WiMax Operator's Manual

42 CHAPTER 3 ■ STRATEGIC PLANNING OF SPECTRUM AND SERVICES
the power of UWB equipment to a point where transmissions of much beyond 100 feet are
impractical.
Originally conceived as a basis for ground- and foliage-penetrating radar systems, UWB
has more recently figured in experimental stealth radios employed by the armed forces.
Commercial prototypes intended for use in public access networks have shown a number of
singular virtues including throughputs in the hundreds of megabits per second, near immunity
to multipath distortion, and pronounced ability to penetrate buildings and dense foliage.
Over-the-air UWB may ultimately play a prominent role in high-speed public communications
networks, but it is going to have to clear some formidable regulatory hurdles before that
happens. And given that powerful lobbies representing broadcast and telecommunications
incumbents are vehemently opposed to it, those hurdles are not apt to be cleared any time
soon, at least not in the United States.
Recently Southern California–based Nethercomm has developed a very interesting UWB
system that could in fact play in metropolitan public networks. The Nethercomm system
revives the old idea of waveguides whereby radio transmissions are sent through metal pipes
that contain interference and permit senders to use as much bandwidth as they want. In this
case the metal pipes are preexisting gas lines. Nethercomm claims that technology will support
throughputs of several tens of gigahertz and will best any residential fiber-optic system. In
theory, the notion should work, but we have not examined any actual implementations.
Licensed vs. Unlicensed Spectrum:
The Operator’s Dilemma
The licensing of radio spectrum has been in effect since the very dawn of commercial radio in
the early 1920s, and the underlying notions informing such licensing are threefold. First, it
sequesters generous allocations of spectrum for purely governmental use. Second, it further
serves the government by deriving abundant revenues from the licensing process. And third, it
prevents commercial users from interfering with one another by restricting each to a specific
portion of the band.
Such considerations still exist today, though, at least in the United States, the second has
assumed paramount importance.
Assuming that you can afford to pay for the license, licensed spectrum would appear to be
a better medium in which to operate. The spectrum itself is a tangible asset with a real financial
value, and the exclusivity of use provisions would seem to be a positive protection from interference.
The issue is not so simple as appearances suggest, however, as the following sections
illustrate.
The Unlicensed Frequencies: A Matter of Peaceful Coexistence
Beginning in the late 1980s a number of nations, including the United States, began to explore
a new concept, sometimes known as Open Spectrum, that called into question the whole
rationale behind the licensing of spectrum, or, in effect, making it the property of the license
holder. The concept of Open Spectrum led more or less directly to the creation of the unlicensed
bands.
This concept is that spectrum, rather than being private property, should be a commons—
a shared resource available to all. To avoid the tragedy of the commons—that is, the mutual