o a reduction in network elements because of a common hardware platform. 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. Access Technologies Access Technologies Finally, cognitive radio allows application developers to create applica- tions that are platform independent and that can be augmented easily through dynamic application of features, patches, and capabilities. Cognitive radio applications span multiple wireless devices including mobile phones, smart phones, PDAs, and computing devices. Today's dig- ital cellular networks use a variety of technologies for the air interface and support multiple data standards. To add to the complexity, the wire- less industry is introducing GPS, Bluetooth, and a variety of equally dis- ruptive protocols to the mix. Cognitive radio offers a solution to accommodate this plethora of standards, frequency bands, and applica- tions by offering end-user devices that can be programmed using over- the-air software. With cognitive radio, a service provider will implement a common hardware platform and accommodate the interworking of all these standards and technologies via instantly downloadable software modules and firmware. Radio Frequency Identification (RFID) Radio frequency identification (RFID) has its origins in the 1940s, when the fundamental technology that underlies modern RFID systems was developed to discriminate between inbound friendly aircraft and inbound enemy aircraft. Allied aircraft carried transponders that broadcast a unique radio signal when interrogated by radar, identifying them as a "friendly." This Identify: Friend or Foe (IFF) system was the basis for the development of the technology set we refer to today as RFID. Modern air- craft still use transponders to automatically and uniquely identify them- selves to ground controllers (the well-known "squawk" function). Many believe that RFI