Energy Efficient Power Allocation Schemes for a Two-User Network-Coded Cooperative Cognitive Radio Network

This paper investigates the outage behavior and power allocation problem in a two-user network-coded cooperative cognitive radio network over Rayleigh fading channels. First, we derive an exact expression for the outage probability of the secondary transmissions, and then we propose an approximate expression whose validity limits are later evaluated. To improve the power efficiency of the secondary network, two power allocation schemes are proposed. In the first scheme, the transmit power is adjusted as a function of the average channel gains and the power control is formulated as a convex optimization problem where the objective is to minimize the total transmit power subject to outage probability constraints. In the second scheme, the transmit power is adjusted as a function of the instantaneous channel gains to guarantee a target signal-to-interference-plus-noise ratio at the receiver. We evaluate the performance of both schemes under cooperative and non-cooperative scenarios considering different network geometries. Our results indicate that the benefits of network coding cooperation are substantial for both power allocation schemes.