Robust precoding with QoS guarantee for cognitive radio networks

In this paper, we develop robust precoding for secondary users (SUs) with quality-of-service (QoS) guarantee based on imperfect channel state information (CSI) to minimize the maximum sum interference power to the primary user (PU). Optimal robust precoder is derived by transforming the original problem into a semidefinite programming (SDP) form. We then propose two suboptimal robust precoding design approaches to simplify the optimization process and to get more structural solutions. Numerical results show the proposed robust precoding methods can provide lower maximal interference powers to the PU compared to the non-robust ones and the performance gaps increase with the channel error region.