Cognitive Radio Architectures

The system architecture for the SDR analog/RF is significantly different from that of traditional narrowband radio systems. In the original software radio proposal by Joseph Mitola in 1992 [8], he proposed an architecture where in the receiver,the RF bandwidth is digitized (no down-conversion), and signal analysis and demodulation is performed in the digital domain. Similarly, in the transmitter, the RF signal is synthesized in the digital domain, converted to analog and transmitted. The conceptual transceiver architecture is shown in Fig. 2.1. The Mitola architecture provides the maximum amount of flexibility through an increase in software capability. However, this architecture imposes impractical requirements on the analog-to-digital and digital-to-analog converters necessary for this architecture. For example, as discussed in [9], a 12 GHz, 12-bit ADC that might be used in a Mitola receiver would dissipate 500W of power! As a result, the ideal goal of communication at any desirable frequency, bandwidth, modulation and data rate by simply invoking the appropriate software remains far from realizable.