Optimal Power Control for Cognitive Relay Networks over Fading Channels

In this paper, we study the outage performance of proposed cognitive relay network which is defined by a source, a destination and a group of clusters each of which consists of a cognitive relay node and a primary node. In suggested model, a source is assisted by cognitive relay nodes which allow coexisting with primary nodes by imposing severe constraints on the transmission power so that they operate below the noise floor of primary nodes. Here, we mainly focus on understanding that the cognitive relay node impacts on the outage performance of proposed system model for Rayleigh fading channels under interference power constraints. A relay transmission scheme, namely, regenerative decode-and-forward (RDF) is considered. Considering a scenario with two relays, we derive the optimal power control policies of the cognitive relay nodes to achieve the minimum outage probability under both the peak and average interference power constraints over Rayleigh fading channels. Finally, the numerical results are presented to validate our theoretical results. Numerical performance results show that outage probability performance improves with the increase of the average interference power constraint and peak interference power constraint, and the power control policy under the average interference power constraint is more effective than that under the peak interference power constraint.