White spaces promise to provide useful test bed
Last week, the FCC approved unlicensed use of the television white spaces — the fallow spectrum between the frequency channels used by over-the-air TV broadcasters. Interference rules that have not yet been written may determine exactly how much of a commercial effect this spectrum will have on the wireless industry, but the existence of unlicensed white spaces should have a noticeable technical impact regardless.
Long considered a “junk” band, the 2.4 GHz band transformed the notion of unlicensed spectrum, driven by the proliferation of a wide array of Wi-Fi devices. Similar success stories have been told in the 5GHz unlicensed band. However, due to the propagation realities of the spectrum in each case, wide-area networks using the technologies have not been economically viable.
This situation could change dramatically in the TV white spaces, where signals can travel significant distances, providing the possibility of making wide-area networking much more affordable. For those entities that lack the financial resources to win spectrum at auction, the white spaces could offer an alternative path into the commercial wireless arena that doesn’t break the bank before a single base station is deployed.
What is particularly intriguing about the timing of the FCC’s action is that the white spaces are being made available just as software-defined radio is maturing and cognitive radio is beginning to emerge as a realistic option. Combining the database technologies espoused by the FCC and the cognitive capabilities being developed by several companies that are able to find unused spectrum and utilize it without interfering with others provides some intriguing possibilities.
At the very least, the white spaces promise to provide an ideal test bed for a variety of interference-avoidance techniques developed by numerous companies, including solutions from Spectrum Bridge and xG Technology.
In the near term, these technologies should prove to be especially helpful in bringing broadband to rural areas, which have tons of white-space spectrum because they typically have few television broadcasters. In more densely populated areas with a lot of TV stations, the challenges will be much greater, because there potentially will be many more users contesting for less spectrum.
It is in these environments that the limits of cognitive radios can be tested in real-world situations. If the problems in the “Wild, Wild West” of the unlicensed world can be resolved on a wide-area basis, it will be only a matter of time before the techniques are implemented to make more efficient use of licensed spectrum owned by commercial carriers or public-safety entities.
Meanwhile, if one of the white-spaces companies manages to find the Holy Grail by developing a system on free unlicensed spectrum that offers the same quality-of-service levels as licensed wireless networks, the impact promises to be felt throughout the wireless industry. Not only could such a discovery upset the apple carts of licensed spectrum holders — from commercial carriers to public-safety entities — it could fundamentally change the value of airwaves and federal spectrum policy.
Of course, all of this may just be a pipe dream espoused by a few RF theoreticians that may not happen for decades, if at all. However, I’ve learned to never underestimate the ability of engineers to find solutions to almost any technological challenge, particularly when investors have a reason to fund their work. Assuming the FCC does not overprotect TV broadcasters’ signals from potential interference, it appears that engineers should have the desired test bed and companies will have plenty of financial incentive to pursue such goals in the white-spaces spectrum.
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