We begin this chapter by defining
software-defined radio (SDR) and cognitive radio (CR). The radio spectrum has historically been managed via centralized planning and the allocation of static licenses. This command-and-control approach effectively addresses the problem of mutual interference with the unfortunate by-product of spectrum underutilization. This is supported by spectrum measurements which indicate that at any given time, a large fraction of the available spectrum is unused . Cognitive radio promises improvements in spectral access and utilization by enabling radios to take advantage of spectral opportunities in the spatial, temporal, and frequency domains and to adapt rapidly to the dynamic conditions. The potential of this technology has been recognized and acknowledged by regulatory agencies such as the U.S. Federal Communications Commission. Frequency-agile and waveform-flexible radio-frequency (RF) hardware is needed to make cognitive radio a reality.
A software-defined radio is one capable of operating over a broad continuous frequency range, regardless of modulation type and channel bandwidth, where the hardware is reconfigurable via software. Most cellular telephones on the market today are multi-band and multi-mode. However, since they only cover specific predefined frequency bands and modulations, they are not considered SDR implementations. ...