On the Gain of Vertical Cooperation in Cognitive Radio Networks

We consider a cognitive radio network where primary users (PUs) and secondary users (SUs) coexist and share the same spectrum. Secondary users access the spectrum randomly and limit the outage probability experienced by the primaries by controlling their transmission probability and by obeying a primary exclusion region (PER), within which all SUs have to be inactive. We propose a vertical cooperative transmission scheme with three geographic relay selection rules. In our scheme, the primary source-destination pairs select a neighboring idle SU, and use the selected SU as a cooperative relay. We derive analytic models on the primary outage probability considering the effects of the secondary random access, the PER and the different relay selection rules. Our results indicate that the proposed vertical cooperation increases significantly the allowed transmission probability of the SUs both without and with PER.