Joint power management and beamforming for base stations in cognitive radio systems

This paper investigates the joint power control and transmit beamforming problem in multiuser Cognitive Radio systems (CR). Comparing to the conventional downlink transmit problems, joint power management and beamforming schemes in CR systems is more complicated because designers must take the interference to primary users (PUs) into consideration. Assuming perfect channel information to both CR users and PUs can be obtained at CR base stations, in this paper, we solve the formulated downlink optimization problem in two different ways. Since the objective with SINR constraint at each CR receiver and the interference threshold at each PU receiver can be regarded as a second order cone programming (SOCP) problem, we first show the problem can be efficiently solved by SOCP tools. Furthermore, we prove that the downlink problem in CR systems can be interpreted as a conventional uplink-like problem by using up and down duality, which provides a more convenient fixed iterative point method to achieve the optimal solution.