Addressing the Dynamic Range Problem in Cognitive Radios

The discrepancy between perceived spectrum shortage from the FCC allocation map and the actual abundance of available spectrum is a motivation for Cognitive Radios, which locate and transmit in the unused or lightly used bands. If a digital approach is taken to provide the necessary radio flexibility to exploit this sparsity, there is a challenging dynamic range requirement in the analog to digital conversion, since there are large interfering signals which are effectively in-band and can not be removed by fixed RF pre-filtering. Using a mixed analog digital system architecture which uses multiple low accuracy ADCs with digital adaptive filters, it is possible to increase the effective dynamic range of the input by subtracting off the unwanted signals in the time domain.