  In this paper, we consider the use of artificial noise for secure
communications. We propose the notion of practical secrecy as a new design
criterion based on the behavior of the eavesdropper's error probability $P_E$,
as the signal-to-noise ratio goes to infinity. We then show that the practical
secrecy can be guaranteed by the randomly distributed artificial noise with
specified power. We show that it is possible to achieve practical secrecy even
when the eavesdropper can afford more antennas than the transmitter.
