Linear precoding and power allocation in the downlink of cognitive radio networks

We consider the downlink of a cognitive radio (CR) system, where secondary users (SUs) share the radio spectrum with primary users (PUs) while ensuring no harmful interference is introduced to PUs. To protect the communications of PUs and in the same time maximize the sum rate of SUs, we propose a joint linear precoding based on minimum mean-square-error (MMSE) criterion and power allocation strategy at the secondary base station (SBS) satisfying the interference power constraints at PUs and the total transmit power constraint for SUs. Simulation results show that the proposed algorithm convergents efficiently and can improve the sum rate of SUs considerably while ensuring the quality-of-service (QoS) of PUs.