  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.
