With the rapid development of cognitive radio technologies, spectrum sharing becomes a promising approach to\nimproving the efficiency of spectrum utilization and mitigating the spectrum scarcity problem. Previous research on\ncognitive networks argues that secondary users can only work under a low-transmission power in an underlay\nspectrum sharing model, especially when the primary transmitter is far away from the primary receiver. Motivated by\nthe idea of cooperative communications, in this paper, we propose a cooperative framework in which a primary\ntransmitter, being aware of the existence of the secondary network, may select a secondary user that is not in\ntransmitting or receiving mode to relay its traffic. The feasible relay location region and optimal power ratio between\nthe primary network and the secondary network are derived in the underlay spectrum sharing model. Based on the\noptimal power ratio, we derive the maximum achievable transmission capacity of the secondary network under the\noutage constraints from both the primary and the secondary network with or without cooperative relaying. Numerical\nresults indicate that secondary users can achieve a higher transmission capacity with cooperative relaying, and that\nthe capacity gain of the cooperative network is significantly affected by the location of the relay and the network\nsystem parameters.
Loading....