Enhancing the Performance of Amplify-and-Forward Cognitive Relay Networks: A Multiple-Relay Scenario

In this paper, we address the problem of maximizing the received signal-to-noise ratio (SNR) of a relay-assisted secondary network. In particular, a pair of cognitive radio nodes communicate through a cluster of K non-orthogonal amplify-and-forward relays sharing the spectrum of a primary network in an underlay fashion. The interference at the primary receiver due to cognitive nodes transmissions must be below a tolerable level leaving the primary activity unaffected. We formulate an optimization problem to choose the transmission power of the secondary transmitter and the relays while adhering to the interference constraint on the primary network and imposing a maximum limitation upon the power consumption at every secondary node. While the optimization problem is nonconvex, we propose a simple iterative algorithm to achieve the solution. We present the performance of the proposed power allocation for different system parameters. Simulation results reveal a significant improvement of the achievable throughput of the proposed power allocation over equal power allocation.