On the Optimal Precoding for MIMO Gaussian Wire-Tap Channels
  We consider the problem of finding secrecy rate of a multiple-input multiple-output (MIMO) wire-tap channel. A transmitter, a legitimate receiver, and an eavesdropper are all equipped with multiple antennas. The channel states from the transmitter to the legitimate user and to the eavesdropper are assumed to be known at the transmitter. In this contribution, we address the problem of finding the optimal precoder/transmit covariance matrix maximizing the secrecy rate of the given wiretap channel. The problem formulation is shown to be equivalent to a difference of convex functions programming problem and an efficient algorithm for addressing this problem is developed. 
Arash Khabbazibasmenj and Maksym A. Girnyk and Sergiy A. Vorobyov and   Mikko Vehkaper\"a and Lars K. Rasmussen
cs.IT math.IT