Multiuser and multirelay cognitive radio networks under spectrum-sharing constraints

In this paper, the outage behavior of dual-hop multiuser multirelay cognitive radio networks under spectrum-sharing constraints is investigated. In the proposed cognitive radio network, the secondary network is composed of one secondary-user (SU) source that communicates with one out of L destinations through a direct link and also via the help of one out of N relays by using an efficient relay-destination selection scheme. Additionally, a selection combining (SC) scheme to select the best link (direct or dual-hop link) from the SU source is employed at the selected SU destination. Adopting an underlay approach, the SU communication is performed accounting for an interference constraint, where the overall transmit power is governed by the interference at the primary-user (PU) receiver, as well as by the maximum transmission power available at the respective nodes. Closed-form expressions for the outage probability are derived, from which an asymptotic analysis reveals that the diversity order of the considered system is not affected by the interference and is equal to N + L for both decode-and-forward (DF) and amplify-and-forward (AF) relaying protocols. The analytical results are corroborated by Monte Carlo simulations, and insightful discussions are provided.