eloped. Then business needs and the benefits of small have diverse characteristics; therefore, a large number of computers became apparent and drove PC technology examples can be drawn from the pool of military radios. into ubiquitous use. This led to the development of more This section presents the continuum of radio technology applications, such as word processors, e-mail, and more leading to the software-defined radio (SDR). Section recently the World Wide Web (WWW). Similar de- 2.4b.3 continues the continuum through to CR. velopment is under way for wireless communication The first radios deployed in large numbers were devices. "single-purpose" solutions. They were capable of one type Reliable cellular telephony technology is now in of communication (analog voice). Analog voice commu- widespread use, and new applications are driving the nication is not particularly efficient for communicating industry. Where these applications go next is of para- information, SO data radios became desirable, and a gen- mount importance for product developers. Cognitive eration of data-only radios was developed. At this point, radio (CR) is the name adopted to refer to technologies our discussion of software and radio systems begins. The believed to enable some of the next major wireless fixed-point solutions have been replaced with higher data applications. Processing resources and other critical rate and voice capable radios with varying degrees of enabling technologies for wireless killer applications are software integration. This design change has enabled now available. interoperability, upgradability, and portability. This chapter presents a CR roadmap, including a It will be clear from the long description of radios that discussion of CR technologies and applications. Section follows that there have been many additional capabilities 2.4b.2 presents a taxonomy of radio maturity, and Sec- realized in radios over their long history. SDRs and even tions 2.4b.3 and 2.4b.4 present more detailed discus- more advanced systems 