On the Secrecy Rate and Optimal Power Allocation for Artificial Noise Assisted MIMOME Channels

This paper considers the artificial noise (AN) scheme, proposed by Goel and Negi for securing wireless communications over multiple-input multiple-output multiantenna eavesdropper (MIMOME) channels. In this paper, we develop a lower bound on the ergodic secrecy rate of the AN scheme and derive an analytic expression of the bound without assuming any asymptotes for system parameters. Thus, the derived bound explicitly elucidates how the system parameters exert influence on the secrecy rate in various cases to some of which the previous work cannot be applied. It will also be shown that the bound is tight over wide combinations of system parameters, and a normalized difference between the bound and secrecy rate vanishes with a growing number of antennas at the transmitter. The derived bound is analytically so amenable that it enables one to not only extend the results of the previous work but also explore untouched aspects of the AN scheme. The bound answers an intriguing question: When is the AN signal beneficial? Besides, it makes possible to study a new important system parameter called the minimum required transmit power for a certain target secrecy rate, which has never been touched before.