Date Added: Jan 2010
This paper presents new techniques that leverage the wireless medium in facilitating secure communications in the presence of eavesdroppers. First, this paper considers the secure transmission of information over an ergodic fading channel with long coherence intervals. The secrecy capacity of such a system is characterized under different assumptions on the available channel state information. This paper then proposes a low-complexity on/off power allocation strategy which becomes asymptotically optimal as the average SNR grows. Remarkably, the results reveal the positive impact of fading on the secrecy capacity and establish the critical role of rate adaptation in enabling secure communications over slow fading channels. Moreover, this paper discusses the utility of user cooperation in establishing secure communication links.