The role of artificial noise in multi-antenna fading wiretap channels: Useful or harmful?

New insights into the role of artificial noise in securing communication in a Gaussian multi-antenna fading wiretap channel are presented. An appropriate secrecy-outage-based optimization framework is developed for the Multiple-Input Single-Output Single-Eavesdropper (MISOSE) case to measure the performance of artificial noise. It is assumed that only the legitimate receiver´s instantaneous channel state information and the average statistics of the eavesdropper´s channel are available at the transmitter. The optimization is based on maximizing the effective secret-message rate constrained by a given maximum secrecy outage criterion. Under this framework, a fundamental investigation is conducted into whether it is worthwhile for the transmitter to allocate any of its available power for artificial noise. By numerically solving the optimization problem, it is demonstrated that there are: (i) scenarios where artificial noise does indeed give significant gains in the secret-message rate, and (ii) scenarios where any amount of power allocation to artificial noise is wasteful in view of the overall performance.