On exploiting co-channel interference to improve secret communications over a wiretap channel

This paper considers a network in which a source-destination pair needs to establish a confidential connection against an external eavesdropper, aided by the interference generated by another source-destination pair that exchanges public messages. Our goal is to identify the secrecy rate performance benefits that can be brought by exploiting co-channel interference. We consider two scenarios: 1) the non-confidential pair designs its preceding matrix in favor of the confidential one, referred to as the altruistic scenario; 2) the non-confidential pair is selfish and it requires to communicate with its maximum achievable D.o.F. The maximum achievable S.D.o.F. of the wiretap channel for both scenarios is obtained in closed form. Based on these analytical expressions, we further determine the number of antennas needed at the non-confidential connection in order to achieve an S.D.o.F. for the wiretap channel equal to the degrees of freedom (D.o.F.).