Robust transmit beamforming in cognitive radio networks

This paper investigates the design of robust transmit beamforming for the secondary user (SU) when it co-exists with the primary user (PU) in a cognitive radio network, and the SU¿s transmitter (SU-Tx) is equipped with multiple antennas. It is assumed that the channel knowledge for the link from SU-Tx to PU is partially known only. By formulating the problem as maximizing the transmission power to the desired SU receiver (SU-Rx) as well as limiting the interference to the PU in a robust manner, the optimal transmit beamforming is designed using convex optimization theory. The robust solution is also derived through taking into account the possible mobility of the PU and the error in the channel state information (CSI) for the link from SU-Tx to PU. Simulations are presented to evaluate the effectiveness of the proposed robust transmit beamforming schemes under various propagation conditions.