Optimum Relay Scheme in a Secure Two-Hop Amplify and Forward Cooperative   Communication System
  A MIMO secure two-hop wireless communication system is considered in this paper. In this model, there are no direct links between the source-destination and the source-eavesdropper. The problem is maximizing the secrecy capacity of the system over all possible amplify and forward (AF) relay strategies, such that the power consumption at the source node and the relay node is limited. When all the nodes are equipped with single antenna, this non-convex optimization problem is fully characterized. When all the nodes (except the intended receiver) are equipped with multiple antennas, the optimization problem is characterized based on the generalized eigenvalues-eigenvectors of the channel gain matrices. 
Ghadamali Bagherikaram, Konstantinos N. Plataniotis
cs.IT math.IT