Date Added: Sep 2011
In underlay cognitive radio networks, unlicensed secondary users are allowed to share the spectrum with licensed primary users when the interference induced on the primary transmission is limited. In this paper, the authors propose a new cooperative transmission scheme for cognitive radio networks where a relay node is able to help both the primary and secondary transmissions. They derive exact closed-form and upper bound expressions of the conditional primary and secondary outage probabilities over Rayleigh fading channels. Furthermore, they proposed a simple power allocation algorithm. Finally, using numerical evaluation and simulation results they show the potential of their cooperative transmission scheme in improving the secondary outage probability without harming the primary one.