Robust Power Control using Efficient Minimum Variance Beamforming for Cognitive Radio Networks

In this paper, the authors have explored the idea of secondary spectrum access by using cognitive radios (CR) in a secondary network deployed in the region of a wireless cellular network. In the CR network, secondary users (SUs) opportunistically access the underutilized spectrum owned by the licensed primary users (PUs) of the cellular network for their own transmissions. Since SUs share the spectrum of PUs, PUs must be protected from any harmful interference by the SUs. It should also be ensured that SUs are able to transmit without any interruption and this can be achieved by maximizing SINRs of SUs. To keep this in mind, we have addressed a joint issue of power control and beamforming for the CR network maintaining insignificant interference level to the PUs as well as maximizing SINRs for all SUs. An iterative algorithm has been proposed to jointly update the transmission power vector and the beamformer weights to maintain the received interferences at PUs below a threshold level as well as to ensure that the SUs who are admitted in the CR system are guaranteed with their SINR requirements. Our proposed algorithm has been evaluated through a detailed analysis with simulation results.