ABSTRACT
A major shift in radio design is just beginning, which attempts to share spectrum in a fundamentally new way. Spectrum-sharing radios operate in much wider frequency bands and require frequency agility and significant dynamic range improvements to accommodate the in-band primary users. To overcome the bandwidth limitations, several great advances in communications system design, such as sophisticated modulations, coding, and multiple antennas, have greatly improved the spectrum efficiency of some commercial radio systems. In spectrum sharing, choosing the radio transmit power that causes minimal interference to primary users presents the crucial challenge. On a radio design level, the implementation of the spectrum-sensing function also requires a high degree of flexibility, since the radio environment is highly variable because of different types of primary user systems, propagation losses, and interference. In addition to mitigating interference, the new sharing radios will need to have awareness of the channel in not only frequency but time and space as well.
