Precoding and power allocation in Cognitive Radio networks

Cognitive Radio (CR) has attracted much attention for its ability allowing secondary users (SUs) to share the spectrum with licensed users (PUs). The precondition that PUs bear the coexistence of SUs is that the interference caused by SUs should be under a given threshold. Therefore the main challenge of CR is interference control or even interference cancellation. In this work we employ zero-forcing precoding at the base station of the secondary network to ensure no interference from SUs to PUs. On the other hand, to maximize the sum rate of the secondary network, optimal power allocation strategy is performed at the secondary base station. The uncoded bit error rate (BER) performance of the SUs and PUs with the optimal power allocation strategy are investigated and compared with that when employing average power assignment. Simulation results show that the proposed precoding scheme completely eliminates the interference from SUs to PUs and the optimal power allocation strategy enhances the sum rate of secondary network considerably.