The FCC today released an order refining, but largely reaffirming, its earlier decision to allow unlicensed devices to operate in the TV band as long as they do not cause interference to existing users such as TV stations and wireless microphone operators. While many refer to this spectrum as “white spaces” on the theory that it is vacant spectrum located between existing television signals, veterans of the digital television transition question whether white spaces more appropriately fall into the same category of mythical creatures as unicorns.
The digital transition’s compression of television stations that previously occupied Channels 2-69 nationwide into Channels 2-51 took a miraculous feat of engineering (and the displacement of a lot of LPTV stations). Many stations had to be wedged into the shrunken TV band with a shoehorn, which, at least in urban areas, left very little free spectrum. While the phrase “white spaces” evokes a mental image of vast open prairies, the densely populated areas that are the target markets for manufacturers of unlicensed equipment are already spectrum congested, and are more likely to offer “white spots” or “white specks” than white spaces. The benefit of the Commission’s order will likely be greater in rural areas, where spectrum congestion is not an issue even after the digital transition.
As long as the FCC lives up to the Prime Directive of not causing interference to existing inhabitants of the TV band, the benefits of better utilization of spectrum are hard to dispute. Broadcasters understand as well as anyone the challenge of eking out every last ounce of potential from spectrum. However, broadcasters are understandably concerned with a significant change made by the FCC in today’s order — the elimination of the FCC’s requirement that white spaces devices be able to sense local signals and avoid causing interference to them. By eliminating that requirement, the FCC removed the “safety valve” it had installed in its original plan. Instead, the FCC is placing its faith entirely in the creation of one or more privately-created and run databases of existing spectrum users that unlicensed devices will consult before selecting a frequency on which to operate.
Many in the broadcast industry have been strong proponents of requiring unlicensed devices to have “sensing” capability rather than relying solely on a national database of existing signals. “System redundancy” is an important feature in designing reliable communications systems, and removing that redundancy inevitably makes for a less reliable system. As the FCC has noted, eliminating the “sensing” requirement will reduce the cost of unlicensed devices, but as we discovered in the recent Gulf oil spill, short term decisions to reduce costs by reducing safety margins can have far greater and more expensive long term consequences.
While lacking any backup protection, a spectrum database could be a workable solution if properly implemented. However, the challenges of implementation are immense. Ensuring the accuracy of the database itself will be a challenge given constantly changing spectrum use by new and existing operators. Also, signals propagate differently depending on frequency, what part of the country you are in, local terrain, and various other factors, making the database either incredibly complex, or inadequate to address real world circumstances.
Viewers of TV stations in Fresno, whose real world signals extend far beyond their predicted contours because of terrain effect, will suddenly be subject to interference from unlicensed devices. In addition, you have to think that users of those unlicensed devices aren’t going to be too happy when their wireless network won’t function because (unknown to them) it is receiving interference from a TV signal that the database swears isn’t there.
Because of these and many other issues, the FCC needs to keep an open mind as it implements its proposed use of white spaces. A well-performing database that keeps licensed and unlicensed operators adequately separated is in everyone’s interest. If some of the FCC’s initial conclusions need to be rethought in order to accomplish that, those discussions will be healthy ones.
Equally important is ensuring that equipment manufacturers fastidiously comply with the FCC’s interference protocols. Broadcasters are rightly concerned that non-compliant or just poorly designed and manufactured unlicensed devices can cause immense damage, and the FCC lacks the tools to put the genie back in the bottle should that occur. Fining such manufacturers after the fact won’t help much if millions of interference-inducing devices are already out there interfering with the public’s ability to watch TV, listen to a sermon, or attend a Broadway show. As the FCC proceeds down this path, getting it right is going to be far more difficult than just getting it done.