have the most capabilities, and sions. Sections 2.4b.5 and 2.4b.6 are about enabling and additional functions are likely to be added over time. required technologies for CRs. They present three clas- ses of cognitive applications, one of which may be the next killer application for wireless devices. Conjectures 2.4b.2.1 Continuum of radio flexibility regarding the development of CR are included in Section and capability 2.4b.7 with arguments for their validity. Highlights of this chapter are discussed in the summary in Section Basing CR on an SDR platform is not a requirement, but 2.4b.8, which emphasizes that the technologies required it is a practical approach at this time because SDR flex- for CR are presently available. ibility allows developers to modify existing systems with Communications Engineering Desk Reference; ISBN: 9780123746481 Copyright © 2006 Elsevier Inc. All rights reserved CHAPTER 2.4b Cognitive radio: The technologies required Software Software Software- Aware Adaptive Cognitive Capable Programmable Defined Radio Radio Radio Radio Radio Increasing Technology/Software Maturity Figure 2.4b-1 SDR technology continuum. As software sophistication increases, the radio system capabilities can evolve to accommodate a much broader range of awareness, adaptivity, and even the ability to learn. little or no new hardware development, as well as to add 2.4b.2.2 Examples of software capable cognitive capabilities. The distinction of being a CR is radios bestowed when the level of software sophistication has risen sufficiently to warrant this more colorful de- Several examples of software capable radios are shown in scription. Certain behaviors, discussed in this chapter, Figure 2.4b-2 and detailed in Table 2.4b-1. The common are needed for a radio to be considered a CR. characteristics of these radios are fixed modulation ca- Historically, radios have been fixed-point designs. As pabilities, relatively small number of frequencies, limited upgrades were desired to increase capability, reduce life data and d