This letter studies joint transmit beamforming and antenna selection at asecondary base station (BS) with multiple primary users (PUs) in an underlaycognitive radio multiple-input single-output broadcast channel. The objectiveis to maximize the sum rate subject to the secondary BS transmit power, minimumrequired rates for secondary users, and PUs' interference power constraints.The utility function of interest is nonconcave and the involved constraints arenonconvex, so this problem is hard to solve. Nevertheless, we propose a newiterative algorithm that finds local optima at the least. We use an innerapproximation method to construct and solve a simple convex quadratic programof moderate dimension at each iteration of the proposed algorithm. Simulationresults indicate that the proposed algorithm converges quickly and outperformsexisting approaches.
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