Hybrid Overlay/Underlay Transmission Scheme with Optimal Resource Allocation for Primary User Throughput Maximization in Cooperative Cognitive Radio Networks

Recent studies to improve the spectrum utilization and efficiency show that Dynamic Spectrum Access and Cognitive Radio are the two techniques to satisfy these requirements. The use of such techniques will overcome the inefficient spectrum utilization due to fixed frequency allocation techniques. To enable the Secondary Users to coexist with the Primary Users, Overlay and Underlay are the two transmission techniques that are widely used. In this paper, we present a hybrid overlay/underlay spectrum access strategy that has the features of both the traditional overlay and underlay strategies. This strategy presents a novel approach in which the primary users can use the secondary users to maximize their throughput. In addition to the hybrid overlay/underlay transmission strategy, this paper also provides a resource allocation protocol that decides the best secondary user to be selected as relay, power levels of these secondary users and best channel to be selected. Unlike the previous works done on hybrid transmission protocols, where the main aim is to maximize the secondary user throughput, this paper aims to maximization of primary user capacity and avoiding harmful interference to other active primary users and avoids the need to switch between the overlay and underlay protocols. Performance analysis is done with simulations of hybrid overlay/underlay, underlay and overlay techniques and discussions on results are presented. Discussions are also provided on the criterion for relay power selection between interference only constraint and power only constraint.