Fixed-rate power allocation strategies for enhanced secrecy in MIMO wiretap channels

This paper studies the use of artificial interference in reducing the likelihood that a confidential message transmitted between two multi-antenna nodes is intercepted by a passive eavesdropper. A portion of the transmit power is used to broadcast the information signal with just enough power to guarantee a certain data rate for the intended receiver, and the remainder of the power is used to broadcast artificial noise in order to mask the desired signal from a potential eavesdropper. The interference is designed to be orthogonal to the multiple-stream information signal when it reaches the desired receiver. A modified water-filling algorithm is proposed that balances the required transmit power with the number of spatial dimensions available for jamming the eavesdropper. Numerical results verify the increase in secrecy capacity under the proposed transmission scheme.