Reliability, Rate and Security in Cooperative Networks

Next, to explore security issues a four terminal network with a single source-destination pair, a relay and a wire-tapper is studied for two different cases. In the first case the relay assists the source-destination communication, whereas in the second the relay assists the wire-tapper. For the former, upper and lower bounds on the capacity-equivocation rate region are established for a degraded wire-tapper for both discrete memoryless and Gaussian cases. It is observed that in the presence of a wiretapper, some conventional beliefs about cooperation may no longer be true. For the latter, different relaying protocols are compared in terms of achievable secrecy rates. It is shown that comparison of relaying protocols and best power allocation schemes, when the relay assists the source-destination communication, do not readily extend to the case when the relay assists the wire-tapper.