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With the continuing rapid increase in the number of wireless devices, the range of applications they support, and the general desire to have a desktop-like experience while mobile, it's fair to ask if we have enough radio spectrum to support this level of activity now and into the future. After all, there is only one electromagnetic spectrum, and only a relatively small set of frequencies suitable and available for mobile communications applications. Are we going to run out of spectrum?
Fear not -- while the amount of spectrum is indeed finite, and new blocks of spectrum are usually made available only in fairly small chunks and, thanks to the auction process used, at fairly high prices, we do have sufficient spectrum -- provided we make the best use of it.
Both technology and regulatory policy are important here, and, fortunately, both are keeping pace with the increasing demand noted above. More spectrum is being made available, and a good amount of this is unlicensed -- available for limited-range activities with no licensing cost. For example, in the United States, just under 700 MHz. of spectrum is available below 5 GHz. (with another 7,000 MHz. (!) around 60 GHz.), plus that in the recently-available White Spaces (see below). The carriers also have a good amount of spectrum available for their exclusive use (with the exact amount varying by carrier), but, granted, this is more limited and thus the carriers will eventually support transparent combined licensed/Wi-Fi operations -- users won't know what spectrum they're using, and won't really care.
Because any given radio signal is effective only over a limited range (due to natural fading of the signal), we can reuse a given block of spectrum over distance. Combine this with clever techniques that improve reliability and capacity, like MIMO, which is used in WLANs and WWANs alike, and the situation is nowhere near as bad as it might otherwise seem.
Finally, you're going to be hearing more about cognitive radio over the next few years. This is a "smart radio" technology that allows radio devices to cover a very broad range of frequencies under the control of a centralized intelligence, kind of like the way the air traffic control system works. The FCC has now authorized the first cognitive radio use, in the so-called TV White Spaces -- unused television channels that exist all over the country, but which are especially plentiful in rural areas. So, while there's no magic here, we really do have quite an arsenal of techniques to deal with what otherwise might seem like a shortage of spectrum.