Cooperative communication with regenerative relays for cognitive radio networks

Cognitive radios hold tremendous promise for increasing spectral efficiency in wireless systems. In cognitive radio networks, secondary users equipped with frequency-agile cognitive radios communicate with one another via spectrum that is not being used by the primary, licensed users of the spectrum. We consider a cooperative communication scenario in which a secondary transmitter can communicate with a secondary receiver via a direct communication link or a relay channel, depending on the state of a primary transmitter. We develop a decode-and-forward transmission strategy that exploits the presence of spectrum holes both in time and in space. A strategy based on pure temporal sensing alone uses the direct link when the primary transmitter is off, whereas a scheme based on spatial sensing alone uses the relay channel. Our numerical results show that the proposed scheme, employing joint spatial-temporal sensing, significantly reduces the average symbol error probability compared to schemes based on pure temporal or pure spatial sensing.