Joint beamforming and secondary user selection in the downlink of cognitive radio networks

In this paper, we consider a scenario that a primary network and a secondary network share the same frequency spectrum. By using subspace theory, we propose a joint beam-forming and secondary user selection algorithm for the downlink of secondary network, which can produce no interference to the primary users and maximize the sum throughput simultaneously. Simulation results agree well with the theoretical analysis and also indicate that little sum rate throughput loss is induced when equal power allocation scheme is deployed.