Date Added: Mar 2010
PHYsical (PHY) layer security approaches for wireless communications can prevent eavesdropping without upper layer data encryption. However, they are hampered by wireless channel conditions: absent feedback, they are typically feasible only when the source-destination channel is better than the source-eavesdropper channel. Node cooperation is a means to overcome this challenge and improve the performance of secure wireless communications. This paper addresses secure communications of one source-destination pair with the help of multiple cooperating relays in the presence of one or more eavesdroppers. Three cooperative schemes are considered: Decode-and-Forward (DF), Amplify-and-Forward (AF), and Cooperative Jamming (CJ). For these schemes, the relays transmit a weighted version of a re-encoded noise-free message signal (for DF), a received noisy source signal (for AF), or a Common Jamming signal (for CJ).