Duality-Based Robust Transceiver Design for Cognitive Downlink Systems

This paper studies robust transceiver optimization for cognitive downlink systems in the presence of imperfect channel state information (CSI). We aim at minimizing the sum mean square error (MSE) of the secondary downlink transmission subject to the interference constraint imposed on the primary users. The MSE duality is developed to describe the uplink-downlink relation, in which imperfect CSI and multiple power constraints are taken into account. Based on the duality result, we propose an efficient robust approach which can effectively avoid the violation of the interference constraint. We also discuss the performance in terms of optimality as well as complexity issue. Compared to the downlink-based approach, the proposed one features faster convergence speed and lower complexity.