r pets, and it may be implanted, rather than worn on a collar, so that it cannot be detected. Such devices could transmit data over the cel- lular network as well. We are already willing to protect our cars and pets with locator technology. Will it be very long before we are willing to protect our children the same way? For some, the notion of hiding or implanting radio devices on ourselves or our children or requiring them for convicts on parole may seem anathema either because it seems to automate us and turn people into commodities or because of its implications related to freedom and privacy. However, increased concern for security as a result of the World Trade Center attack on September 11, 2001, and other events is causing many Americans to reevaluate their priorities. One of the authors (Kemp) attended a meeting of state police technology experts where the importance of being able to iden- tify individuals correctly in real time was at issue, and such devices were suggested as likely innovations in the not-too-distant future. 3.3 Conclusion The user terminal has grown a long way from the early mobile telephones installed in cars, or perhaps it would be better to say that it has shrunken and morphed. As many sizes, shapes, and uses as there are for wireless devices, there will be more in coming years. However, there are numerous engineering challenges to be overcome, especially Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. The User Terminal Key Radio Concepts with the advent of the 3G world of Enhanced Data rate for GSM evolution (EDGE), uni- versal mobile telephony system (UMTS), cdma2000, and wideband code division mul- tiple access (WCDMA). The ability to deliver high-speed data will require more sophis- ticated, more expensive radios with more exacting manufacturing tolerances. And these expensive precision piecesof equipment wi