Cooperative communication with regenerative relays for cognitive radio networks

Abstract

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.