Novel interference alignment in multi-secondary users cognitive radio system

New interference alignment (IA) design for secondary users´ transceivers in multi-secondary users cognitive radio system is presented. The proposed scheme allows opportunistic transmitters (secondary users) equipped with multiple antennas (MIMO) to use the same frequency band already occupied by the pre-existing primary user. This can be done by aligning and cancelling the interference on the primary user when local channel state information (CSI) is known. A novel closed form solution for precoding, postcoding, power allocation designed for the secondary users is derived. The proposed solution eliminates the interference of secondary users on primary user while whitening the interference caused by the primary user and other secondary users on each secondary user in the system. Numerical results prove the effectiveness of our novel IA scheme compared to other iterative methods that are used for the same purpose.