Recent measurements show that the spectrum is under-utilized by licensed users inwireless communication. Cognitive radio (CR) has been proposed as a suitable solutionto manage the inefficient usage of the spectrum and increase coverage area ofwireless networks. The concept is based on allowing a group of secondary users (SUs)to share the unused radio spectrum originally owned by the primary user (PUs). Theoperation of CR should not cause harmful interference to the PUs. In the otherhand, relayed transmission increases the coverage and achievable capacity of communicationsystems and in particular in CR systems. In fact there are many typesof cooperative communications, however the two main ones are decode-and-forward(DAF) and amplify-and-forward (AAF). Adaptive relaying scheme is a relaying techniqueby which the benefits of the amplifying or decode and forward techniques canbe achieved by switching the forwarding technique according to the quality of the signal.In this dissertation, we investigate the power allocation for an adaptive relayingprotocol (ARP) scheme in cognitive system by maximizing the end-to-end rate andsearching the best carriers pairing distribution. The optimization problem is under the interference and power budget constraints. The simulation results confirm theefficiency of the proposed adaptive relaying protocol in comparison to other relayingtechniques, and the consequence of the choice of the pairing strategy.
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