output broadcast channel in the presence of multiple primary users (PUs). Under the
assumption of imperfect channel state information (CSI) of the PUs, the objective of this letter
is to maximize the sum rate of the secondary system, subject to the power budget at the
secondary base station and the interference power constraints at the PUs. The design
problem is non-convex, and thus is difficult to solve in general. Herein, we first convert a non …