Secure diversity-multiplexing tradeoffs in MIMO relay channels

Wireless networks are susceptible to eavesdropping due to the inherent broadcast nature of the wireless medium. However, it is also this broadcast nature of wireless communications that allows cooperation among multiple users or relay nodes. Thus, it is unclear how cooperation and secrecy interacts, particularly in the scenario when each node in the network is equipped with multiple antennas (MIMO). In this paper, we consider the information theoretic secure transmission in a classical four node wiretap relay network, consisting of a source node, a destination node, and a relay node, in the presence of a fourth adversarial wiretapper node that can observe all transmissions from the source as well as the relay node. For a MIMO quasi-static fading channel model between every pair of nodes, we explore the importance of degrees of freedom in providing secure transmissions, through secrecy outage analysis in the high signal-to-noise ratio regime. We characterize the achievable diversity versus secure multiplexing gain tradeoff for decode-and-forward as well as compress-and-forward relaying, under the full-duplex constraint.