Cooperative Beamforming in Cognitive Radio Network with Network-Coded Bidirectional Filter-and-Forward Relaying

In this paper, for an underlay cognitive radio network with network-coded bidirectional filter-and-forward (FF) relaying, two cooperative beamforming schemes are proposed. The first scheme maximizes the worst signal-to-interference-plus-ISI-and-noise ratio ((SINR)-N-2) of the secondary users such that the interference level at the primary receiver does not exceed an allowable threshold. The second scheme maximizes the sum rate of the secondary users under a total power constraint for the relay nodes as well as an interference temperature constraint for the primary network. The simulation results demonstrate that the proposed schemes have significant performance improvement compared to the amplify-and-forward (AF)-based beamforming schemes.