Amplify-and-forward based cooperation for secure wireless communications

A physical layer approach to security for wireless networks is considered. In single-antenna wireless systems, such approaches are hampered by channel conditions in the presence of one or more eavesdroppers. Cooperation has the potential to overcome this problem and improve the security of of wireless communications. In this paper, an amplify-and-forward based cooperative protocol is proposed. Assuming availability of global channel state information, system design that maximizes the secrecy capacity is considered. Since the optimal solution to this problem is intractable, suboptimal closed-form solutions are proposed that optimize bounds on secrecy capacity for the case of a single eavesdropper, or that introduce additional constraints, such as nulling of signals at all eavesdroppers, for the case of multiple eavesdroppers.