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Previous research on cognitive networks argues that secondary users can only work under a low transmission power condition in an underlay spectrum sharing model. Motivated by the idea of cooperative communications, in this paper we investigate the achievable transmission capacity of a cognitive network that provides cooperative relaying to the primary network over the underlay spectrum sharing model. The feasible region of the relay, the lower bound of the power ratio between the primary network and the secondary network with or without cooperative relaying, as well as the maximum achievable transmission capacity of the secondary network with or without relaying under the outage constraints from both the primary and the secondary network, are carefully studied. Numerical results indicate that secondary users can achieve a higher transmission capacity with cooperative relaying as they can transmit at a higher power while satisfying the outage probability constraints from both systems.
Note: This article was mistakenly omitted from the original submission to IEEE Xplore. It is now included as part of the conference record.