tware purpose microprocessors. The block diagram of a conven- /digital function than for analog. tional radio is shown in the top section of Figure 1.0-5. The idea behind software radio is to move as much of Ultrawideband signals the radio functionality (including the physical layer) as possible into software. However, performing the high Ultrawideband (UWB) has been promoted as a tech- rate sampling and signal processing required for a fully nology for applications ranging from high-speed com- software radio has not yet proven to be commercially munications to location determination to short-range feasible. More recently, the related concept of software- ground-penetrating imaging. With pulse modulation and defined radio has emerged as an R&D topic. In this case, bandwidths in excess of 1 GHz, UWB potentially takes dynamically reconfigurable logic arrays execute specific the advantages of spread spectrum one step farther. The computationally intensive functions, such as coding or intent is to operate UWB transmitters in an unlicensed encryption, as needed. A logic block may be configured mode overlapping licensed frequencies. After significant as a decoder during reception, then reconfigured as an study, the FCC issued rules allowing limited UWB encoder during the next transmit cycle. The lower sec- operation, but questions still remain in the minds of tion of Figure 1.0-5 shows a block diagram of a software- spectrum license holders who are concerned about defined radio. interference. For both software radio or software-defined radio, the advantages are similar: Smart antennas Flexibility-the radio no longer needs to be designed "Smart" antennas have been used for years in specialty with foreknowledge of the exact characteristics of applications, especially by the military. There are con- the target usage. tinuing efforts to develop commercially attractive solu- Upgradability-operation with a new radio technology tions for applications such as cellular base stations and can be achieved simply with a new softwar