TABLE OF CONTENTS The accuracy of time measurements for time-of-flight range estimations is a direct function of signal bandwidth. Particularly in the case of indoor location and short range systems in general, range, and position accuracy on the order of 1m demand pulse widths or rise times of several nanoseconds, and bandwidths of several hundred megahertz, with equivalent clock rates. Similar time resolution is necessary to distinguish between line-of-sight and multipath (nonline-of-sight) signals particularly important in environments with many reflecting objects such as are encountered indoors. Better distance resolution is obtained by averaging techniques, as was described for spread spectrum systems in Chapter 3, but the ultimate distance measurement performance, considering both distance accuracy and measurement time, are derived from the signal bandwidth. Ultra-wideband (UWB) communication systems are therefore especially appropriate as a platform for ranging and location.
Regulating the use of radio communications signals having very wide bandwidths necessitated a completely new approach to spectrum allocation. It was not feasible to assign frequency channels of such widths to specific users or for specific applications, as is common with narrowband signals, because free spectrum is simply not available. On the other hand, ultrawideband technology has the potential for important applications, among them those that concern public safety and emergency response, that are hard to accomplish with conventional wireless communication methods. The allocation solution was to overlay ultrawideband spectrum on channels that are occupied by narrowband (and what is normally considered wideband) users and to constrain power density to levels that...
