Secret communication in presence of colluding eavesdroppers

We consider the problem of secret communications between two nodes over a wireless link in the presence of multiple passive eavesdroppers which may collude. Both the transmitter and the receiver are assumed to have multiple antennas and the multiple colluding eavesdroppers are modeled by an eavesdropper with multiple antennas. Communication is secret if the eavesdropper is unable to decode the message whereas the receiver can decode the message without making any errors. Thus, we deal with the problem of secrecy in a MIMO scenario. It is shown how the transmitter can use the multiple antennas to add artificially generated noise to the information signal such that the artificial noise only degrades the eavesdropper´s channel. Thus, even if the eavesdropper has a ´better´ channel than the receiver, secret communication is made possible by selectively degrading the eavesdropper´s channel. The secrecy of communication is achieved by exploiting the physical characteristics of the wireless medium and it is independent of the secrecy of channel state information (CSI)