Transmitter precoding for the multiantenna downlinks in cognitive radio networks

We consider the radio resource management in a cognitive radio network where the secondary users cause NO interference to the primary users. The interference between these two groups of users is nulled out by orthogonal precoding vectors. Orthogonal frequency division multiplexing is used to obtain a flat fading channel per subcarrier. Transmitted power over all subcarriers is minimized using convex optimization method. A complexity-reduced method is then proposed, i.e., the greedy allocation. Simulation results show that the greedy solution can achieve a significant portion of the optimal results.