Outage performance and cooperative diversity under amplify and forward relaying in cognitive radio networks

This paper investigates the outage and diversity performance in a cognitive radio (CR) network, in which data are transmitted through amplify-and-forward protocol. A fixed CR node is selected as relay to combat fading effect. The CR user transmits or relays data when the result of cooperative spectrum sensing indicates that primary user (PU) channel is free and the relay node stops performing the protocol as soon as the PU is detected to be active. A closed-form expression of outage probability for the CR network is calculated based on which diversity order is derived. The results show that the proposed scheme suffers a loss in diversity order. To compensate for this loss, a repetition-based scheme is proposed in a delay-insensitive system at the cost of the challenge in implementation. In this case, we evaluate the outage performance and the average transmit duration and then compare them with the ones in the delay-sensitive system. Asymptotic analysis is also presented to show the outage performance advantage of using a relay over the one without using it. The numerical results presented in the paper verify our analysis.