On secondary network interference alignment in cognitive radio

We consider a peer-to-peer cognitive radio (CR) network with single primary user and multiple secondary users. We propose an interference alignment technique for this network, and show that desired secondary user performances can be archived without degrading the primary user performance for both single and multiple antenna networks. For the multiple antenna networks, we optimize both the precoding vectors and power allocation to enhance the secondary user rates using a gradient method. Numerical results are given for primary and secondary users rates, which show that the proposed precoding vectors and power allocation algorithm enhance the performance of the CR network. Hence the proposed interference alignment scheme significantly enhances the spectrum efficiency.