e architecture. A super-heterodyne receiver offers consis- tent performance across a large range of frequencies Ideally the designer of an SDR would like to put the while maintaining good sensitivity and selectivity [7, 8]. data converters directly on the antenna. However, as Although not trivial to design, the possibility of com- stated previously, this is not a practical solution. In bining wideband analog techniques and multiple front reality, some AFE must be used-before the ADC in the ends would allow operation across different RF bands. In receive path and after the DAC in the transmit the case of multi-carrier applications, this could be done path-that does the appropriate frequency translation. simultaneously if necessary. The most common of these architectures is the super- heterodyne architecture. Although many decades old, new semiconductor technology and high levels of in- Multi-carrier tegration have kept this architecture vitalized and in Depending on the applications, one or more receive popular use both in the transmit and receive signal paths channels may be desired. Traditional applications may CHAPTER 2.3 Software defined radio only require a single RF channel. However, applications While both such examples would provide a lot of that require high capacity or interoperability may require utility, perhaps a more interesting example would be to a multi-carrier design. SDRs are well suited for configure the receiver such that part of the channels multi-carrier applications since they employ a highly could be CDMA while the other would be configured as oversampled ADC with ample available bandwidth. An GSM! Furthermore, if one of the configurations is at oversampled ADC is one in which the sample rate is capacity and the other is underutilized, CDMA channels operating beyond that which is required to meet the could be converted into several GSM channels or vice Nyquist criterion [18], which states that the converter versa, providing the flexibility to dynamically reallocate sample rate must be twic