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...t. In [27] and [28], cooperative diversity in detection of the PU was applied, and it was shown that and the detection time can be reduced greatly through the cooperation between the SUs. In [29] and =-=[30]-=-, the secondary transmitter (ST) was allowed to act as a relay for the primary transmissions, which showed that the throughput of the secondary network can be improved in certain network topologies. A...

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...ories. For the first category, the PUs are not aware of the existence of the SUs. The SUs are able to detect the available spectrums and then use them for their own data transmission if the interference to the PUs is not harmful. For the second category, the PUs leverage parts of its spectrums to the SUs in exchange for appropriate remuneration. Recently, by exploiting the cooperative diversity, the cooperation technique has been incorporated into the CRNs [2, 3]. Based on the above categories for the dynamic spectrum sharing, the cooperation in CRNs can be divided into two categories as well [4]. For the first category, the SUs are located in different areas and thus have different channel conditions. In this case, some SUsmay be selected as relays to help forward other SUs’ data [5–9]. It is named as cooperation among SUs. For the second category, the PUs lease some resources (time or frequency) to the SUs; thus the SUs will act as relays to forward the PUs’ data. When the data of the PUs are completely transmitted or the data rate requirements of the PUs are satisfied, then the SUs can transmit their own data [10–12]. We call it cooperation among PUs and SUs. In this paper, we will...

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...its of achievable rates in CR systems. Obviously, this model is ideal and needs cooperative communications among SUs. Finally, Simeone et al. studied the cognitive relaying scheme between PUs and SUs =-=[9]-=-, which is of course a simple and elementary discussion. Consequently, in this article we expand the models of Ghasemi and Devroye, and give an overview of the cooperative diversity cognitive models, ...

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...he cooperation technique has been incorporated into the CRNs [2, 3]. Based on the above categories for the dynamic spectrum sharing, the cooperation in CRNs can be divided into two categories as well =-=[4]-=-. For the first category, the SUs are located in different areas and thus have different channel conditions. In this case, some SUsmay be selected as relays to help forward other SUs’ data [5–9]. It i...

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...erative transmission [7]-[10] in Cognitive Relay Networks (CRNs). In [6], the authors showed the importance of cooperative diversity to circumvent with the hidden terminal problem. The authors in [7]-=-=[8]-=- assumed that a secondary user can act as a relay node for primary transmissions. The main benefits are reducing the delay of the primary transmissions and increasing the access opportunities to the l...

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...also one of the key methods to enhance the development of CR networks. Recently, the number of studies in the field of cognitive radio capability in cooperative networks has grown considerably [100], =-=[103]-=-, [35] and [104]. Generally, the inclusion of cognitive radio in cooperative communications implies equipping the intermediate relay nodes with cognitive radios to provide the capability of radio spec...

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... Distributed Breamforming in cognitive radio networkssRecently introduced key technology for tackling the challenges of practicalsimplementation of CR network is distributed cooperation between users =-=[26]-=-. By applyingsbeamforming technique, CR can direct beam towards intended receiver and suppresssinterference in unintended directions to improve the network performance. In distributedsbeamforming each...

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... as a promising solution for the spectrum shortage problem based on the observation that most parts of the spectrum are not utilized efficiently and left idle for a large percentage of time [6], [7], =-=[8]-=-. Indeed, the fixed spectrum allocation under the regulatory polices leads to the result that some of the spectrum bands are overloaded while others may be under-utilized. In cognitive radio, it is pr...