Impact of Opportunistic Spectrum Sharing on the Performance of Amplify-and-Forward Incremental Relaying

Multihop communication is widely used in cognitive radio networks to facilitate agile access to opportunistically available spectrum resources while adequately protecting primary users (PUs). However, the performance of this collaborative communication is sensitive to spectrum sensing accuracy and the unpredictable activities of PUs. To quantify the impact of these factors, this article studies the performance of amplify and forward based incremental relaying (IR) in an opportunistic spectrum sharing environment. Using rigorous mathematical analysis, closed form expressions are derived for the average spectral efficiency and the outage probability. The derived results show that imperfect spectrum sensing and the unpredictable activities of PUs degrade the quality of the direct link and thwart the relay from assisting the destination, hence causing significant performance losses. To recover some of these losses, this article proposes a novel selective IR protocol that allows the source to retransmit whenever the relay fails to assist the destination. Hence, creating a second chance of assistance. This protocol is shown to outperform IR while not sacrificing spectral efficiency. Computer simulations are used to verify the accuracy of the derived results.