Secondary Transmitter Design with Imperfect Channel State Information for Cognitive Radio Downlink

It is generally agreed that channel state information (CSI) is of great importance for downlink and interference channels. In practice, however, since the CSI is imperfect due to finite-rate channel feedback, the secondary transmitter is hard to control the interferences to the primary users and among the secondary users in cognitive radio network. In this paper, we propose an algorithm to efficiently control the interferences for the secondary transmitter under imperfect CSI. The proposed algorithm determines the secondary transmit power considering the maximum channel error between actual and feedback channel, therefore, it can perfectly control the interferences to the primary users. Furthermore, we propose the efficient power allocation algorithm based on water-filling for the secondary users. To verify the performance of the proposed algorithm, we derive the lower and upper bounds of the secondary user´s sum-rate. We show that the theoretically derived bounds are in good agreement with the simulation results.