Linear precoding in MISO cognitive channels with degraded message sets

In this work, the coexistence of a single-input single-output (SISO) primary link and a multiple-input single-output (MISO) secondary link is considered, where the secondary transmitter has non-causal knowledge of primary message and transmits both primary and secondary messages. The optimal beamforming vectors and power allocation at the secondary transmitter are derived to maximize the achievable secondary rate while satisfying the primary rate requirement. Moreover, the optimal linear precoding is obtained by semidefinite relaxation and rank-one decomposition, when the number of antennas at the secondary transmitter is larger than two. Finally, the performance of the proposed scheme is evaluated through numerical simulations.