  Due to the broadcast nature of the wireless medium, wireless communication is
susceptible to adversarial eavesdropping. This paper describes how
eavesdropping can potentially be defeated by exploiting the superposition
nature of the wireless medium. A Gaussian wire-tap channel with a helping
interferer (WTC-HI) is considered in which a transmitter sends confidential
messages to its intended receiver in the presence of a passive eavesdropper and
with the help of an interferer. The interferer, which does not know the
confidential message assists the confidential message transmission by sending a
signal that is independent of the transmitted message. An achievable secrecy
rate and a Sato-type upper bound on the secrecy capacity are given for the
Gaussian WTC-HI. Through numerical analysis, it is found that the upper bound
is close to the achievable secrecy rate when the interference is weak for
symmetric interference channels, and under more general conditions for
asymmetric Gaussian interference channels.
