Multi-user diversity for secrecy in wireless networks

The ability to transmit a message securely in the presence of eavesdroppers in a dense wireless network is considered. As with a number of recent schemes, system nodes other than the transmitter and receiver are chosen to generate noise that confuses the eavesdropper. By exploiting the dynamics of the fading, significantly improved performance is achieved beyond that generated from the standard multi-user diversity gain expected from opportunistic relaying. In particular, the node with the best fading characteristics takes responsibility for message relaying, while those whose fading will significantly reduce their impact on the desired communication play the role of noise generators. For a source transmitting to a destination using a set of intermediate relays, we consider the number of eavesdroppers that can be present without the interception of packets, in both the case where the eavesdroppers operate independently and in the case where they collude. The latter case also encompasses the more likely scenario of a single eavesdropper with a sophisticated receiver.