Secrecy rate of a class of state-dependent untrusted relay channel with orthogonal components

In this paper, we consider a state-dependent relay channel with orthogonal components where the message must be kept secret from the relay node and the channel state information is known non-causally at the source node. A lower bound on the secrecy capacity is derived by the state description scheme proposed in this paper. The source node transmits a description of the channel state information (CSI) to the destination. The message that passes through the relay node is encrypted by a key which is generated from this state description and shared between the source and destination nodes. This scheme enables the relay node to cooperate with the source node to send messages to the destination without getting any information of the message. We show that the achievable secrecy rate by the scheme in this paper is larger than that by the scheme of X. He who showed that the relay is useless in the state-independent untrusted relay channel with orthogonal components.