One of the fundamental assumptions while deploying a cognitive radio network is that the primary users are willing to tolerate additional interference generated by secondary users and are willing to share their spectrum resource with secondary users. So, the general question that arises here is that why the primary users should tolerate additional interference and share resources? In this paper, we presented a new scheme that can provide additional SNR for the primary users by allowing secondary users to coexist. Hybrid overlay/underlay strategy is the proposed scheme in which the idle secondary users are used to maximize the throughput of the primary users. The features of both underlay and overlay are incorporated into this hybrid transmission technique such that the both the licensed and unlicensed users get benefited, as their communication link is uninterrupted. Also, we presented a resource allocation algorithm for the hybrid overlay/underlay transmission method and the performance of the opportunistic and partial relay selection is investigated. This resource allocation algorithm is used for selection of the best relay, power allocated to the relay and best channel from relay to destination. Simulation results are presented to demonstrate the performance of the proposed hybrid technique over the traditional methods. The effectiveness of usage of the partial and opportunistic relay selection techniques is compared and the conclusions are drawn. The simulations show that the proposed hybrid overlay/underlay transmission scheme gives optimal performance when paired with partial relay selection.
Cognitive radio, hybrid CR scheme, underlay, overlay, partial relay selection, opportunistic relay selection, resource allocation
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