, I guess my real point was, even in spite of this, I don't think this white space idea will be trouble-free, for the reasons I suggested.
On the other hand, it could help to accelerate the demise of free over the air television. If TV web sites carry free TV anyway, perhaps that will become the trend anyway.
Yes, in the US anyway. A big part of this effort to use white spaces is to explain what the white space devices have to do before they can assume the space is free. This is controlled by a location database and by signal detection, down to something like -115 dBm.
IEEE 802.22 goes into this. It's available for free now, at the IEEE standards web site.
In fact, 802.22.1 is a separate document devoted to answering your question.
Seems to me that we've been seeing one company after another claiming that they have fully mastered this TV white space use problem, and yet the same laws of physics have always applied. When I read articles or press releases that give the motivation for using white spaces, but offer no details of how the supposedly new scheme is implemented, I remain skeptical.
The meter reading task might work well, depending how it is implemented. If the electric meter transmits only for a short time, when queried, the disruption to nearby TV receivers might be very tolerable.
The fundamental problems remain. First, there is the inverse square law. The power density created by a close-by, low power transmitter can be much greater than the power density of that distant, high powered TV transmitter. And TV receivers out there have only so much selectivity for adjacent channels or even other combinations, such as N +/- 2 and even further. These selectivity figures can be as low as 30 dB or sometimes less. The FCC knows this, because they have done a survey.
So when these factors are not mentioned, but only the (rather obvious) motivation for use of someone else's spectrum, I'm left wondering what the whole truth is.
Blog That A-Ha Moment Larry Desjardin 6 comments Have you ever had an a-ha moment? Sure, you have. The Merriam-Webster dictionary defines it as "a moment of sudden realization, inspiration, insight, recognition, or ...