Secure space-time block coding via artificial noise alignment

(STBC) for MIMO Gaussian wiretap channels. It is assumed that the transmitter has the receiver's channel state information, but not that of the eavesdropper. We first propose a full-rate STBC that provides separate decoding complexity (rather than pairwise) at the intended receiver, while requiring an exhaustive search for Maximum Likelihood (ML) decoding at the eavesdropper. Next we make the code more secure by including artificial noise symbols which (for the asymptotically high SNR regime) are aligned with each other and subtracted from the information symbols at the intended receiver, but which can not be cancelled at the eavesdropper. Simulations demonstrate the enhanced physical-layer security that results.