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Cognitive Radio (CR) can significantly improve the utilization of the precious radio spectrum by allowing Secondary Users (SUs) to borrow the licensed spectrum if they do not cause harmful interference to Primary Users (PUs). As a wireless technology, CR confronts the challenges of wireless channels inevitably and thus wishes to employ node cooperation to achieve spatial diversity gain. However, conventional...
In this paper, we propose an opportunistic scheduling scheme to serve bursty traffics in cognitive radios, where cooperative beamforming is exploited to access busy timeslots or spatial spectrum holes to forward messages without causing interference to primary users. Specifically, based on cooperative beamforming in the physical layer and automatic repeat request for error recovery in the link layer,...
We propose a cooperative beamforming aided incremental relaying scheme to improve spectrum efficiency of cognitive radio systems. In this scheme, the source and relays can utilize cooperative beamforming to activate packet retransmission in busy timeslots or spatial spectrum holes, if the destination fails to receive the packets transmitted from the source. Therefore, cooperative diversity gain is...
To take full advantage of wireless mesh networks and cooperative transmission simultaneously, a WiMAX-based cooperative PMP/Mesh hybrid topology, CoWiMAX is presented in this paper. Firstly, a hierarchy mesh topology and a PMP/Mesh hybrid frame structure are introduced for CoWiMAX. Secondly, a cooperative PMP and relay transmission scheme is presented to support cooperative PMP and relay links. Simulation...
Recent work has shown that distributed (or cooperative) beamforming can achieve cooperative gain, such as throughput gain and diversity gain, with no need for extra spectral holes in Cognitive Wireless Networks (CWNs). However, how to efficiently schedule cooperative beamforming to improve the quality of service of unlicensed secondary users has not been well addressed. In this paper, a simple opportunistic...
Cognitive radio (CR) is a powerful solution that can significantly improve the utilization of the precious limited radio spectrum. It allows secondary users (SUs) to opportunistically access spectral holes of the licensed spectrum without causing harmful interference to primary users (PUs). However, waiting for idle timeslots may induce very poor quality of service (QoS) for SUs. To alleviate this,...
Cognitive radio is a powerful solution that can significantly improve the utilization of the precious limited radio spectrum. It allows secondary users (SUs) to opportunistically access spectral holes in the licensed spectrum without causing harmful interference to primary users (PUs). However, the secondary communication opportunity becomes extremely poor when primary systems are heavily loaded....
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