A general overlay/underlay analytic expression representing cognitive radio waveform

Several studies have revealed that spectrum congestion is primarily due to the inefficient use of spectrum versus unavailability. Cognitive Radio (CR) and Ultra Wide Band (UWB) technologies have been proposed as candidates to address this problem. Currently, a CR determines unused frequency bands and transmits overlay waveforms in these bands, while UWB transmits underlay waveforms that span the entire frequency band while coexisting with primary users. This suggests that most of the spectrum occupied by primary users is underused. This work proposes a general Soft Decision Cognitive Radio (SDCR) framework, based on a previous developed Spectrally Modulated, Spectrally Modulated (SMSE) framework, to combine benefits of overlay/underlay techniques while maximizing channel capacity. We also show that current CR and UWB implementations represent two extreme SDCR cases and that current overlay/underlay waveforms are two special cases of the general waveform platform.