An engineer takes a look at the latest information dump from the FCC on the TV repacking front.
[Blogmeister’s Note: The FCC’s Incentive Auction Task Force recently released a number of materials relating to TVStudy, the software that FCC engineers devised to assist them in the modeling and analysis necessary to repack the TV spectrum. Those materials included a public notice, a Technical Appendix, and a boatload of other goodies, all intended to give us a peek into the way the Commission is approaching the repacking process. Unfortunately, the materials are a bit, um, technical in nature, so unless you’re well-versed in a lot of sophisticated engineering stuff – stuff that, as it turns out, wasn’t offered in law school – you’re likely to have a hard time understanding what’s what. No problem. Our friend Mike Rhodes, P.E., of the highly-respected engineering firm of Cavell, Mertz and Associates, has come to our rescue. We asked Mike if he could break down the FCC’s releases into morsels that might be digestible by non-engineers. Happily, Mike agreed to take on that daunting challenge. Thanks, Mike.]
The materials recently released by the Incentive Auction Task Force provide considerably more details than had previously been available about the Commission’s move to repack the TV spectrum.
Move? Let’s stick with that analogy for a moment.
Think of the available spectrum as the empty moving van and all the TV Stations (as well as some other spectrum users) as the entire contents of your house that need to be moved. The first chore in moving is to get organized so that everything will fit in the moving van in one trip. In its recent releases, the FCC has put the entire contents of its TV spectrum house out on the driveway. They’re now looking, first, at the piles of boxes and furniture and, next, at the empty moving truck. They’re scratching their heads trying to figure out what pieces to start with.
So, like any good engineer, they wrote some software to help solve the problem.
The software determines how many combinations and permutations of all that stuff need to be analyzed before they can start loading the truck. The list of furniture includes: 2,177 U.S. Stations (Full service and Class A); 2,557 Canadian Allotments; 603 Mexican Allotments; 25 Land Mobile Channel preclusions; and 424 other Land Mobile (“T-band”) users currently operating in the TV bands. Oh, and don’t forget to reserve Channel 37 for the radio astronomy listening channel (E.T.). That’s a lot of stuff to pack!
The software is a new and apparently improved version of the Commission’s TVStudy software first released back in February, 2013. The FCC solicited comments about the program and, after evaluating the numerous comments and complaints filed in response, the Office of Engineering and Technology (OET) has apparently concluded that it is going to continue to use TVStudy for the repacking.
In releasing its preliminary conclusions about TVStudy along with a considerable amount of related information, OET is trying to make good on the FCC’s commitment to “transparency” as the agency works its way through the vastly complex problem of repacking (and the equally – if not more – complex problem of designing the forward and reverse auctions processes). Still, some additional explanation may help non-engineers to get a sense of just what’s going on here.
How did they look at every possible repacking combination?
Step One for movers usually involves determining the dimensions of all the boxes and furniture. So, using TVStudy, the FCC has done the equivalent by first calculating the coverage area and population for every station (or international allocation) in the U.S., Canada, and Mexico. The FCC started by dividing much of North America into little 2 km blocks and counting the people in each block. For every TV station, they calculated the coverage at every block within every station’s protected contour. Then they calculated interference from all the other stations in each block. After removing the interference blocks, what was left was the interference-free coverage and population for each television station in the country. That became the baseline population for each station.
Step Two. Narrow down the number of channel/station combinations. Use all the international and land mobile constraints (don’t forget E.T.) to determine a list of channels (2 to 51) on which each station could potentially operate. The resulting list of stations and potential channels determines the starting point for an allocations scheme.
This exercise provided interesting results. For example, a preliminary version of the resulting list shows the critical locations in the U.S. where the number of available channels is severely limited. [Blogmeister Update Tip: It has come to our attention that the link in the preceding sentence, and a couple of others below, take you to “csv” files that may open up in your browser as plain text files consisting of a bewildering bunch of numbers seemingly indecipherable unless you happen to own the secret decoder ring they hand out to engineering school graduates. Prof. Rhodes assures us that these csv files – that’s apparently engineer-ese for “comma separated value” – are supposed to be opened in Excel “relatively painlessly”.] We expected this to be in the Northeast – and, sure enough, we were correct.A handful of stations in western New York and Vermont have only one or two possible channels available after everything else is culled out. There are also a few stations in south Texas, Washington State and Maine with only a handful of available channels.
Step 3. Find the Pairs. In order to repack stations, the FCC needs to determine which stations could not operate on co-channel and first adjacent channels to each other. Instead of calculating every station on every channel relative to every other station, they came up with a clever short cut. Using only three channels called “Proxy Channels” (a Lo-VHF, a Hi-VHF, and a UHF channel – in this case Channels 3, 10, and 20, respectively), the Commission calculated whether stations could operate on the same or an adjacent channel. If operation on these channels was predicted to cause interference to more than 0.5% of the baseline population of the desired station, it was added to the Interference Paired list. [Blogmeister’s Tip: This link takes you to another “csv” file. You have been warned.] The Technical Appendix is not clear on how the Proxy Channel facilities relate to a station’s actual facilities (i.e., how the software calculates the power level used for a VHF proxy of a UHF station.) But for the time being we won’t worry about that.
You may ask why the FCC is calculating station pairs in the Lo-VHF band or UHF station coverage in either VHF band. The Technical Appendix (footnote 21, to be precise) addresses this issue. While the Spectrum Act does not permit stations to be involuntarily relocated to a lower band, some stations could offer to voluntarily relocate in exchange for a piece of the auction proceeds. In case this happens, the FCC is ready to evaluate that request.
Let’s try a short example. For a given station – we’ll call it WAAA – we find all the TV stations that might be near enough to cause interference to that station (i.e., WAAA). Then we analyze every station individually paired with WAAA as if it was operating cochannel, then again on an upper adjacent channel to WAAA, and once more on the lower adjacent channel. Let’s first run WAAA on Channel 20, the “proxy channel” for all of UHF. First interferer on the list is Station WBBB.
Start with the UHF option. WAAA’s coverage as a Channel 20 station is predicted in TVStudy against interference from WBBB also operating on Channel 20. If WBBB would create interference to more than 0.5% of WAAA’s baseline population (from Step 1), we record this combination (WAAA & WBBB cochannel on UHF) as “prohibited”. Change WBBB to first adjacent Channel 19, rerun it and analyze the result. Can they coexist on adjacent channels with no more than 0.5% interference? Next run WBBB on Channel 21. Same question: does the WBBB operation meet the interference threshold or not? In each case, if prohibited interference is caused, we record the failed stations and channel relationship.
Then move WAAA to the next proxy channel, Channel 10, and do the same thing with WBBB (on Ch 10, then 9, then 11), and again on Channel 3 (with WBBB on 2, 3, and 4).
Then we go to the second station in the list of stations near WAAA and run it through the same process on Channels 3, 10, and 20 with WAAA as our desired station. Nine studies for each pair of stations. Wash. Rinse. Repeat.
The end result of this process is a list of stations with a corresponding list of stations that will not work on co- and/or first adjacent channels if they were operating in each of the three TV bands. (Heads up: the list consists of a spreadsheet with more than 25,000 channel pairings . . . and it's a csv file, to boot.)
Of course, this is all based on some preliminary assumptions made by the OET staff. As OET appropriately emphasizes, final decisions about the parameters that will be used for the actual repacking process will be made by the full Commission . . . although, in making those calls, the full Commission will almost certainly be taking its cues from OET. But we digress.
So what can we do with all this transparent information?
While it’s nice that the Commission has given us all this access to the sausage-making process, what are we to do with it?
First and foremost, TV Station licensees should check to see if the facilities being used in these repacking studies are the correct ones. For full service TV stations, this should be the facility that was licensed on or before February 22, 2012. There’s no reason to suspect the Commission got the wrong data but it doesn’t hurt to check, because let’s face it, accidents do happen. Class A stations (and full service stations with incoming interference from a Class A stations) should take note. The Class A facilities used were also from the February 2012 database, although the Spectrum Act allows for protection of Class A facilities licensed as of a yet to be determined date in the future. You can check the facilities used for any particular station by perusing the FCC-provided report which includes a lot of interesting statistics (if you’re a math major). Along with the statistics, Appendix A of the report (which runs from page 20 to page 48) shows coverage contours for each station on a large US map for each channel in the TV band. Appendix B, starting on page 49, lists all the television facilities and their pertinent details (power, height, and FCC File Number, etc.) included in the study.
Second, using TVStudy, you – or, more likely, your preferred engineering consultant – should independently calculate the coverage and interference of your station(s) based on the current set of FCC assumptions. The interference-free population and coverage calculated by this software will determine the baseline or starting point for relocated stations. (The FCC has provided the results of their sample study as well.) Running TVStudy is not for the faint of heart (or the technologically challenged) – it requires decoding several gigabytes of data and importing it into a GIS program, which is not a trivial task. Nevertheless, the program, the input data, and some sample results have been made available here for us to use. The FCC has even included a template for viewing the results in an open source GIS program.
Third, if you are so inclined, use the tables the FCC has provided to run scenarios on what stations may change channels and where they might go. That isn’t trivial either. However, now that we have an indication how the FCC will perform the preliminary repacking analysis, it becomes a little clearer to see how various repacking scenarios can be developed by the FCC, the broadcasters, and the wireless industry.
As complicated and seemingly well-developed as all this may seem, OET stresses that this is NOT the final version. The facilities included in the study were “intended for illustrative purposes only.” Moreover, “some assumptions had to be made about which facilities to include for protection.” Still, we applaud the OET staff for making the effort to publish the methods and data used in this process.
Back to our moving van analogy.
Now we know everything that might need to be packed in the truck, and we have a preliminary idea of which combinations might work and which probably won’t. But wait, there’s more. We will still need to factor in wireless spectrum which, in some areas, will probably require some television stations choosing to stay behind to move to a different location on the spectrum (i.e., to the VHF band). In other words, we’re still a considerable ways away from any final determinations of how we’re going to pack the truck. Indeed, the questions of how much spectrum (and which stations) should get repacked are likely to remain a moving target for some time. But at least the FCC has created a tool to help along the way . . . and it has shared that tool with us so that we have a better understanding of the way it works and also so that we may be able to assist in honing it to provide the best possible results.