Joint beamforming and power control in the downlink of cognitive radio networks

We consider a system where a licensed radio spectrum is shared by two networks, namely the primary network and the secondary network. The spectrum is licensed to the primary network, however the secondary network makes opportunistic access of the unused and/or underutilized portions of it by using cognitive radio technology. For such a system, we study the problem of joint power control and beamforming in the downlink of the cognitive radio network and formulate two iterative algorithms considering two different scenarios of spectrum sharing. In the first case, the primary network cooperates with the secondary network to jointly optimize the transmit beamforming weights and total transmitted power by both networks subject to signal to interference plus noise ratio (SINR) constraints of both primary and secondary users. In the second case, the secondary network jointly optimizes the transmit beamforming weights and its total transmitted power satisfying the SINR constraint of the secondary users and maximum tolerable interference constraint to the primary user. Simulation results are provided to show convergence behavior of the iterative algortihms.