In this paper, we consider a two-phase cooperative relay transmission setup with relay's private information (CRT-RPI). A half-duplex decode-and-forward (DF) relay not only helps the source-to-destination transmission, but also transmits its own private information mR to the destination. Distributed space-time coding is employed across the source and the relay to obtain cooperative diversity gain for the source message, and superposition coding between the source and relay messages is used at the relay to transmit mR. We derive the achievable rate region of CRT-RPI and design i) the optimal time sharing factor between two phases and ii) the power allocation factors for the two messages, based on the rate region. Numerical results are also provided to verify the effectiveness of our proposed optimization schemes.
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