Achieving Robust, Secure and Cognitive Transmissions Using Multiple Antennas

In this paper, we investigate the optimal transmitter design, under the restriction of Gaussian signalling without preprocessing of information, for a secure multiple-input single-output (MISO) cognitive radio network (CRN), which consists of four terminals: a pair of secondary user transmitter (SU-Tx) and receiver, an eavesdropper and a primary user (PU). It is assumed that all the channel state information is not perfectly known at the SU-Tx due to the channel estimation errors and the loose cooperation between the SU and the PU. The design involves a nonconvex semi-infinite optimization problem, which maximizes the rate of the secondary link while avoiding harmful interference to the PU and preventing the eavesdropper from decoding the messages sent regardless of the uncertainties in the CSI. For this challenging optimization problem, we relate it with a sequence of semi-infinite capacity-achieving transmitter design problems in an auxiliary CRN without any eavesdropper, which can then be solved through transformations and using convex semidefinite programs. Finally, numerical examples are presented to evaluate the performance of the proposed algorithm.