 and are starting to gain favor in the more expensive, but is better tailored to show the commercial world, as explained in Section 2.4b.2. We are benefits of CR. Spectrum awareness using a spec- now seeing the emergence of aware radios, adaptive radios, trum sensor has the best information to exploit un- and finally CRs, and we have traced the continuum among occupied spectrum. This custom capability also has these various degrees of capability, as well as providing a computational resources sized to execute a policy few examples of each. Sections 2.4b.3 and 2.4b.4 explored constraint engine. the properties and capabilities of each of these classes of radios. 2.4b.7.1 Decisions, directions, and Section 2.4b.5 outlined the enabling technologies for standards CRs. Numerous technologies have matured to the point where CR applications are possible and even attractive. Numerous organizations and standards bodies are work- The ability to geolocate a system, sense the spectrum, ing in the area of CR. The SDR Forum, the Institute of know the time and date, sense biometric characteristics Electrical and Electronics Engineers (IEEE), the Federal of people, access new software capabilities, and de- Communications Commission (FCC), the National termine new regulatory environments are all working Telecommunications and Information Administration together to enable CR. (NTIA), and the International Telecommunication Geolocation through the use of GPS or other methods Union (ITU) all have interests in this area. is now available. This enabling technology allows a radio CHAPTER 2.4b Cognitive radio: The technologies required to make spatially variant decisions, which may be applied where it is right now, given the priorities of current cir- to the selection of policy or networking functions. cumstances. AI applications at a very high level, net- Sensing of the local RF environment is available. This working services in the middle levels, and signal information may be used to mitigate a deeply fading processing primitives at a v