Cooperation for secure wireless communications with resource-bounded eavesdroppers

Wireless communications system designs are sought that rely on the potential of the physical (PHY) layer to allow a transmitter-receiver pair communicate securely in the presence of one or more eavesdroppers. Communication is performed with the help of multiple trusted relays, via the decode-and-forward (DF) protocol, and assuming knowledge of global channel state information (CSI). Instead of dealing with information-theoretic security, we assume that eavesdroppers have bounded resources, and therefore we need to assure that the transmitted information is computationally secure; this is shown to impose constraints on the maximum power of the signals received by the eavesdroppers. The optimal relay weights that maximize the signal-to-noise ratio (SNR) difference SNR_d - SNR_e between the destination and the eavesdroppers are determined under various (transmit, security, reliability) power constraints. Closed-form solutions are obtained in some problem formulations for one eavesdropper, whereas an iterative algorithm is proposed if more eavesdroppers are present. Simulation results indicate that a higher SNR value (compared to the non-cooperative case) is attained at the destination, while satisfying the security constraints.