A UWB approach violates all conventional notions of good radio engineering practice, using much more bandwidth than information theory requires for a given amount of content. To put this in terms of nightscapes and flashlights, every UWB user has the same kind of white-light flashlight, but each is assigned a different distinctive timing pattern to use with a blinker switchand is given a pair of glasses whose lenses can switch between being opaque or transparent, controlled by the same coded pattern.As activity by other users increases, each user will be able to make an independent choice about trading bandwidth for quality. By settling for fewer independent views per unit of time, users will be able to use statistical techniques to elevate what they want to see above the noise. This phenomenon is called processing gain, in contrast to the amplification gain of a conventional volume control. This is where UWB techniques start to defy common sense. A simple spreadsheet, using random-number formulas and a mix of logical and statistical functions, is all thats needed to demonstrate that a signal can be detectedat any desired accuracy leveleven when that signal is actually weaker than the random noise of static and the other interfering signals in the same spectral band. If the story stopped here, at the level of mathematics and information theory, then UWB proponents would therefore be justified in using phrases such as "spectrum glut"as did the normally restrained international journal, The Economist, on its Aug. 14 cover. When the math meets the metal of actual radio hardware, though, things get much more complicated. Strong nearby signals, for example, induce a behavior called front-end overload, which reduces the sensitivity of a radio receiver across its entire range. Moreover, some radio applications, such as radio astronomy, cant depend on Moores Law to make processing gain more affordable as channel activity grows; they have to detect the signals that they find. An elevated noise floor, with ever-more users transmitting growing numbers of coded sequences, could drive astronomical users literally to the far side of the moon in search of a quiet radio shadow within which they could make their observations. Freescales XS110 approval lets the UWB genie out of the bottle, even if the other messy contents of that bottle are so far being spilled only in the band between 3GHz and 10GHza spectral region of limited application because basic physics limit the range of signals in that band. Powerful interests will almost certainly contend, however, that the benefits of UWB should be combined with the greater range and versatility of radio frequencies that are currently used by other established user communities. The contest that follows will be unlike any other in the history of technologynot a duel between alternative uses of a resource but one between essentially different ideas of what the resource is. Technology Editor Peter Coffee can be reached at firstname.lastname@example.org. Check out eWEEK.coms Mobile & Wireless Center at http://wireless.eweek.com for the latest news, reviews and analysis.
At any given moment, a person will see glimpses of things that his or her communication partners didnt intend to illuminate, but, over time, that person will mostly see the targets that his or her own coded pattern is picking out. If other users or groups are idle, an active user will see a less confused signal or will be able to get a larger number of clear and distinct views over any given period of time.