Robust transmit beamforming against steering vector uncertainty in cognitive radio networks

A robust transmit beamforming scheme is proposed for green cognitive radio networks in presence of incorrect steering vector estimations. The beamformer is designed using a stochastic optimization approach. The proposed beamforming scheme achieves three objectives: a) Probability for large-than-a-threshold for secondary user´s received power in the steering direction is maximized; b) Probabilities for less-than-a-threshold interferences to the primary users in different locations are bounded; and c) Transmitted power along the directions of the moving secondary receiver is maintained as a constant. In addition, we present an algorithm to calculate the inverse Marcum Q function, and use it to solve the optimization problem for proposed beamforming scheme. Simulation results demonstrate that the proposed robust beamformer can achieve significant BER reductions for primary users while ensuring secondary user´s BER is not sacrificed.